textproduct: Central Illinois

KEY MESSAGES

- A semi-stationary frontal boundary will meander over central Illinois through the remainder of the week resulting in a wide range of temps that span from the 40s north of the front to 60s south. NBM shows a greater than 70-90% probability SE of the Illinois River to reach at least 55 degrees Friday and Saturday

- Fog is expected to become widespread across much of central Illinois near and north of a warm front late this evening and overnight. HREF probs for a quarter mile or less visibility is maximized between the Illinois River and I-70 corridor at around 60-80%. A Dense Fog Advisory will be in effect late this evening and overnight.

- A pair of waves will result in light rain or drizzle today and again later Thursday. Precip amounts will be light with only a 20% chance to exceed 0.10 inches of rain each event.

DISCUSSION

Issued at 1225 PM CST Wed Dec 24 2025

An amplified upper ridge will continue to drive unseasonably mild temperatures across the region through the remainder of the week with a pattern change occuring this weekend. This afternoon, loosely organized area of low pressure is in place across the central Great Plains while a cold front that pushed through the local area yesterday has stalled near the Ohio Valley. The front will start to lift back north into portions of central Illinois late this afternoon and evening in response to a low amplitude shortwave trough topping the longwave ridge. Ahead of the front, low level isentropic ascent focused along the 290-300 K surfaces will lift northeast across central Illinois resulting in some very light rain or drizzle as well as some fog. A near repeat of this scenario occurs Thursday evening and overnight after the frontal boundary wobbles over central Illinois with more light rain or drizzle expected. NBM probs for exceeding a tenth of an inch of rain remains quite low, only around 20 percent or less for both events.

Meanwhile, temperatures will be a bit tricky for portions of central Illinois over the next few days, most notably in the vicinity of the frontal boundary where a temperature gradient will be in place. 25th to 75th percentile spread remains around 5 degrees for much of the forecast area today and increases to 7-9 degrees Thursday and Friday. Much of this is due to some lingering uncertainty in the frontal position on any given day. In general, though, anticipate temps to top out in the upper 40s to mid 50s north of the front with mid 50s to mid 60s south.

A strong mid level disturbance will dig into the Great Lakes late this weekend helping to finally break down the strong upper ridge. At the surface, a deep surface low will develop in response, tracking from Lake Michigan midday Sunday into Quebec Monday deepening to below 980mb. A strong cold front will push across central Illinois during the day Sunday. Locations with an early enough frontal passage should see non-diurnal temperature trends with temps falling behind the front in the moderately strong northwest flow. Precip along the front will fall as rain initially then change over to snow briefly. The deformation axis behind the low could also clip portions of central Illinois with some additional light snow. Highs in the 60s Saturday will give way to widespread teens Sunday night with wind chills below zero as the system departs to our east.

Deubelbeiss

AVIATION

(For the 00z TAFs through 00z Thursday Evening) Issued at 529 PM CST Wed Dec 24 2025

As a cold front lifts northward into central IL this evening, cigs are expected to lower as vsbys lower in fog and drizzle. IFR cigs are expected by 00Z, with most areas reaching LIFR by 01Z-02Z. vsbys of a quarter mile are possible much of the night, especially south of KPIA, as the front stalls near the area, then gradually improving conditions should begin after 10Z-14Z as the front pushes southward again, potentially resulting in conditions reaching MVFR during the day Thursday. Winds SE 5-8 kts this evening, becoming light and variable by around 02Z. Winds returning from the north 4-8 kts by around 10Z.

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ILX WATCHES/WARNINGS/ADVISORIES

Dense Fog Advisory from 9 PM this evening to 10 AM CST Thursday for ILZ037-038-040>057-061.