(7:00AM - 1/11/19) Taking a look at the latest computer model guidance from overnight, everything looks to remain on track for the most part with regard to the impending snowstorm that will be making its presence known in the Midwest and Illinois as soon as this afternoon.
A brief update follows below...
Our main upper level low is slowly making its way into the Four Corners Region early this morning and will continue to slowly move eastward as we go through the day today. As mentioned over the previous few days, this upper level low will lead to the development of a surface cyclone emerging from the lee side of the Rockies last night and this morning, moving out into the southern plains. Warm, moist air to the east of this area of low pressure will help lead to a developing area of widespread precipitation and snow throughout the day today.
As you can see below, this area of snow will slowly move east and northeast during the afternoon today and into the evening, moving into portions of western, southwestern, and southern Illinois during that timeframe, including the St. Louis Metro area.
Snow will slowly continue northeast overnight tonight into Saturday and as well as Saturday afternoon, finally beginning to reach portions of northern Illinois during that time. Model guidance continues to struggle somewhat where the northern cutoff will be of accumulating snowfall but it looks like it will be somewhere across northern Illinois, as you can see in the image below, going from no snow to snow fairly quickly the further south you go.
This still looks to be quite the slow moving storm system, which is why the southern half of Illinois will see high snowfall totals, possibly into the double digits in spots with 9-12" looking possible in some areas. This will mean that snow could fall for 24-30 hours across portions of southern and central Illinois, leading to hazardous on area roadways and interstates. Most model guidance, like the image below, still shows snow ongoing into the evening hours on Saturday.
Below is our latest thinking on snowfall totals across Illinois from tomorrow afternoon into the afternoon hours on Sunday. Stay tuned for continued updates on this significant winter storm to impact the state over the weekend.