February 19th-20th Tues-Wed Accumulating Snow Event For Much of Illinois Update #3 (Beginning Tonight)
We continue to keep an eye on this system along with latest computer model guidance from last night and overnight as it begins to slowly develop across the southern plains and southern Ohio Valley region later today and early this evening. It still looks like this system is going to bring fairly widespread accumulating snowfall to much of Illinois, potentially a period of heavy snow, beginning this evening across downstate and continuing late tonight/overnight as it moves northward across much of the state.
I dig into the latest below including timing and expected snowfall totals across the state...
Our system of interest is currently across the southwestern United States and into the Baja region of Mexico as it swings around the base of the main upper level trough, centered further north. This wave, circled in blue, will then eject northeast later today and tonight into the southern and central plains, before entering portions of the Midwest.
By tomorrow evening and late tomorrow night, low pressure will have developed across the southern/central plains with very strong low level winds out ahead of it across the southern Mississippi and Ohio Valley regions. These strong winds over near 70-80mph and centered 5,000ft above the ground, will aid in developing a fairly expansive area of moderate to heavy precipitation that is going to stream northward into the southern Midwest, including portions of Illinois by tomorrow evening, as you'll see below.
As precipitation expands northward into the colder air at low levels, there will be an area of potentially moderate to heavy snow on the leading edge as it moves through the southern half of the state this evening and into the overnight hours tonight. It will not be a long duration period of snow but it could snow rather heavily this evening/late tonight as it moves northward across a good chunk of Illinois as you can see below.
Below is a loop showing just about the entire evolution of this system and how it will affect us here in Illinois. This runs from noon today till noon tomorrow, showing precipitation, possibly moderate to heavy at times, expanding northward into southern Illinois this evening and continuing northward overnight into tomorrow morning. The best chance for a period of heavy snow will come at onset and a few hours after for a given location before temperatures warm both aloft and at the surface, leading to a chance for freezing drizzle or just plain rain further south.
Below is our latest forecast for expected snowfall totals. There is the potential for snowfall amounts to be higher than what is currently forecast, especially in the large 1-3" area. Like it was mentioned above, there could be a several hour window of heavy snowfall rates which some models are hinting at and could lead to higher snowfall totals but we will fine tune this as we go through the day today.