Pictured above is the ECMWF model (henceforth called the European model), forecasted for Day 9 (9 days away). The image shows mean sea level pressure values for this system, and the system is defined in the Midwest with a central minimum pressure of just above 1001 millibars. This is not a particularly strong system, but is still worth watching closely, as this model is projecting widespread amounts over 6 inches for many big cities in the Great Lakes and Midwest.
Now pictured above is the GFS Model (henceforth called the American model), also valid for Day 9. This time, however, the American model is projecting mean sea level pressures to be as low as 993 millibars, indicating a very strong storm system. Storm placement is relatively similar, with both models indicating the storm will be somewhere in the central half of Illinois. There is definitely that big strength difference, and this strength difference will eventually determine just where the storm goes and how much snow is produced. The American model prints out nearly a foot of snow in the Upper Midwest in response to this storm system, higher than the European model.
I could go on and on about other models and ensembles supporting such a solution, but we need to take a step back and analyze the atmospheric pattern that will be in place when this storm potentially occurs.
What is apparent is that a negative Pacific North American index (PNA) will be present during this timeframe. A negative PNA acts to produce persistent low pressure in the West US, and this then instigates high pressure formation in the Southeast US. This high pressure formation is a barricade to Nor'easters and any winter weather for the East US. We do see a pretty solid negative PNA in the forecast by February 21st as shown in the image above. If this does happen, we can expect high pressure formation in the Southeast US in response.
The North Atlantic Oscillation then gets more specific with the West-based and East-based phases. The West-based negative NAO means that high pressure over Greenland is centered to the west of that land mass, hence west-based negative NAO. It is this specific phase that is best for Nor'easters. The East-based negative NAO means that high pressure is strongest to the east of Greenland, and this means storms and cold are preferred in the Midwest over the Northeast. Looking over more model forecasts, the negative NAO will be nearly evenly distributed among both regions, but the East-based is definitely a favored phase by the time this storm's timeframe rolls around.
The negative PNA will set off the storm originally going through the Southern US, but high pressure in the Southeast will try to force it north into the Northern Plains, a common storm track this winter. However, the east-based negative NAO will suppress that high pressure to the point that the storm system is able to stay on a more eastward track that then goes through the Midwest and Lower Great Lakes, delivering snow to those areas. For those wondering if the Southeast ridge could disappear and the storm goes up the coast, chances are nil. The negative PNA, having a stronger influence on the US weather as it is upstream from the nation, will make the Southeast ridge prevail to an extent that matches my description in the first few sentences of this paragraph.
Here's my current prognosis: