After what was quite the snow drought across much of Illinois during the month of December and the very warm start to the month of January, the pattern is beginning to shift towards a colder and potentially snowier pattern across the Midwest, including our area here in Illinois.
Model guidance over the last several days has been showing the potential of a storm system moving through the southern/central plains on Friday and then into the Midwest on Friday night and into the day Saturday. Now that we are in the heart of winter, cold air usually isn't too hard to come by and that will be the case with this system as this will be mainly a snow maker for Illinois.
I dig a little more into the details below...
At first, there will be several smaller weather disturbances that move across the western United States between now and Friday rather than one potent, large system from the get go that traverses the entire country. These several waves or disturbances will phase together as they approach the Rockies out west and eventually consolidate/strengthen into one upper level low as it moves out into the plains on Friday.
This will then lead to an area of low pressure developing at the surface and aloft across the southern and central plains with winds responding to the pressure falls. These winds will be "warm winds" and what is called warm air advection. This warm air advection on the east side of the system will help to develop a large area of precipitation and snow to our west and southwest Friday afternoon and evening.
By Friday night, a large area of snowfall across Kansas and Missouri will begin moving into portions of Illinois, favoring southern and central Illinois at first Friday night and into Saturday morning, with snow to continue into the afternoon hours as things look now. Further north across northern Illinois, questions remain regarding how much dry air will be in place and this in turn will determine just how far north snow gets and how soon it gets further north.
All in all, this is looking like a significant snowstorm across central and southern Illinois, including the major cities such as St. Louis, Springfield, and Champaign with some areas forecast to receive 6-9" further downstate and the outside shot that a few areas in and around the St. Louis area (which looks like the jackpot zone currently) gets close to a foot of snow.