NOAA Technical Memorandum ERL PMEL-44

MARINE WEATHER OF THE INLAND WATERS

OF WESTERN WASHINGTON

James E. OverlandBernard A. Walter, Jr.

Pacific Marine Environmental LaboratorySeattle, WashingtonJanuary 1983

UNITED STATESDEPARTMENT OF COMMERCE

Malcolm Baldrige,Secretary

NATIONAL OCEANIC ANDATMOSPHERIC ADMINISTRATION

John V. Byrne,Administrator

Environmental ResearchLaboratories

George H. LudwigDirector

CONTENTS

Abstract 1

1. Introduction 2

2. Climatological Summary 22.1 Air temperature 22.2 Preci pitation 62.3 Cloud cover and fog 62.4 Wind and waves 122.5 Air qual ity 122.6 Surface hydrology 23

3. Large-scale Meteorological Characteristics 23

4. Regional Meteorological Phenomena 304.1 Overview 304.2 Gap winds and bora 324.3 Orographic low-pressure formation 36

in the lee of the Olympic Mountains4.4 Effects of orography on precipitation--the 46

Puget Sound convergence zone4.5 Diurnal wind variations--the sea breeze 51

and valley breeze

5. Summary 576. Acknowledgements 597. References 60

iii

Figures

Figure 1. Location map for western Washington 3and southwest British Columbia.

Figure 2. Topographic map of northwest Washington. 4Figure 3. Annual temperature cycle at SEATAC 5

Airport (1945-1970).Figure 4. Mean annual precipitation (1930-1957) 8

for western Washington.Figure 5. Annual cycle of precipitation at SEATAC 9

Airport (1945-1970).Figure 6. Annual cycle of clear or partly cloudy 10

days at SEATAC Airport (1945-1980).Figure 7. January and July surface wind roses for 14

western Washington.Figure 8a. One-year time series of the N-S wind 17

component for West Point.Figure 8b. Frequency spectra for the north and east 18

components of wind for West Point during winter.Figure 8c. Frequency spectra for the north and east 19

components of wind for West Point during summer.Figure 9. Annual wave climatology computed for West 20

Point from the wind climatology at SEATAC Airport.Figure 10. Mean annual particulate concentration 22

for 1980.Figure 11. Mean annual runoff (m3 s-l) for Puget Sound. 24Figure 12a. Mean annual cycle of discharge for 25

Puget Sound's three major tributaries.Figure 12b. Interannual variability of discharge 26

for Puget Sound's three major tributaries.Figure 13. Typical weather patterns (LIt L2 t HIt H2) 27

affecting the Pacific Northwest.Figure 14. Typical local wind patterns for the 31

passage of a front through western Washington.Figure 15a. Sea-level pressure analysis for 00 GMT 33

24 February 1980 for western Washington.Figure 15b. Local wind field on 23 February and sea- 33

level pressure analysis for 21 GMT 23 February 1980for the Straits of Juan de Fuca and Georgia.

Figure 16a. Sea-level pressure analysis for 00 GMT 3414 February 1980.

iv

Figure 16. (b) Local wind field on 13 February 1980 34and sea-level pressure analysis for 21 GMT13 February 1980.

Figure 16. (c) Wind and dewpoint fields from surface 35and aircraft reports 21-24 GMT 13 February 1980.(Overland and Walter, 1981).

Figure 17. Surface map, 12 GMT 28 November 1979. 37Figure 18. Cross section of potential temperature 38

(KO) across the state of Washington.Figure 19. Regional surface map for 12 GMT, 40

13 February 1979.Figure 20. (a) Sea-level pressure analysis at 41

00 GMT 19 February 1980, and (b) mesoscale windand pressure field at 21 GMT 18 February 1980.

Figure 20. (c) Sea-level pressure analysis at 4200 GMT 29 February 1980 and (d) mesoscale windand pressure field at 21 GMT 28 February 1980.

Figure 20. (e) Sea-level pressure analysis at 4300 GMT 10 March 1980 and (f) mesoscale windand pressure at 21 GMT 9 March 1980.

Figure 21a. Plumes from upwind stacks at various 44elevations (after Hunt and Snyder, 1980).

Figure 21b. Comparison of experimental and analytically 45computed streak-lines in the horizontal plane atmid-level of a Gaussian-shaped obstacle for a Froudenumber of 0.154 (after Riley et al., 1976).

Figure 22. Sum of the perturbation pressure field from 47Smith's hydrostatic linear model and a hypo-thetical synoptic pressure field (Smith, 1981).

Figure 23. Polar representation of the wind speed and 49direction at Hoquiam, Washington, during tenconvergence zone events (after Mass, 1981).

Figure 24. Streamlines over the Puget Sound area during 50the convergence zone event of May 2-3, 1978.

Figure 25. Schematic view of the low-level flow during 52a convergence event (Mass, 1981).

Figure 26. (a) Summary of the number of times the lowest 53cloud deck in Puget Sound occurred in each compos-ite zone during five convergence zone events.(b) Temperature deviations (OF) from the Puget Soundmean for each composite zone. (c) Summary of thenumber of precipitation events that occurred in eachcomposite zone during ten convergence zone events(after Mass, 1981).

Figure 27. Annual variation of precipitation for the 54rain shadow and northern, central, and southernPuget Sound regions (Mass, 1981).

v

Figure 28. Percentage contributions to total precipi- 55tation at three coastal stations and three inlandstations from warm sector, narrow cold-frontal, widecold-frontal, and post-frontal rainbands on8 December 1976.

Figure 29. Resultant wind hodographs for stations 56in the Strait of Juan de Fuca, north, central,and south Puget Sound for July 1950.

Figure 30. Average sea-level pressures at each hour 58of the day for July 1950 at Tatoosh Island, PortAngeles, Everett, Bellingham, and sea-level pressuredifferences between Port Angeles and Bellingham,Port Angeles and Everett, and Tatoosh Islandand Port Angeles.

vi

Tables

Table 1. Probability of freezing temperatures for 7three stations in the Puget Sound region.

Table 2. Average total hours of sunshine and mean 11daily total solar radiation for SEATAC Airport(1966-1975).

Table 3. Percentage frequency of occurrence of fog 13for all observations by month.

Table 4. Monthly wind speed/direction frequencies 15(1949-1958).

Table 5. Annual average concentration of suspended 21particulates for stations in the Puget Soundregion (1972-1979).

Table 6. Number of days per month with synoptic 29weather patterns Ll, L2, HI, H2.

Table 7. Comparison of winds reported by Reed (1980) 48in Hood Canal 14-15 GMT 13 February 1979 andthose calculated from Eq. 1.

vii

Marine Weather of the Inland Waters of Western Washington l

James E. Overland and Bernard A. Walter, Jr.

ABSTRACT. The mid~latitude, west coast marine climate of westernWashington is typified in summer by high sea-level pressure as partof the North Pacific weather pattern and in winter by a sequence ofstorms which originate to the west. Mean and extreme temperaturesare moderated by the proximity of the Pacific Ocean and Puget Sound,resulting in an mean temperature of 4°C in January and 17°C inAugust at Seattle.

Local variations in precipitation and wind are influenced byboth large-scale weather patterns and the region's topography. Fiftypercent of the annual precipitation for most of the inland region fallsin the four months from November through February, and less than fivepercent falls in July and August; the driest region is to the northeastof the Olympic Mountains. Over the inland waters, the winds flow fromhigh to low sea-level pressure in the direction of the local channels.

Recent studies by the University of Washington and PMEL on thePuget Sound convergence zone, sea and valley breeze, precipitationpatterns and local wind patterns are summarized. The storm whichresulted in destruction of the Hood Canal Bridge has shown that thepresence of the Olympic Mountains can induce a regional low-pressuresystem in their lee which can result in strong surface winds overthe inland waters.

lContribution number 595 from the NOAA/ERL Pacific Marine EnvironmentalLaboratory, 3711 15th Avenue N.E., Seattle, Washington 98105.

1

1. Introduction

The climate of the Puget Sound Basin in western Washington State is amid-latitude, west coast marine type. The source regions of the predominantair masses reaching Puget Sound are over the Pacific Ocean; this produces amoderating influence on the weather in both summer and winter. A prevailingwesterly-to-northwesterly flow of air associated with high sea-level pressurein the eastern Pacific results in a dry season beginning in June and reachinga peak in midsummer. l In the late fall and winter the high-pressure arearetreats to the south allowing a series of storms to cross the region, thuseffecting a wet season that begins in October, reaches a peak in winter, anddecreases in the spring. This winter pattern is occasionally interrupted bythe influence of continental high pressure which is accompanied by cold tem­peratures and dry air.

Topography has a large influence on the weather of Puget Sound (Figs. 1and 2). The region is flanked on the west by the Olympic Mountains and on theeast by the Cascade Range. The elevation of the region varies from sea levelon the Sound to 2500 mand higher in the mountains. The Cascades and theCanadian Rocky Mountains shield Puget Sound from cold air masses moving south­ward across Canada. To the west, the Willapa Hills (which lie south of Hoquiam,Washington), the Olympic Mountains, and the Coastal Range on Vancouver Islandare effective in protecting the area from more intense winter storms thatreach the coast by forcing orographic precipitation on the western slopes(Hobbs et al., 1975). The Strait of Juan de Fuca, the Strait of Georgia, andthe Chehalis River Valley provide low-level passages for maritime air to moveinland and are the primary determinant of surface winds.

The next section provides a climatological overview of air temperature,precipitation, winds, and other important climatological variables for thePuget Sound Basin. Section 3 discusses the synoptic or large-scale distribu­tion and propagation of high and low sea-level pressure patterns that influencethe meteorology of western Washington. Section 4 provides a summary of anumber of regional meteorological phenomena that contribute to the climatologyof the region.

2. Climatological Summary

2.1. Air temperature

The yearly cycle and variability of monthly mean temperatures measured atSEATAC Airport, 20 miles south of Seattle, are shown in Fig. 3. During the

lThe meteorological convention of specifying the direction from which thewind is blowing is used throughout this memorandum.

2

49

48

47N

VANCOUVERISLAND

PACIFICOCEAN

? 2,5 5.0 7,5 Iqo

KILOMETERS

BRITISH COLUMBIA

Mt. Baker

n»enn»ofTl

~ocZ----1»Zen

Figure 1. Location map for western Washingtonand southwest British Columbia.

3

~ 0-300 meters

M;!{:i.Vl 300-1500 meters

o 30 60km

Figure 2. Topographic map of northwest Washington.

4

25

20-uo---W0:: 15:::>

~0::W

~ 10wr-

5

MONTHLY TEMPERATURENORMALS AT SEATAC

JFMAMJJASOND

--- AVERAGE MAXIMUM

---- MEAN

-------- AVERAGE MINIMUM

Figure 3. Annual temperature cycle at SEATAC (National ClimaticCenter, 1980). Values are the official normals (1945-1970).

5

summer months, afternoon temperatures at lower elevations are often 20°C to25°C. Maximum temperatures reach 29°C to 32°C on a few days during a givenyear; temperatures of 38°C or higher occur infrequently. In winter, tempera­tures in the Puget Sound lowlands usually range from 3°C to 7°C in the after­noon and from -2°C to 5°C at night. Almost every winter the temperature dropsto between -7°C and -12°C on a few nights, with the coldest weather occurringduring a few short outbreaks of cold, dry air from the north or the east.

