Area Forecast Discussion
Issued by NWS Central Illinois
Issued by NWS Central Illinois
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105 FXUS63 KILX 211911 AFDILX Area Forecast Discussion National Weather Service Lincoln IL 211 PM CDT Tue May 21 2024 .KEY MESSAGES... - Strong south winds will gust up to 40 mph into early this evening. This will create blowing dust in spots where fields have recently been plowed. - There is a level 4 of 5 (moderate) risk for severe weather this evening west of the Illinois River, with gradually lower chances further east. While all severe hazards are in play, the greatest risks will be damaging wind gusts and brief tornadoes. A level 1 of 5 (marginal) risk will linger south of I-70 tomorrow afternoon. - An active pattern continues into this weekend with another risk of severe storms on Sunday. && .DISCUSSION... Issued at 211 PM CDT Tue May 21 2024 18z surface map placed 996 mb low pressure over extreme southeast Nebraska, which is forecast to deepen as it tracks northeast into northern WI tonight. Well within the warm sector this afternoon, central IL is being bathed in summertime heat and humidity with temperatures in the upper 80s and dewpoints in the mid 60s as of 1 pm. A tight MSLP gradient will promote 30-40 mph southerly winds gusts into early this evening. Dry top layers of soil and active farming activity will lead to blowing dust in spots through late afternoon. A warm layer aloft centered near 775 mb should keep convection suppressed in the warm sector this afternoon, and our attention is focused on the cold front trailing south of the low, which is forecast to fill in with convection over the next few hours. With the better kinematic fields lifting northeast along with the surface low, mesoanalysis suggests the more significant severe weather potential (long track tornadoes, very large hail, widespread wind damage) affecting areas to our northwest across IA, far northwest IL, and southern WI into this evening. We do maintain a risk of severe storms this evening locally, particularly west of I-55 in a 7 to 11 pm window. As the line of storms moves into this area, strong deep layer shear and moderate instability will favor damaging straight line wind gusts in the more intense line segments. While instability will decrease with time and eastward extent, a 925-850 mb jet will strengthen overhead, which may keep the severe threat going toward midnight or a little later than the CAMs have been trending. The tornado risk will mainly be tied to QLCS tornadoes, based on favorable 0-3km shear vectors northwest of the IL River. Behind the front, a more typical May airmass will filter into most of central later tonight and Wednesday with cooler highs in the 70s and lower humidity. The exception will be south of I-70 where the front is slower to clear, leading to another warm day and a few afternoon storms. The severe weather risk is much reduced in this area from previous forecasts with higher instability (CAPEs 1000+ J/kg) suppressed near and south of the Ohio River based on the 12z HREF. Still a couple strong afternoon storms can`t be ruled out given 30 kt deep layer shear and SPC has a Marginal risk (level 1/5) near/south of I-70. For Thursday through early next week an active pattern will remain in place across the region, with shortwaves shown crossing the Midwest every 36-48 hours. Significant uncertainty in the forecast details exist given differences in timing and placement of these features, however Friday and Sunday look to be the favored periods for more widespread showers and storms and this is where higher PoPs have been placed. For severe weather prospects, Sunday is currently the most concerning, especially if the 21/12z ECMWF verifies with low pressure deepening just to our northwest. Again, widely varying solutions are noted in the ensemble envelope, so keep updated on later forecasts as the pattern evolves. 25 && .AVIATION... (For the 18z TAFs through 18z Wednesday Afternoon) Issued at 1216 PM CDT Tue May 21 2024 South winds will gust 30-35 kt into this evening ahead of a cold front. A broken line of TSRA is expected to cross the central IL terminals this evening, and have a 3-hr tempo for IFR conditions and gusty winds associated with the storms. Winds veer west behind the frontal passage and lose gustiness. Patchy MVFR ceilings could develop behind the front, primarily at KBMI-KDEC- KCMI and have added a scattered cloud group there for the overnight hours. 25 && .ILX WATCHES/WARNINGS/ADVISORIES... None. && $$