textproduct: Central Illinois

KEY MESSAGES

- Record-breaking heat continues through Tuesday afternoon, with high temperatures reaching the upper 80s to lower 90s.

- A Marginal Risk (level 1 of 5) for severe thunderstorms exists Tuesday night. Some storms will be capable of producing localized damaging wind gusts and hail.

- Unsettled weather Tuesday night through Thursday brings periods of wet weather, with a 60 to 80 percent chance of 1 to 2 inches of event total rainfall.

- A sharp cold front transitions the region to much cooler conditions late week into the weekend, bringing a potential for early morning frost both Saturday and Sunday.

DISCUSSION

Issued at 1222 PM CDT Mon Oct 12 2026

Strong low-level warm air advection remains established across the Midwest under a building upper-level ridge. Mid-level height rises and persistent south-southwesterly surface winds gusting up to 25 mph will push high temperatures into the upper 80s and lower 90s this afternoon, likely breaking daily high temperature records. Unseasonably warm conditions persist through Tuesday ahead of an approaching upper-level trough. Highs on Tuesday again top out in the upper 80s to lower 90s, roughly 20 degrees above seasonal norms. Record highs remain susceptible to being broken across central and southeast Illinois. High resolution guidance shows the front working into the central CWA through Tuesday afternoon, and CAMs depict a few post-frontal showers/sprinkles over the northwest CWA. To account for this, added some 20 PoPs for the Galesburg and Peoria areas.

Convective initiation occurs Tuesday evening into Tuesday night as a lead shortwave tracks northeast toward the region. HREF guidance shows MUCAPE values building to 1000-1500 J/kg paired with 0-6km bulk shear of 30-40 knots. ML/AI severe guidance, along with the SPC Day 2 Outlook, maintain a Marginal Risk (level 1 of 5) for central and western portions of the forecast area. Primary convective hazards feature isolated severe wind gusts up to 60 mph and large hail up to quarter size.

The frontal boundary stalls in the area Wednesday into Thursday, becoming oriented parallel to upper-level southwest flow as more shortwave energy ejects from the trough to our west. Deep- layer moisture surges along the boundary, with precipitable water (PWAT) values reaching 1.75-2.00 inches, exceeding the 95th percentile for mid-October. High-resolution ensemble forecasts (HREF) and medium-range guidance (ECMWF, GEFS, and ECMWF-AI) support a few rounds of rain and embedded thunderstorms, with sizable breaks, Wednesday and Thursday. WPC excessive rainfall outlooks highlight a Marginal Risk for heavy rain across central and southeast Illinois both days. Ensemble guidance (LREF) yields high confidence (60-80% chance) for event total rainfall exceeding 1 inch, with localized totals up to 2 inches. Some spread is noted in the footprint of heavier rainfall during this period, with recent guidance trending the higher values to the northwest sections of the CWA.

A sharp airmass change arrives Friday as an expansive Canadian surface high pressure system builds into the Plains and Midwest. The GFS/GEFS continues to be a cold outlier among the guidance suite, showing temperatures several degrees colder than the preferred NBM. Nonetheless, strong cold air advection on Friday will keep highs below normal in the lower 60s, along with gusty northwest winds. The first frost of the season will be in play this weekend, though this will likely hinge on the exact position of the ridge axis. Confidence in the ridge axis being overhead during the early morning hours for calm winds and widespread frost formation is low, but with the cold airmass in place, lows in the 30s are likely both Saturday and Sunday morning.

AVIATION /18Z TAFS THROUGH 18Z TUESDAY/

Issued at 1222 PM CDT Mon Oct 12 2026

VFR with SKC to SCT high clouds will dominate the central IL terminals through Tuesday morning. SW winds will gust near 20 kt this afternoon, then subside near/under 10 kt by sunset. A 40-45 kt low level jet will develop this evening, and cause LLWS through much of tonight before diminishing in the pre-dawn hours.

CLIMATE

Issued at 612 AM CDT Mon Oct 12 2026

Record high temperatures for today and Tuesday:

Location Monday Tuesday ======== ======= ======= Bloomington 88/1930 91/1899 Champaign 87/1962 86/1989 Charleston 89/1962 87/2017 Decatur 92/1962 90/1899 Jacksonville 88/1901 91/1899 Olney 89/1928 93/1928 Peoria 87/2024 88/1899 Springfield 89/1962 88/1975

Records for latest 90 degree high temperature for the year:

Location Date ======== ================ Bloomington October 15, 1899 Champaign October 14, 1899 Charleston October 15, 1897 Decatur October 15, 1938 Jacksonville October 30, 1950 Olney October 22, 1953 Peoria October 15, 1897 Springfield October 11, 1962

ILX WATCHES/WARNINGS/ADVISORIES

None.