Well, as we high lighted early this month just under two weeks ago, there was the potential that the pattern for the middle part of February could be *very* active across the Midwest, including portions of Illinois. That continues to be the case with the next system already having our attention for the middle of this week and one that could bring another round of accumulating snow to the area. This is the 5th system that will bring wintry weather to the state of Illinois in about the last ten days or so.
I dig into the setup and details of our next system below....
By tomorrow morning across portions of Nevada, Utah and Arizona sits a large and fairly impressive upper level low (marked by the L on the image below) and this will be one of the main drivers for our system later this week. Over the next 24-36 hours it is going to slowly meander its way through the southern Four Corners region and eventually come out into the southern/high plains on Tuesday afternoon and evening.
The other big player in this setup will be the very strong area of high pressure or upper level ridge that will be parked southeast of Florida during the early to middle portion of this week. This will allow for favorable trajectories off the Gulf of Mexico for moisture to advect northward into the southern Midwest, marked below by the orange arrows. As our upper level area of low pressure (in red) moves out into the plains, winds will significantly respond/strengthen across the lower Mississippi River valley and aid in advecting that moisture northward.
You're able to see this a little more clearly looking at a precipitatable water image below. This is a measure of the available moisture content in the atmosphere and the higher/brighter the values (darker green, gray and eventually purple) show very impressive moisture being advected northward off the Gulf of Mexico and eventually into the southern Midwest and Ohio River Valley.
All of this in conjuction with the added forcing from the wave itself and strong warm air advection/insentropic lift to our south will lead to a blossoming area of precipitation, as you'll see in the loop below. This precipitation is going to stream northward Tuesday afternoon and evening, initially making its way through southern Illinois late Tuesday night as things look now. This area of precipitation, including snow, will be running into a strong area of high pressure at the surface with plenty of cold air associated with it. This leads to the point that nearly all of Illinois could see sticking snow out of this from late Tuesday night through Wednesday afternoon as it moves from south to north.
Below is our first thinking on expected snowfall totals from this system. As you can see, we are expecting nearly all of Illinois to see accumulating snow out of this but the heaviest snow totals will be across the western and northwestern portions of the state as things look now, where several inches could accumulate. Stay tuned for continued updates along with new snowfall maps.