Forecasting the Inland Extent of Lake-Effect Snow (LES) Bands:

Application and Verification for Winter 2010-2011

Joseph P. VillaniNOAA/NWS Albany, NY

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

Jason KrekelerNOAA/NWS State College, PA

Outline

• Introduction• Forecast

Application• Verification of App.• A few case studies• Composite Plots• Future Work

Introduction

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

• Examined over 20 LES events across the Eastern Great Lakes (Erie/Ontario) during 2006-2009 winter seasons

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

Introduction

• Wind regimes stratified by mean flows:–250-290° for single bands–300-320° for multi bands

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

• Data points:– Locations inside and north/south band

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 of LES bands

• Values for the best correlated parameters statistically significant to the 99.95% level with N > 500

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)

Results from Correlations

• Environments that promote greater inland extent (IE):

–Multi-Lake Connection (from upstream lakes)

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

km layer– High capping inversion height

Favorable Environment far-reaching IE

• MLC present (not shown)

• Strong 0-1 km shear; little shear in 1-3 km layer

• High capping inversion height over 3 km

0-1 km

1-3 km

0°C

Inversion

AWIPS Forecast Application

• Equation developed to determine inland extent of lake effect snow bands based on most strongly correlated parameters

• Forecast application based on equation created for use in NWS AWIPS software

• Application integrated on experimental basis at Albany and Binghamton NWS offices

Example of Forecast Application

Multi-Lake Connection (MLC)

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

• 850 hPa low center tracks

Verification of Application

• 10 event times verified via radar with >15 dBZ– Avg error = 10 miles– Excluding two narrow/multi-band/NW flow

events• Avg error = 4 miles

– Avg bias = (-7) miles (under-forecasting IE)– Avg bias = (1) miles (excluding the two outliers)– Avg bias = (-35) miles (for 2 outliers)

Need more events to support verification

Example of single-band event

• 27 November 2010– Single band event – extensive IE–MLC Present– IE forecast from application:• 1100 UTC = 94 miles–Verification = 92 miles

• 1600 UTC = 90 miles–Verification = 100 miles

27 November 2010 – 1600 UTC

• MLC present from Georgian Bay

• Well-developed single band depicted by satellite

27 November 2010 – 1200 UTC

• MLC present• Strong 0-1

km shear; little shear in 1-3 km layer

• High capping inversion height over 3 km

0-1 km

1-3 km

0°C

Inversion

27 November 2010 – 1100 UTC

• IE Forecast from application = 94 miles

• Actual IE = 92 miles

• Good performance of app.

Example of single-band event

• 02 December 2010– Single band event – IE not extensive– No MLC Present– IE forecast from application:• 1400 UTC = 46 miles–Verification = 45 miles

• 1500 UTC = 43 miles–Verification = 37 miles

02 December 2010 – 1400 UTC

• No MLC present (not shown)

• Modest 0-1 km shear; greater shear in 1-3 km layer

• Lower capping inversion height

0-1 km

1-3 km

0°C

Inversion

02 December 2010 – 1400 UTC

• IE Forecast from application = 46 miles

• Actual IE = 45 miles

• Good performance of app.

Example of multi band event

• 08 December 2010–Multi band event – IE extensive–MLC Present– IE forecast from application:• 2100 UTC = 67 miles–Verification = 120 miles

08 December 2010 – 2100 UTC

• IE Forecast from application = 67 miles

• Actual IE = 120 miles

• Poor performance of app.

Example of single-band event

• 16 January 2011– Single band event – IE extensive–MLC Present– IE forecast from application:• 0200 UTC = 92 miles–Verification = 87 miles

• 0600 UTC = 103 miles–Verification = 104 miles

16 January 2011 – 0200 UTC

• IE Forecast from application = 92 miles

• Actual IE = 87 miles

• Good performance of app.

Composite Plots using NARR

• Composite maps of surface pressure and 500/700/850 hPa mean geopotential height plotted for far-reaching IE of LES bands

• Plus favorable environments with:–Multi-Lake Connection (from upstream

lakes)–Conditional instability class–Strong 0-1 km shear, weaker shear in1-3 km

layer–High capping inversion height

850 hPa Mean HeightComposite

Mean Sea-Level PressureComposite

500 hPa Mean HeightComposite

700 hPa Mean HeightComposite

Composite Plots using NARR

• Plots obtained from NOAA’s Earth System Research Laboratory (ESRL) using North American Regional Reanalysis (NARR)

• Favorable positions for low centers generally in South-Central Quebec for far-reaching IE of LES bands into Albany forecast area

Conclusions

• In general, application represented IE well for well-developed single bands in W to WSW flow.

• Application under-forecasted IE (significantly at times) for narrow multi-bands in NW flow

• Additional changes may be needed for multi-band events

Ongoing/Future Work

• Solidify operational functionality of application through additional real-time events

• Develop graphical representation of the inland extent of snow bands, compare to models

Acknowledgements

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

University of NY at Albany

• Vasil Koleci– NOAA/NWS Albany, NY

• 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