textproduct: Central Illinois

KEY MESSAGES

- A Tornado Watch is in effect for locations along and south of a Shelbyville to Paris line through 9pm this evening.

- Below normal temperatures will persist through the week before a marked warming trend pushes readings well into the 80s close to 90 degrees by next weekend.

DISCUSSION

Issued at 341 PM CDT Sun Jun 21 2026

*** Tornado Watch ***

20z/3pm radar imagery shows a band of rain with embedded thunderstorms pushing across central Illinois. The pre-storm environment remains stable across a large portion of the area: however, MLCAPEs have increased to 500-1000J/kg south of a warm frontal boundary draped along the I-70 corridor. With surface dewpoints in the upper 60s/lower 70s in the warm sector, RAP suggests further destabilization over the next 3-4 hours as MLCAPEs reach 1000-1500J/kg. Deep-layer shear is currently being augmented by an approaching MCV, while 0-1km shear has increased to 20-25kt near the boundary. As a result, the southern part of the rain band now contains rotating supercells capable of producing tornadoes and damaging wind gusts. A Tornado Watch has subsequently been issued for locations along/south of a Shelbyville to Paris line through 9pm. Based on radar trends and latest HRRR/RAP data, it appears the primary storm risk will push into Indiana by 6-7pm. Meanwhile further west, will have to keep an eye on a broken line of much weaker cells currently firing along a Quincy to Kansas City line. These storms are in a much more unfavorable environment and are not expected to become severe: however, gusty winds will still be possible into the evening as they spread E/SE into central Illinois...mainly along/south of the I-72 corridor.

*** Quiet Mid-Week ***

Cool/dry weather will settle into the region for Monday and Tuesday with daytime highs well below normal for this time of year in the 70s and overnight lows dipping into the 50s. Given persistent upper troughing over Canada, northwesterly flow will continue for the rest of the week. The next embedded short-wave trough and accompanying cold front will push through central Illinois on Wednesday. While deep-layer moisture will be lacking, there will be strong enough forcing to warrant low chance PoPs (30-40%) for showers/thunder, especially during the afternoon and evening.

*** Weekend Warm-Up and Storm Risk ***

The mid-week frontal boundary is progged to stall across the Ohio River Valley on Thursday, then begin lifting slowly back northward by the weekend as upper heights rise in response to an upstream trough digging west of the Rockies. While the exact speed of this process is still in question, model consensus indicates the most favorable period for rain will be from late Friday through late Saturday when several bouts of convection may develop along/north of the front. It is still too early to discuss any specific severe weather risks: however, all machine learning algorithms show low probabilities (less than 15% chance) for severe. Once the boundary lifts into the Great Lakes, a return to more typical summertime weather is anticipated for early next week. In fact, the 12z NBM shows a 30-50% chance for temperatures climbing above 90 degrees by next Sunday.

AVIATION /00Z TAFS THROUGH 00Z TUESDAY/

Issued at 652 PM CDT Sun Jun 21 2026

2330z/630pm radar imagery shows scattered convection persisting along/east of the I-55 corridor. Based on radar trends and latest HRRR/RAP analysis, have opted to leave thunder mention out of the TAF for the I-74 terminals. Further south, have maintained a 1-3 hour window of thunder between 00z and 03z at KSPI/KDEC. Once the convection pushes further east, the primary aviation forecast concern will be low ceilings tonight into Monday morning. A large area of IFR clouds across Iowa into western Illinois will pivot southeastward into the area over the next several hours...with the HRRR suggesting all sites down to IFR after 05z. The low clouds will gradually dissipate/scatter from northwest to southeast toward midday Monday...with partial clearing expected across the board during the afternoon. Winds will become NE with gusts of 20-25kt at KPIA/KBMI this evening as low pressure tracks through the heart of central Illinois. Further south, winds will veer to NW tonight, then eventually to NE by Monday morning.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 1 AM CDT Monday for ILZ038-042>046-048>057- 061>063-066>068-071>073.