The longest growing season, 190 to 220 days, occurs on the San JuanIslands and in areas nearest to Puget Sound. Variations of several weeks inthe duration of the growing season can occur within short distances. Near thewater, the average date of the last OoC temperature in the spring is mid-April,and the average date of the first OoC temperature in the fall is near the endof October (Table 1). Temperatures of -2.2°C or lower are usually recorded 15to 30 days later (Phillips, 1968).

2.2. Precipitation

The moist maritime air that reaches the Washington coast in late fall andwinter is approximately the same temperature as the surface waters. Thus,orographic lifting and cooling of these air masses moving inland readilyresult in widespread cloudiness and precipitation. The mean annual precipi­tation chart for western Washington illustrates the extreme horizontal var­iation in precipitation (Fig. 4). The driest sections of the Sound are to thenortheast of the Olympic Mountains and receive 45 to 75 cm of precipitationannually. Over most of the lowlands, annual precipitation ranges from 100to 130 cm, increasing to 190 cm in the foothills and from 380 to 510 cm on thewettest slopes of the mountains. Due to the mild weather of the Puget SoundBasin, most of the precipitation below 500 m is in the form of rain. Theyearly cycle of rainfall measured at SEATAC Airport indicates that a largevariability of rainfall can be expected in any given month (Fig. 5). Fiftypercent of the annual precipitation for most of the inland region falls in thefour-month period from November through February. The combined rainfall forthe months of July and August is less than five percent of the annual total.

Since 1900 there has been a decrease and then an increase in the 10ng­term trend of precipitation. The ten-year mean rainfall for 1901-1910 atSeattle was 87 cm; the mean then decreased to 70 cm for 1921-1930, and hasincreased to 93 cm for the period 1961-1970 (Church, 1974).

Total snowfall in the Puget Sound lowlands is generally less than 25 cmper year and normally occurs from November to March, with maximum amounts inJanuary.

2.3. Cloud cover and fog

The P~get Sound climate is characterized by a high percentage of overcastdays (Fig. 6). The number of clear or partly cloudy days each month rangesfrom 5 to 7 in the winter, 8 to 14 in the spring and fall, and 17 or more inthe summer. Table 2 gives the average total hours of sunshine and mean dailytotal solar radiation (in calories cm-2), by month for SEATAC.

6

Table 1.--Probability of freezing temperatures forthree stations in the Puget Sound region*

(at 0°, -2.2°, -4.4°C)

Spring Months Fall Months

Station Temp. 90% 50% 10% 10% 50% 90%

Bothell OoC Apr 18 May 13 June 7 Sept 12 Oct 5 Oct 28

(1931- -2.2 Mar 19 Apr 13 May 8 Oct 7 Oct 30 Nov 221952)

-4.4 Feb 7 Mar 8 Apr 2 Oct 22 Nov 15

SEATAC OoC Mar 15 Apr 9 May 4 Oct 10 Nov 2 Nov 25

(1945- -2.2 Feb 5 Mar 9 Apr 4 Oct 26 Nov 17 Dec 161960)

-4.4 Feb 9 Mar 9 Nov 20

University OoC Feb 26 Mar 23 Apr 17 Oct 26 Nov 18 Dec 11

of -2.2 Feb 2 Mar 2 Nov 21 Dec 18

Washington -4.4 Jan 17 Feb 19 Dec 3

(1931-1960)

*After Phillips, 1968.

7

MEAN ANNUAL PRECIPITATION, 1930-1957WESTERN WASHINGTON STATE

I1240

Figure 4. Mean annual precipitation (1930-1957) for western Washington.Contours are in inches (1 in =2.54 cm). (From Philipps, 1968.)

8

35 MONTHLY PRECIPITATIONAT SEATAC

30 \ /\ /\ /

25 \ /\ ,/

./,.-..

"'" /E " /u 20 \'"-'" /z \ /0- \ /~r- 15 \ J0.. /- \u Iw

\'/""0:: /0.. 10 \ /\\ /J

5,-'/ ,

,- "'-0

............ _-- .............---J F M A M J J A S 0 N 0

---- GREATEST MONTHLY

--- MEAN

-------- LEAST MONTHLY

Figure 5. Annual cycle of precipitation at SEATAC (National ClimaticCenter, 1980). The mean is the official normal (1945-1970) and theextremes are for the period of record (1945-1980).

9

25

20

15

NUMBER OF CLEAR ORPARTLY CLOUDY DAYS ATSEATAC PER MONTH

J F M A M J J A SON D

I I CLEAR DAYS OR PARTLY CLOUDY

V/lJl//IM CLEAR

Figure 6. Annual cycle of clear or partly cloudy days (1945-1980) atSEATAC (National Climatic Center, 1980).

10

Table 2.--Average total hours of sunshine and mean daily total solarradiation for SEATAC Airport 1966-1975* (in Langleys, by month)

J F M A M J J A S o N o

Hours ofsunshine

61 122 180 208 274 257 318 287 230 140 75 45

Total solar 80 162 266 390 513 531 581 478 353 203radiation

*After Critchfield, 1978.

11

98 62

· Frequently during the summer and fall, fog or low clouds, 300 to 600 mthick, form over Puget Sound and the lowlands during the night and dissipateby afternoon (Table 3). In the fall, there is a high incidence of fog becauseof radiational cooling at night. In the summer, cool, moist coastal air isadvected into the Strait of Juan de Fuca and northern Puget Sound resulting infog formation.

2.4. Wind and wavesPuget Sound wind patterns are influenced by mountain barriers and low­

level passages (Fig. 7). In southern Puget Sound the strongest winds comefrom the south to southwest when the more intense Pacific storms move inland.During winter, the occasional presence of high pressure over the interior ofBritish Columbia can produce strong easterly winds blowing down pressuregradient through the Strait of Juan de Fuca (Reed, 1931). In summer, windsare generally light in the afternoons; a northerly sea breeze develops overPuget Sound and the lowlands, and a westerly sea breeze develops in the Straitof Juan de Fuca. Over the Main Basin of Puget Sound, extremes in wind speed canbe expected to exceed 25 ms-l once in 2 years, 40 ms-l once in 50 years, and45 ms-l once in 100 years (Phillips, 1968). The wind statistics for SEATACare given in Table 4; wind statistics for other stations, including Bellingham,Everett, and Olympia, are given in the Climatological Handbook, Columbia RiverBasin States (1968). A study of regional wind patterns for western Washingtonand southern British Columbia is given by Schoenberg (1983).

The time series of the N-S wind component and energy spectra derived froma one-year record (1975-1976) of winds at West Point, a representative locationfor the Puget Sound Main Basin, are shown in Fig. 8a (Cannon and Laird, 1978).The energy spectrum of both the N-S and E-W wind components for winter (Fig. 8b)shows peaks at 0.25 cycles day-1 (i.e., frequency of storm passage), and thespectrum for summer (Fig. 8c) has a diurnal peak in the E-W component indicatingthe dominant sea breeze/valley breeze influence between the Sound and theadjacent lowlands to the east.

The height and dominant period of wind-waves are a function of windspeed,wind duration, and fetch. An annual wave climatology for West Point (fig. 9)was calculated from windspeed and duration from SEATAC and fetches for PugetSound (Skjelbreia, 1981) using relations from the Shore Protection Manual(1973). The largest waves come from the south along the major axis of theSound during storm events. In addition, a large frequency of intermediateheight waves come from the southwest; in this case wave heights are fetch­limited during the strong post-frontal southwesterly winds.

2.5. Air qualityIn general, air quality problems are less serious in the Puget Sound

region than in other major metropolitan regions because of the proximity ofthe ocean and the tendency for considerable advection north and south throughPuget Sound. However, pollutants accumulate during periods of stagnation whenlight winds or stable stratification prevail. Since 1965, the Puget Sound AirPollution Control Agency has operated a network of monitoring stations through­out the Puget Sound region to measure suspended particulates and concentrationsof S02' CO, and 03.

12

Tab

le3.

--P

erce

ntag

efr

eque

ncy

ofoc

curr

ence

offo

gfo

ral

lob

serv

atio

nsby

mon

th*

JF

MA

MJ

JA

So

ND

Ann

Bel

lingh

am8.

45.

93.

21.

31.

72.

12.

44.

510

.017

.410

.75.

16.

0

Hoq

uiam

20.2

19.7

12.6

10.0

4.9

7.5

8.5

11.9

14.9

19.5

28.6

26.8

15.2

Pt.

Ang

eles

1.9

5.1

1.7

0.9

2.8

6.7

11.8

15.2

16.3

15.6

6.1

5.1

7.5

......

wE

vere

tt21

.820

.712

.17.

77.

012

.511

.715

.620

.829

.628

.223

.817

.6

Oly

mpi

a23

.523

.214

.78.

44.

14.

86.

09.

917

.928

.830

.425

.816

.4

Sea

Boe

ing

13.7

11.3

6.1

3.7

1.9

2.7

3.2

4.9

12.1

17.5

20.7

14.5

9.3

SEAT

AC13

.712

.56.

74.

43.

14.

66.

97.

814

.820

.321

.214

.510

.9

Whi

dbey

5.6

8.7

4.0

2.6

2.5

4.5

8.4

10.3

14.1

20.7

15.9

6.6

8.7

Tat

oosh

7.9

9.2

5.7

6.1

8.1

14.6

22.8

23.7

19.7

10.6

7.6

9.9

12.2

*Fr

omth

eC

lim

atol

ogic

alH

andb

ook

t19

68.

Mos

tst

atio

ns

repr

esen

tre

cord

sfo

r19

49-1

958.

#'

~IO

-NO

RT

HD

ALL

ES

(I)

"":':.

',.

.J~.

II-E

VE

RE

TT

(2)

~l(E

~) "-----*

41

-NO

RT

Ht"

BE

ND

(I)

'43

-TA

CO

MA

(2)

.,.. ~3

2-

CH

EH

ALI

S(I

)

.3

7-C

AS

TL

ER

OC

K(I

)

.24

-KE

LS

O(2

)4

-N

OR

THH

EA

D(I

)

46

-NO

RT

HD

ALL

ES

(I)

*-

'~Sl::ATTLE'(I)

.~33-NORTH

"B

EN

D(I

)

56

-TA

CO

MA

(2)

*,2

2-C

HE

HA

LIS

(I)

'.!2~C

AS

TLE

RO

CK

(I)

24

-KE

LS

O(2

)

.......

4=>0

JANU

ARY

JULY

SP

EE

DS

YM

BO

L

-- ®

IND

EX

CLA

SS

IND

EX

CLA

SS

III4

-15

12 14

-12

I16

-31

213

-31

I3

2-4

72

32

-46

I4

8+

24

7+

AL

LS

TA

TIO

NS

HA

VE

TH

ES

AM

ER

AN

GE

(0-3

MP

H)

SC

ALE

INP

ER

CE

NT

OF

TIM

E

II

1--.

o25

50

75

Figu

re7.

Janu

ary

and

July

surf

ace

win

dro

ses

for

wes

tern

Was

hing

ton

(aft

erP

hil

lip

s,19

68).

Thi

sfi

gure

mus

tbe

inte

rpre

ted

with

som

eca

reas

stro

nges

tw

inds

atea

chst

atio

ndo

not

nece

ssar

ily

occu

rdu

ring

the

sam

esy

nopt

icev

ent.

