the inland extent of lake- effect snow (les) bands joe villani noaa/nws albany, ny michael l....

The Inland Extent of Lake-Effect Snow (LES) Bands Joe VillaniNOAA/NWS Albany, NYMichael L. Jurewicz, Sr.NOAA/NWS Binghamton, NYJason KrekelerState Univ. of NY, Albany, NY

18th GLOMW, Toronto, OntarioMarch 22-24, 2010

Outline

Motivation Goals Methodology Results Case Studies Ongoing / Future Work

Motivation

Considerable research has been devoted to LES processes and forecast issues over the last 2-3 decades– However, among these,

comparatively little attention has been given to inland extent

Goals

To identify atmospheric parameters that commonly have the most influence on a LES band’s inland penetration – Use these results in the forecast

process to improve: The quality/detail of information given

to the public (nowcasting) The NWS Watch/Warning/Advisory

program

Satellite Depiction of an Intense Band all the way to Albany, NY

Well developed single band from Lake Ontario to the Hudson Valley

Upstream moisture sources

Methodology/Data Sources Examined 20 LES events across

the Eastern Great Lakes (Erie/Ontario) during the 2007-2010 time frame– For each event, parameters were

evaluated at 6-hour intervals (00, 06, 12, and 18 UTC), using the NAM12 and RUC models, as well as BUF/ALY soundings

– Events averaged 24-30 hours in length

Wind regimes varied from a mean flow of 250-260 (WSW-ENE oriented bands) to 300-320 (NW-SE oriented bands)

Methodology (Continued) LES bands’ inland penetrations

(miles) calculated from radar mosaics, and a distance measuring application

Data points– Locations both inside bands and on

their peripheries were used (north, south, and just downstream of the band)

Data stratified based on location relative to band

Example of Data Points

Points in and near the LES band

BUF sounding

ALY 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 (n 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. magnitude (0-1, 0-3 km)

Vector difference between wind at top and bottom of layer (kt) (from Storm Prediction Center)

6) Vertical wind shearb. direction/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 data

Strategy to Determine “Best” Parameters Used statistical correlations to

determine the most influential factors for inland extent– Overall, locations relative to bands

made little difference in the correlations (within the bands vs. north or south)

A few notable exceptions

Statistics

Best correlators to inland extent (all points together):– Multi-lake connection (0.75)– 850/700 mb Lake-air differentials (-

0.65)– Mixed-layer speed shear (0.27)– Mixed-layer directional shear (-0.23)

Results (Continued)

Also a few healthy correlators in locations outside of the bands: – Points south of the band:

Height of capping inversion (-0.4) Mixed-layer speed shear (0.35)

– Points north of the band: Mixed-layer directional shear (-0.4) Surface winds (0.3)

Brief Case Study Examples Both events featured 260-270

mean flow single bands– 8 January 2009

Only small inland penetration– 16 January 2009

Much greater inland extent

8 January – Radar + 1 km Shear

Strong mixed-layer flow - 30 to 40 kt

8 January – BUF Sounding

- Lake to 850 mb Delta T of 13C

- Lake to 700 mb Delta T of 22C

- Only conditionally unstable LR’s

16 January – Radar + 1 km Shear

Strong mixed-layer flow – 30 to 40 ktWeaker mixed-layer flow - 10-20 kt

16 January – BUF Sounding

- Lake to 850 mb Delta T of 26C

- Lake to 700 mb Delta T of 37C

- Much steeper LR’s

Take-Home Points

Environments that promoted greater inland extent of LES bands seemed to feature these characteristics:– Strong, well aligned flow in the

mixed layer (especially north of the band)

– Only conditional terrestrial instability Moderately to extremely unstable cases

tended to produce disorganized/cellular structures, confined closer to the shoreline

More Summary Points

South of the band:– Stable, sheared environments

seemed favorable for inland extent Cold low-level inflow into the band Lower cap/EL

Multi-Lake connection (MLC) is another factor that strongly related to inland extent

Ongoing / Future Work

Further develop an algorithm/equation that provides an estimate of inland extent, based on favorably correlated parameters– To be used in cases where LES band

development seems likely– Has already been tested on some of our

cases, with favorable results Individual/composite plots for MLC

patterns– MSLP/850/700 low tracks– Based on flow regimes

Present/Future Work (Continued) Perhaps better delineate

significant thresholds for strongly correlated parameters

Single banded vs. Multi-banded cases

The End

Questions ??