Rain, Snow or Ice this Week?

Winter Precipitation Forecasts in the Ohio Valley are Always Challenging!

Forecasting precipitation type in the Ohio Valley is not for the faint of heart! Unlike many locations to our north or in higher elevations near the Rockies, the Ohio Valley is notorious for nearly always being along the transition line between liquid, freezing, or frozen precipitation.  Unfortunately, it's much more complicated than whether or not its above or below freezing at the earth's surface, where we have a relatively large number of observations.  What's REALLY important for determining whether precipitation falls as rain, snow, sleet, or freezing rain - or a combination of two or more of those types - is the temperature of the lowest few thousand feet in the earths atmosphere above the ground at your location (the temperature "profile"), where direct observations are few and far between.  A difference of just a few degrees in temperature, or the difference in the height of the critical freezing temperature (0 degrees Celsius / 32 Degrees Fahrenheit) can mean the difference between a soggy drive to work and the shutdown of all commerce and transportation due to paralyzing ice or snow accumulation.  

Complicating matters even more is the fact that the many computer models of the atmosphere used by meteorologists to forecast the weather here on the ground often have very different solutions in the temperature profile for any given location at a point in time.  As an example consider the three images below, showing forecat temperature profiles at for Louisville, Lexington and Bowlling Green this Friday (Dec 6, 2013).  Note the color differences for the three models shown.  In all cases, the NAM (North American Model) is the warmest, with rain forecast, the GFS (Global Forecast Systems) Model the coldest (forecasting snow), and the ECMWF (European) Model the middleman, forecasting ice (in the form of freezing rain or sleet).  

7 AM EST Friday, Dec 6, 2013 - Louisville, KY

Forecast Sounding for SDF - 12Z 12-6-2013


1 PM EST Friday, Dec 6, 2013 - Lexington

Forecast Sounding for LEX 18Z 12-6-2013


6 PM CST Friday, Dec 6, 2013 - Bowling Green

Forecast Sounding for BWG - 00Z 12-7-2013

While many times the computer models that are in closest agreement have the best handle on the situation, that is not always the case; sometimes the "outlier" model is more accurate.  As the forecast time draws nearer, the computer models tend to come into closer agreement, but sometimes that is not until the last 12-18 hours. 

To help ALL forecasters - NWS - TV, and other media - know what type of precipitation you observe with this and all storms, download the mPING app for your iPhone or Android moblie device.  Your observations help keep everyone safe when winter weather occurs! 



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