(11:45AM - 1/13/21) A storm system will move through the region Thursday through Saturday, bringing the chance for a minor accumulating snowfall to portions of the state.
A storm system is expected to develop in the Midwest on Thursday, quickly becoming occluded and vertically stacked as it meanders around the Midwest Thursday through Friday, eventually sliding through the Great Lakes on Saturday. A shield of precipitation that develops out west will spread across the state on Thursday, as the storm system initially moves into the region. As the storm system occludes and becomes vertically stacked, precipitation will continue to wrap around the storm system and across a large portion of the state, Thursday into Saturday. A period of rain/snow/sleet is expected along the front portion of the precipitation shield on Thursday, before changing to snow for the rest of the event for affected areas. Model guidance has been all over the board with this storm system the past several days. Even at this time approximately 24 hours out from the start of the event, there is a large spread in solutions, ranging from a relatively minor event across portions of the state to a more moderate event across portions of the state. With this first forecast, we have gone with the slight consensus, which supports a minor snow event for portions of the state. However, it needs to be stressed that given the large amount of uncertainty and spread in model guidance, changes are quite possible in future updates.
A shield of precipitation that develops out west will first spread across the state, from Thursday morning into Thursday evening. It is likely that precipitation will initially start as period of rain or a mix for Northern and Central Illinois, before steadily changing over to snow. Behind the aforementioned initial shield of precipitation, periods of snow and snow showers are then expected across Northern and Central Illinois from Thursday evening into Saturday evening, as the storm system becomes occluded and vertically stacked. Snow showers will possibly even make it into Southern Illinois, Friday afternoon into Saturday afternoon. Periods of snow and snow showers across the state will coe to and end by early Saturday night.
Final snowfall totals upwards of 1-3" are expected across portions of Northern Illinois, to a dusting to 1" or so across much of the rest of the state.
Below is the snowfall forecast for this event.