There continues to be a large spread amongst the forecasting models as far as which solution is the most likely to verify. Shown above is the North American Ensemble Forecasting System, or NAEFS forecast for Hour 96, which converts to 4 days away from today. We see our system is in Kentucky at this time. If you've been reading my recent posts, you will understand that there has been a north trend with this storm that some models have had. This trend then resulted in the storm going to Wisconsin and other areas in the Northern Plains/Upper Midwest. It has been within the last 48 hours that we have seen a sudden revolt, so to speak, among the ensemble systems. This includes the NAEFS, the Canadian ensemble system and the American ensemble system. All three are considered big ensemble forecasting systems and have all been in fascinating agreement with the system going south rather than north.
Now that we've identified the indices at play here, let's look over that 500mb anomaly map and identify why the models are not handling this well. In that image, we can see high pressure centered over Canada and stretching into the US. This stretch into the US is helped by the negative PNA. By Hour 72 (when this image is valid), the high pressure system has started to extend north, leaving a gap of high pressure in the Southeast that is weaker than the high pressure in the Upper Midwest. Some models, like the European model, want to take this system north and have it ride the stronger high pressure wave into the Upper Midwest. The ensembles seem to believe it will go towards the weaker area of high pressure and this take a more southern route. The logical solution would be to take this system to the south, towards the weaker area of high pressure, as the ensembles are showing. I can understand why the models want to take the system more into the Upper Midwest, and it's due to where the system ejects from the Rockies. The farther north it comes out of the mountains, the farther north the track is going to be. Likewise, the further south the system ejects from the Rockies, the further south the storm track will be, like the ensembles are forecasting. In my personal opinion, if the system will be moving out of the Rockies from Southeast Colorado and the jet stream will be flowing towards the northeast (with winds over 100 knots), I could see the Northern track work out.