textproduct: Central Illinois

KEY MESSAGES

- No major storm systems are expected to impact the region over the next week. As a result, the severe weather risk across central Illinois will remain low (less than a 5% chance) through next Sunday.

DISCUSSION

Issued at 325 AM CDT Mon May 25 2026

*** Patchy Morning Fog ***

While skies cleared and much of central Illinois experienced considerable boundary layer mixing/drying yesterday afternoon, the E/SE KILX CWA was slower to clear and is thus hanging on to more moisture early this morning. 07z/2am obs indicate temp/dewpoint spreads of 3-6 degrees across most of the area, but just 0-2 degrees along/south of a Danville to Taylorville line. With high pressure overhead and winds nearly calm, patchy fog will develop over the next couple of hours. While no fog has yet been observed in central Illinois, the latest report from Terre Haute shows 1/4 mile visibility. CAMs from 24 hours ago had originally shown a band of fog as far N/NW as Springfield and Bloomington, but this is not coming to fruition due to the drier air there. Latest CAMs focus the fog south of I-72 and this makes sense given the current obs. After any early morning fog dissipates, am expecting a pleasant Memorial Day with afternoon highs topping out from around 80 degrees along I-70 to the middle 80s northwest of the Illinois River.

*** Mid-Week Rain Chances ***

As has been advertised by the past several model cycles, a quasi-blocking pattern will develop this week...featuring an upper low over the Lower Mississippi River Valley and a high over the Upper Midwest. The low in question is evident on the latest water vapor imagery over eastern Texas and is progged to begin pivoting slowly northward later today into Tuesday. As a vigorous low off the coast of British Columbia digs southward, it will induce strong downstream ridging over the Northern Rockies/Northern Plains. As the high strengthens and shifts E/SE, it will eventually stop the northward progress of the low and its associated precip. The main forecast question has been and continues to be how far north the precip can spread before the high eventually wins out. The 00z May 25 model suite is offering a bleaker picture for widespread rainfall than previously forecast...with general consensus suggesting areas north of I-72 receiving little to no rain. Based on the timing of this process, have kept Tuesday dry across the bulk of the KILX CWA with low chance PoPs (20-30%) south of I-70 by afternoon. The primary time frame for showers and a few thunderstorms will be Tuesday night into Wednesday when forcing is strongest and the richest Gulf moisture approaches from the south. Given good model agreement concerning the building upper high to the north, have spread likely PoPs (60-70% chance) as far north as a Paris to Taylorville line on Wednesday, but have kept locations north of a Normal to Macomb line completely dry. As the high builds southward, synoptic subsidence and a drier airmass will arrive from the north...thus ending the rain chances for Wednesday night through Friday. The latest projections now show rainfall of 0.25 to 0.50 along/south of a Paris to Taylorville line...with higher totals further south closer to the Ohio River.

After that, forecast confidence becomes poor for next weekend as questions remain regarding the eventual break-down of the blocking pattern. Previous runs of the ECMWF had shown the high weakening and a short-wave pushing eastward out of the Plains by Saturday/Sunday: however, the latest run keeps this feature and its associated rain mostly south of central Illinois.

While rain is in the forecast for parts of the area this week, the lack of a strong storm system and overall weak instability/shear will prevent severe weather development. As a result, the latest machine learning algorithms feature little to no chance (less than a 5% chance) for severe weather across central Illinois through at least next Sunday.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 438 AM CDT Mon May 25 2026

VFR conditions will prevail through the entire 12z TAF period. Patchy fog has formed across parts of east-central and southeast Illinois early this morning: however, it appears it will remain S/SE of the I-72 terminals over the next couple of hours. Aside from FEW-SCT diurnal clouds at around 4000ft, skies will remain mostly clear today. Winds will initially be calm, but will become SE at less than 10kt from mid-morning through the afternoon.

ILX WATCHES/WARNINGS/ADVISORIES

None.