textproduct: Central Illinois

KEY MESSAGES

- Scattered storms are forecast overnight into Friday. There is a low (5%) chance for severe weather west of I-55 between midnight and 4am, with locally damaging wind gusts the main risk.

- Another round of thunderstorms is likely (80% chance) Sunday night through Monday. There is a 15-30% risk for severe weather with these storms, with the greatest concern Monday afternoon and evening.

DISCUSSION

Issued at 1249 PM CDT Thu Apr 23 2026

***** WARM AND BREEZY TODAY, STORMS TONIGHT-TOMORROW *****

Early this afternoon, shortwave ridging was in place across the Ohio Valley, with an upper level trough approaching from the Great Basin/Northern High Plains. A tightening pressure gradient between these two features has resulted in moderately strong warm advection across our area with southerly wind gusts to 30 mph and temperatures already in the upper 70s at 1245pm. Localized blowing dust could occur near increased field activity in preparation for planting, but the probability of significant visibility reductions appears low.

This warm advection will keep the remainder of the afternoon and evening dry, breezy, and warm, but precipitation chances will increase from the west after around 10pm as a decaying line of storms approaches. SPC maintains a level 1 of 5, marginal, risk for damaging wind gusts with these storms west of I-55 where a few of the CAMs depict sporadic gusty (40+ mph) winds between midnight and 4am. Scattered showers and storms will likely (50-70% chance) linger through mid morning in east-central and southeast Illinois, but then a subsident region in the wake of that activity should limit coverage of showers and storms to 20% or less the remainder of the day.

***** STORMS RETURN SUNDAY NIGHT AND MONDAY *****

High pressure will settle over the region on Saturday, offering us a moment of repose before a southern stream wave lifts into the Midwest late Sunday into early Monday. Deterministic models and their respective ensembles still have some differences in the timing and strength of this system, but confidence is growing in severe storms somewhere over/near our neck of the woods. For CAPE and shear, the ECMWF Extreme Forecast Index (EFI) is 0.7-0.9 with a shift of tails (SOT), suggesting medium-high confidence in a climatologically anomalous quantity of instability and shear and at least a low (10%) chance for a highly unusual (above the 99th percentile) event. The Low Resolution Ensemble Forecast (LREF) system gives a 50-70% joint probability (highest south) for more than 50 kt of 0-6km bulk shear and more than 1000 J/kg MUCAPE, which would be more than sufficient for organized convection. In addition, deterministic models suggest the shear will be oriented largely perpendicular to the cold front (trigger), which would favor at least initially discrete storms capable of all hazards; if and when these storms grow upscale into a line, a continued risk for QLCS tornadoes would also be favored given 35-50 kt 0-3km shear oriented largely parallel to the expected line's orientation. This is highlighted in SPC's Day 5 (Monday) probabilistic outlook, which features a 30-45% risk for severe weather near/south of Springfield and a 15-30% risk elsewhere.

This system will also bear watching for heavy rain if any training storms occur. Confidence in if and where this occurs is low, but the National Blend of Models (NBM) advertises a 10-15% chance for more than 2 inches of rainfall in any given location across central and southeast Illinois; if this falls in a short enough timeframe (less than 3 hours), the River Forecast Center's Flash Flood Guidance (FFG) suggests it could result in flooding. Outside of showers and storms, it will be breezy on Monday with south winds potentially (40- 50% chance) gusting upwards of 40 mph during the late morning and afternoon. In any areas that don't receive rain Sunday night and Monday morning, this could result in blowing dust, especially near increased agricultural activity in preparation for planting.

***** TURNING COOLER MID NEXT WORK WEEK *****

Behind the cold front, conditions will turn cooler Tuesday into Wednesday, with forecast highs in the mid 60s to low 70s - seasonable for late April. CPC's day 6-10 outlook (April 28-May 2) features a 40-50% chance for below normal temperatures.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1230 PM CDT Thu Apr 23 2026

VFR conditions are forecast to persist through the period, though transient visibility reductions could occur tonight as a weakening line of showers and thunderstorms moves west to east across the airfields. Confidence was high enough in thunder at each terminal to include it in a prob30 group, with gusty west- northwest winds also mentioned at SPI, BMI, and PIA along the gust front. South-southwest winds will gust to 25 kt or higher at times this afternoon and evening, decrease slightly overnight, and then veer to a west-southwesterly direction near the end of the forecast period when residual shower activity will taper.

ILX WATCHES/WARNINGS/ADVISORIES

None.