Table 4.--Monthly wind speed/direction frequencies*(1949-1958) for SEATAC

JAN U A R • F E B R U A R •

HCURLY CaSERYAT 10~S OF .I~O SPEEO HOURLY CBSERYATlO~S OF .I~O SPEEO"IUS PER HOUR "ILES PER HOUR

1 • 8 13 19 25 32 39 1 • 8 13 19 25 32 39Ie TO TO TO TC TO TO TO OYER AYE TO TO TO TO TO TO TO TO OyeR AYE

lolR 3 1 12 18 2. 31 38 'b .b TOUL SPEEO OIR 3 1 12 18 2' 31 38 'b .b TOUL SPEEO

.. J .b ';.9 2.5 1.5 0.5 ).1 b.O 11.0 ~ 0.' 0.9 2.0 1.5 0.3 0.1 5.2 11.2NNe J.3 1.) l.8 2.1 ".3 • b.5 11.2 ~He 0.' 1.1 2.9 1.1 0.2 b.3 10.b~E J.l 1.1 2.2 J.l • 5 •• 8.2 HE 0.5 I.' 1.9 O.b • •• 5 B.5E~E :i.l\ J .1 C.b J.l 1.1 1.0 E~E 0.3 0.1 0.1 001 I.B 1.0E 1.1 2.J 2.2 O.B 0.1 bol 8.0 E 0.1 I •• 1.1 O.b •• 3 1.8ESE 1. ) 3.·"" •• 9 1.2 0.1 1001 B.b nE O.b 2. B 2.9 1.0 0.1 1.5 8.5~E 1.3 3.1 '.b 1.0 • 10.1 1.9 SE O.b 2.1 303 0.5 • 1.2 1.9HE 0 •• 1.B 2.b ).b 0.1 5.b B.l SSE 0.3 2.0 2.2 O.b 0.1 • 5.' B.lS ';.3 1.5 3.1 3.e 0.9 0.2 9.b 12.2 S 0 •• 1.1 3.5 2.9 0.1 0.2 9.3 11.bSS. J .2 J.B 3.1 5.' 2.2 0 •• '.1 12.B 1'.1 SS. 0 •• 1.1 3.1 b.l 2.B O.b 0.1 1•• 9 1'.8S. 0.3 J.l 2.3 •• 1 2.b 0.1 • 10.B 15.6 S. 0.3 0.9 2.B '.b 3.3 0.1 12.1 15.5.S. J.2 J.' J.l O.b 0.3 J.2 • 2.3 13.2 .S. 0.3 0.1 O.B 1.0 O.b 0.3 3.5 13.3

• 0.1 ~.3 ·J.2 • · • 0.1 1.5 • 0.2 0.' 0.5 0.1 0.1 · 1.3 B.5.". j .2 J.I Jol · a•• 5.8 .~. 0.2 0.5 0.2 . • 0.9 b.O~. J.I ".2 Jol · 0.5 101 ~. 0.2 O.b 0.3 . • 1.2 b.lif",.. ~.3 .,;,.It ::'.4 ·).3 J.1 1.5 9.b ~~. 0.1 0.1 1.0 0.' 0.1 2 •• 10.1CUll 9.3 9.3 CALM 11.b 11.bTOTAL 1b .b 19•• 33.5 21.b 1.3 1.b 0.1 100.0 9.9 TOUL 11.' 19.b 30.b 22.0 8.' 1.9 0.1 100.0 10.0

)II IRe ~ APR I L

HOURL. CBSERYAT ICHS OF •• "0 sp~eo HOU~LY OBSERYATlO~S OF .I~O SPEEO~ILES PEA HOUR MILES PER HCUR

1 • 8 13 19 25 32 39 1 • B \3 19 25 32 39T~ TO TO TO TO Til TO TO OYER AYE TO TO TO TO TO 10 10 TO OYER AYE

UlK 3 1 12 18 2' 31 3B .b 'b TOTAL SPEEe OIR 3 1 12 18 2' 31 38 'b .b TOTAL SPEEO

N 0.2 J.B 2.2 1.1 ".2 5.1 11.1 ~ 0 •• 1.1 3.1 2.1 0.3 0.1 b.9 n.9~~E J •• 1.J 2.1 1.5 0.2 5.B 10.2 ~~E 0.2 1.2 3.3 2.0 0.3 1.0 11.0~E J .b 1.2 2.J ).7 · '.5 8.5 ~E 0.5 1.B 2.B 1.2 0.1 b•• 9.1ElfE 0.3 ~.B 0.9 J.2 · 2.2 1.9 E~E 0.3 O.B 1.0 0.2 · 2.3 1.9E O.B 1.5 1•• J.8 .J .1 '.b B.5 E 0.5 1.0 1.0 0.3 • 2.8 1.5E~E J •• 2.3 3.2 1.0 0.1 1.5 B.5 ESE 0.3 I.B 1.1 0.3 0.1 3.5 1.bSE ':;.8 2.9 2.b J.5 · b.B 1.b SE J.l 2.3 2.2 0 •• '.5 1••S~E J.5 1.1 2.·; '.6 ~.I •• B B.b SSE 0.3 1.b 1.9 0.5 0.1 • •• 3 B.B5 J.5 1.8 3.2 2.1 0 •• : .1 B.1 10.1 S ) .. 1.b 2.b 1.8 0.3 0.1 b.9 10.655. ).3 I •• •• 5 5 •• 1.B ) .2 13.1 13 •• 55. J.3 I.' 3.9 3.1 0.9 0.1 10.3 12.2s. J .3 1.1 •• 0 5.b 3.8 c•• 15.1 15.3 S. 0.3 I.' ••• 5.9 3.2 0.5 16.0 I','.. ~ .. J .1 0 •• 1.5 1.1 C., :" .2 5.5 13.5 "5" 0.3 1.3 2.3 2.2 0.8 0.1 b.9 12.'.. 0.1 J.b 0.8 Col 0.1 · 1.9 '.8 • 0.5 0.9 1.3 C.b 0.1 · 3•• 9.0wNW 0.3 J.B J.b · 1.1 b.5 ..~ .. 0.3 0.8 0.9 0.2 2.2 1.8~ .. 0.3 J.b 0.1 ).1 l.b 1.3 ~. 0.3 0.9 1.3 0.3 2.9 a.b~~. :J.2 J.b C•• ~.7 0.1 2.5 10.1 ~H.. 0.3 o.a 1.2 I.' 0.1 3.8 10.9CAL" 8.0 B.O CAL" a.8 a.8TOUL 1'.5 1'.8 33.1 23.1 1 •• 1.5 ~ .1 100.0 10.2 TOTAL l'.b 20.b 3'.2 23.1 b•• 1.1 0.1 100.0 9.B

~ A • J U ~

HlJURL. 08SERYA T10~S OF .. I~O SPEEU HOURL. OBSERY AT I O~S OF "INO SPEED"ILES PER HUUR MILES PER HOUR

I • 8 13 19 25 32 39 1 • a 13 19 25 32 39TO TO TO TO TO TO TO TO OYER AYE TO TO TO TO TO TO TO TO OYER AYE

OIR 3 1 12 18 2. 31 38 4b 4b TOTAL SPEED OIR 3 1 12 1B 24 31 3B 4b 4b TOUL SPEED

N , .4 1.3 '.b 2.1 0.1 9.1 10.b ~ 0.3 1.3 3.5 2.0 0.2 1.2 10.bNNE 0.3 1.5 3.B 1.9 0.1 1.b 10.3 NNE 0.3 I.' 3.2 1.b 0.1 b.l 10.1HE v •• 1.1 3.9 1.9 0.1 8.0 9.9 ~E 0.2 1.3 2.9 1.2 0.1 5.b 9.1ENE ~.2 ".1 ;.9 0.2 2.0 8.1 E~E 0.2 0.5 0.1 0.1 1.b 1.1E 10.5 J.B 0.1 0.1 2.1 b.5 E 0.3 O.b O.b 0.1 1.5 1.1ESE 0.' 1.1 0.9 ).1 2.b 1.0 nE 0.' O.B 0.' 0.1 1. B b.2SE u.1t 1.8 1.2 0.1 3.1 b.' SE 0.3 1.1 1.1 0.1 2.1 1.2SSE 0.2 1.1 1.2 0.1 3.3 1.3 SSE 0.3 1.0 1.2 0.1 2.5 1.5S e.3 1.9 3.0 0.5 • 5.1 B.5 S 0.' 2.1 303 0.9 • b.l B.lSS. 0.' 2.' ••• 2.3 0.2 9.a 10.0 SS. 0.5 2.3 5.8 3.0 J •• • 11.9 10.bsli 0.3 2.1 b.' 5.5 1.1 0.1 lb. 1 12.' S.. 0 •• 2.9 8.B b.9 1.3 0.2 20.' 11.a"5.. 0.2 1.5 3.J 1.9 0 •• • 6.9 10.9 .S.. 0.3 1.9 3.b 1.8 0.2 1.9 10.1.. v.3 1.1 1.9 0.5 0.1 · 3.9 9.2 • 0.3 1.b 2.3 O.b · '.a a.l..... 0.2 1.2 1.3 0.2 2.9 1.9 ..... 0.3 1.3 1.b C.2 3.5 1.1... 0.2 1.3 2.0 0 •• • •• 0 B.5 ".. 0.3 0.9 1.5 0 •• 3.1 B.5H". 0.2 I... 2.2 1.b 0.1 5.1 10.5 H~. 0.2 1.0 1.1 0.8 0.1 3.1 9.9CALM 1 •• 1.b CALM 8•• B••TUTAL 12.1 23.1 .1.2 20.0 2.B 0.2 100.0 9.2 TOTAL 13.' 21.9 '2.1 20.0 2 •• 0.2 100.0 9.1

From the Climatological Handbook, 1968.

15

Table 4.--cont.

J U l Y AUG U 5 T

HOURLY o~~~RVAT IONS OF wIND SPEEU HUURlY 08SERVATIONS UF WINO SPEEDMileS P':A HQUR NILES PER HOUR

1 ~ 8 13 U 25 32 39 1 ~ 8 13 19 25 32 3910 TO TO TO TO TO TO TO OVeR AVE TO TU TO TO TO TO TO TO OVER AVE

olA 3 7 12 18 2~ 31 38 ~6 ~6 TUTAl SPEED olR 3 7 12 18 H 31 38 ~6 ~6 ToUl SPEED

N J.~ 1.7 ~.5 2.2 0.1 8.9 13.1 II O.~ 1.~ ~.7 1.~ 7.9 9.6NNE 0.3 1.9 5.0 1.9 0.1 9.1 10.0 NNE 0.5 1.7 ~.2 1.6 • 8.1 9.5NE ~.4 1.9 3.8 1.7 0.1 7.9 9.6 NE 0.7 1.8 3.~ 1.0 • 7.0 8.8ENr u.3 J.8 0.9 ,).2 • 2.3 7.9 E..E 0.3 0.7 0.8 0.1 1.9 7.3i a;,.3 ; ... e.1 • 1.0 5.~ E o.~ 0.9 0.3 1.7 5.3ESE C.2 J.5 0.3 1.0 5.7 ESE O.~ 0.7 O.~ • 1.6 5.9~E J.3 J.8 ~.8 • 2.0 6.6 SE '.5 1.5 1.0 • 3.0 6.5SSE 0.2 0.9 1.1 • 2.2 7.2 SSE 0.3 1.7 1.1 • 3.1 6.7S c .4 1.7 2.7 0.5 • 5.3 8.2 S 0.8 2.2 2.9 0.3 • 6.3 7.5S~W ,.~ 2.2 Sol 1.3 C.2 9.3 9.2 SSw '.7 2.6 ~.7 1.5 0.1 9.5 9.0~w J.7 3.3 8.0 3.5 ~.4 16.0 1C.1 SW ,).8 2.8 6.2 2.9 0.3 • 13.0 10.0wSW :: ... 1.9 3.3 1.1 0.1 6.7 9.1 wSw '.5 1.9 3.3 1.0 0.1 • 6.7 8.9W ~.~ 1.9 2.6 V... 0.1 5.~ 8.5 W 0.5 1.8 2.2 ,.~ • ~.8 7.9WNW " .2 1.6 1.8 o.~ ~.O 8.2 WNW O.~ 1.5 2.1 0.3 • ~.2 8.0..W 0.3 1.~ 2.1 C.7 ~.5 8.7 N. 0.5 1.5 2.3 0.6 ~.9 8.~

