textproduct: Central Illinois

KEY MESSAGES

- Freeze potential Monday night: There is a high chance (70%) for a hard freeze (28degF or colder) along and north of I-74 Monday night into Tuesday morning. Residents should protect sensitive early-season vegetation.

- Returning rain chances: A passing system will bring a 30% to 40% chance of showers and thunderstorms Wednesday and Thursday. The threat of severe weather is currently low due to limited moisture.

DISCUSSION

Issued at 145 PM CDT Sat Apr 4 2026

Cool Down and Dry Spell A cold front has swept across central and southeast Illinois this afternoon, effectively ending the recent period of showers and storms outside of a few lingering pockets of light rain across east central Illinois. Gusty west to northwest winds are now advecting significantly colder air into the region. Temperatures will drop tonight, settling into the mid to upper 30s for most of the area. Breezy conditions will persist through the overnight hours but are expected to gradually subside on Sunday as high pressure builds eastward from the southern/central Great Plains, relaxing the pressure gradient across central Illinois.

A weak clipper system will dive across the Upper Midwest and Great Lakes late Sunday. This system may bring some light precipitation to portions of northern Illinois Sunday night, but central Illinois is expected to remain dry. Ahead of this wave, winds will briefly back to the southwest, which will help to keep temperatures in the upper 30s.

Freeze Potential Early Next Week High pressure, with a central pressure of 1035+ mb, will build across the Upper Midwest into the Midwest on Monday and Tuesday, reinforcing our stretch of dry and colder weather. The coldest temperatures of this period are anticipated Monday night into Tuesday morning, with lows falling below freezing across the majority of the area. The LREF probability for a hard freeze (28degF or colder) is highest, around 70% or greater, along and north of the I-74 corridor. Farther south, near the Beardstown to Casey line, the chance is around 20-30%. Residents with sensitive early-season vegetation should take protective measures.

Midweek Warm-Up and Increased Rain Chances The upper-level troughing centered over the Midwest during the first half of the week will begin to flatten and turn into a more zonal flow regime through the latter half of the upcoming week. As the surface ridge shifts towards New England, southwesterly flow will return across the Mississippi Valley, allowing temperatures to moderate back to above-normal levels. High temperatures are forecast to reach the upper 60s and 70s from Wednesday through Saturday, with overnight lows generally staying in the 50s.

A low-pressure system is progged to track along the US-Canada border midweek before lifting toward James Bay on Thursday. A warm front preceding this low will lift through central Illinois on Wednesday, bringing a chance (30%) for precipitation. Better chances (40%) for showers and thunderstorms will materialize along the trailing cold front on Thursday. Early analysis suggests the southwesterly return flow will be too brief to advect significant moisture into the region before the cold frontal passage on Thursday, with surface dew points likely struggling to reach 50F. This limited moisture advection is expected to greatly mitigate any severe weather threat on Thursday. The frontal boundary is expected to stall over the region, which will maintain additional chances for showers and storms into Friday and Saturday, though exact locations still need to be ironed out.

AVIATION /00Z TAFS THROUGH 00Z MONDAY/

Issued at 607 PM CDT Sat Apr 4 2026

MVFR ceilings will clear KCMI early this evening, with BKN-OVC VFR stratocu prevailing across the central IL terminals overnight. Guidance shows medium probabilities of MVFR ceilings redeveloping near the I-74 corridor early Sunday morning. For now have a TEMPO group to address this. Winds will be persistent WNW through the period gusting near 25 kt at times.

ILX WATCHES/WARNINGS/ADVISORIES

None.