(10:30PM - 10/28/19) A storm system that will develop and move through the region is expected to bring an early season accumulating snowfall to portions of the state, Tuesday night through Thursday night.
There is still some model variability at this range regarding fine details with this storm system. Even with that, accumulating snow is likely across portions of the state, including on Halloween. While this will not be a significant snowstorm by any means, it will be noteworthy for a few reasons... This will be the first accumulating snow of the season for many areas. This storm also may end up as one of the bigger snow events on record in October for some areas, and potentially provide one of the snowiest Halloweens on record for some areas as well.
Things will kick off Tuesday night, as advection and overrunning precipitation develops across the state. Much of Central and Southern Illinois will see rain, and potentially some t'storms. However, there will likely be a narrow corridor of snow on the north end of the precip shield, across portions of Northern and Western Illinois. Snow will be possible in this corridor from Tuesday night through Wednesday morning. Beyond this time, with slightly warming temperatures advecting in, precip will flip to rain for many areas during the afternoon and evening, with the exception being far Northwest Illinois. Upwards of a couple inches of snow is looking possible within the aforementioned corridor across portions of Northern and Western Illinois, prior to changing to rain.
By Wednesday night as the system organizes and lifts into the Ohio Valley and Great Lakes, colder air will begin to filter in on the backside. This will allow for a gradual change over from rain to snow across portions of Northern and potentially portions of Central Illinois, from Wednesday night through the day on Thursday. After the change over occurs, a period of snow will be likely across the aforementioned areas, with upwards of a couple of inches of snow being possible.