National Weather Service United States Department of Commerce

HEADLINE

A warm summer-like weekend is in store...before a major pattern change brings much cooler weather to central Illinois next week.  

 

DISCUSSION

Upper-level ridging currently in place from the Desert Southwest to the southern Great Lakes will get displaced west of the Rockies by early next week.  Meanwhile, a series of waves dropping out of Canada will carve a significant trough downstream over much of the eastern U.S.  Before this process unfolds, ample sunshine and increasing southwesterly winds will push high temperatures into the middle to upper 80s across central Illinois on Saturday, September 26th.  As the ridge begins to shift westward, a strong cold front will approach from the northwest by late in the weekend.  While the front will push into central Illinois during the day Sunday, the airmass will initially be too dry to support rain.  With deep-layer moisture increasing and forcing becoming much stronger, it appears showers and perhaps a few thunderstorms will develop along and behind the front Sunday night into Monday.  Current projections suggest rainfall amounts will range from one half to one inch...with the highest totals focused along and east of the I-55 corridor.  

Once the front pushes further east, cooler air will arrive by Monday, September 28th as high temperatures drop into the middle to upper 60s.  A reinforcing shot of cool Canadian air will spill into the Midwest by the middle and end of next week, with highs struggling to rise out of the 50s by Thursday, October 1st.  While it's still too early to tell for sure, if favorable sky and wind conditions develop within this chilly airmass...the potential exists for frost across parts of central Illinois by next weekend.           

 

The latest 6-10 day outlooks (Sep 30-Oct 4) from the Climate Prediction Center (CPC) suggest below normal temperatures and below normal precipitation across central Illinois.

 

Issued: 9/25/20