WINTER WINTER WEATHER WEATHER

FORECASTING FORECASTING IN THE IN THE

SOUTHEASTSOUTHEAST

BACKGROUND RESEARCHCollaborative Science, Technology, and Applied Collaborative Science, Technology, and Applied Research (CSTAR) ProjectResearch (CSTAR) Project

*NWS Offices*NWS Offices*NC State University*NC State University*NC State Climate Office*NC State Climate Office

Evaluation of the Real-Time MM5 Modeling SystemEvaluation of the Real-Time MM5 Modeling System*NC State University*NC State University*NC State Climate Office*NC State Climate Office*Capitol Broadcasting*Capitol Broadcasting*NCSC/MCNC*NCSC/MCNC

SPECIAL THANKS TO DR. GARY LACKMANN FOR PERMISSION SPECIAL THANKS TO DR. GARY LACKMANN FOR PERMISSION TO USE SEVERAL VALUABLE POWERPOINT SLIDESTO USE SEVERAL VALUABLE POWERPOINT SLIDES

FORECASTING CHALLENGES

(1)Cold Air Damming

(2)Coastal Low Pressures

(3)Precipitation Type

BUILDING HIGH

PRESSURE

CONFLUENCE ALOFT

SURFACE DIVERGENCE

&PRESSURE

RISES

CAD as a Geostrophic Adjustment Process

Stable atmosphere & terrain impede flow, alter force balance

Mass accumulation creates pressure ridge

Geostrophic, terrain-normal flow

Mass depletion west of barrier reinforces trough

Climatological ResultsTotal Number of Events = 353

Cold Season Events = 180Warm Season Events = 173

• September -Highest frequency of events (?!!)

• July - lowest frequency of events

• Highest frequency of strong events in Winter months

• Lowest frequency of strong events in summer months (June - August)

Classical (dry onset):• High > 1030 mb•>24 h duration•dry onset

Weak Onset•High < 1030•or < 24h duration•dry onset

Hybrid•High < 1030•or < 24h duration•precip. W/in 6h of onset

Southern Onset•high S of 40•dry onset

In-Situ

In-Situ

Classification based on location, strength of “parent high”:

Classical (Diab. Enh):• High > 1030 mb•>24 h duration•precip w/in 6-h of onset

Classical (Diabatically Enhanced) T00 Peak Centered

250-mb Geo. Ht., Isotachs

850-mb Geo. Ht., RH

500-mb Geo. Ht, Anomalies

SLP, anomalies

Classical (Diabatically Enhanced) T00 Onset Centered

250-mb Geo. Ht., Isotachs

850-mb Geo. Ht., RH

500-mb Geo. Ht, Anomalies

SLP, anomalies

E-W Elongated High

Confluence with little or no ridging at 500mb

Cold front just off-shore

DIABATICALLY ENHANCED CLASSICAL(SYNOPTIC FORCING)

Classical (Dry Onset) T00 Onset Centered

250-mb Geo. Ht., Isotachs

850-mb Geo. Ht., RH

500-mb Geo. Ht, Anomalies

SLP, anomalies

Classical (Dry Onset) T00 Peak Centered

250-mb Geo. Ht., Isotachs

850-mb Geo. Ht., RH

500-mb Geo. Ht, Anomalies

SLP, anomalies

N-S Elongated High

Confluence with more ridging at 500mb

Cold front far off-shore

DRY ONSET CLASSICAL(SYNOPTIC FORCING)

Hybrid (HYBR) T00 Onset Centered

250-mb Geo. Ht., Isotachs

850-mb Geo. Ht., RH

500-mb Geo. Ht, Anomalies

SLP, anomalies

In-Situ (INST) T00 Peak Centered

250-mb Geo. Ht., Isotachs

850-mb Geo. Ht., RH

500-mb Geo. Ht, Anomalies

SLP, anomalies

HYBRID CADEqual synoptic/diabatic processes

Weak and progressive high

IN-SITU CADDiabatic processes prevail

High in unfavorable location

Little or no CAA

Surface P

lot

CONTAINS:* Mean Sea Level Pressure Isobars (mb)* 6-hour Total Precipitation (in)* 1000-500 mb Thickness (dm)

WHATDO YOU

LOOK FOR?