..NW ) .2 1.2 2.8 1.~ 5.6 10.2 ..NW O.~ 1.0 3.0 1.0 5.5 9.5tUN 8.e 8.8 tAlN 11.0 11.0ToUl ".3 H.3 44.9 15.6 1.J l.JC.O 8.~ ToUl 19.0 25.7 ~2.5 12.1 0.6 100.0 7.7

5 E P 7 ~ ~ 8 E R OtT 0 8 E R

HOURLY o8SERVATI0.. s OF WI ..o SPEED HOURLY 08 SERV AT I O"S OF WI ..o SPEEDIIILES PER HOUR NILES PER HOUR

1 ~ 8 13 19 25 32 39 1 ~ 8 13 19 15 32 39TU TU TO TO TO TO TO TO OVER AYE TO TO TO TO TO TO TO TO OVER AVE

UIR 3 7 12 18 2~ 31 38 ~ .. ~6 TOUL SPEEO aiR 3 7 12 18 H 31 38 ~6 ~6 TOUl SPEED

.. J.7 1.8 S.:' 3.1 J.3 11.0 10.5 N 0.5 2.0 ~.~ 1.3 • 8.3 9.3NNe '.7 1.9 5.0 2.7 0.2 10.5 10.2 "NE O.~ 2.~ ~.5 2.3 0.3 9.8 10.2NE , .7 2.3 3.9 1.~ 0.1 8.~ 9.0 NE 0.6 2.2 2.5 0.9 0.1 6.~ 8.5ENE ~ .3 J.6 0.6 J.1 1.6 6.8 ENE 0.3 0.7 0.6 0.1 • 1.8 7.1E 0.5 1.3 :;.5 • 2.3 5.8 E 0.7 1.2 1.2 O.~ 0.1 3.5 7.9ESE '.5 1.2 1.0 • 2.8 6.6 ESE 0.8 1.9 2.5 0.7 0.1 6.0 8.0SE 0.8 1.9 2.J ~.2 ~.8 7.1 SE 0.6 2.5 3.9 0.7 • 7.7 8.3S)E 0.7 1.5 1.~ '.1 • 3.7 6.8 SSE o.~ 1.7 2.~ 0.7 0.1 5.2 8.7) .1.6 1.8 3.3 0.8 0.1 6.6 8.8 5 0.5 2.2 3.8 2.8 0.8 0.1 10.3 11.1SSW ~.~ 1.9 ~.6 2.2 ';'.3 9.5 10.~ SSW O.~ 1.~ ~.1 3.7 1.~ Ool 11.3 12.9SW u.b 2.2 ~.~ 2.7 0.6 J.1 10.6 10.6 SW 0.2 1.0 2.6 3.3 1.3 0.2 8.6 13.3WSw 0.5 1.J 1.~ ':.6 0.1 • 3.7 9.0 WSW 0.1 0.7 1.1 0.6 0.3 • 2.7 11.1W 0.1 1.2 1.2 J.3 • 2.9 7.7 W 0.3 0.5 0.6 Col • 1.5 7.6WNW o.~ 1.2 0.8 '.1 2.5 6.6 WNW '.2 0.7 0.6 • 1.6 6.8NW 0.1 l.~ 1.' -:'.2 2.5 7.' NW 0.3 0.7 0.7 0.1 • 1.8 7.3NNW .1.3 I.e 2.1 1.1 0.1 ~.6 9.9 NNW 0.2 0.7 1.2 o.~ 0.1 2.6 9.1tAlII 11.9 11.9 tAlII 10.9 10.9TOUl 20.1 23 ... 3~.' 15.5 1.8 0.2 100.0 8.1 TOUl ll.~ 22.5 36.7 18.2 ~.7 0.6 100.0 8.9

~ a V E ~ 8 E A OEtEM8ER

Hl;UAlY C8SEAVAT ICNS OF W'''O SPEEO HoUAl Y 08SERVATTONS CF WI"O SPEEO~ILES PEA ~UUA MILES PER ~DUR

1 ~ 8 13 19 25 32 39 1 ~ 8 13 19 25 32 39TO TU 10 TO TO TO TO TO UVEA AVE 10 TO TO TO TO TO TO TO DVEA AVE

UIA 3 7 12 18 2~ 31 38 ~6 ~6 ToUl SPEEO OIR 3 7 12 18 2~ 31 38 ~6 ~6 TOUl SPEED

II 'J.' 1.2 J.a I.e e.3 • 6.8 10.6 .. 0.2 0.9 1.5 0.9 0.2 3.8 10.3....E J.~ 1.~ 3.0 l.J .) .1 ;.1 7.0 1C.3 ....E 0.3 ).9 2.~ 1.9 0.3 '.8 11.0.;E vol 1.1 1.8 J.9 • ~.1 9.~ "E 0.3 1.' 1.5 0.6 • 3.~ 8.9

E"E 0.3 ,.6 :l.T j.2 1.7 7.7 ENE 0.2 0.6 0.3 0.1 • 1.3 7.6[ J.B 1.~ 1.~ J.~ ~.O 7.3 E 0.8 1.~ 1.5 0.8 0.2 ~.7 8. ,

ESE J.8 2.1' 3.6 1.3 0.2 7.9 9.1 ESE 0.7 2.(' 3.5 2.1 0.3 8.5 10.0SE 0.8 3.5 5.2 1.~ 0 .. 1 11.0 8.5 SE 0.6 3.3 ~.~ 1.6 0.1 10.1 8.9SSE J.~ 2.,) 2.8 1.) 0.1 6.5 8.8 SSE o.~ 1.7 3.0 1.1 001 6.~ 9.3

S J.5 1.9 3.6 2.9 0.8 c.2 J •.1 9.9 11.' 5 0.5 2.2 ~.~ ~.~ 1.~ 0.3 13.2 12.3))w '-.1.4 1.) 2.7 3.7 1.9 :".4 10.1 ...C SS. 0.2 1.2 3.9 6.5 3.~ 0.8 0.1 16.1 15.1SW J.3 1.1 2.3 J.2 1.9 0.6 0.1 9.5 1~.6 SW o.~ 1.0 3.0 3.9 3.1 1.1 0.2 12.6 1'.7WSW 0.3 J." 0.7 '.6 o.~ ).1 • 2.7 12.3 wSw 0.1 0.2 0.5 0.6 0.2 0.2 • 1.7 13.7W O,J ,.~ ":.3 0.1 • 1.0 7.C W 0.2 0.3 0.2 001 • • 0.8 8.6w..w 0.2 J.3 J.2 • 0.7 5.9 W... 0.1 0.1 0.1 O.~ 6.~

N. 0.2 ':'.4 C.~ 0.1 ) .1 1.2 8.8 Nw 0.1 VIOl J.1 O.~ 7.6..Nw J.3 J.5 O.T ·J.1 • 1.7 8.1 NNW 0.1 0.2 0.2 C.1 0.7 8.8CALli ... ; ".0 CalM 10.2 10.2TOUl .21.", 19.5 32.3 19.6 6.J 1.5 C.2 100.0 9.1 TOUl 15.~ ll.~ 3C.6 2~. T 9.3 2.~ 0.3 100.0 10.6

16

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~ 0 ~-lJ-'~--Ii-~-HJl--!H--,J--JH!-.WH'~---t-t-b't

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S -20 ~~""""'T~""""i"li'i'",'"

SEPT 75 OCT NOV

N 20 r--------------~---~--~----I

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N 20 .,.----------------~--~---____r

u ~Iv,Q) -I-h-~~~+J-+-_II_+'.\_____+.l,._jUJj~Ii4!_~Ithtt_l__J+rlI_\h_t_:___ttttHf!ttH_++.+~ \iLi~ 0 ,(: J I:i IE I ~ f ~

~, , iii iii iii iii ii' ii' iii iii ii' , iii iii iii ii' iii iii' iii iii i , , i , i , iii i" i , iii i i rrrrrJMAR APR MAy

S -20

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~ 0 +f-:l+-fIflHHl--Il+:-H-I-lJI-II+l+-+----H+++JI.4hI--+lIh--I-:-+J+\jH­E

JUNE JULY AUG

Figure 8a. One-year time series of the N-S wind component for West Point.For this chart a positive north component means the wind is from thesouth (Cannon and Laird t 1978).

17

WES

TPTW

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(Can

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).

WEST POINT WIND-WAVE ROSE

PERCENT OCCURANCE2 4 6 8 10 12

)MAXIMUM STORM CONDITIONS-I1---

Hs =4.9 ~

Ts =4.6 MAXIMUM STORM CONDITIONSHs =6.0 _____

Ts =5.0 PERCENT CALM 16.3

-----­MAXIMUM STORM CONDITIONSHs =4.3_____

~TS'4.4

Me~I~~!MS~TOR(;MCONDITIONS

T?4.2

MAXIMUM STORM CONDITIONSHs =4.1Ts=4.1

LEGENDCHARACTERISTIC WAVE

Hs (ft)

Ts (sec)

UP TO 1.0,Ts =2.0Hs=1.0, Ts=2.0 TO Hs=2.5, Ts=3.5

OVER Hs=2.5, Ts=3.5

,., , ..::..,

Figure 9. Annual wave climatology computed for West Point from the windclimatology at SEATAC (Skjelbreia, 1981).

20

Suspended particulate concentrations in the air over the industrializedDuwamish Valley and the tide flats of Tacoma have regularly exceeded estab­lished local and national standards since monitoring was initiated (Table 5and Fig. 10). The long-term trend in suspended particulate concentrations overthe region decreased until 1976 and then leveled off or increased slightly from1976 to 1979. Increases in particulates were observed in both industrial andsuburban residential areas in 1979, with seven stations exceeding the nationalstandard of 75 ~g m- 3. Monthly averages above 160 ~g m- 3 have been measuredin the two major industrialized areas.

Of the stations monitoring ozone concentrations, four of ten in 1978and seven of nine in 1979 measured levels that exceeded national standards.Ozone concentrations are higher in summer months due to more hours ofsunlight per day, with maximum concentration normally occurring 10-30 krnsoutheast of major urban centers.

Of the stations monitoring CO concentrations, ten of twelve in 1978 andnine of thirteen in 1979 reported levels that on at least two occasions ex­ceeded an 8-hour average of 9 ppm, the national ?tandard. High ambientlevels of CO occur near congested areas where there is slow-moving motorvehicle traffic and when low-level winds are light and stable meteorologicalconditions exist.

Table 5.--Annual average concentration of suspended particulates lfor stations in the Puget Sound region 1972-1979*

Year Everett Duwamish Tacoma Auburn

1972 60 97 94 551973 53 111 82 631974 40 77 69 511975 36 66 54 381976 45 83 87 491977 43 94 91 541978 45 100 98 541979 50 101 107 62

l(~g m- 3).*(Puget Sound Air Pollution Control Agency, 1972-1980).

