textproduct: Central Illinois

KEY MESSAGES

- Areas of dense fog are likely to redevelop overnight into Monday morning. The latest REFS guidance depicts a medium-high (50-70%) chance that visibility will fall below one-quarter mile in areas near and east of the Illinois River, expanding toward east- central and southeast Illinois.

- Unseasonably warm air (20-25 degrees above normal) arrives this week, peaking Wednesday and Thursday with mid-to-upper 60s temperatures. Gusty southwest winds (30-40 mph) on Tuesday & Wednesday will accompany this warmup.

- A conditional threat for severe weather remains possible but not particularly likely in the Wednesday-Thursday timeframe.

DISCUSSION

Issued at 1205 PM CST Sun Feb 15 2026

Drier weather has returned across the Plains and Midwest as surface high pressure settles in behind the departing storm system. Although strong solar insolation has dissolved this mornings dense fog, it is expected to return overnight into Monday. A damp surface and thawing sub-surface will promote a strong moisture flux, which will become trapped beneath the overnight thermal inversion.

Near and east of the Illinois River Valley, 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. High-level clouds and a slight tightening of the pressure gradient may slightly lessen the fog potential in areas to the north and west of the Illinois River. We will continue to monitor trends this evening and issue a dense fog advisory as warranted.

An aggressive warm-up is then anticipated 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 Monday through Thursday, with the upper tail of guidance pushing 70 degrees for Wednesday and Thursday.

The main concern for the middle of the week is the potential for severe weather. Despite strong atmospheric dynamics and excellent forcing mechanisms for lift, global deterministic models currently do not define a clear convective signal. This is due to limited moistening and poor thermodynamics within the developing warm sector, which the global guidance has been steadfast in depicting run-over-run. At this point, there is very little support for thunderstorms to accompany the cold front early Wednesday. What we might see instead are a few elevated convective showers that pose a marginal threat for sporadic damaging wind gusts given the top- shelf kinematics in place (50+ kt LLJ).

A potentially better signal emerges for Thursday, tied to another shortwave trough pivoting through the Upper- to Mid-Mississippi Valley region. However, moisture and instability profiles in deterministic guidance are not particularly promising for this period either, at least at the current time. The exception could be down across southeast Illinois where boundary-layer moistening brings mid-50s sfc dewpoints and a few hundred joules of SBCAPE ahead of another frontal passage.

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 lower 40s and overnight lows in the upper 20s. Temperatures then drop near normal for Sunday with highs near 40 degrees and lows near 20.

MJA

AVIATION

(For the 00z TAFs through 00z Monday Evening) Issued at 534 PM CST Sun Feb 15 2026

FEW to SCT high clouds are approaching from the west with light west- southwest winds in place at the surface. Dense fog appears likely once again late tonight into Monday morning as low-level moisture becomes trapped beneath a temperature inversion. IFR to occasionally LIFR visibility is forecast, though a tightening pressure gradient/increasing winds overnight could lower this potential especially west of the IL River. Fog/low clouds should scatter out by mid to late morning as southwest winds become breezy.

NMA

ILX WATCHES/WARNINGS/ADVISORIES

None.