(11:45PM - 3/13/21) A storm system is expected to move through the region on Monday, bringing an accumulating snowfall to portions of Northern Illinois.
A storm system will move from the Plains on Sunday night and into the Ohio Valley by Tuesday morning. This storm system will bring a period of precipitation to the state on Monday, and windy conditions to the state Sunday afternoon through Monday afternoon. Model guidance continues to be in some disagreement regarding placement of the snowfall axis across Northern Illinois, and snowfall amounts. However, all other aspects of the storms system has high agreement.
An area of precipitation will first enter Northwest Illinois very early Monday morning. Precipitation will likely start as rain or a mix, before changing over to snow. This precipitation will then spread across the remainder of Northern Illinois Monday morning, also starting as rain or a mix, before changing over to snow. A period of snow is then expected across a good portion of Northern Illinois, Monday morning through Monday afternoon. Snow will be of varying intensity during this time. This will be a heavier/wetter, with marginal temperatures expected, which will lead to some melting as the event is ongoing. Snow will then end Monday evening, potentially as a mix in some areas. Further south across Central and Southern Illinois, this will likely be an entirely rain event.
In addition the the snow potential, windy conditions are expected Sunday afternoon through Monday afternoon. High winds aloft, characterized by a low level jet of 45-65KT, will be in place. The amount of mixing is questionable and will likely be limited, thus preventing even higher winds.However, expected mixing depth will support easterly wind gusts of 25-45MPH across the state, Sunday afternoon through Monday afternoon.
Snowfall totals of 1-3" are expected along/north of I-80 across Northern Illinois, with amounts tapering to the south. Higher snowfall amounts of 2-5" are possible across Northwest Illinois.
Below is the snow and wind forecasts for this event.