textproduct: Central Illinois

KEY MESSAGES

- Areas of fog near and west of roughly I-55 will likely (60-80% chance) result in visibilities under a half mile at times from 4 to 9am, with gradual improvement thereafter. Drivers should allow themselves additional time for the morning commute, and leave extra stopping distance on the way.

- Beneficial rain is forecast Thursday into Thursday night, though rain amounts will vary widely. In any given location, there is a roughly 20% chance for more than an inch of rainfall, which could help the ongoing drought.

- There is a level 1 of 5 (marginal) risk for severe weather with showers and storms Thursday evening and night. The main hazard would be gusty to locally damaging wind gusts.

- Mild conditions will continue through tomorrow night. Seasonably cool weather will return this weekend, with a 50-60% chance of high temperatures below freezing by Sunday.

DISCUSSION

Issued at 215 AM CST Wed Jan 7 2026

***** FOG THIS MORNING, SUNSHINE RETURNS THIS AFTERNOON *****

Early Wednesday morning, a weak shortwave trough was shifting east across the Great Lakes, while upper level ridging was slowly nudging into the Midwest in its wake. Boundary layer moisture compression via subsidence associated with this incoming ridge, coupled with easing winds with surface high pressure, is fostering fog development across Iowa and west-central Illinois. The HRRR, RAP, ARW, and NAMNest generally suggest this will shift east into central and southeast IL over the next couple hours. There is a little uncertainty on how far north the persistent/widespread fog will build given the ongoing stratus, but as it is slowly pulling away to the east thinking is areas west of a Taylorville to Champaign line will have the most persistent visibility reductions this morning. In those areas, 50-80% of HREF membership depicts visibilities less than a half mile from 4-9am when a Dense Fog Advisory (DFA) may be needed. Mid to late morning, this fog should lift to low stratus which will slowly retreat northward on southerly breezes. Due to uncertainty in precisely when this stratus pulls away (and surface heating ensues), there remains some question as to how warm temperatures get this afternoon mainly across our north, but the 00z HRRR suggests the dry airmass, southerly flow, and sunshine could warm some spots into the low 60s. We didn't get quite that warm in the forecast, but blended NBM to the HRRR and Consshort to boost temperatures a couple degrees mainly south of a Macomb to Shelbyville line where highs should at least reach the upper 50s.

***** RAIN LIKELY (90% CHANCE) THURDSAY-THURSDAY NIGHT *****

Global models and their respective ensembles agree that a cut off low currently off the coast of southern/central California will get swept up by the jet stream over the Southern Plains and lift into the MS River Valley/Midwest Thursday into Thursday night. Strong divergence in the left exit region of a 150+ kt 250mb jet streak will foster cyclogenesis at the surface over Missouri, with the low subsequently shifting through eastern Iowa or extreme northwest IL Thursday evening into Thursday night, per low tracks from the GEFS and EPS. Rich deep layer moisture brought northward from the Gulf will bring PWATs into the 1.1-1.3" (above the daily record from ILX raobs) range according to the GEFS and EPS ensemble means, so with a warm cloud layer depth of ~ 9-10kft showers and thunderstorms should be seasonably efficient rainfall producers. LREF and NBM ensemble means bring precip totals to generally a 0.3 to 0.6 inches across the area, with the axis of heavier totals (1 inch or more) associated with the deformation/FGEN band on the northwest side of the surface low across Iowa. However, given the potential for convective showers and even a few thunderstorms across our area, narrow stripes of higher totals exceeding an inch, such as those advertised by the REFS storm total precip LPMM, seem plausible. NBM continues to advertise a 15-30% chance of more than an inch in any given location across our area.

Given limited instability, the severe weather risk remains unclear this far north to both us and the experts at SPC, though the most recent outlook update brought the 5% damaging wind risk north to encompass portions of central IL near and east of roughly the IL River. After all, we'll be clouded over most or all of the day Thursday with periods of stratiform rain during the afternoon, but with moisture advection bringing dewpoints into the upper 50s we'll certainly need to keep an eye out for any breaks in cloud cover during the late afternoon. The 00z RRFS (and tail end of the 00z HRRR) suggests a broken line of showers with perhaps a few rumbles of thunder will move east through portions of our area after roughly 5pm. During this time, the 50kt 925mb LLJ could result in sporadic severe wind reaching the surface, while gradient winds from the south will run 20-25 mph with gusts to 35 mph outside of convection. The tornado risk appears low given the 40-50kt 0-3km shear vectors are largely parallel to the line, but any bowing segments will bare close watching. Friday morning, the cold front should sweep through our area from west to east, and we could wind up with some gusty west-southwest winds behind it depending on how tight the gradient gets. Bufkit mixing techniques from the NAMNest suggest sustained speeds upwards of 25 mph with gusts approaching 40 mph - roughly the EPS ensemble mean peak gust for our area.

***** TURNING SEASONABLY COOL AGAIN THIS WEEKEND *****

The stronger push of cool air should arrive with the parent trough and a developing second low lifting from the Ohio Valley into the Great Lakes Friday night into Saturday. Some guidance, most notably the deterministic (00z) GFS, even suggest sufficient wrap around moisture behind that low to bring rain or a rain/snow mix to our neck of the woods Saturday morning, followed by some snow showers Saturday afternoon. With the increasingly dry airmass sinking into the region from the northwest, the chance for robust snowfall totals appears low. While many locations may see some flakes or even a dusting on grassy surfaces, the chance for more than an inch of accumulation is generally less than 15% from the LREF - except 20- 25% northwest of an Avon to Lacon line. The cooler air should be solidly over our area Saturday night into Sunday, by which time LREF mean 850mb temps sink to roughly -10 degC and NBM gives a 50-60% chance for daily high (surface) temperatures below freezing.

Bumgardner

AVIATION

(For the 06z TAFs through 06z Wednesday Night) Issued at 1026 PM CST Tue Jan 6 2026

Low stratus is in place over most of the area late tonight with ceilings ranging from MVFR to IFR. Fog is expected to develop overnight into Wednesday morning, with the lowest visby and ceiling reductions most likely from KBMI/KDEC westward. Conditions should improve by mid to late morning, though low stratus may stick around through early afternoon at northern terminals. West-northwest winds will become light overnight as surface ridging slides overhead. Winds turn southerly on Wednesday with speeds peaking around 10 kts.

NMA

ILX WATCHES/WARNINGS/ADVISORIES

None.