textproduct: Central Illinois

KEY MESSAGES

- Windy and much warmer conditions are on tap for today over central and southeast IL. HREF guidance has a 40-80% chance of southwest wind gusts exceeding 30 mph, which will push afternoon high temperatures into the middle to upper 70s.

- There is a 20-30% chance of showers and thunderstorms over the IL river valley by late afternoon, and a 30-50% chance of showers and thunderstorms over central IL tonight. A few cells could contain small hail and gusty winds over 40 mph north of I-72 late this afternoon and into mid evening. A stronger storm system will spread widespread showers and thunderstorms into central Illinois Thursday night into Friday. At this time, it appears the risk for severe weather will remain low (less than a 15% chance).

DISCUSSION

Issued at 345 AM CDT Tue Apr 21 2026

The 08Z/3 am surface analysis shows 1027-1028 mb high pressure across the Atlantic States while weak 1008 mb low pressure was near the southern MN/SD border with its warm front through central Iowa and sw IL. IR Satellite loop shows high clouds spreading se over central and northern IL. South to SE winds keeping temps milder early this morning, in the mid 40s to lower 50s. Mid to upper 50s in the warm sector from Keokuk Iowa, Quincy and Pittsfield and Salem sw.

Warm front to lift quickly ne across central/se IL during early this morning, with breezy sw winds developing by mid to late morning. Wind gusts of 25-35 mph look likely by late morning and afternoon, with a few spots reaching 40 mph this afternoon. Fire danger is low today though MIN RH values reach 25-35% from I-55 east this afternoon. Gusty SW winds could cause minor blowing dust in recently tilled fields se of the IL river this afternoon with ground surface having chance to dry out more since Saturday. Warmer highs in the mid to upper 70s and few spots reaching 80F from I-55 west. Low pressure to track into southeast WI by sunset and move across the southern Great Lakes tonight, while pushing a cold front south into northern parts of IL/IN. Latest CAMs show a band of convection developing during mid/late afternoon over the IL river valley from Peoria northeast and then 30-35 kt west/sw low level jet and PW 0.8-1.2 inches late this afternoon and evening over central IL to help produce scattered convection shifting southward during tonight. MUCAPES reach 1000-1200 j/kg over northern/nw CWA late afternoon into mid evening with 0-6 km shear of 25-30 kts. Could see a few cells with small hail and wind gusts over 40 mph north of I-72. HRRR shows fog/dense fog drifting sw from southern Lake MI into northeast IL during overnight and early Wed morning in ne flow behind cold front, but feel the front should stay north/ne of CWA along with the fog. Mild lows tonight in the upper 50s and highs Wed of 74-78F with lighter sw winds 7-14 mph.

We have just slight chance of convection in east central and possibly se IL on Wed though most areas should be dry on Wed. The front in northeast IL on Wed morning to push back ne during Wed afternoon/Wed night in response to stronger low pressure ejecting from Pacific Northwest into northern ND by dawn Thu. Dry conditions expected Wed night and Thu with breezy southerly winds gusting to around 30 mph on Thu. LREF has a 30-70% chance of wind gusts over 30 mph west of I-57 by Thu afternoon. Warm highs around 80F in eastern IL Thu and lower 80s from I-55 west. Strong low pressure to track eastward toward western upper MI by dawn Fri and push a cold front east toward the IA/IL border. Should see increasing chances of convection over the IL river valley during Thu evening and into eastern IL during overnight Thu night. SPC Day3 outlook keeps slight risk over western half of Iowa and nw MO into eastern parts of NE/KS Thu afternoon/Thu night with marginal risk as far east as west central IL and into western Schuyler county for Thu night.

Cold front moves east across IL on Friday likely bringing showers and thunderstorms, with highest pops shifting into eastern/se IL Fri afternoon. There could be a few strong to severe storms on Fri especially over southern CWA south of I-72. Highs Fri in the low to mid 70s, with upper 70s by Lawrenceville.

Forecast models diverge with handling wx system late this week. GFS is showing moderate QPF into central/se IL Fri night (especially Fri evening) while Ecmwf and GEM keep qpf further southeast with the front passing to our southeast by Fri evening. GFS, Ecmwf and GEM models then look drier Saturday into Sunday over CWA with weak upper level ridging into IL. NBM has slight chance of showers over southern CWA, south of I-72 on Saturday, then slight chance of convection Sunday afternoon over western/sw CWA from Peoria and Taylorville west. Temperate highs around 70F to lower 70s Saturday thru Monday with mid 70s se of I-70. Another stronger wx system moves into the area from the Central Plains Sunday night and Monday bringing a good chance of showers and thunderstorms back into the prairie state.

The Climate Prediction Center 8-14 Day Outlook for Apr 28-May 4th has a 40-50% chance of below normal temperatures across IL, with precipitation trending near normal or slightly below normal (from I-74 northeast).

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 555 AM CDT Tue Apr 21 2026

Marginal LLWS conditions to occur until 14Z over the central IL airports with 1.5-2k ft WSW winds of 40-45 kts. South to SSW surface winds of 8-13 kts at dawn, to veer SW and increase to 16-22 kts with gusts of 26-33 kts late morning/afternoon. SW winds to decrease to 8-13 kts after sunset this evening. VFR conditions to prevail through tonight outside of any convection. Continued mention PROB30 of MVFR vsbys with convection from 22Z-02Z especially along I-74 TAF sites. More isolated showers and possible thunderstorms are possible later in evening and overnight se of IL river/PIA, but coverage appears limited at this time. LLWS late evening and overnight (after 03Z/10 pm) to be southeast of central IL airports.

ILX WATCHES/WARNINGS/ADVISORIES

None.