21

PUGET SOUND RIR POLLUTION CONTROL RGENCYSDlJl17'---+--~---.:--r--'--+-_""'""'----._---.::--'--+---+----+----t-----c_--+---+----+----t--_------t

TI1T WATER RES

+10 r--

N

~

SUSPENDED PRRTICULRTES1980 RNNURL GEOMETRIC MERNS

(MICRClGRAMS/CU METERI

'"20

. . ., , , , ,. .""-["5

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THUAS TON CO I, PIERCE CO

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---~~~~_fQ._--------KING CD

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!I2ll5Jl+----+---t---+...::::".-t---+---+---t---+--t---+----+----+---+--t---+---+---t---+----+mo 5Is"o S!O.O z.o D:I.D ~.D '10.0 !5It5.D !!5O,o ~ S1.O 565.D 57O.D .,.,.",0 580.0 ~.D ~ 9!l.O 600.0 &m.£J

UTM (KILOMETERS ERST!

Figure 10. Mean annual particulate concentration for 1980 (Puget SoundAir Pollution Control AgencYt 1980).

22

2.6. Surface hydrology

The mean annual flow for the major rivers of the Puget Sound regionvaries greatly with locality (Williams et a1., 1982). By far the largestinput is from the northern tributaries, with the Skagit River being thelargest single source (Fig. 11).

There are two periods of high stream flow each year (Fig. 12). Oneoccurs during the fall and winter, coinciding with the season of maximum pre­cipitation. The other, in late spring and early summer, is caused by snowmelt in the mountains, augmented by rainfall. Streams rise to near or aboveflood stage several times during each rainy season; the highest flood crestsoccur in late fall and early winter. Stream flow also shows large variabilityfrom year to year (Fig. 12b).

3. Large-scale Meteorological Characteristics

Throughout the winter the synoptic (large-scale) meteorology over PugetSound is characterized by a sequence of cyclonic (low sea-level pressure) dis­turbances (Klein, 1957) that move over or to the north of the region. Thissequence is interrupted infrequently by anticyclones (high sea-level pressureregions). Spring and autumn are transition periods when the frequency andintensity of cyclones diminish and increase respectively. Summer is markedby light cyclonic activity and by long periods of anticyclonic influence dueto the intrusion of a high-pressure region from the north Pacific.

Winter cyclone tracks for the Northeast Pacific indicate that most ofthe air masses affecting Puget Sound have their origin in the central Pacific.While it is difficult to generalize all synoptic weather charts, two typicalstorm types suggest themselves (Reed, 1932). In the first type, designatedLl (Fig. 13a), pressure patterns are associated with a large and extensivelow-pressure area in the Gulf of Alaska and a series of accompanying coldfrontal systems. The center of the low pressure usually drifts slowly,whereas the frontal systems advect rapidly across the Pacific, rotatingabout the center of the low. The warm sector ahead of the front is usuallyof small extent by the time it is in the vicinity of the coast; therefore,classical warm fronts are often weak and diffuse although they are stillassociated with stable air masses.

As the storms approach the coast, they are modified by the effect of thecontinent (Lau, 1979). The surface features of the cold front in Ll oftenrapidly approach the coast and slow, while higher level features continue tomove over Puget Sound. The severity of the weather associated with the frontis not always as great as it is when the storm system is over the Pacific.Thus, it is often difficult to forecast the timing and severity of frontalfeatures over Puget Sound by extrapolating the speed of the storm while itis over the Pacific. The CYCLES project is an extensive study of the meso­scale and microsca1e organization and structure of clouds and precipitationin storms affecting western Washington (Hobbs, 1978; Hobbs et a1., 1980;Parsons and Hobbs, 1982).

23

N ~

48

0

47

0

124

012

30

122

0

Fig

ure

11.

Mea

nan

nual

runo

ff(m

3s-

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get

Soun

d.P

erio

dsof

reco

rdva

ry(W

illia

ms

etal

.t

1982

).

MEAN MONTHLY RUNOFF

1400

SKAGIT

SUM

AUG SEPJUNAPR

MONTH

FEBDEC

/----, ~--\

/' / \/ " // \

/ - / \/ ---- \/ \

/ '\.'\.

~------ ... _-- -----........" SNOHOMISH...- ------------------- " '---

.-- '--",------. PUYALLUPO-+----.---....-----r---..,.------,-----,

OCT

200

400

1200

1000

lJ) 800........l""l

ELLLL0 600z:::::l0::

Figure 12a. Mean annual cycle of discharge for Puget Sound's three majortributaries (Williams et al., 1982). The period of record for the Skagitwas 1941-1979, the period for the Snohomish was 1963-1979, and the periodfor the Puyallup was 1914-1979.

25

AN

NU

AL

RU

NO

FF

1200

SU

M

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IT

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1000

80

0

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78

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66

oI

II

II

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64

YE

AR

Figu

re12

b.In

tera

nnua

lv

aria

bil

ity

ofdi

scha

rge

for

Puge

tSo

und1

sth

ree

maj

ortr

ibu

tari

es(W

illia

ms

etal.

,19

82).

a

.~.~~

b

.~.~-

....

d

Figure 13. Typical weather patterns affecting the Pacific Northwesta) Ll, b) L2, c) HI, d) H2 (Maunder, 1968; Overland, 1981).

27

In the second type of storm, L2 (Fig. 13b), small disturbances form inthe central Pacific and move across the Pacific on a northeast trajectory,commonly passing parallel to the coastline or crossing over British Columbia.Such systems can rapidly intensify as they propagate north, seaward of thecoastline, and produce some of the most severe P~get Sound weather, such as theColumbus Day storm in 1962 (Lynott and Cramer, 1966). A subset of this typeis small synoptic-scale cyclones or II vortices ll

" that form in the western Pacificbehind major frontal bands such as Ll (Reed, 1979; Mullen, 1979; Locatelli etal., 1982).

At some time during most winters an upper-level blocking ridge of highpressure will develop over northwest Canada, accompanied by high pressureover the Puget Sound region, HI (Fig. 13c). As a result, there are clearskies due to air mass subsidence induced by the high-pressure area, near­freezing temperatures, and very stable air in the surface layer of the atmos­phere (Overland and Walter, 1981).

The summer season in Puget Sound is influenced by marine air from thePacific moving over the region by way of the Strait of Juan de Fuca (Mass,1982). From the end of June through August the synoptic situation is char­acterized by a marine high-pressure system influencing the area, H2 (Fig. 13d).This high-pressure influence leads to a dry season with many clear days, warmtemperatures, and prevailing winds from the west to northwest. Cyclonicdisturbances may still occur, but their severity is greatly lessened and theirfrequency is likewise diminished compared to winter.

The spring season is not significantly different from winter except thattemperatures are higher due to increased insolation; the frequency of cyclonicdisturbances decreases, and their distribution over time is irregular. Thestrength of the upper-level flow diminishes in intensity as spring progresses.

Autumn is another transition period. A common characteristic of earlyautumn is the continuing influence of the Pacific high-pressure system in thearea. The high-pressure ridge eventually breaks down, shifting the prevail­ing winds to southwesterly and strengthening the upper-level flow. With thisshift come the cyclones and fronts associated with winter.

The frequency of occurrence of these major map types is summarized byTable 6 derived from Maunder (1968). During winter months, December throughFebruary, lows predominate over highs by 3:1; type Ll forms 62% of the observedlows. By contrast, for the summer months, July through September, type H2dominates on 48% of the days. Further discussion of typical synoptic weathersituations for western Washington is given in Halladay (1970).

28

Table 6.--Number of days per month with synoptic weatherpatterns L1, L2, HI, H2*

Weather Monthpattern

J F M A M J J A S 0 N 0 YEAR

L1 14 10 7 12 7 4 5 5 5 14 10 13 106

L2 9 4 11 10 6 6 4 7 6 4 13 11 91

HI 4 2 3 0 1 1 1 1 3 6 3 4 29

H2 3 14 8 7 13 15 16 14 16 5 2 3 116

*Adapted from Maunder, 1968.

29

4. Regional Meteorological Phenomena

4.1. Overview

Regional weather phenomena are the result of the superposition of forcingon synoptic (1000 km), meso- (50 km), and local (5 km) scales. The inter­action of synoptic-scale weather patterns and the topography of the regiondetermines mesoscale and local meteorological features. For example, theOlympic Mountains affect wind and precipitation patterns because air massstability confines airflow to the low-level marine channels, the N-S-orientedCascade Mountains have a blocking effect on large-scale weather systems, andthe proximity of the inland waters to the Pacific Ocean to the west and thehighlands to the east of Puget Sound produces a strong diurnal variation ofthe summer wind pattern due to generation of land and sea breezes and valleywinds.

The mountains restrict the free movement of air at sea level, whichprevents geostrophic adjustment between pressure and wind, so that the earth'srotation has little effect on the direction of the wind; winds blow predom­inantly from high- to low-pressure in a direction dictated by the orientationof the low-level channels. Since Puget Sound is oriented at approximately aright angle to the Strait of Juan de Fuca, high pressure to the east giveseasterly (i.e., down-gradient) winds in the Strait of Juan de Fuca and lightwinds in Puget Sound, while low pressure to the north gives strong southerlywinds in Puget Sound and light winds in the central part of the Strait of Juande Fuca. Wind speed (in knots) for the Strait of Juan de Fuca is roughly tentimes the difference in the sea-level pressure (in millibars) at Bellinghamand Quillayute; the wind speed for Puget Sound is roughly ten times the dif­ference in pressure at Olympia and Bellingham (R. Anderson, personal communi­cation; Overland, 1981).

Because of the different orientation of Puget Sound and the Strait ofJuan de Fuca, a frontal passage can lead to differing time sequences of windsin the two regions (Church, 1938). For a typical example (Fig. 14), at 0500Pacific Daylight Time (PDT), the lowest sea-level pressure is at the coast,which creates east winds in the Strait of Juan de Fuca. By 1100 PDT, thefront has passed over the inland waters, and pressures are beginning to in­crease to the south behind the front giving rise to southerly winds in PugetSound. By 1700 PDT, the front has passed to the northeast of Bellingham, andpressures have increased at the coast reversing the wind direction to westerlyin the Strait of Juan de Fuca. Thus, the winds in Puget Sound have increasedand then decreased from the south during the frontal passage, while the winddirection in the Strait of Juan de Fuca has reversed from east to west.

The following sections review studies that have recently led to a consider­able increase in understanding of the factors affecting the meteorology of thePuget Sound region.

30

49

0

~'~--1:'

W1

48

I.....

.'-

--Q

UI\

I,o

vute

~,.

,'"

\..J

'I

)\,IIOY

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mb

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r-j

VJ

VVrU~~f:

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I11

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1250

124

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ure

14.

Typ

ical

loca

lw

ind

pat

tern

sfo

rth

epa

ssag

eof

afr

ont

thro

ugh

wes

tern

Was

hing

ton

(Ove

rlan

d,19

81).

4.2. Gap winds and bora

Several times during most winters a cold high-pressure area is es­tablished east of the Cascade Mountains with a low-pressure system offshore(Fig. 15a). This situation results in a large east-west pressure gradientover the Puget Sound region and the formation of locally strong and at timesdestructive winds. Reed (1931) applied the term "gap winds" to the strongeasterly winds observed in the Strait of Juan de Fuca under these conditionsand characterized these winds as II not being, properly speaking, gradient windsin that geostrophically balanced pressure gradients are totally inadequatealone to account for the velocities observed." He defined "gap winds" as theflow of relatively homogeneous air in a sea-level channel with a source regionor reservoir at one end. A component of the pressure gradient parallel to thechannel causes the flow to accelerate along the channel. Reed also concludedthat the high velocities in the Strait of Juan de Fuca were due to a venturieffect caused by the converging sides of the channel.

