Anticipating Structure Anticipating Structure in Lake-Effect Snow in Lake-Effect Snow

Events (Updated Events (Updated Results)Results)

Michael L. Jurewicz, Sr.Michael L. Jurewicz, Sr.

NOAA/NWS, Binghamton, NYNOAA/NWS, Binghamton, NY

Justin ArnottJustin Arnott

NOAA/NWS, Gaylord, MINOAA/NWS, Gaylord, MI

2013 U.S./Canada Great Lakes 2013 U.S./Canada Great Lakes Meteorology Workshop Meteorology Workshop

April 16, 2013April 16, 2013

OutlineOutline

MotivationMotivation GoalsGoals Brief review of concepts / earlier Brief review of concepts / earlier

research on the morphology of Lake-research on the morphology of Lake-effect precipitationeffect precipitation

Study MethodologyStudy Methodology ResultsResults Demonstration of potential utility in an Demonstration of potential utility in an

operational forecast settingoperational forecast setting

MotivationMotivation

Anticipating how well organized a lake-effect Anticipating how well organized a lake-effect snow event will become can be tricky business snow event will become can be tricky business

““Conventional thinking” dictates that changes in mode Conventional thinking” dictates that changes in mode / organization tend to be impacted by the diurnal / organization tend to be impacted by the diurnal heating cycleheating cycle

– More fractured cellular elements in the afternoon, with More fractured cellular elements in the afternoon, with better defined banded structures from late at night into better defined banded structures from late at night into the morning the morning

However, this doesn’t always workHowever, this doesn’t always work– Well defined bands have occasionally been observed Well defined bands have occasionally been observed

during peak heating (afternoon); with unexpected during peak heating (afternoon); with unexpected occurrences of disorganized, open-cellular snow showers occurrences of disorganized, open-cellular snow showers late at night or in the morninglate at night or in the morning

Suggests these processes are more complex than Suggests these processes are more complex than simply being tied to diurnal heating / cooling, or time simply being tied to diurnal heating / cooling, or time of yearof year

GoalsGoals

To identify the atmospheric To identify the atmospheric parameters most responsible for parameters most responsible for governing the organization / different governing the organization / different modes of Lake-effect snow modes of Lake-effect snow

Utilize this information to formulate a Utilize this information to formulate a technique for predicting convective technique for predicting convective mode in Lake-effect snow situationsmode in Lake-effect snow situations

Brief Overview of Brief Overview of Earlier ResearchEarlier Research

It has been shown that well defined roll-type It has been shown that well defined roll-type convection (banded structures) tends to convection (banded structures) tends to prevail when:prevail when:– The low-level environment (1-2 km AGL) has The low-level environment (1-2 km AGL) has

moderate to strong speed shear; although little moderate to strong speed shear; although little directional shear directional shear

– Some low-level heat flux / instability is presentSome low-level heat flux / instability is present However, there seems to be an upper-limitHowever, there seems to be an upper-limit

– If too unstable, can detract from overall organization If too unstable, can detract from overall organization Weckwerth, et al. (1997); Stull (1988); and Weckwerth, et al. (1997); Stull (1988); and

Miura (1986) Miura (1986) These findings also substantiated by the Lake-These findings also substantiated by the Lake-

Ice Field Experiment over Lake Michigan Ice Field Experiment over Lake Michigan (Kristovich, Laird, and Hjemfeldt (2003))(Kristovich, Laird, and Hjemfeldt (2003))

Satellite View of Satellite View of “Lake-Ice” Project “Lake-Ice” Project

AreaArea

Formation of BandsFormation of Bands

Clouds are suppressed in between bandsClouds are suppressed in between bands

A Plan Coming A Plan Coming TogetherTogether

Given that we’ve established the Given that we’ve established the importance of importance of both vertical speed both vertical speed shear and at least some CBL shear and at least some CBL instabilityinstability to the existence of to the existence of horizontal rolls / Lake-effect bands; horizontal rolls / Lake-effect bands; these questions logically follow:these questions logically follow:– Is there a preferred amount of either one; Is there a preferred amount of either one;

or an optimal balance between them?or an optimal balance between them?– How would one best quantify and then How would one best quantify and then

illustrate these parameters?illustrate these parameters?

