December 10-12 Long Range Potential Winter Storm (Updated 12/3)

There has been a movement towards a potential winter storm between the 10th and the 12th, and signs are looking good for the Plains and Midwest. Let's get going over the models.

This is the GFS model forecast for the morning of December 11th. As you can see, there will be a good low pressure system in southern Illinois/southern Indiana, with cold air wrapping around behind it. That dashed red line nearest the low pressure system is the rain-snow line. Ignore any other dashed red lines. If we look at the bottom image, we see precipitation forecasts. Any precipitation north of the black line is theoretically snow, and precip to the south is rain. This could end up being a severe weather event as well, depending on the temperature gradient between the warm air and cold air in front and behind the system, respectively.

This is the Canadian CMC model forecast, with the low pressure system now on the Illinois/Wisconsin border. The same rules apply with the black line on the bottom image, and the red dashed rain/snow line on the top image is still closest to the low pressure system in question. The CMC extends the warm sector further north than the GFS, and the track overall is further north. While I do think the extended warm sector is possible, the CMC has been known to forecast ridiculously in the long range, so this could be one of those instances where it's kind of there, but not really (with the track).

The ECMWF falls into a semi-GFS forecast, with a more eastern track. The warm sector is extended, but not as much as the CMC. The system is also stronger than the CMC model, enhancing my idea that the CMC isn't making its best forecast for this system at this point in time. 

Here's where things get interesting! These are different forecasts from today's 12z GFS Ensemble members, with the top four images being of the 6 hour precipitation and sea level pressure forecasts. The blue line is the rain-snow line. The bottom four lines are snow depth forecasts, and legends for both sets of images are in the middle. The GFS Ensembles shown here are pretty darn aggressive with this system, with one member obliterating central Illinois with over 2 feet of snow! Alas, I do not expect these forecasts to pan out in the slightest. While they should be watched, as some Gulf of Alaska energy should be involved here, do not get your hopes up for 25+ inches of snow.

The models are pretty scattered here, but I think the GFS/ECMWF models have a pretty good idea on this system. The Plains should get snow, and the battleground rain/snow line should stay in the Midwestern regions. Waiting another 48 hours will give us a slightly better idea for this system, and another 72 hours should bring much better clarity.

Andrew