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January 17-18 Winter Storm


Snowstorms
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Ricky put the caution tape up early for us.  That had me side eying the possible snowier outcomes shown even up here.   Still time to correct things like we've witnessed models trend back south for what seems like a decade now.  What could possibly go wrong with winds out of the  S/SE  - Garbage 

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The recent trend that's not good for us is slowing down precip onset into later Friday PM. However, with the magnitude of isentropic ascent forecast, we have to keep in mind the possibility the models are too slow to saturate the modified Arctic air mass. It's not always the case, but sometimes saturation happens quicker than forecast.

Using the 12z NAM as an example again, by about 21z Friday I-88 and south, the dry layer is centered below 850 mb and saturation starts around 850 mb. A cloud base of around 850 mb/4-5kft is a decent rule of thumb for being low enough to allow snowflakes to reach the surface.

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1 hour ago, UMB WX said:

Ricky put the caution tape up early for us.  That had me side eying the possible snowier outcomes shown even up here.   Still time to correct things like we've witnessed models trend back south for what seems like a decade now.  What could possibly go wrong with winds out of the  S/SE  - Garbage 

Yep... when have the models ever over estimated WAA in a winter storm... Rainer fo sho. 

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54 minutes ago, RCNYILWX said:

The recent trend that's not good for us is slowing down precip onset into later Friday PM. However, with the magnitude of isentropic ascent forecast, we have to keep in mind the possibility the models are too slow to saturate the modified Arctic air mass. It's not always the case, but sometimes saturation happens quicker than forecast.

Using the 12z NAM as an example again, by about 21z Friday I-88 and south, the dry layer is centered below 850 mb and saturation starts around 850 mb. A cloud base of around 850 mb/4-5kft is a decent rule of thumb for being low enough to allow snowflakes to reach the surface.

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Is evaporative cooling underestimated too?

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42 minutes ago, RCNYILWX said:

GFS definitely trended back south with surface low vs 00z and 06z runs. If the GEFS and rest of the guidance doesn't jump NW, would think that trend will continue.

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It wouldn't shock me if this does trend south, typically in a loaded pattern your rule of thumb is storms keep going south of previous ones. Not always correct, but typically your cold is entrenched enough to kind of guide the low. 

If anything I don't like the dry air off to the east. It could eat into some snow totals a bit

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3 minutes ago, nwohweather said:

It wouldn't shock me if this does trend south, typically in a loaded pattern your rule of thumb is storms keep going south of previous ones. Not always correct, but typically your cold is entrenched enough to kind of guide the low. 

If anything I don't like the dry air off to the east. It could eat into some snow totals a bit

Fwiw the models are supposed to account for virga. So for instance, if one of those maps would verify, radar would likely be ahead of the actual forecast qpf shield due to the virga, which naturally will cause weenie freak outs when an active radar and dry clouds are being seen.

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7 minutes ago, nwohweather said:

It wouldn't shock me if this does trend south, typically in a loaded pattern your rule of thumb is storms keep going south of previous ones. Not always correct, but typically your cold is entrenched enough to kind of guide the low. 

However, the preceding storm system is not strong and there is some ridging ahead of this storm system.

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5 minutes ago, Chicago Storm said:

However, the preceding storm system is not strong and there is some ridging ahead of this storm system.

Yeah I guess there is that baby low sweeping through tomorrow. Regardless of accumulations, that is one heck of a shot of freezing rain/sleet that goes through Northern IL/IN/OH on the Euro Friday night-Saturday morning. That alone is enough to cause significant travel impacts

 
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