Justin ArnottSenior ForecasterWFO Northern Indiana - IWX

Incredible Persistence ~5 days of nearly continuous LES

Modest Strength 24 hour warning snowfall values only

seen once ~1/2 of 5 day snowfall fell in < 12 hrs

Examine Event from a Sounding Perspective Can we explain the evolution through sounding-

derived parameters? Goal: Similar Sounding tool akin to the BGM

model▪ Possible further refinements?

Examine Event from a Modeling Perspective Not enough time for this today!

BGM Variables Instability Variables

▪ T850 and delta T

▪ Inversion Height▪ Low level lapse rates

Moisture Variables▪ Moisture Depth

▪ Tdd below 900

Kinematic Variables▪ Mixed Layer Wind Direction▪ Mixed Layer Wind Speed▪ Wind Shear

DGZ Variables (snow:liquid)▪ DGZ Depth▪ DGZ Omega

We’ll examine these and try a few more

RUC Analysis (00hr) soundings RUC/NAM sounding parameters very

similar overall

When: Hourly (144 soundings)▪ Is increased temporal resolution helpful (vs.

BGM tool)?

Where: South Bend, IN (KSBN)▪ Qualitative results superior to LM2

Examine 3 interesting periods Intense single band

Null Event (you’ll see why later!)

Seeder-Feeder Enhancement

Can you find the 12 hour period with ~1/2 of the event total snow?

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Perhaps another variable would help?

oC

Intense Single Band

1’

NullEvent1-3”

SeederFeeder Event4-6”

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Instability/moisture variables define events/null events successfully T850 ~ On/Off Parameter T700/Inversion Height suggest potential strength Moisture variables indicate if potential is realized

Kinematic/DGZ variables less promising But, should a favorable DGZ result in a strong

band?▪ Apples/Oranges?

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Step 1 - Instantaneous “Radar Match” Band Location/Orientation (wind direction) Band appearance (single vs.

multiband)/strength (instability/moisture variables)

Step 2 – Snow Accumulation Potential Residence Time ( wind direction) Snowfall Rate Potential (Lake Snow

Parameter?)

Compile 2005-2010 LES Sounding parameters COMET NAM/Local RUC BUFR Archive

Refine “Important Parameters” and develop matching algorithm Separate Step 1/Step 2 variables

Deploy Operational Tool for 2010-2011 Season

Mark Steinwedel, Nick Greenawalt, Sam Lashley (IWX) for developing IWX 5 year climatology

Dolores Kiessling (COMET) for archived BUFR data

Jeff Logsdon, SOO IWX

IWX Forecasters

Evans and Murphy 2008: A proposed methodology for reconciling high-resolution numerical model guidance with pattern recognition to predict lake-effect snow. EJOM. Available from: http://www.nwas.org/ej/2008-EJ2/

Smith and Boris 2009: The Lake Snow Parameter. Available from: http://www.crh.noaa.gov/apx/?n=lake_snow_parameter

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