We continue to watch and analyze the latest computer model guidance as it comes in last night and this morning and everything continues to point to a fairly impressive storm system affecting the Midwest, including here in Illinois. This system will bring some rain to the area but the big story will be the rarity of accumulating snow to portions of Illinois before and on Halloween and what could be several inches at that. I dig into the latest details below....
Our storm system this morning has now entered the western U.S. and will continue to dig south and southeast through some of today before turning more easterly and entering the plains. After that, it will set its sights on the Midwest and our area by later tomorrow and into Thursday.
The loop below runs from 1pm this afternoon till 7am on Thursday. There is a lot going on in this loop so lets break it down into a few steps.
1. Precipitation (in the form of rain at first) will initially develop this afternoon and evening well to our southwest across the southern and central plains and spread northeast aided by a strong low level jet.
2. As precipitation gains some ground northward, it will encounter colder temperatures at the surface and aloft, allowing for it to changeover to snow from about northern Missouri into portions of northern Illinois very late tonight and more so into the heart of the overnight hours. Model guidance continues to hint at a band of snow early Wednesday morning across portions of northern Illinois that could lead to a few inches of snow accumulations.
3. As surface temperatures warm Wednesday afternoon, it is possible that most of the precipitation across the state flips over to all rain for a period outside of maybe far northwest Illinois.
4. As surface winds turn out of the northwest late tomorrow night into Thursday morning, colder temperatures will advect into portions of the state from western Illinois on northeast into northern Illinois, changing precipitation back to snow as things stand now. This looks to be the next period of potential snow accumulations on Thursday afternoon and evening as temperatures cool into the low 30's. Wind will also be quite gusty out of the west and northwest during the day and evening hours on Thursday.
Exact snowfall amounts and the location of the most snow is still not set in stone yet so continue to stay on the lookout for more updates as we near the start of this event late tonight and early tomorrow morning.
To recap.....the first window for accumulating snow will exist very late tonight into a good portion of Wednesday morning (locations not yet determined as band of snow could be quite narrow. Rain then is expected Wednesday afternoon and evening before colder air works back into western and northern Illinois, going back to snow for a good portion of Thursday and into Thursday night with more snow accumulations look likely but amounts still up in the air.