In a more recent investigation of gap wind conditions, Overland andWalter (1981) combined high-resolution, low-level (50-m) wind fields derivedfrom aircraft flights over the Straits of Juan de Fuca and Georgia with surfacedata and upper-air soundings. It was found that the presence of convergingsides of the channel was incidental to the increased wind speeds and thatacceleration due to the pressure gradient along the channel alone was suffi­cient to explain the observed wind magnitudes. An example for the period2040-2400 GMT 23 February 1980 is shown in Fig. 15b. Winds in the Strait ofGeorgia were light and variable where the pressure gradient was flat; in theeastern part of the Strait of Juan de Fuca the flow was generally disorganizedbut tended to have an easterly component. In the central and western portionof the Strait of Juan de Fuca the component of the pressure gradient along theaxis of the channel remained nearly uniform, while the winds increased to14 m s-l at the entrance to the Strait. Vertical wind speed measurements fromthe aircraft indicated that subsidence was occurring over the inner part ofthe Strait of Juan de Fuca and the Strait of Georgia, whereas vertical motionwas upward west of 124°20'W.

For the inland waters of Puget Sound and the Strait of Juan de Fuca, theacceleration of the wind provides the primary balance to the component of thesea-level pressure-gradient force imposed by the synoptic weather situationalong the direction of the various channels. For flow at constant height theincrease in wind speed due to a constant sea-level pressure gradient is givenby the Bernoulli equation:

(1)

where u is velocity, Uo is an initial velocity, ~p is the pressure difference,and p is a density.

A situation similar to 23 February occurred on 13 February 1980, but inthis case the major pressure gradient was situated over southern BritishColumbia (Fig. 16a). The pressure gradient accelerated the cold, dry contin­ental air from the interior of British Columbia through the Fraser River

32

45°

~4

0°

a

Figu

re15

.(a

)S

ea-l

evel

pres

sure

anal

ysis

for

00GM

T24

Febr

uary

1980

for

wes

tern

Was

hing

ton

(Ove

rlan

dan

dW

alte

r t19

81).

55°

50°

45

°

48

0

126°

W

b

1250

1240

1230

49

0

{<V~~l-48°

15.

(b)

Loca

lw

ind

fiel

don

23Fe

brua

ryan

dse

a-le

vel

pres

sure

anal

ysis

for

21GM

T23

Febr

uary

1980

for

the

Str

aits

ofJu

ande

Fuca

and

Geo

rgia

(Ove

rlan

dan

dW

alte

r t19

81).

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ght

leve

lw

ind

mea

sure

men

tsar

esh

own

assm

all

win

dar

row

s.B

old

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with

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les

indi

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ace

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ion

orbu

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port

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ind

conv

entio

nis

inkn

ots.

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heav

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line

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ceto

the

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ait

ofJu

ande

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ical

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ion

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ard

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122°

123°

124°

126°

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°

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140°

135°

130°

125°

._-

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48

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r48 °

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ab

Fig

ure

16.

(a)

Sea

-lev

elpr

essu

rean

alys

isfo

r00

GMT

14Fe

brua

ry19

80(O

verl

and

and

Wal

ter

t19

81).

(b)

Loc

alw

ind

fiel

don

13Fe

brua

ry19

80an

dse

a-le

vel

pres

sure

anal

ysis

for

21GM

T13

Febr

uary

1980

(Ove

rlan

dan

dW

alte

rt

1981

).

49°N

480

47·-

c

1260

126°W 1250

1250

1240

2100 GMT13 FEB 80

1240

123 0

1230

1220

49"

480

470

1220

Figure 16. (c) Wind and dewpoint fields from surface and aircraftreports 21-24 GMT 13 February 1980 (Overland and Walter t 1981).

35

Valley near Vancouver (Fig. 16b). This dry air displaced the more moist,marine air as it flowed across Georgia Strait and was ultimately channelledout the Strait of Juan de Fuca (Faulkner, 1980). The change of dewpointtemperature marked the air mass boundaries (Fig. 16c). The dry air maintainedan essentially constant velocity while spreading laterally and growing indepth, as shown by a downstream increase in inversion height. The momentumcontained in the jet increased with downstream distance due to the presence ofa pressure gradient along the flow direction. The eddy-like feature beyondthe entrance to the Strait of Juan de Fuca, which had light SE winds to the westof its boundary and strong (10-12 m s-l) winds from the E to the east of theboundary, may have been due to the presence of a hydraulic jump. Verticalwind speeds as recorded by the aircraft were downward at 1 ms-1 on the eastside and upward at 0.4 ms-1 on the west side of the boundary.

Another response of the flow in Puget Sound to pressure differences isthe creation of a downslope wind called a bora, which blows out of the passesin the Cascade Range when high pressure exists to the east of the mountains.Since the source region for the air in eastern Washington is often very cold,the adiabatic heating of the air upon descent out of the passes is not suf­ficient to raise the temperature to levels equal to ambient conditions in thePuget Sound Basin, so the cold air spreads out over the lowlands. Reed (1981)discussed a windstorm that led to a bora-like flow in Stampede Pass and gapwinds in the Columbia River Gorge. Figure 17 shows the extremely largegradient of sea-level pressure in the vicinity of the Cascades for 28 Novem-ber 1979. This gradient was for the most part fictitious, merely indicatingthat the mountain barrier sustained a large pressure difference between the coldair in central and eastern Washington and the warm air over western Washington.An E-W cross section (Fig. 18) of potential temperature across the State ofWashington from Spokane (GEG) to Quillayute (UIL) showed the intense horizontaltemperature gradient that developed over and to the lee of the mountains asthe upper-level inversion tilted and lowered in the subsiding airflow.Rewriting (1) using pressure coordinates gives:

aDg ax ax , (2)

where g is gravity, D is the geopotential height deviation from the standardvalue for a particular pressure level and ax is the difference in horizontaldistance between the end points of the trajectory. Calculations using Eq. (1)in the Columbia River Gorge and Eq. (2) for flow in the lee of Stampede Passestimated sufficient wind magnitudes to account for those observed.

4.3. Orographic low-pressure formation in the lee of the Olympic Mountains

During the winter (December-February), synoptic weather patterns giverise to S-SW flow conditions over the Puget Sound region 75% of the time.When synoptic-scale winds are from the south-to-southwest, the Olympic Moun­tains can induce the formation of a low-pressure area directly in the lee·of the mountains over Puget Sound or the Strait of Juan de Fuca (Overland etal., 1979), and Vancouver Island can induce low pressures over the Strait of

36

\-0

74

54

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4)

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-06

487

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84

84

40

42

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/25

0

50

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Figu

re17

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rfac

em

ap,

12GM

T28

Nov

embe

r19

79.

Isob

ars

are

draw

nat

inte

rval

sof

2m

b.T

empe

ratu

re(O

e)is

plot

ted

tole

ftof

stat

ion

and

pres

sure

(mb)

tori

gh

tof

stat

ion

(Ree

d,19

81).

W -....I

w 00

mb

50

0

60

0L

3/0

70

0

80

0

90

0

~280~~--

---10

00

UIL

100

km

Figu

re18

.C

ross

sect

ion

ofpo

tent

ial

tem

pera

ture

(OK)

acro

ssth

est

ate

ofW

ashi

ngto

n(R

eed

t19

81).

Sta

tion

UIL

isQ

uill

ayut

et

SEA

isS

eatt

let

and

GEG

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okan

e.

4 4

Georgia (Myers, 1966). The importance of the presence of such a low-pressurearea was dramatically demonstrated on 13 February 1979 when the Hood Canal Bridgesank ~uring surface winds in excess of 50 m s-l. Reed (1980), who analyzed themeteorological conditions for this event, found that although the gradient ofsea-level pressure at the bridge was strong due to the synoptic pressuregradient, it was greatly enhanced by the formation of a mesoscale low-pressurearea in the lee of the Olympics (Fig. 19). In the restricted channels ofPuget Sound the air flow at the surface accelerated toward the low pressureproducing the observed high wind speeds. In contrast, Walter and Overland(1982) made measurements with the NOAA P-3 aircraft on three days duringS-SW conditions in February and March 1980 (Fig. 20a-f) and found a regionof light wind speed and flat pressure gradient in the lee of the OlympicMountains and only slight troughing in the pressure field over the easternStrait of Juan de Fuca.

To explain this difference one needs to consider a non-dimensional number,the internal Froude number, F, which compares the momentum of the incidentflow to the stratification of the flow. This number is the critical parameterin determining whether the upstream air will go over (large F) or around(small F) an isolated obstacle such as the Olympic Mountains. For a fluidhaving continuous stratification the Froude number is given by

F - V- hN 'e

(3)

where V is upstream flow velocity, h is the height of the mountain, and Ne isthe stratification parameter, the BrUnt-Vaisala frequency,

N 2 =9.- dSee S dz'e

(4)

where g is gravity, Se is the equivalent potential temperature, and z is thevertical coordinate. The vertical derivative of equivalent potential tempera­ture accounts for stratification due to moisture as well as ambient temperature.On the three days discussed by Walter and Overland (1982), the boundary layerwas slightly stable throughout its depth with the internal Froude number inthe range F = 1.0-1.4. For the Hood Canal Bridge storm a smaller value of Netogether with high upstream winds led to a calculated value for F of 4.6.

For strong relative stratification, the primary flow about an obstacleis in quasi-horizontal planes (Fig. 21a and b) where the flow in each planeis given by a two-dimensional potential solution defined by the contour ofthe terrain at that level (Drazin, 1961; Riley et al., 1976; Hunt and Snyder,1980). Small vertical displacements of the streamlines passing around theside of the obstacle are due to the need for the potential energy to decreasein order to balance the increase in kinetic energy of the flow around theobstacle. Although the Froude numbers for the low wind studies in Walter andOverland (1982) were in the range of 1.0-1.4, the pressure and wind fields(Figs. 20 b,d,f) show qualitative agreement with experimental results for

39

Figure 19. Regional surface map for 12 GMT 13 February 1979 (after Reed,1980). Isobars are drawn at one millibar intervals (dashed at higherelevations). Winds are in knots. Maximum gusts (G) at observation timeand in preceding hour are plotted below stations.

40

+::> ......

40

°

a11

5°

49°N 48

°

126°

W

1260

b

125°

1250

124°

1240

123°

1230

122°

49

°

48

°

47

0

1220

Fig

.20

.(a

)Se

a-le

vel

pres

sure

anal

ysis

for

00GM

T19

Febr

uary

1980

and

(b)

mes

osca

lew

ind

and

pres

sure

fiel

dat

21GM

T18

Febr

uary

1980

.

~ N

45

0

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50

1250

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12

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ure

20.

(e)

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Mar

ch19

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.

.j:::>

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re21

a.Pl

umes

from

upw

ind

stac

ksat

vari

ous

elev

atio

ns(H

unt

and

Snyd

er,

1980

).To

pis

for

F=

0.2.

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isco

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aine

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mov

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ally

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rizo

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igh

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lic

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poc

curs

just

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nstre

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the

hil

l.B

otto

mis

for

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0.4.

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inth

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on

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der.

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gov

erth

eto

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para

tes

half

-way

dow

nth

ele

esl

ope.

