(11:30AM - 12/14/19) A winter storm is set to move across the region Sunday and Monday, bringing accumulating snow to a large portion of the state during this time.
As seems to be the norm these days, model guidance has been significantly struggling with this expected storm system over past several days. On Friday, a majority of guidance honed in on a general overall idea regarding how this winter storm will evolve. Even with that, there was some some guidance that was not in agreement, and instead showed either weaker/south or amped/northern solution. Since that time, some of the outlier guidance has also come into an agreement with the consensus, though there are still a few stragglers at this time.
The main two changes this update were to extend timing of the event, as there has been a continued slowing trend on model guidance. What once looked like a Sunday morning-Monday evening storm, is now a Sunday morning-Monday night storm. Also, we have increased snowfall totals int he main axis, including into St. Louis and adjacent areas.
An area of snow is expected to begin to enter Western and Southwest Illinois by mid-late Sunday morning. This area of snow will overspread across Central Illinois by afternoon, continuing through Sunday night or early Monday morning. There is the potential for a lull in the snow for a time Monday morning. Another area of snow will then push across Central Illinois later Monday morning, then continuing into late Monday night, before ending. Further south, a mix of precipitation will be likely across Southern Illinois; including snow, ice and rain. Minor snow and ice accumulation is possible across this areas.
A swath of 3-6" of snow will be likely across the heart of the state, with totals tapering to the north and south of this axis. Within the main swath, a corridor of 6-9" snowfall totals will be possible. Additionally, minor ice accumulation will be possible across Southern Illinois.
Below is the TAM snowfall forecast for this event.