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As you probably have heard, there is going to be an interesting winter weather event unfolding Friday Night into Saturday. Recent model guidance has the storm taking a "more southern track" with every progressing model run. The GFS has come in with snowfall totals of 2"-3", and the NAM has come in with a more robust and very cold storm with 4" of snow for the timeframe. Temperatures will definitely be cold for snow at the onset of snow, with a low of 27 degrees. The snow will fall steadily for 4-5 hours at the onset of the storm. Towards dawn, warm air is forecast to infiltrate the system, and the cold air will eventually give way to a layer of warm air, as indicated by the push or increase in temperature in the mid-level atmospheric temperature profile indicated below:

The forecast sounding is for Saturday afternoon, and is from the 00Z GFS. This shows a period of snow and sleet, as the warm layer in the atmosphere is forecast to hang around during the late morning/afternoon of Saturday. Forecast Ice Accretions (Accmulations) are 0.05"-0.10", which would certainly be enough to cause problems. At this time there is a high probability of sleet and not freezing rain. The accumulations as posted by the models are a little robust, but not by much. The NAM tends to overdo precipitation outputs, but I accept its temperature profile. The GFS tends to do a fairly reasonable job with the dynamics, and the precipitation output. However, the temperature profiles are somewhat unstable. The CMC has just updated and was very consistent with the dynamics of the storm, and has a 2.5"-3.5" forecast for accumulating snow.

My Forecast?!

I believe that 2.0"-3.0" of snow will fall, and then mix with sleet and fall as a mixture of snow and sleet in the late morning/afternoon. In the end because of the light precipitation ending the storm, a period of light rain may be observed at the very end, but is not a problem at this time. 

Note: It is very important that this is forecast data, and changes in the forecast is expected with every model run. A 20 mile shift south could spell a much different story, and the same goes for a shift north. However, the probability that the storm will shift south (+10 miles) is high, while as a shift north is a very low probability based on all of the model's current trends. The probability that the storm will be colder than modeled is high, while the storm will be warmer than modeled is very low based on all of the model's trends. 

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