textproduct: Central Illinois

KEY MESSAGES

- Mild conditions are forecast during the work week with daily highs generally in the 50s.

- Amidst persistent drought conditions, the best opportunity for beneficial rain will be Thursday into Friday. Chances for more than a half inch of rainfall range from 40-50% south of I-70 to 20-30% in west-central IL.

DISCUSSION

Issued at 135 AM CST Sun Jan 4 2026

***** SEASONABLY COOL TODAY *****

Surface high pressure sprawled over the Midwest continues to maintain tranquil conditions over the forecast area this morning, while subsidence associated with upstream ridging has compressed boundary layer moisture and resulted in widespread low clouds. The NBM and NAM, which are handling this stratus best, suggest it'll retreat northward as low level warm advection develops across the area this afternoon. Though mid-high clouds will persist, even the filtered sunshine should be sufficient to warm areas south of a roughly Macomb to Robinson line to 40+, while temperatures top out in the mid 30s north of I-74. We'll have to watch out for some fog developing in west-central IL by early tomorrow morning as temps drop with departing mid-high clouds and moisture advection persists; HREF suggests 15-30% chances for visibilities less than 1/2 mile west of the IL River by 6am tomorrow.

***** CLOUDY BUT MILD MONDAY INTO TUESDAY *****

Wherever this fog and/or low stratus lingers (most likely west of the IL River), temperatures on Monday may run a little cooler than guidance, but further south expect highs to climb into the 50s. Warm, moist advection will continue tomorrow night, and as a result another round of, perhaps more widespread, low clouds, fog, and/or drizzle seem plausible. Both the NAM and GFS advertise negligible probabilities of cloud ice, negative omega (upward motion) and near saturation (RH > 85%) in the lowest 1km, with the NAM also advertising diminished visibility (< 1 mile) and light QPF (T - 0.03") north of roughly I-72. Temps should be too warm for any drizzle to freeze, so while there could be impacts if fog becomes dense, confidence was too low to make those changes to the forecast at this time.

***** RAIN CHANCES (40-60%) CLOSE THE WORK WEEK *****

Conditions are forecast to remain mild through at least Thursday, after which time ridging will begin to shift east as a more potent upper level trough approaches. Global models and their respective ensembles continue to differ dramatically in the evolution and track of a surface low developing in the left exit region of a 100+ kt 500mb jet streak. For example, the current GFS has the surface low tracking along the Ohio River to keep our area cool and dry, while the ECMWF has the low lifting north along the Mississippi River into the IA/IL/WI tristate area - which would bring our area sufficient moisture and warmth for a beneficial rainfall and perhaps some thunderstorms late Thursday into Friday. For what it's worth, raw ensemble guidance (LREF) gives 40-50% chances for more than a half inch of rainfall over southeast IL, with those probabilities tapering to 20-30% west of the IL River in west-central IL. Behind this system, conditions will turn seasonably cold and breezy once again.

Bumgardner

AVIATION

(For the 06z TAFs through 06z Sunday Night) Issued at 951 PM CST Sat Jan 3 2026

Low stratus continues to spread southward late this evening with ceilings across the area ranging from 2-4k ft. Guidance that has a better handle on the ongoing conditions (NBM, GLAMP) are indicating that all airfields will be MVFR through the overnight hours. Confidence in how long the stratus sticks around is quite low, though upstream observations would suggest it may linger through most of Sunday, with perhaps occasional breaks at times. Light winds overnight will veer to the south by late morning/early afternoon with speeds increasing closer to 7-10 kt.

NMA

ILX WATCHES/WARNINGS/ADVISORIES

None.