textproduct: Central Illinois

KEY MESSAGES

- There is a level 3 of 5 (enhanced) risk for severe weather this evening. Damaging winds, large hail, a couple tornadoes, and flash flooding are all concerns, especially near and south of I-70.

- There is a 30-50% chance for frost Friday night. Tender vegetation may need to be covered in order to prevent damage.

UPDATE

Issued at 858 PM CDT Mon Apr 27 2026

We extended the tornado watch another 2 hours until 11 pm cdt in east central and southeast IL. We also extended the Flood Watch another hour until 11 pm cdt from Christian, Macon, Moultrie, Douglas and Edgar counties south.

The squall line with strong to severe thundertorms (including possible tornadoes) was near or southeast of a Danville to Effingham line, and west of Mount Vernon, racing eastward at 50-60 mph. The HRRR has been handling this convection fairly well and has the squall line passing southeast of Lawrence county IL by 04Z/11 pm. Will still be risk of severe storms with damaging winds, large hail and possible tornadoes with this line next 1-2 hours. Also rainfall amounts of 1-2 inches in 2-3 hours with locally 2-3 inches possible in southeast IL which already seen 1.5-3 inches of rain so far today. The cold front was pushing east toward the IL river at mid evening and will push through se IL between 1-3 am overnight. Most of the convection should be east/se of CWA after 1 am tonight with quieter weather returning. Lows overnight to range from upper 40s over the IL river valley from I-55 west (mid 40s by Galesburg) and 55-60F in southeast IL.

DISCUSSION

Issued at 226 PM CDT Mon Apr 27 2026

***** SEVERE WEATHER THIS EVENING *****

Mid level water vapor satellite reveals a negatively tilted upper level trough spinning over the Midwest. At the surface, WPC has analyzed a 996mb low in eastern Iowa which is forecast to lift northeastward across Wisconsin this evening. Much of the warm sector has been worked over at this point via a morning-early afternoon MCS, but these storms left an outflow boundary near/south of the I- 70 corridor which will serve as a differential heating/convergence zone for renewed storms later this afternoon. A wake low continues to foster wind gusts up to 35mph from the southeast, which should help maintain stable low levels further north. Nonetheless, a few elevated storms could generate locally severe hail and wind in those areas. Meanwhile, south of the I-70 corridor, dewpoints should surge into the mid-upper 60s while a 50 kt LLJ maintains 40-55 kt effective bulk wind shear and 400-700 (679 on the VWX vad profiler) m^2/s^2 0-3km SRH via strongly cyclonically curved hodographs. CAMs generally suggest convective activity developing upstream over the next couple hours and moving through this environment during the evening will start discrete and eventually grow upscale into another MCS. Hence, the initial hazards will be very large hail and tornadoes, with the risk transitioning to damaging winds, locally severe hail, and QLCS tornadoes with time. Training storms will pose a risk for flash flooding (REFS and HREF ensemble max precip have swaths of 4+ inches of rain falling in <6 hours), for which we have issued a Flood Watch which extends through 10pm. A Tornado Watch is in effect for Effingham to Crawford Counties and areas further south, where the chance of surface based (and hence potentially tornadic) storms is highest. Storms should exit the ILX County Warning area by 11pm, while a cooler and more stable airmass arrives from the west-northwest behind a cold front.

***** DRY CONDITIONS LIKELY WEDNESDAY AND BEYOND *****

Another shortwave will lift northeast through the area tomorrow night, bringing another opportunity for some rain and perhaps a rumble of thunder. Thankfully QPF with this system is lighter, with a low (<20%) chance for an additional inch of rainfall. Since this will occur around 24 hours after this evening's heavy rainfall in southeast Illinois, the ground may have some time to absorb the water, though we'll still be keeping one eye on it.

By Wednesday morning, a drier pattern should take hold of the region, with less than a 20% chance for rain through the weekend. High temperatures each day are forecast in the 60s, with locations near and north of the I-74 corridor potentially (60% chance) not climbing out of the 50s on Friday. The National Blend of Models (NBM) indicates a 30-50% chance temperatures fall below 37 degF Friday night into Saturday morning, which should be cold enough for frost given the expected light winds.

AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 640 PM CDT Mon Apr 27 2026

A squall line consisting of strong to severe thunderstorms was along I-55 at 640 pm with a severe cell ahead of this line between DEC and CMI and racing eastward at 50-60 mph. Convection was also over PIA which was on the back side of this complex. We have gradient SE winds 25-35 kts with gusts 40-50 kts ahead of this squall line especially at DEC and CMI. A severe storm would produce wind gusts over 50 kts possible at DEC and CMI next hour. IFR to MVF conditions expected with this strong to severe convection as HRRR has it tracking east of DEC and CMI between 01-02Z at mid evening. May see a brief period of VFR conditions late evening/early overnight before MVFR ceilings likely spread into central IL during overnight and linger into Tue morning. the MVFR ceilings could scatter out at PIA and possibly as far se as I-55 at BMI and SPI during Tue afternoon. Breezy south to SE winds gusting 25-35 kts to weaken and shift west to WNW behind cold frontal passage overnight.

ILX WATCHES/WARNINGS/ADVISORIES

Flood Watch until 11 PM CDT this evening for ILZ052>057- 061>063-066>068-071>073.