textproduct: Central Illinois

KEY MESSAGES

- Patchy dense fog will create potentially hazardous driving conditions for this morning's commute along and south of a Paris to Shelbyville line.

- 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 very low (less than a 5% chance) through next Wednesday.

DISCUSSION

Issued at 311 AM CDT Thu May 28 2026

07z/2am surface analysis shows a weak cold front along the I-74 corridor. While a drier boundary layer airmass characterized by surface dewpoints in the upper 40s and lower 50s gradually settles southward from the Great Lakes, a considerably moister airmass lingers south of the boundary where dewpoints are still in the middle 60s across much of central and southeast Illinois. The front will continue to drop southward through daybreak:however, the drier air will lag behind. Thanks to nearly calm winds and only a high/thin overcast, fog is forming in the moist airmass...particularly where ample rainfall occurred yesterday along/south of a Paris to Shelbyville line. CAMs have been consistently highlighting this area for the past several runs and obs at both Robinson and Lawrenceville have occasionally dipped to between 1/4 and 1/2 mile over the past two hours. Given trends and a clear signal from the CAMs, have issued a Dense Fog Advisory through 8am. Think the fog will be fairly shallow, but may create a driving hazard for the morning commute...especially in low-lying rural spots.

After the morning fog dissipates, am expecting a partly sunny day with a high/thin cirrus overcast. Afternoon highs will top out in the middle 80s: however, it will not feel as hot as yesterday thanks to a northeasterly breeze gusting 15-20mph behind the departing front.

Much of the forecast period will be dominated by an Omega Block pattern across the CONUS featuring deep upper lows over the West Coast and New England with a ridge sandwiched between them over the Midwest. Synoptic subsidence beneath the ridge will ensure little to no precipitation will occur across central Illinois as short-wave energy remains W/SW of the region. Will need to keep an eye on the prominent wave visible on latest water vapor imagery extending from Colorado to Texas. As this feature pivots northeastward, it will try to push its associated cloud cover and precip toward central Illinois...with model consensus showing this process occurring Friday night into Saturday morning. The ridge will likely hold firm, but think precip will get close enough to warrant a 20% chance for showers along/southwest of a Jacksonville to Effingham line Friday night. Additional short-wave energy may try to push toward the upper ridge axis again Sunday night, but have maintained a dry forecast for now. After that, the 00z May 28 models all show the eastern Canada/New England upper low strengthening and digging further southward, essentially shunting the Omega Block a bit further west by early next week. Given increasing northerly flow around the low, dry weather will prevail Monday through at least Wednesday. After the above normal temperatures in the middle 80s today, a return to seasonal norms in the upper 70s and lower 80s is expected through the remainder of the forecast period.

AVIATION /12Z TAFS THROUGH 12Z FRIDAY/

Issued at 537 AM CDT Thu May 28 2026

VFR conditions will prevail through the entire 12z TAF period. As a weak cold front passes, winds will become northeasterly and gust 15-20kt from late morning through the afternoon. The gustiness will subside toward sunset, with northeasterly winds of 5-10kt continuing through the night. A high/thin overcast will be noted.

ILX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory until 8 AM CDT this morning for ILZ056-057- 061>063-066>068-071>073.