


Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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484 FXUS63 KILX 161832 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 132 PM CDT Wed Jul 16 2025 .KEY MESSAGES... - A broken line of thunderstorms will push across parts of central Illinois this afternoon...bringing a risk of strong winds and locally heavy rainfall. - Heat and humidity will build next week...with early projections suggesting heat index values climbing well above 100 degrees by next Tuesday and Wednesday. && .DISCUSSION... Issued at 132 PM CDT Wed Jul 16 2025 ...Severe Weather Risk This Afternoon... 18z/1pm water vapor imagery shows a vigorous short-wave trough over northeast Iowa that will be the primary forcing mechanism for severe convection across Wisconsin and far northern Illinois as the afternoon progresses. Further south across central Illinois, it appears a broken line of thunderstorms will form along a trailing surface trough currently just west of the Illinois River. The latest SPC mesoanalysis shows a moderately unstable, but weakly sheared environment with MLCAPE values of 2000-2500J/kg and 0-6km bulk shear of just 20-25kt. As temperatures rise into the lower 90s, MLCAPEs will increase into the 2500-3000J/kg range over the next couple of hours...while shear increases to 25-30kt north of the I-72 corridor. As is typically the case, the CAMs are a bit too slow with their convective development...as radar is already showing thunderstorms approaching the Illinois River. The WRF-ARW and NSSL WRF were the fastest models and seem to have the best handle on the situation albeit 2-3 hours too slow. Based on the latest radar trends, think the broken line of storms will cross the Illinois River and reach the I-55 corridor by 3pm...then further east to I-57 by around 5pm. Given the current instability/shear parameters, think a few of the storms will be capable of producing damaging wind gusts in excess of 60mph and brief heavy downpours. Most of the activity will be confined to areas north of I-70...with hot and dry weather persisting further south. The line of storms will settle southward toward I-70 early this evening: however, models suggest it will be in a weakening state as it moves further away from the marginally favorable wind shear and daytime instability gradually wanes. While previous solutions suggested showers/storms would potentially re-develop along the resulting outflow boundary overnight, the latest guidance has backed off considerably. NAM shows only a weak 25-35kt 850mb nocturnal jet developing from Texas oriented northward into Kansas, which is where most of the overnight convection will focus. Further east, think only scattered showers/thunder will develop mainly along/south of I-72. ...Additional Rain Chances Over the Weekend... A cold front will sink southward through central Illinois on Thursday, then become stationary near the I-64 corridor Thursday night into Friday. The boundary will remain close enough to warrant low chance PoPs mainly across the S/SW KILX CWA during that time: however, think many areas will stay dry. As upper ridging gradually builds over the Lower Mississippi River Valley, the front will get nudged back northward over the weekend. Given the presence of the boundary, a series of short-waves riding along the northern periphery of the upper ridge, and ample deep-layer moisture...the stage will be set for a few rounds of showers and thunderstorms across Illinois from Friday night through Monday. While timing of individual waves will be difficult, confidence is growing that upper support will lead to a significant uptick in PoPs during the day Saturday, then again by Sunday afternoon and evening. While the exact track of the waves and their corresponding swaths of enhanced rainfall are still somewhat in question, the latest NBM guidance suggests widespread rainfall of 1-2 inches across all of central Illinois this weekend...with the potential for even higher totals north of the I-74 corridor. WPC has highlighted much of central/northern Illinois with a Slight Risk of excessive rainfall both Saturday and Sunday accordingly. ...Building Heat Next Week... The upper ridge is progged to steadily strengthen this weekend and by early next week will shift the "ring of fire" northward into the Upper Midwest and Great Lakes. As a result, rain chances will decrease on Monday...then will disappear by Tuesday and Wednesday. Thanks to rising upper heights, lesser rain chances, and more sunshine...temperatures will climb into the lower 90s by Tuesday and into the middle 90s by Wednesday. Given the expected rainfall this weekend, the moist soils and actively growing crops will contribute to dewpoints in the upper 70s and perhaps lower 80s in a few spots. This will likely push heat index values well above 100 degrees and into Heat Advisory/Warning territory by next Tuesday and Wednesday. Barnes && .AVIATION... (For the 18z TAFs through 18z Thursday Afternoon) Issued at 1244 PM CDT Wed Jul 16 2025 1730z/1230pm radar/satellite imagery shows a broken line of convection developing just west of the Illinois River. CAMs are about 2-3 hours too slow with convective evolution, so am relying heavily upon observational data for the immediate short-term aviation forecast. With that said, have opted to include a TEMPO group for thunder at KPIA between 18z and 19z...then further east to the I-55 terminals between 19z and 21z...and to KCMI between 20z and 22z. Once the line passes, any lingering storms will settle south of the TAF sites by early evening. Earlier solutions suggesting the potential for additional widespread showers/storms overnight have backed off considerably and now focus much of the activity further west across Kansas/Missouri. As a result, have dropped thunder mention everywhere tonight and have only carried a PROB30 for showers at KSPI/KDEC/KCMI between 08z and 13z. Winds will initially be S/SW at 10-15kt, then will veer to W/SW after passage of the convective line. Winds will then gradually veer to NW late tonight into Thursday morning as a cold front settles southward through the region. As winds become NW, the HRRR/RAP show low clouds developing and spilling into the area Thursday morning. Have therefore lowered ceilings to MVFR after the 11z-13z time frame. Barnes && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$