SWOP Weekly Weather Discussion

HEADLINE

Several waves of convection will bring beneficial rainfall to much of central Illinois this weekend...followed by very hot and humid conditions next week.  

DISCUSSION

A flat west-to-east zonal flow pattern across the U.S. will ensure the continuation of near normal temperatures through the upcoming weekend.  As a frontal boundary sags slowly southward and becomes parallel with the upper flow, it will stall across the region later today through Monday, July 21st.  A series of disturbances expected to track along the northern periphery of an upper ridge of high pressure centered over the Southern Plains will interact with the boundary to trigger several rounds of thunderstorms over the next few days.  While Friday looks to be mainly dry, the first wave of convection is slated to arrive late Friday night into Saturday...followed by a couple more rounds through early next week.  While the exact track of the waves and their corresponding swaths of rainfall remain somewhat in question, confidence is growing that beneficial rains will occur across much of central Illinois.  The latest data suggests that the heaviest rainfall will focus along and northeast of a Galesburg...to Decatur...to Effingham line where amounts of 1 to 2 inches will be likely.  Further southwest, rainfall will generally be under 1 inch.  All models are showing the upper ridge building northward into the Midwest and Ohio River Valley by early next week.  This will gradually shift the boundary northward into the Upper Midwest/Great Lakes and put an end to the rain chances by Tuesday, July 22nd.  Thanks to rising upper heights, increasing amounts of sunshine, and a southerly flow, temperatures will soar into the lower to middle 90s by the middle and end of next week.  Given the expected rainfall this weekend and the actively growing crops, surface dewpoints will rise into the upper 70s and perhaps even the lower 80s in a few locations.  This will push heat index readings well above 100 degrees.      

The latest 6-10 day outlooks (Jul 22-26) from the Climate Prediction Center (CPC) suggest ABOVE normal temperatures and NEAR normal precipitation across central Illinois.

Issued: 7/17/25