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me

rica

lR

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cm)

o3

04

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me

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lts

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low Froude number flow. However, from the magnitude of the isotherm displace­ment in cross-section plots of constant e surfaces along the east side and inthe lee of the Olympics, it was evident that the flow was approaching thetransition region between small and large Froude number theory.

For the case where F » 1, Smith (1980) developed a hydrostatic linearmodel for stratified flow over an isolated mountain. His results for a bell­shaped mountain showed an asymmetric perturbation surface pressure field withhigh pressure over the windward slope and low pressure on the lee side. Thispressure distribution caused the surface streamlines to be deflected aroundthe sides of the mountain and to maintain a permanent outward deflectiondownstream. Horizontal divergence in the lee of the mountain caused a sinkingof warm air from aloft and a decrease in the vertical distances between down­wind, low-level, constant-density surfaces. When this perturbation pressurefield is added to the background synoptic-scale pressure field (Smith, 1981;Fig. 22), the result is in agreement with the sea-level pressure analysis forparameters from the Hood Canal storm (Fig. 19).

Reed (1980) indicated that in the vicinity of the Hood Canal Bridge on13 February 1979 the pressure gradient was a maximum of 6 mb in 15 km or0.4 mbkm-1. Comparison of the observed winds at the time of the bridge col­lapse (from Reed, 1980, Table 2) with those calculated for a confined channelfrom Eq. (1) and a value of the pressure gradient of 0.4 mb km-1 shows goodagreement (Table 7).

When the internal Froude number has a value on the order of 0.5-1.5, theflow response in the lee of the Olympics will be relatively benign with lightand variable winds. However, when the Froude number is of order 4-5, a closedmesoscale low-pressure region will be induced in the lee of the mountains.The flow at the surface in the restricted channels of Puget Sound responds bya rapid acceleration toward low pressure to give extreme wind speeds in alocalized area.

4.4. Effects of orography on precipitation--the Puget Sound convergence zoneThe surrounding mountains not only have a strong effect on the wind

fields but also on the precipitation patterns in Puget Sound as shown by Mass(1981) and Parsons and Hobbs (1982). In the spring transition months (April­June), when high pressure builds northward into the eastern Pacific Ocean, thecoastal winds change from a predominantly southerly to a northwesterly direc­tion. As southerly winds veer to the northwest after a frontal passage at thecoast, there is a narrow range of wind directions and speeds (Fig. 23) wherethe air will simultaneously flow eastward both north and south of the OlympicMountains. This flow pattern results in the formation of an area of con­vergence over Puget Sound (Fig. 24). Mass (1981) studied 25 cases of thisconvergence phenomenon and concluded that the controlling parameters were thewind direction and speed on the Washington coast, although most convergencezone events were also associated with weak atmospheric stability typical ofspring. He found that a convergence event was most likely to occur when, forfour continuous hours, the Hoquiam wind direction was between 2600 and 3200

and the wind speed ranged from 2 to 7 m s-l. AlthoUgh convergence events canoccur any time of the year, they are most probable from April to June when twoto four major events per month are expected.

46

~ -......J

----

----

----

----

--

-------------- -----------

o5

010

0km

,,

I

-4 -3 -2 -Io I 2 3 4m

b

Fig

ure

22.

Sum

ofth

epe

rtur

bati

onpr

essu

refi

eld

from

Sm

ith'

shy

dros

tati

cli

nea

rm

odel

and

ahy

poth

etic

alsy

nopt

icpr

essu

refi

eld

(Sm

ith,

1981

).

Table 7.--Comparison of winds reported by Reed (1980) in Hood Canal14-15 GMT 13 February 1979 and those calculated from Eq.1*

Bridge9.25 km SSW18.5 km SSW

Observed-140 m s

3022.5

Calculated

40.5 m s-l

3322.5 (assumed)

*Initial velocity used for the calculation is 22.5 ms-l.

48

N36

8\S

E

o

Figure 23. Polar representation of the wind speed and direction atHoquiam, Washington, during ten convergence zone events (Mass, 1981).

49

[May 2-:19781900GMT

IMay 2,1978l?.QOOGMT

\.\

May 2,/97812100G~T I

Figure 24. Streamlines over the Puget Sound area during the con­vergence zone event of May 2-3, 1978 (Mass, 1981). The position ofthe surface convergence line is indicated by a dashed line.

50

A composite vertical structure of the convergence zone was constructed byMass (1981), who indicated that it is similar to that of a classical front.Northerly winds enter Puget Sound and propagate as a wedge into the pre-exist­ing southerly winds (Fig. 25). The windshift line separating the opposingflows slopes upward to the north. Enhanced clearing is observed both northand south of the main convergence zone cloud band. Mass (1981) indicated thatthe clear area north of the zone is due to subsidence associated with thesurface divergence created as air flow in the eastern Strait of Juan de Fucasplits and moves both north into the Strait of Georgia and south into PugetSound. The clear region to the south of the zone is due to subsidence of airin the mesoscale circulation set up above the convergence line.

The presence of the convergence zone has pronounced effects on the cloud­iness, temperature, and precipitation patterns over the region, and its effectscan be seen in Figures 26 a-c, which are composites of these parameters forthe cases studied by Mass (1981) plotted with reference to the location of theconvergence line. Most of these convergence events showed a band of cloudsacross central and northern P~get Sound with the southern boundary close tothe windshift line. These clouds were generally shallow, with tops between1500 and 2500 m in the central Sound and 3000 m near the mountains. Thelowest cloud deck in the Sound frequently reached to the ground.

The effect of the convergence zone on precipitation can be seen in thelong-term climatology. Mass (1981) constructed a N-S cross section of monthlyprecipitation for Puget Sound (Fig. 27). There is a normal annual cycle atall stations except in the northern Sound where there was sustained precipita­tion through May and June caused by convergence zone precipitation.

Parsons and Hobbs (1983) studied the effects of orographic features inthe Puget Sound region on mesoscale structures and precipitation processes indifferent types of rainbands embedded in synoptic-scale storms as they passacross the region. They studied warm-frontal, warm-sector, narrow and widecold-frontal, and post-frontal rainbands and found that the influence oforography was dependent on the rainband type, the size of the orographicfeature, and the airflow. Figure 28 shows that a large percentage of precip­itation from warm-sector (i.e., pre-frontal) rainbands occurs at three coastalstations due to slight lifting of the airmass and from post-frontal rainbandsat three stations about 100 km inland, where precipitation is considerablyenhanced over the windward slopes of the Cascades. Local airflow convergencecaused by the restricted flow in channels of the Puget Sound Basin also playedan important role in enhanced post-frontal precipitation.

4.5. Diurnal wind variations--the sea breeze and valley breeze

In the warm months of the year the wind field shows a strong diurnal var­iation that is related to differential heating between the land and adjacentwaters and heating on the mountain slopes. Staley (1957) presents hodographs-­plots of the rotation of wind vector end points with time of day (Fig. 29)--for July 1950, where resultant winds were derived by averaging components of thewind observed at each hour during the day over a month. In the Strait of Juande Fuca, Port Angeles showed W-NW flow and counterclockwise rotation whileVictoria showed southerly and southwesterly flow with clockwise rotation.

51

800-

1r6

I-.....

........

...-.

...~

........

w850~

Iw l.1

..

........

~r4~

"t

"\

..c

9°°1

EI

Cf)

I0

<.T1

,\

Iz

N

J, ',

\2<

{950~.-

/'

Cf)

........

-...

'"".

:J 0

"""

:::r:.-

•.....

........

..."~

..-

t-1

00

0C

lea

rC

lou

dy

IC

leo

ra

NS

urf

ace

SC

onve

rgen

ceL

ine

Figu

re25

.Sc

hem

atic

view

ofth

elo

w-l

evel

flow

duri

nga

conv

erge

nce

even

t(M

ass,

1981

).

LOWEST DECK20

ao'----J'--:8::-'-:7::-'--=-6-'--=-5-'-4~3-'---:-2...L-1--L...:0--'---_-1L_2,,---1-_3,,---1-_4--L._-=-5...L_-6...L_-7--'-----'_8

COMPOSITE ZONE RELATIVE TO CONVERGENCE ZONE

~

uwoo~

o...JU 10t-Cf)W~o...J

U.oa::wCD~~

z

TEMPERATURE COMPOSITE

b

- - r-

- r-

r-

-f--

-'--

u.~

z 3ot- 2«> I

~ 0

~ -I

; -2

~ -3w~ -4wt- 4 3 2 I 0 -I -2 -3 -4

N COMPOSITE ZONE SCf)t­ZW> 40wz9 30t-«t-

~ 20uwa::a. 10u.o

~ 7 6 5 4 3 2 I 0 -I 2 -3 -4 -5 -6 -7 -8 C~ COMPOSITE ZONESZ RELATIVE TO SURFACE CONVERGENCE LINE

Figure 26. (a) Summary of the number of times the lowest cloud deck inPuget Sound occurred in each composite zone during five convergence zoneevents (Mass, 1981). (b) Temperature deviations (OF) from the PugetSound mean for each composite zone (Mass, 1981). (c) Summary of thenumber of precipitation events that occurred in each composite zoneduring ten convergence zone events (Mass, 1981).

53

,

••,•

•,,I

Rain Shadow /,\ --- N. Sound /

, C. Sound '\ _.-.- S. Sound ,I,

\ /, ,

\. /\, i

\", I ., \ ,

~ '\ I f'~ . "~:

I" \.. \.. ,/,'.~.~ I '

1'1 '. - \ !I.'I I ". \ /:'. , , , ~ ,

---------..",.' " '" \ //. ' .:'to ..-," ---- .

I •

2

6

8

4

O---,r---___.,.----r--...,.--~-r__ -___.,.-.......,...-_r__-_r__---...I

J F M A M J J A S 0 N

Figure 27. Annual variation of precipitation for the rain shadow andnorthern, central, and southern Puget Sound regions (Mass, 1981).

54

50

40

30

20

10oL-l----l.:..:.:....:..:.Il....L.II _

LONG BEACH

50

40

30

20

10

°CHEHALIS

WARM-SECTOR;":'.:::; NARROW COLD-FRONTAL.. ' .:

WIDE COLD-FRONTALPOST-FRONTAL

O.......--&o.:~ ........

ELMA

50

40

....o. ",".....

. '"0.- .:':'~'~'~

50

40

30

20

10

z«0::

--l

~oI-I.J....oW<.9

~ZwU0::WCl.

50

:".: ~;~::............: :....•" .1".". ".o. "0

°OLY~':~IA

Figure 28. Percentage contributions to total precipitation at threecoastal stations (Long Beach, Moclips, Pt. Brown) and three inland sta­tions (Chehalis, Elma, Olympia) from warm sector, narrow cold-frontal,wide cold-frontal, and post-frontal rainbands on 8 December 1976 (Parsonsand Hobbs, 1982). Note the large contribution from warm-sector rainbandsat the coastal stations and the large contribution from post-frontal rain­bands at the inland stations.

55

VICTORIA

4.0

2.0

18

-2.018

PORT ANGELES

1.02.0

1.09 12

-'~D12

0-1.5- 0

1521 18 21 18

1.0

EVERETT OLYMPIA SEATACAIRPORT

Figure 29. Resultant wind hodographs for stations in the Strait ofJuan de Fuca t north t central t and south Puget Sound for July 1950(StaleYt 1957).

