After a mostly quiet Sunday and Monday across Illinois, attention will quickly turn to a potent upper level trough and developing weather system as it moves across the Rockies and out into the plains. Numerical model guidance has remained quite consistent on the development of this system across the central plains later Monday, before moving it northeast into the Midwest, including portions of Illinois. Given the cold low level air-mass that will be in place, there is growing concern for wintry precipitation, including the threat of freezing rain with this system, especially if the system tracks along the southern side of model guidance.
I briefly dig into the details below...
As mentioned above, a fairly impressive upper level trough will come ashore and move eastward, crossing the Rockies and into the plains by late tomorrow night and early Tuesday morning, before continuing off to the east and northeast.
This strong upper level system will induce cyclogenesis, or the birth of a surface low across the central plains with strong warm air advection leading to the development of a widespread area of precipitation in the cold air immediately north of the surface low
Model guidance at this range continues to differ on the strength and track of the surface low which means all the world across Illinois and the difference between all rain (further north track) and a freezing rain/snow threat (further south track).
The loop below is not a forecast and is just one scenario of what a colder, more southern track would look like, leading to a higher chance of freezing rain and accumulating snow across northern Illinois.
This southern track, although not at all set in stone is somewhat concerning due to the fact that with the very cold air currently in place, any precipitation moving into that environment would have the potential to freeze on impact and this will be something that will have to be watched. Even with strong warm air advection on Tuesday, some model guidance suggests temperatures are still well into the 20's.
Updates will continue on this system as we get closer to Tuesday and model guidance showed get a better handle on things once this system comes ashore California late tonight and early tomorrow morning.
As mentioned, it will all depend on the track of the low pressure system as seen below. This system could easily move further north and lead to a mostly rain event, as some model guidance is showing.
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