Model guidance is slowly coming into better agreement with our middle of the week winter system and for this reason, our confidence is increasing for widespread accumulating snow across the state. Let's dig into the latest below....
Our main upper level low is slowly meandering its way through the Baja region of Mexico this afternoon and will continue to slowly move east over the next 36-48 hours, interacting with several other smaller disturbances as it does so. The second "ingredient" to this eventual winter system is a northern stream wave still out over the northern Pacific Ocean at this time and will be coming ashore British Columbia in western Canada later tonight. This smaller disturbance is forecast to phase with our main southern upper level low across the plains on Wednesday. The amount of phasing and when it occurs will determine the strength and track of our area of low pressure.
Numerical model guidance, including ensemble guidance continues to slowly get a better consensus on the track of our surface low and position of it by Wednesday evening (valid below). This is usually a favorable spot to have the area of low pressure for a swath of accumulating snow on the north and northwest side as drawn out below. This isn't locked in stone just yet but confidence is slowly increasing.
Below is one models take on the evolution of this system but it is also not set in stone to play out exactly this way and more used to give a broad overview of how things look at this time. We will all remain dry through late Tuesday night but expect precipitation to eventually move into downstate Illinois by Wednesday morning with a potpourri of precipitation types. By the mid-late afternoon, the system as a whole and precipitation (including accumulating snow) associated with it will continue north and northeast making its way into central Illinois and eventually northern Illinois and the Chicago metro area by Wednesday evening. Snow would then continue through much of the night into Thursday morning across about half the state. Beyond Thursday morning, there's a secondary disturbance coming down from the northern plains which could keep snow going through Thursday afternoon across northern Illinois, albeit in a light fashion.
Below is our latest thinking on expected snowfall totals across the state....stay tuned for continued updates though as this is subject to change over the next 36 hours.