Sunday, December 23, 2018

Highest Impact Winter Storm Thus Far in the Season

Parts of the Midwest will be digging out from their largest snow storm since last year by the end of the week. A storm system is expected to develop in the southern Plains Wednesday and slide to the north and east through Thursday and Friday. Heavy snow will begin to breakout Wednesday night into Thursday morning as it overspreads the entire Upper Midwest through the day Thursday. A swath of 6"+ of snow is expected to fall to the northwest of the track by Friday, with rain further east.

With the storm system still 3-5 days out there are still more questions than answers at this point. As per usual, the exact track of the low pressure system will greatly determine who sees the heaviest snow and who sees mainly rain. In addition to the usual track error in the models, there are major differences in the temperature profiles of the atmosphere ahead of the system. While an area of high pressure is expected to develop north of the Dakotas, there just isn't the amount of cold air in place we would usually have at this time of year. The low will have to generate some of its own cold air through advection and latent heat release. The GFS and the EURO have varying opinions. The GFS for example has a much more saturated atmosphere ahead of the first batch of precipitation, which will impact temperatures as dry air and precipitation can act as a cooler process due to latent heat release. Whereas the EURO model has more dry air to help cool the column ahead of the heavier snows. Furthermore, the grid spacing on the EURO is smaller so will better resolve the cooling process over the GFS, so the cooler solution is currently favored. Below is a look at the GFS model, with the main EURO rain and snow line overlayed. The GFS has a much larger percentage of the storm as rain, while the EURO suggests more snow. Still a lot to work out with this one, so be sure to follow on Twitter and Facebook for continued updates. Can always check out the Computer Snow Output page as well.