textproduct: Central Illinois

KEY MESSAGES

- There is a medium-high (50-70%) chance for patchy dense fog overnight into Tuesday morning, primarily in areas near and east of Interstate 55.

- April-like warmth, with daily temperatures in the 60s, is forecast through Thursday. Elevated fire concerns are possible by Wednesday afternoon, especially across west- central Illinois, due to the combination of warm and breezy conditions.

- Thursday brings an increased risk for severe weather to areas across east-central and southeast Illinois.

DISCUSSION

(through next Monday) Issued at 217 PM CST Mon Feb 16 2026

Patchy dense fog is once again a concern overnight into Tuesday morning as a damp surface and thawing sub-surface promotes a shallow moisture flux which will become trapped beneath the overnight thermal inversion.

Near and east of Interstate 55, there is a medium-high likelihood of dense fog, with the latest REFS guidance showing a 50-70% probability of visibility dropping below one-quarter mile between 09z-15z. High-level clouds and a slight tightening of the pressure gradient may lessen the fog potential in areas to the west of Interstate 55. We will continue to monitor trends this evening and issue a dense fog advisory as needed.

Our well-advertised warm-up will persist through the middle of the week. This pattern will be driven by a deep trough digging into the eastern Pacific, which will spread deep southwest flow across the intermountain west and the Plains states. As this trough moves eastward and a surface lee cyclone strengthens, the Midwest will experience gusty southwest winds (30-40 mph) Tuesday into Wednesday. The net effect will be the warmest temperatures of the season so far. Current NBM median guidance strongly supports 60s each day through Thursday, with the upper tail of guidance pushing 70 degrees for Wednesday and Thursday.

Elevated fire danger is possible on Wednesday, driven by the unusually warm and breezy conditions. The primary risk area will likely be west-central Illinois, which has seen particularly sparse rainfall over the last 30 days. This threat is expected in the afternoon, with minimum RH values dropping below 30% as wind gusts gradually decrease.

The primary concern mid-week is the potential for severe weather. However, despite strong atmospheric dynamics and excellent synoptic ascent, global deterministic models continue to mute the convective signal for Tuesday night into Wednesday. This is attributed to limited moisture and poor thermodynamics within the developing warm sector, a feature that global guidance has shown consistently over consecutive runs. Consequently, support for widespread thunderstorms accompanying the cold front late Tuesday evening into Wednesday morning is currently very low. Instead, we may see a few elevated convective showers, presenting a marginal risk for isolated damaging wind gusts if momentum is transferred beneath the 50+ kt LLJ.

Global deterministic guidance now indicates a more favorable environment for severe weather on Thursday as another shortwave trough moves through the Upper- to Mid-Mississippi Valley. The highest probabilities for severe weather are centered over portions of the lower Ohio and lower Wabash river valleys. In these areas, boundary-layer moistening is expected to bring surface dewpoints into the mid-to-upper 50s and create 500-1000 J/kg of SBCAPE across a broadening warm sector. The combination of strong deep-layer shear (60+ kts) and sufficient instability will be conducive to supercellular structures capable of producing all severe weather hazards Thursday afternoon across portions of southeast Illinois.

A shift to cooler weather is expected to return and persist from Friday through next weekend. The NBM deterministic guidance suggests daily temperatures will remain slightly above normal on Friday and Saturday, with afternoon high temperatures around the middle 40s and overnight lows in the mid 20s. Temperatures then drop near normal for Sunday and Monday with highs near 40 degrees and lows near 20.

MJA

AVIATION

(For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1111 AM CST Mon Feb 16 2026

The main forecast concern through this TAF period will be the potential for patchy dense fog to once again develop across the regional terminals. Current hi-resoultion model guidance supports the highest chances near and east of Interstate 55 between 08z-15z, when visibility could fall to one mile or less. But until that time, VFR conditions will prevail with occasional high-level cloudiness. Meanwhile, south winds will maintain a southerly component with sustained speeds between 10-15 kts this afternoon before diminishing this evening.

MJA

ILX WATCHES/WARNINGS/ADVISORIES

None.