textproduct: Central Illinois

KEY MESSAGES

- Unseasonably warm conditions will continue through the weekend, with daily high temperatures reaching the 70s. There is a 60% to 80% chance that temperatures will reach or exceed 80 degrees on Sunday, especially for areas south of Interstate 72.

- A cold front on Sunday brings a low chance (20% near I-70) for thunderstorms; if storms develop, a few could become strong to severe.

DISCUSSION

Issued at 143 PM CDT Thu Mar 19 2026

Unseasonable Warmth Dominates Through the Weekend...

A stout upper-level ridge centered over the Desert Southwest will be the main driver of our weather pattern through the weekend, effectively pushing the polar jet stream well into Canada. This setup places Central Illinois firmly on the warm side of the jet, allowing for a significant period of unseasonable warmth. Expect daily high temperatures to climb into the 70s starting today and continuing through Sunday.

A minor weather feature will pass to our north on Friday. A clipper system digging across the Great Lakes will induce a fresh breeze across the area. We do not anticipate any precipitation from this feature locally, but a trailing cold front will result in a shift in wind direction. Southwest winds in the morning will give way to breezy northwest winds in the afternoon hours.

Pattern Change and Severe Potential Sunday...

The upper ridge is forecast to begin breaking down late this weekend in response to an approaching, stronger shortwave trough digging across the Upper Midwest and Great Lakes. Model guidance shows some notable differences in the surface response. The 12Z GFS is aggressive, developing a sub-1000mb low tracking across northern Illinois. In contrast, the GEM and ECMWF are less intense and a little faster, depicting a stable wave along the baroclinic zone that fills as it crosses the state. Regardless of the surface lows exact strength, an attendant cold front will push across Central Illinois during the day Sunday, marking the end of the extended warmth.

This frontal passage also provides our next chance for precipitation, albeit a low one currently. Forecast soundings suggest weak to moderate instability will develop ahead of the front Sunday afternoon and evening, coinciding with strong deep- layer shear. However, a stout capping inversion and the displacement from the main upper-level forcing are the primary limiting factors for widespread convective development. If the cap can be sufficiently eroded, the highly favorable parameter space does support a risk of severe storms. Forecasters will continue to monitor this potential closely over the next 48 hours.

Meanwhile, Sunday presents the best opportunity for temperatures to reach or exceed the 80-degree mark. NBM probabilities for reaching 80 degrees or higher are highest across the southern half of the CWA, ranging from around 30 percent in Galesburg to 60 percent in Springfield and up to 80 percent in Lawrenceville.

Brief Cooldown Followed by a Gradual Warm-up Next Week...

Temperatures will briefly return closer to seasonal norms on Monday as high pressure builds southeastward from the Canadian Prairies. North winds behind the cold front will keep Monday afternoon highs limited to the 50s. The surface ridge axis then shifts east starting Tuesday, allowing the baroclinic zone to lift back north across the region. This pattern shift will initiate a gradual warming trend through the rest of the work week. The main jet stream will remain overhead for much of the week, with low- amplitude waves potentially bringing scattered showers. However, model agreement is currently poor, and the blended NBM guidance reflects this uncertainty, keeping PoPs low (generally below 15 percent) through the middle of next week.

Deubelbeiss

AVIATION

(For the 00z TAFs through 00z Friday Evening) Issued at 620 PM CDT Thu Mar 19 2026

A low pressure system working through the Great Lakes Region tonight will send a cold front through the area on Friday. Southerly winds will veer to the southwest by morning, then shift to the west- northwest as the front moves through Friday afternoon. Scattered mid to high clouds will pass through at times, but otherwise VFR conditions prevail.

NMA

ILX WATCHES/WARNINGS/ADVISORIES

None.