The Inland Extent of Lake Effect Snow (LES) Bands

Joseph P. VillaniNOAA/NWS Albany, NY

Michael L. Jurewicz, Sr.NOAA/NWS Binghamton, NY

Jason KrekelerNOAA/NWS State College, PA/State University

of NY at Albany

Outline

• Goals• Methodology• Results• A few case

studies/examples• Summary

Goals

• Identify atmospheric parameters which commonly have the greatest influence on a LES band’s inland extent

• Infuse research findings into operations

• Improve forecasts to support NWS Watch/Warning/Advisory program

Satellite depiction of developing LES band

Well developed band from Lake Ontario to the Hudson Valley

Upstream moisture sources

Methodology/Data Sources

• Examined around 25 LES events across the Eastern Great Lakes (Erie/Ontario) during the 2006-2009 time frame

– For each event, parameters evaluated at 6-hour intervals (00, 06, 12, and 18 UTC), using mainly 0-hr NAM12 model soundings

– Event duration varied from 6 hours to multiple days

Methodology/Data Sources

• Wind regimes stratified by mean flows:–250-290° for single bands (WSW-ENE

oriented)–300-320° for multi bands (NW-SE oriented)

• LES bands’ inland extent (miles) calculated from radar mosaics, distance measuring tool

• Data points:– Locations inside and north/south band• Data stratified by location relative to band

Example of Data Points

Points in and near LES band

BUF soundingALY sounding

Parameters1) Mixed layer (ML) wind Avg. direction/speed (deg/kt)

2) Ambient low level moisture

Surface dewpoint (°C); Max ML dewpoint depression (TdD) (°C)

3) Snow band width/length

>= 15 dBZ contour (mi)

4) Niziol instability class Lake–air T(°C) at 700/850 hPa

5) Capping inversion Inversion height: top of ML (m)

6) Vertical wind sheara. bulk shear (0-1, 0-3 km)

Vector difference between wind at top and bottom of layer (kt)

6) Vertical wind shearb. directional/speed

Estimated values between surface and top of ML (deg/kt)

7) Low-level convergence

From 0-hour 12km NAM

8) Multi-lake connection?

Satellite/radar data

Strategy to Determine Best Parameters

• Used statistical correlations in Excel spreadsheet to determine most influential factors driving inland extent

– Overall, locations relative to bands made little difference in the correlations (within the bands vs. north or south)• A few exceptions

Statistical Correlations

• Best correlators to inland extent (all points together): ALY events

–850 hPa Lake-air ∆T (-0.63)–Multi-lake connection present

(0.59)–Capping inversion height (0.53)–0-1 km bulk shear (0.44)

Statistical Correlations

• Also notable correlators in locations outside of the bands: – Points south of the band:• Mixed-layer wind speed (0.33)• Mixed-layer directional shear (-0.18)

– Points north of the band:• Surface convergence (0.34)• 925 hPa convergence (0.12)

Results from Correlations

• Environments that promote greater inland extent:

–Multi-Lake Connection– Conditional instability class– Strong 0-1 km shear, weaker shear in1-3

km layer– High capping inversion height

Event Types from Results

• Event types favorable for inland extent based on strongest correlations– Instability and Multi-Lake Connection (MLC)

• Niziol Instability Class: – Conditional Instability• Lake-850 hPa difference: 12°C to18°C• Lake-700 hPa difference: 17°C to 24°C

–Moderate-Extreme Instability• Lake-850 hPa difference: >18°C• Lake-700 hPa difference: >24°C

• Use these parameters to classify events:

– Type A – MLC & Conditional Instability (most favorable type for inland extent)

– Type B – MLC & Moderate/Extreme Instability

– Type C – No MLC & Moderate/Extreme Instability

– Type D – No MLC & Conditional Instability

Classifying Event Types

0 20 40 60 80 100 120

Inland Extent (mi)

Lake–850 TD (°C)

Lake-700 TD (°C)

Inversion Height (km x 10)

Type C

Type B

Type A

Results by Event Type

Vertical Wind Profiles of Mixed Layer

• Type A – greater 0-1 km shear, less above 1 km

• Other Types – less 0-1 km shear, greater above

0-3 km

0-1 km

Z

X

Type A – Surface – 29Oct2006 18Z

Type A Sounding - 29Oct2006 18Z

• Strong 0-1 km speed shear, weaker 1-3 km

• Little directional shear in mixed layer

• High (if any) capping inversion

• Conditional Instability– Lake temp: 10°C– 850 temp : - 4°C– 700 temp: - 15°C

0°C

• Broad cyclonic flow associated with Low pressure in Quebec

• Multi-Lake Connection indicated by visible satellite

Type A – Satellite – 29Oct2006 18Z

850 hPa wind

Upstream Bands

• LES band inland extent around 169 mi

Type A – Radar – 29Oct2006 18Z

0-1 km bulk shear

Type C – Surface – 07Feb2007 18Z

Type C Sounding – 07Feb2007 18Z

• Less 0-1 km speed shear, greater shear in 1-3 km layer

• More directional shear in mixed layer

• Extreme Instability– Lake temp:

4°C– 850 temp : -

18°C– 700 temp: -

28°C

0°C

• NO Multi-Lake Connection indicated by visible satellite• Well-developed single band, but with little inland extent

Type C – Satellite – 07Feb2007 18Z

850 hPa wind

No connection with upstream bands

• LES band inland extent only 34 mi

Type C – Radar – 07Feb2007 18Z

0-1 km bulk shear

• Type A events result in greatest inland extent, often over 100 miles

• Key factors are: Instability, MLC, Shear– Ideal conditions: • Conditional instability• MLC• Strong mixed layer flow with minimal

speed shear between 1-3 km • Nearly unidirectional flow through mixed

layer

Summary

• Refer to event types when forecasting inland extent– Forecast the event type, which will yield good

first guess for inland extent potential

• Use pattern recognition of favorable surface, 850/700 hPa low tracks in forecasting MLC

• Use AWIPS forecast application (based on equation derived from correlated parameters), which provides estimate of inland extent

Application

850 mb Low center tracks

Example of Real-time Application

Example of Real-time Application

Ongoing/Future Work

• Infuse forecast applications into operations

• Develop graphical interface for output from equation

• Evaluate output from AWIPS forecast application

Acknowledgements

• Jason Krekeler– NOAA/NWS State College, PA/State

University of NY at Albany

• Hannah Attard– State University of NY at Albany

References

• Niziol, Thomas, 1987: Operational Forecasting of Lake Effect Snowfall in Western and Central New York. Weather and Forecasting.

• Niziol, et al., 1995: Winter Weather Forecasting throughout the Eastern United States – Part IV: Lake Effect Snow. Weather and Forecasting.

Questions?

Joe.Villani@noaa.govMichael.Jurewicz@noaa.govJason.Krekeler@noaa.gov

www.weather.gov/alywww.weather.gov/bgmwww.weather.gov/ctp