(11:00AM - 12/15/19) The expected winter storm that will move through the region today and Monday is beginning to affect portions of the state this morning. This storm system will bring several inches of snow, along with some mixed precipitation for some areas of the state.
This update is just to do one final minor fine-tuning of snowfall amounts, with the main change just to tighten the north and south gradients on either side of the main snowfall axis.
This winter storm will come in two distinct parts...
Part 1: As the lead disturbance ejects out into the region, an area of snow has begun to enter portions of Western and Southwest Illinois this morning. This area of snow will then spread across Central Illinois during the early afternoon, continuing through later tonight, before ending by early Monday morning. Periods of moderate to heavy snow, with snowfall rates of 1-2"/hour, will be possible at times during this period. A period of snow may also make it into portions of Northern Illinois for a time, this evening and tonight. Across Southern Illinois, mixed precipitation in the form of rain/snow/freezing rain, is likely from late this morning on into later tonight.
A lull in the snow and mixed precipitation will likely occur for much of the state, during a couple to several hour period of time Monday morning.
Part 2: As the main disturbance ejects out into the region, another area of snow will push into and across Central Illinois late Monday morning or early Monday afternoon. This activity will continue through Monday evening, eventually ending Monday night. Once again, periods of moderate to heavy snow, with snowfall rates of 1-2"/hour, will be possible at times. Across Southern Illinois, mixed precipitation in the form of rain/snow/freezing rain, is likely from late this morning on into later tonight. Monday morning and evening rush hour travel will likely be significantly impacted across Central and Southern Illinois.
A large swath of 3-6" snowfall totals will be likely across the heart of the state, with a corridor of higher snowfall amounts of 6-9” possible. On either side of the main axis, amounts will quickly taper. Additionally, some ice accumulation is likely across Southern Illinois, with the potential for in excess of 0.10" for some areas.
Below is the TAM snowfall and ice forecasts for this winter storm.