The Inland Extent of Lake-Effect Snow (LES) Bands: Project Update Joe VillaniNOAA/NWS, Albany, NYMichael L. Jurewicz, Sr.NOAA/NWS, Binghamton, NY
U.S./Canada Great Lakes Meteorology WorkshopApril 16, 2013
Outline Goals Methodology Results
– Forecast application Latest improvement efforts
Future Work
Goals Single out the atmospheric
ingredients typically most influential on the inland extent (IE) of LES bands
Use this information to formulate predictive techniques in an operational setting
Methodology Investigate LES events over an
extended period (2006-2009 across Central/Eastern NY)
Pick a number of locations both inside and just outside of LES bands at specified time intervals (0000, 0600, 1200, and 1800 UTC)
Select parameters and see which correlate best to IE distances– 12 km NAM initial-hour soundings
Example of Data Points
Points in and near the 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 (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
Correlations Best IE parameters: (ALY) [BGM]
– Multi-Lake connection (MLC, Yes or No) = [0.73] (0.59)
– 850 mb lake-air differentials = (-0.64)
[-0.63]– Capping Inversion Hgts = (0.53)– 0-1 km speed shear = (0.44) [0.34]– 0-3 km speed shear = [0.03]
Bottom line: Lake-lake influence + Elevated ML + Cond/Mdt Instab + Strong 0-1 km flow = Deep IE (Type A)
Favorable IE (Type A)Example Sounding Corresponding Radar
Unfavorable IE (Type B)Example Sounding Corresponding Radar
Another Recent Type BRadar Image (22 Jan 13) IE Application Output
IE Application Example * Prior statistics / correlations boil down to a multi-element regression equation
* Produces an IE estimate for Lk Ont bands
IE Application Results For LES events that impacted
Central NY (WFO BGM), results were fairly similar to those from Eastern NY (WFO ALY)– W flow events (250-280 wind vector)
Mostly single-band cases– Usually good IE estimates (within 10-20
miles)– Tendency to under-estimate for deep inland
bands– NW flow events (290-330 wind
vector) Mix of single and multi-bands
– Under-estimated at times
Under-Estimate Source ? Which term(s) of the IE equation
were most problematic?– It would seem those dealing with
moisture availability A simple Y/N for MLC likely not adequate
– How do we improve?
“Effective Fetch” This concept was designed to
better represent moisture contributions from upstream lakes – Tries to simulate the additive effects
of long fetch distances
IE Term Adaptation
Choice of upstream lakes now available
Example from 6-7 Dec 2010 in WFO BGM’s Area
IE Output: 80 nm
Visible Satellite Image* Effective fetch across Georgian Bay/Lake Ontario was nearly 200 nmi* Modifying the MLC term improved the IE output substantially
Anticipating MLC Not necessarily intuitive in
forecast mode What tools can be provided to
help operational meteorologists in this regard?– Trajectories– Analogs / Composites– Simulated Satellite / Radar products
Forward Trajectory
Using Synoptic Analogs/Composite Plots
* Can help forecasters identify favorable patterns when extensive IE might be expected* Could conceivably stratify by flow regime / type of event
The Future Better visualization
– Efforts are underway to add a graphical component to the current AWIPS IE application
IE application could conceivably be adapted to other portions of the Great Lakes region
Do high-resolution models reasonably simulate inland extent ?