Initial MethodologyInitial Methodology

Interrogated Central NY Lake-effect snow Interrogated Central NY Lake-effect snow events archived from the winters of 2005-06 events archived from the winters of 2005-06 up through 2008-09up through 2008-09– Originally, only looked at Feb., March, and April Originally, only looked at Feb., March, and April

casescases– Later filled in cases from Oct.-Jan. Later filled in cases from Oct.-Jan.

Utilized radar and sounding information Utilized radar and sounding information – Radar imagery was the basis for categorizing Radar imagery was the basis for categorizing

individual events (banded structures vs. open-individual events (banded structures vs. open-cellular convection)cellular convection)

– NAM BUFKIT soundings used to determine shear NAM BUFKIT soundings used to determine shear and stability parameters at 6-hourly time steps and stability parameters at 6-hourly time steps (0000, 0600, 1200, and 1800 UTC)(0000, 0600, 1200, and 1800 UTC)

Specific site was chosen based on proximity to Specific site was chosen based on proximity to greatest radar coveragegreatest radar coverage

Updated MethodologyUpdated Methodology

Addition of LES cases from Northern MI; and also Addition of LES cases from Northern MI; and also more recent Central NY events (2010 to Present)more recent Central NY events (2010 to Present)– Still adding more events to databaseStill adding more events to database

Slightly different radar/sounding strategy used for Slightly different radar/sounding strategy used for MI cases MI cases – Instead of using specific sites, an “areal average” Instead of using specific sites, an “areal average”

methodology was employed methodology was employed Helps avoid potential pitfalls of choosing a single Helps avoid potential pitfalls of choosing a single

“contaminated site” (artificially high CAPE within a well “contaminated site” (artificially high CAPE within a well organized LES band)organized LES band)

““Background state” stability more representativeBackground state” stability more representative Analogous to avoiding a sounding location affected by Analogous to avoiding a sounding location affected by

thunderstorms in the warm season thunderstorms in the warm season – Currently in the process of tabulating “areal Currently in the process of tabulating “areal

average” values for the NY events (not yet fully average” values for the NY events (not yet fully correlated) correlated)

Sampling of Originally Sampling of Originally Chosen Parameters Chosen Parameters – For Stability: For Stability:

Lapse Rates Lapse Rates CAPE (Terrestrial and Lake-Induced) CAPE (Terrestrial and Lake-Induced)

– For Shear (including normalized For Shear (including normalized values) values) Mixed Layer (ML) Speed ShearMixed Layer (ML) Speed Shear 0-1 km Speed Shear 0-1 km Speed Shear

Better Correlations Better Correlations (NY Cases, So Far)(NY Cases, So Far)

For statistical purposes, we assigned For statistical purposes, we assigned Banded events a Banded events a value of 0 and Disorganized / Cellular events a value value of 0 and Disorganized / Cellular events a value of 1of 1– Diffuse Diffuse (Broken / Discontinuous Bands) (Broken / Discontinuous Bands) events events

were given a value of 0.5were given a value of 0.5 Here’s how some of the numbers currently look [normalized Here’s how some of the numbers currently look [normalized

values for Mixed Layer depths in brackets]:values for Mixed Layer depths in brackets]:– CAPE = 0.36 [0.34]CAPE = 0.36 [0.34]– Lake-Induced CAPE = (-0.11) [-0.28] Lake-Induced CAPE = (-0.11) [-0.28] – Bulk Speed Shear = (-0.28) [-0.36]Bulk Speed Shear = (-0.28) [-0.36]– 0-1 km Speed Shear = (-0.30)0-1 km Speed Shear = (-0.30)

There seemed to be sensitivity to the depths over which There seemed to be sensitivity to the depths over which Bulk Speed Shear occurredBulk Speed Shear occurred

