textproduct: Central Illinois

KEY MESSAGES

- Multiple rounds of thunderstorms are expected on Monday. There is an Enhanced Risk (level 3 of 5) for tornadoes, damaging winds, and large hail. Flash flooding is also possible.

- Windy conditions are expected on Monday, with southerly gusts up to 45 mph at times. This could cause difficult travel and perhaps a blowing dust threat for areas that don't receive adequate morning rain.

DISCUSSION

Issued at 145 PM CDT Sun Apr 26 2026

***TODAY***

Upper analysis early this afternoon shows ridging over the eastern US with deep troughing over the western CONUS. Surface high pressure is positioned off to our northeast with a developing low in the lee of the Rockies. South-southeast winds between these two features have allowed temperatures to warm into the 70s early this afternoon. Cloud cover will increase from the west this evening ahead of our next approaching system.

*** MONDAY'S SEVERE WEATHER THREAT / STRONG WINDS ***

A compact shortwave trough will eject northward toward the Great Lakes Region on Monday with an associated surface low expected to work through central Iowa/southwest Wisconsin by Monday evening. Several waves of storms are possible throughout the day with the first being Monday morning along a leading shortwave impulse/remnant MCS. CAMs are still in disagreement on storm coverage and timing, though the 12Z guidance seems to have favored a line segment sweeping across the area (NAMnest, NSSL WRF, ARW). Depending on storm mode and coverage, warm sector recovery may be slow before the main show arrives late Monday afternoon into evening.

Assuming rapid warm sector destabilization, dewpoints should climb into the 60s by afternoon with temperatures in the upper 70s. Lapse rates will quickly steepen by afternoon as mid-level heights fall with the approaching upper wave. Instability will increase from west to east as a 60-70 kt mid-level jet overspreads the area and boosts our wind shear. Forecast soundings for mid to late afternoon show large CAPE profiles, an inverted V signature, and cyclonically curved hodographs. This type of environment is favorable for all severe hazards, including the threat for strong tornadoes.

Storms should develop in west-central IL by late afternoon, initially taking on a discrete storm mode before growing upscale into a linear segment as a cold front is forced in from the west. The Day 2 convective outlook still holds onto a level 3 of 5 (enhanced risk), with a 10%/intensity 2 tornado threat (EF3+) and a large 45% wind threat across most of the state. The hail threat is highest in the west, coinciding with any discrete supercells that develop early on. Heavy rain is also a threat on Monday due to climatologically high PWATs and repeating storms. The 26.12Z SPC HREF shows a 20-40% chance for localized pockets of rain amounts over 3", which would exceed 6 hour flash flood guidance for some.

Strong south winds will develop by mid to late morning as a result of the deepening surface low working through Iowa. Gusts up to around 45 mph are possible, leading to difficult travel and perhaps some reduced visibility due to blowing dust. However, if adequate rain is observed with morning storms the blowing dust threat will be greatly minimized.

*** TUESDAY ONWARD ***

Low meridional flow sets up heading into Tuesday with the cold front being pushed off to the south of the area. A shortwave trough will work through the central US later on Tuesday, sparking the redevelopment of showers and storms near and south of I-70 Tuesday evening. The threat for severe weather should stay just outside of the area, but remains close enough to bear watching. Cooler temperatures with occasional low chances for precipitation (20% or less) appear likely through the remainder of the week.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 1231 PM CDT Sun Apr 26 2026

VFR conditions will prevail through the remainder of today. Southeast winds will increase in speed late tonight with gusts approaching 25-30 kts by Monday morning. Periods of showers and thunderstorms are possible around or after 12Z, but confidence in coverage and timing remains low. PROB30 groups have been introduced at all airfields through the end of the TAF period to account for this.

ILX WATCHES/WARNINGS/ADVISORIES

None.