The Inland Extent of Lake-Effect Snow (LES) Bands
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Transcript of The Inland Extent of Lake-Effect Snow (LES) Bands
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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
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Outline Motivation Goals Methodology Results Case Studies Ongoing / Future Work
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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
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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
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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
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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)
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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
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Example of Data Points
Points in and near the LES band
BUF soundingALY sounding
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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
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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
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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)
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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)
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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
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8 January – Radar + 1 km Shear
Strong mixed-layer flow - 30 to 40 kt
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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
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16 January – Radar + 1 km Shear
Strong mixed-layer flow – 30 to 40 ktWeaker mixed-layer flow - 10-20 kt
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16 January – BUF Sounding- Lake to 850 mb Delta T of 26C
- Lake to 700 mb Delta T of 37C- Much steeper LR’s
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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
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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
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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
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Present/Future Work (Continued) Perhaps better delineate
significant thresholds for strongly correlated parameters
Single banded vs. Multi-banded cases
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The EndQuestions ??