High Pressure ~1030mb in

New England

U-shaped Isobars east of Appalachians

546 line- Mix540 line-

Snow

Timing of Precip

(am/pm)

850 mb P

lot

CONTAINS:* 850 mb Height (dm)* 850 mb Temperature (C)* 850 mb Winds (kts)

WHATDO YOU

LOOK FOR?

Southerly to easterly winds

Temperatures < 0C Snow< 3C Mix

Warm Air Intrusion

700 mb P

lot

CONTAINS:* 700 mb Heights (dm)* Relative Humidity (%)* Omega (mb/s)

WHATDO YOU

LOOK FOR?

Relative Humidity

>70%

Negative Omegas Co-located with

RH

Dry Air Intrusion

Westerly Winds

500 mb P

lot

WHATDO YOU

LOOK FOR?

Southwest Winds

Tilt of 500 mb Trough

Confluent Flow over

New England

CONTAINS:* 500 mb Heights (dm)* Absolute Vorticity (s^-1)* 500 mb Winds (kts)

300 mb P

lot

WHATDO YOU

LOOK FOR?

Confluent Flow over

New England

Jet stream and streaks

Split Flow/ Dual Jet Structure

CONTAINS:* 300 mb Heights (dm)* 300 mb Isotachs (kts)* 300 mb Winds (kts)

PRECIPITATION TYPE FORECASTING

FEBRUARY 5-6, 2004

Potential SC Ice Storm/CAD Event

(1)What is p-type?

(2)How do we make an educated guess?

(3)PUTTING THE METHOD TO USE…

32 F 0C

COLD AIR DAMMING&

WINTER PRECIPITATION TYPES

Warm, moist air

COLD, DRY AIR

Rain Freezing Rain Sleet Snow

WARM WARM NOSENOSE

NORTHSOUTH

(1)

(2)

(3)

PARTIAL THICKNESS AND GENERAL PARTIAL THICKNESS AND GENERAL FORECASTING RULESFORECASTING RULES

Partial thickness - the distance between intermediate levels in the atmosphere found in the model output, typically between 1000 and 500 millibars (i.e. 1000-850, 850-700, 700-500) that represent the thermal structure in the atmosphere with increasing height

TO DO ON-THE-FLY FORECASTING:TO DO ON-THE-FLY FORECASTING:

For snow to fall:

1000-850 THK < 1290m850-700 THK < 1540m

For sleet/freezing rain to fall:

850-700 THK 1540-1555m Sleet> 1555m Freezing Rain

(larger values of the 850-700 THK indicate warmer air aloft)

5540 1575

3160 5790

Surface 850 mb

700 mb 500 mb

1000-500 THK

&

850 HEIGHT

700 HEIGHT

&

500 HEIGHT

????????????????

WILL IT BE……

SNOW, SLEET, OR

FREEZING RAIN

????????????????

So for the Columbia Area in the Event from Thursday, Feb. 5th…

500mb 5790m

700mb 3160m

700-500 THK 2630m

700mb 3160m

850mb 1575m

850-700 THK 1585m

1000-500 THK 5540m

700-500 THK 2630m

850-700 THK 1585m

1000-850 THK 1325m

>1540m => no snow, warm nose present

>1300m => too warm to freeze

•

                                                                                                                                                                                                                     

                        

P-TYPE FORECASTING NOMOGRAM

1325/1585

1000

-850

mb

TH

K

850-700mb THK

RAIN

Actual Observations

Related/Future Research

CAD Erosion (Stanton 2003, MS Thesis, NCSU)CAD Erosion (Stanton 2003, MS Thesis, NCSU)

High-resolution modeling (Caldwell 2004, MS Thesis, High-resolution modeling (Caldwell 2004, MS Thesis, NCSU)NCSU)

Coastal Frontogenesis (Appel 2002, MS Thesis, Coastal Frontogenesis (Appel 2002, MS Thesis, NCSU)NCSU)

Quantitative Precipitation Forecasting (QPF)Quantitative Precipitation Forecasting (QPF)