Scatter Plot for NY Scatter Plot for NY CasesCases

CAPE vs. Normalized Bulk Shear

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0 20 40 60 80 100

CAPE

No

rma

lize

d B

ulk

Sh

ea

r

•Dark Blue = Well defined Bands

•Yellow = Diffuse Bands

•Purple = Open-cellular Snow Showers

Lines of Best FitLines of Best FitCAPE vs. Normalized Bulk Shear

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0 20 40 60 80 100

CAPE

No

rma

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d B

ulk

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ea

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Open-Cellular Snow Showers

Diffuse Bands

Well defined Bands

Scatter Plot for MI Scatter Plot for MI CasesCases

* Most Banded Cases had CAPE < 15 J/kg

LI CAPE vs. CAPE (NY)LI CAPE vs. CAPE (NY)Terrestrial vs. Lake-Induced CAPE

0

200

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600

800

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1200

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0 20 40 60 80 100

Terrestrial CAPE

Lake-I

nd

uced

CA

PE

Banded = Dark Blue

Diffuse Bands = Yellow

Cellular Snow Showers = Purple

* Most Well-defined Bands had Terrestrial CAPES < 20 J/kg

Is This Worth It?Is This Worth It?

As mentioned earlier, the value of As mentioned earlier, the value of this technique will be measured this technique will be measured by how much skill it can show by how much skill it can show over normal diurnal trends over normal diurnal trends

To that end, let’s look at some To that end, let’s look at some statistics, then a case study statistics, then a case study exampleexample

Graphical ComparisonGraphical Comparison

0

0.1

0.2

0.3

0.4

0.5

0.6

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0.8

0.9

1

Banded Cellular Banded Cellular

POD POD FAR FAR

Diurnal Method vs. New Technique

Diurnal

New

Example March CaseExample March Case

Appeared to be a situation where Appeared to be a situation where consolidated LES bands typically consolidated LES bands typically develop / evolve in Central NY:develop / evolve in Central NY:– Steady-state and moist 290 to 300 degree Steady-state and moist 290 to 300 degree

flow in the CBLflow in the CBL– Little directional shear Little directional shear – Late night / early morning time frameLate night / early morning time frame

Despite these factors, LES remained Despite these factors, LES remained disorganized / cellular in naturedisorganized / cellular in nature– Not enough vertical shear to balance Not enough vertical shear to balance

lingering terrestrial instability? lingering terrestrial instability?

Radar Images at 0600 Radar Images at 0600 UTC, 03/13/04UTC, 03/13/04

Sounding from Ithaca, Sounding from Ithaca, NY at 0600 UTC, NY at 0600 UTC,

03/13/0403/13/04

Snowfall TotalsSnowfall Totals

Where This Event FallsWhere This Event FallsCAPE vs. Normalized Bulk Shear

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0 20 40 60 80 100

CAPE

No

rma

lize

d B

ulk

Sh

ea

r

Open-Cellular Snow Showers

Diffuse Bands

Well defined Bands

Early Morning, 3/13/04

SummarySummary

How well LES bands were able to How well LES bands were able to remain consolidated inland, remain consolidated inland, seemed to hinge on a preferred seemed to hinge on a preferred balance of CBL CAPE and balance of CBL CAPE and Normalized Bulk Speed ShearNormalized Bulk Speed Shear

Better vertical shear and some instability were Better vertical shear and some instability were most conducive; while too much instability most conducive; while too much instability and/or too little shear were the primary and/or too little shear were the primary detractorsdetractors

Fits conceptual model of Horizontal Rolls well Fits conceptual model of Horizontal Rolls well and supports previous LES researchand supports previous LES research

Summary (continued)Summary (continued)

““Best fit” line was drawn on scatter Best fit” line was drawn on scatter plot of CAPE vs. Normalized Speed plot of CAPE vs. Normalized Speed ShearShear– Discriminated fairly well between Banded Discriminated fairly well between Banded

and Cellular LES events and Cellular LES events – New technique showed improvement over New technique showed improvement over

simply using diurnal trendssimply using diurnal trends ““Odd ball” cases provided the best support (well Odd ball” cases provided the best support (well

developed LES bands near peak heating or developed LES bands near peak heating or disorganized cellular convection late at night / disorganized cellular convection late at night / early in the morning) early in the morning)

Future WorkFuture Work Finish tabulating parameters and Finish tabulating parameters and

correlations for the entire body of correlations for the entire body of events (2005-Present); and over events (2005-Present); and over both areas (NY/MI) both areas (NY/MI)

If necessary, refine Scatter Plots / If necessary, refine Scatter Plots / NomogramsNomograms

Modified BRN ?Modified BRN ? Publish ResultsPublish Results BUFKIT Application ?BUFKIT Application ?

A Model for Future A Model for Future Application?Application?

Questions ??Questions ??