textproduct: Central Illinois

KEY MESSAGES

- An Enhanced Risk (level 3 of 5) for severe weather exists on Monday. All severe hazards will be possible Monday afternoon and evening as a potent storm system lifts through the region.

UPDATE

Issued at 835 AM CDT Sat Apr 25 2026

Subsidence associated with high pressure building into the region this morning has compressed boundary layer moisture associated with the Lake Michigan marine layer, which has made it as far south as a Kewanee to Paris line at 840am. This has primarily manifest in the form of a stratus deck around 200-500 ft, but sharply reduced visibilities to 1/4 mile along the leading edge also occurred. Given the transient nature of these troublesome visibilities and the improvement noted at surface observation sites over the past 30 minutes, we elected to hold off on issuing a Dense Fog Advisory. However, the forecast through the next hour now mentions patchy dense fog for the impacted areas.

DISCUSSION

Issued at 316 AM CDT Sat Apr 25 2026

*** Severe Weather on Monday ***

A vigorous short-wave trough evident on 0730z/230am water vapor imagery well off the coast of southern California will come onshore later today, then lift northeastward into the Upper Midwest by Monday. As the negatively tiled wave approaches, surface cyclogenesis will take place in the lee of the Rockies across southeast Colorado on Sunday...with the low deepening to around 992mb by the time it tracks into northern Wisconsin by Monday evening.

The airmass ahead of the approaching storm system will initially be stable thanks to E/SE boundary layer flow around high pressure over the Great Lakes. As WAA begins, elevated instability will increase late Sunday night into Monday morning when the first round of convection is anticipated. Based on 00z Apr 25 model consensus, it appears the initial storms will focus along/west of the I-55 corridor with a marginally severe hail/gusty wind risk.

As the low lifts further north, it will gradually pull a warm front northward into central Illinois by Monday afternoon. Morning convection and a continued easterly component to the wind will keep the boundary layer stable until late afternoon when richer moisture arrives. While mesoscale details are impossible to properly resolve at this time range, the 00z RRFS offers the first glimpse into the potential severe weather scenario...showing MLCAPE values of 2000-2500J/kg along/south of a Macomb to Champaign line by late afternoon/early evening. Deep-layer shear will be more than sufficient at 45-55kt and 0-1km SRH increases to 300-400m2/s2 west of the Illinois River by 21z. If this solutions pans out, the initial supercells will most likely form across southeast Iowa, northeast Missouri, and western Illinois late Monday afternoon where the greatest tornado and very large hail risk may be maximized. The RRFS then suggests the storms will congeal into a line and track E/SE across the remainder of the KILX CWA Monday evening. While daytime instability will wane somewhat after dark, strong shear will support a continued risk for damaging wind gusts and tornadoes as the storms sweep eastward into Indiana by around midnight.

The other higher-resolution model that currently covers the event is the 12km NAM, and it shows a similar flavor to the RRFS albeit with initial storm development perhaps a bit further W/NW into Iowa and northern Missouri. Even if this solution verifies, central Illinois would still be in line for a volatile Monday evening with an attendant damaging wind and tornado threat. While it is still too early to pinpoint exact details and timing, confidence is growing for a significant severe weather episode. Stay tuned to later forecasts for more details.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 543 AM CDT Sat Apr 25 2026

Northeasterly flow is bringing low clouds from Lake Michigan southwestward into parts of central Illinois early this morning. Models are not handling the moisture field particularly well: however, 1030z/530am satellite imagery shows the leading edge of the IFR/MVFR cloud deck along a KPNT to KDNV line. Based on satellite timing tools, have gone with MVFR ceilings at both KBMI and KCMI starting at 12z...and have introduced scattered clouds at around 2500ft as far southwest as KSPI by 14z. Think the cloud cover will gradually thin as the morning progresses, so have scattered the ceilings by 16z. After that, mostly clear skies are expected for the remainder of the 12z TAF period. Winds will initially be NE at 10-15kt this morning, then will become E/SE at less than 10kt tonight.

ILX WATCHES/WARNINGS/ADVISORIES

None.