56

6. Acknowledgements

This work is a contribution to the Marine Services Project at thePacific Marine Environmental Laboratory. We wish to thank Robert Andersonand W. Burton of the NWS Seattle Ocean Services Unit, Don Faulkner, SteveNikleva, and Ron McLaren of the Canadian Atmospheric Environment Servicein Vancouver,. B.C., for their support and encouragement of this project.

We wish to thank Drs. Peter Hobbs, Cliff Mass, Richard Reed, Ron Smith,and James Connell for their contributions and suggestions. We also thankJournal of Fluid Mechanics (Cambridge University Press) for permission to usefigure 21a.

We acknowledge the assistance of Professor Richard Reed, Department ofAtmospheric Science, University of Washington, Seattle, Wash. 98195, in providinga copy of an unpublished manuscript by V.F. Morris titled "A study of meso-scale mountain barrier effects in western Washington and Vancouver Island."

59

and water prop­In: Hydrodynamics

Amsterdam,

7. References

Cannon, G.A. and N.P. Laird (1978): Variab"ility of currentserties from year-long observations in a fjord estuary.of Estuaries and Fjords, Nihoul, J.C.J. ed., Elsevier,515-535.

Church, P.E. (1938): Surface details of a warm front in the Strait of Juande Fuca. Bulletin of the American Meteorological Society, 19, 400-402.

Church, P.E. (1974): Some precipitation characteristics of Seattle. Weather­wise, 27:244-251.

Climatolo ical Handbook Columbia River Basin States Hourl Data, Vol. 3,an, : eteoro oglca ommlttee, aCl lC ort west

River Basin's Commission.Critchfield, H.J. (1978): Sunshine and solar radiation in Washington State.

Office of the State Climatologist, Western Washington University,Bellingham, Washington, 98225, 38 pp.

Drazin, P.G. (1961): On the steady flow of a fluid of variable density pastan obstacle. Tellus, 13:239-251.

Faulkner, D.A. (1980): Mesoscale observations of an outflow wind over theSouthern Strait of Georgia. Pacific Region Technical Note 80-022, A.E.S.,Vancouver, B.C., 6 pp.

Halladay, N.E. (1970): Whidbey Island Forecaster1s Handbook, NAV WEA SERVCOM INST 3140.2, U.S. Naval A,r Station, Oak Harbor, Washington, 115 pp.

Hobbs, P.V., R.A. Houze, Jr., and T.J. Matejka (1975): The dynamical andmicrophysical structure of an occluded frontal system and its modifica­tion by orography. Journal of the Atmospheric Sciences, 32:1542-1562.

Hobbs, P.V. (1978): Organization and structure of clouds and precipitationon the mesoscale and microscale in cyclonic storms. Reviews of Geophysicsand Space Physics, 16:741-755.

Hobbs, P.V., T.J. Matejka, P.H. Herzegh, J.D. Locatelli and R.A. Houze, Jr.(1980): The mesoscale and microscale structure and organization ofclouds and precipitation in mid-latitude cyclones, I: A case study ofa cold front. Journal of the Atmospheric Sciences, 37:568-596.

Hunt, J.C.R. and W.H. Snyder (1980): Experiments on stably and neutrallystratified flow over a model three-dimensional hill. Journal of FluidMechanics, 96:671-704.

Klein, W.H. (1957): Principal tracks and mean frequencies of cyclones andanticyclones in the northern hemisphere. Research pa7er No. 40, U.S.Weather Bureau, Washington, D.C., 60 pp. CAvailablerom National WeatherService, Techniques Development Laboratory, Washington, D.C. 20233.)

Lau, N.C. (1979): The structure and energetics of transient disturbances inthe northern hemisphere wintertime circulation. Journal of the AtmosphericSciences, 36:982-995.

Locatelli, J.P., P.V. Hobbs and J.A. Werth (1982): Mesoscale structures ofvortices in polar air streams. Monthly Weather Review, 110: 14·17-1433.

60

Analysis of the pressure oscillations at several stations (Staley, 1957;Fig. 30) showed a diurnal component that reached its maximum and minimum laterat Tatoosh Island on the coast than at the eastern end of the Strait of Juande Fuca or in Puget Sound. Pressure differences between stations were greatestin the afternoon and early evening driving the westerly sea breeze, but theexact time of maximum pressure difference varied as different pairs of stationswere considered. For example, the pressure difference between Port Angelesand Bellingham reached a maximum three to six hours after the maximum pressuredifference between Port Angeles and Everett.

Ideally, hodographs should be elliptically shaped, rotate clockwise withtime, and fall in strength during the night and increase during the day reach­ing a maximum between 1330 and 1830 Local Time (LT). Superposition of otherfactors related to topography, mean flow field, and valley or slope winds uponthe sea breeze, however, leads to distortion of this ideal shape and behavior(Mass, 1982); the existence of counterclockwise hodographs must be attributedto topographic constraints. For example, the maximum wind component towardthe Cascades during the day and toward Puget Sound at night would be expectedon the basis of upslope and drainage winds regardless of sea breeze. In cen­tral and northern Puget Sound the winds turn clockwise on the eastern side andcounterclockwise on the western side of the Sound. A similar situation existsin the Strait of Juan de Fuca, where Port Angeles on the Olympic Peninsulashows counterclockwise turning while Victoria on Vancouver Island has anoppositely directed hodograph. The figure-eight-shaped hodograph at Olympiais interesting because Olympia is situated at the boundary between tworegional sea breeze circulations; it is influenced by the Chehalis Gap tothe south and Puget Sound to the north.

5. Summary

The mid-latitude west coast marine climate of the Puget Sound region istypified in summer by a pattern of high pressure and in winter by a sequenceof storms that originate over the ocean to the west. Local variations inclimatic indicators such as precipitation and wind are substantially influ­enced by the region's topography. The maximum precipitation occurs in earlywinter which results in a bimodal distribution of runoff into Puget Sound:there is a winter maximum associated with increased rainfall and a late springmaximum associated with snow melt. The proximity to the Pacific Ocean and thepresence of Puget Sound has a moderating influence on extreme temperatures inboth summer and winter. Over the waters of Puget Sound the winds near thesurface flow from high to low sea-level pressure as imposed by the large-scale or regional weather pattern. Several local wind phenomena are important,the most notable being the formation of an orographically induced, mesoscalelow-pressure region in the lee of the Olympic Mountains during strong onshorewinds associated with major coastal storms. Such an event produced winds inexcess of 50 m s-l in a localized area of Puget Sound at the time of thedestruction of the Hood Canal Bridge.

57

-..cE-CL

1020

1019

1017

.•.•.•. TTl.. .. '.. .. .. .~....~..

~..."'....

••••

0.3 6.3 12.3 18.3TIME (pst)

2.0

-..cE

1.0 CL<J

Figure 30. Average sea-level pressures at each hour of the day forJuly 1950 at Tatoosh Island (TTl), Port Angeles (PAE), Everett (EVE),Bellingham (BlI) (upper four curves); and sea-level pressure differencesbetween Port Angeles and Bellingham, Port Angeles and Everett, andTatoosh Island and Port Angeles (Staley, 1957).

58

Lynott, R.E. and D.P. Cramer (1966): Detailed analysis of the 1962 ColumbusDay windstorm in Oregon and Washington. Monthly Weather Review, 94:105-117.

Mass, C. (1981): Topographically forced convergence in western Washingtonstate. Monthly Weather Review, 109:1335-1347.

Mass, C. (1982): The topographically forced diurnal circulations of westernWashington state and their influence on precipitation. Monthly WeatherReview, 110:170-183.

Maunder, W.J. (1968): Synoptic weather patterns in the Pacific Northwest.Northwest Science, 42:80-88.

Mullen, S.L. (1979): An investigation of small synoptic-scale cyclones inpolar air streams. Monthly Weather Review, 107:1636-1647.

Myers, R.A. (1966): Lee troughing west of Vancouver Island. CIR-4410, TEC-608,Department of Transport-Meteorological Branch, 5 pp.

National Climatic Center (1980): Local Climatological Data, Annual Summary,Seattle-Tacoma Airport. National Climatic Center, Asheville, N.C.,28801, 4 pp.

Overland, J.E., M.H. Hitchman and Y.J. Han (1979): A Regional SurfaceWind Model for Mountainous Coastal Areas. NOAA Technical Report,ERL-407 PMEL-32, Environmental Research Laboratories, NationalOceanic and Atmospheric Administration, Boulder, Colorado, 34 pp.

Overland, J.E. (1981): Forecasting the Pacific Northwest winds. Castoff,April 1981, 10-13.

Overland, J.E. and B.A. Walter (1981): Gap winds in the Strait of Juan deFuca. Monthly Weather Review, 109:2221-2233.

Parsons, D.B. and P.V. Hobbs (1983): The mesoscale and microscale structureand organization of clouds and precipitation in midlatitude cyclones.VIII: Some effects of orography on rainbands. Submitted to Journal of theAtmospheric Sciences.

Phillips, E.L. (1968): Washington climate for these counties, King, Kitsap,Mason, Pierce. Cooperative Extension Service, Washington State University,Pullman, Washington, 66 pp.

Puget Sound Air Pollution Control Agency (1972-1980): Air Quality DataSummary for Counties of King, Kitsap, Pierce, Snohomish. Puget Sound AirPollution Control Agency, 410 W. Harrison St., Seattle, Washington 98119.

Reed, R.J. (1979): Cyclogenesis in polar airstreams. Monthly Weather Review,107:38-52.

Reed, R.J. (1980): Destructive winds caused by an orographically inducedmesoscale cyclone. Bulletin of the American Meteorological Society, 61:1346-1355.

Reed, R.J. (1981): A case study of a bora-like windstorm in western Washing­ton. Monthly Weather Review, 109:2383-2393.

Reed, T.R. (1931): Gap winds of the Strait of Juan de Fuca. Monthly WeatherReview, 59:373-376.

61

Reed, T.R. (1932): Weather types of the northeast Pacific Ocean as relatedto the weather of the north Pacific coast. Monthly Weather Review, 60:246-252. --

Riley, J.J., H.T. Liu, and E.W. Geller (1976): A numerical and experimentalstudy of stably stratified flow around complex terrain. u.s. EPA Environ­mental Monitorin~ Series Report No. EPA-600/4-76-021, Research TrianglePark, North Caro ina, 30 pp.

Schoenberg, S.A. (1983): Regional wind patterns of the inland waters of westernWashington and souther British Columbia. NOAA Technical Memorandum,Environmental Research Laboratories, National Oceanic and AtmosphericAdministration, Boulder, Colorado, (in press).

Shore Protection Manual (1973): Vol. 1, U.S. Army Coastal Engineering ResearchCenter, U.S. Government Printing Office, 496 pp.

Skjelbreia, N. (1981): Floating breakwater prototype test program, Departmentof the Army, Seattle District, Corps of Engineers, (unpublished manu-script). .

Smith, R.B. (1980): Linear theory of stratified flow past an isolated moun­tain. Tellus, 32:348-364.

Smith, R.B. (1981): An alternative explanation for the destruction of theHood Canal Bridge. Bulletin of the American Meteorological Society, 62:1319-1320.

Staley, D.O. (1957): The low-level sea breeze of northwest Washington.Journal of Meteorology, 14:458-470.

Walter, B.A. and J.E. Overland (1982): Response of stratified flow in thelee of the Olympic Mountains. Monthly Weather Review, 110: 1458-1473.

Williams, R., H. Pearson, and J. Wilson (1982): Streamflow statistics anddrainage-basin characteristics for the Puget Sound Region, Washington.Technical Reeort, U.S. Geological Survey, Water Resources Division,Tacoma, Washlngton, in press.

62