textproduct: Central Illinois

KEY MESSAGES

- There is a Marginal Risk (level 1 of 5) for severe weather along and west of the I-55 corridor late Thursday night into Friday morning.

- Periodic storm chances will persist through early next week...with the greatest probability for convection focusing on Saturday, then again late Monday into Tuesday.

- After a couple more mild days, a preview of summer will arrive by early next week as highs soar well into the 80s by Sunday and Monday.

DISCUSSION

Issued at 136 PM CDT Wed May 13 2026

*** Thunderstorms Thursday Night into Friday Morning ***

As high pressure shifts toward the East Coast, a short-wave trough crossing the Rockies will trigger scattered strong to potentially severe convection across portions of Nebraska/Kansas by late Thursday afternoon and evening. While boundary layer moisture will initially remain meager further east, a 45-55kt 850mb jet is progged to develop from northern Texas northeastward into Missouri after sunset. This will transport sufficient moisture/instability northward to support a risk for marginally severe wind and hail east of the Mississippi River late Thursday night into Friday morning. The 12z NAM suggests MUCAPE will increase to 200-600J/kg along/west of a Peoria to Springfield line by dawn Friday. At the same time, 0-6km bulk shear will hover in the 30-35kt range. The combination of an approaching forcing mechanism and a weakly unstable/sheared environment will be enough to support a risk for marginally severe wind and hail. 12z HRRR and RRFS both indicate clusters of convection forming on the nose of the low-level jet across eastern Missouri into western Illinois after midnight...with the activity spreading eastward toward I-57 by dawn Friday. The convection will then push eastward and exit the eastern KILX CWA by late Friday morning, followed by a return to dry weather across the board by Friday afternoon. Given the morning clouds and showers, have opted to lower NBM high temps to closer match CONSALL readings ranging from the lower 70s around Danville to the upper 70s in the Illinois River Valley.

*** Periodic Storm Chances Saturday Through Tuesday ***

After a lull in precip chances Friday afternoon, the nocturnal low-level jet will bring a renewed round of showers and thunderstorms Friday night...particularly along/north of the I-72 corridor. Saturday appears to be an unsettled day as a frontal boundary drops southward and stalls across north-central Illinois. While current SPC outlooks place the greatest risk for severe weather further west, several machine learning algorithms suggest an increased risk for strong convection further east into Illinois...with the Colorado State Machine Learning algorithm indicating a 15-30% chance for severe across a large portion of central Illinois. Given much-improved boundary layer moisture and the presence of a forcing mechanism, think showers and thunderstorms will become widespread by Saturday afternoon. Will need to keep an eye on how much destabilization can occur, as this will determine the exact risk/extent of severe on Saturday.

The frontal boundary will surge back northward on Sunday, leading to a very warm and largely dry day. After that, the next chance for potential severe weather will materialize late Monday into Tuesday. There are still some timing discrepancies among the synoptic models, with the ECMWF being slower with the approach of a significant short-wave trough and its associated cold front. The GFS indicates FROPA Monday evening while the ECMWF holds it off until Tuesday afternoon. The actual solution may lie somewhere in between...with round one of strong convection firing along/ahead of the front across Missouri/Iowa Monday afternoon and spilling into at least the western half of the KILX CWA Monday evening. The latest Day 6 SPC Outlook has a good handle on this...featuring a 15-30% chance for severe along/west of I-55. If the slower ECMWF verifies, another round of convection may develop across the E/SE CWA by Tuesday afternoon before the front departs into Indiana. Stay tuned to later forecasts for additional details.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1226 PM CDT Wed May 13 2026

VFR conditions will prevail through the entire 18z TAF period. A short-wave trough pivoting around an upper low centered near Lake Huron is providing enough lift to create SCT-BKN diurnal Cu along/northeast of a KPIA to K1H2 line. The most robust Cu has been focused along/east of I-57 where skies have been BKN-OVC at KCMI over the past couple of hours. Forecast soundings and NAM Cu-rule suggest SCT-BKN clouds at 4000-5000ft through the afternoon, followed by a return to clear conditions this evening through Thursday morning. Winds will initially be N/NW with gusts of around 20kt, then will become light/variable tonight as high pressure drifts overhead.

ILX WATCHES/WARNINGS/ADVISORIES

None.