textproduct: Central Illinois

KEY MESSAGES

- This afternoon and evening, strong winds pose a double threat. Non-thunderstorm gusts are expected to reach 40-50 mph. Furthermore, thunderstorm wind gusts could be stronger, ranging from 55 to 75 mph. Given the recently saturated soils, these high winds will not only create difficulties for high- profile vehicles but also present a risk of uprooted trees.

- In addition to the damaging wind concerns, there remains a localized threat for tornadoes and large hail through this evening as a cold front pushes through the region.

- Another round of severe weather and potential flooding is expected Friday afternoon and evening. Rainfall totals between Friday and Saturday have a medium-high probability (50-70%) of exceeding 1 inch areawide.

- Overnight lows are likely (50-80% chance) to fall into the mid 30s or lower each morning Sunday through Tuesday. Action may be needed to protect newly- emerged, tender vegetation.

DISCUSSION

Issued at 1133 AM CDT Thu Apr 2 2026

A quick glance at the mid-level water vapor imagery depicts our compact, negatively-tilted shortwave trough lifting across the Missouri Valley with its attendant surface low positioned over central Iowa.

Scattered, elevated morning convection has been observed out ahead of the cold front within a broad warm sector and beneath strong ascent characterized by an upper-level difluent zone and strong kinematic profile.

High-resolution model guidance consistently predicts widespread thunderstorms developing across west-central Illinois early this afternoon. The environment, characterized by surface temperatures in the low 70s and dewpoints in the low 60s, is expected to quickly destabilize due to low-level jet (LLJ) moisture transport, synoptic lift, and adiabatic cooling aloft.

With MLCAPE values ranging from 500-1500 J/kg and deep-layer shear between 40-50 kts, supercells and multicell clusters are anticipated this afternoon and evening as a pre-frontal trough advances from the west. The robust low-level wind field, highlighted by a 60 kt LLJ core veering ahead of the cold front, will promote rapidly rotating updrafts. This potential is well- supported by 0-3 km Storm Relative Helicity (SRH) values exceeding 300 m2/s2 and a pronounced, humped low-level hodograph.

While the parameter space clearly supports a tornado threat this afternoon through early evening across central Illinois, the uncapped warm sector will likely hinder supercells from staying discrete. The reality may be a much messier storm-scale environment with numerous mergers, nudgers, and boundary interactions.

Aside from the tornado risk, a significant wind threat also exists given the top-shelf kinematic field in place. The momentum transfer augmented by precip-loading within any storm this afternoon and evening has the potential to put down 60 mph gusts, with the upshot being 75 mph gusts within any bowing segments or RFD surges that develop.

The hail risk might be highest later this evening behind the pre-frontal trough and immediately along the cold front as a mid-level cold pocket overtakes the front and increases CAPEs through the hail growth zone. The current outlook supports hail up to the size of golf balls.

Storms will exit the area late this evening, moving from northwest to southeast, as the cold front traverses central Illinois and becomes stationary. This stalled front will quickly retreat northward on Friday as a warm front, ahead of a significant upper-level trough that will track across the Missouri Valley toward the Upper-Mississippi Valley.

This approaching disturbance and its associated surface low will set the stage for another round of nocturnal convection in central Illinois on Friday evening, likely taking the form of a decaying squall line pushing into west-central Illinois overnight.

While a damaging wind risk is possible upon the squall lines arrival, the primary concern is the potential for flooding. Despite diminishing instability overnight, strong isentropic ascent preceding the front and weak low-pressure development along the front are expected to produce a long-duration rainfall event through Saturday morning. With the ground already saturated from recent heavy rains, widespread urban and small stream flooding, and potentially localized flash flooding, is anticipated by Saturday morning. Recent NBM guidance supports a medium-high probability (50-70%) of exceeding 1 during the Friday-Saturday timeframe.

A transition to a drier and seasonably cool pattern is expected next week as elongated surface high pressure establishes itself over the central US. Current NBM guidance consistently forecasts daily high temperatures in the 50s from Sunday through Tuesday, with overnight lows in the 30s, raising renewed concerns for frost and freeze given the start of the growing season. Temperatures are then anticipated to rebound to warmer levels by the middle of next week as the high pressure system moves out and a southerly flow returns across the Plains and Midwest.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 622 PM CDT Thu Apr 2 2026

Line of strong to severe thunderstorms is most likely to impact KPIA over the next couple hours. It may take a few hours for any storms to get over into eastern Illinois. With KPIA most likely, will cover the threat with a TEMPO group, but use PROB30 for the other sites. Currently thinking the thunder threat should be out of the terminals before 06z.

Otherwise, the strong southerly winds will gradually ease up this evening, as they shift more toward the west. By daybreak, winds should be relatively light as a front settles over the area, but will go back southerly again through Friday morning. On the north side of the front, a period of MVFR ceilings appears likely during the morning into early afternoon. Late in the period, another chance of thunderstorms.

ILX WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 7 PM CDT this evening for ILZ027>031- 036>038-040>057-061>063-066>068-071>073.