textproduct: Central Illinois

KEY MESSAGES

- Cooler and drier weather settles into the region through Thursday, though a few light morning showers remain south of Interstate 72. Daytime high temperatures will stay near 70 degrees.

- Widespread rain will move across central Illinois Friday afternoon and evening. While rain is highly likely, total amounts remain uncertain and could range between 0.10 and 0.90 inches. - Temperatures warm into the upper 70s this weekend and continue to climb next week. High confidence exists that afternoon heat in the mid 80s will return by the middle of next week.

DISCUSSION

Issued at 252 AM CDT Wed May 20 2026

Scattered showers may persist through late morning for areas near and south of Interstate 72 as a mid-level shortwave trough over SE Missouri tracks northeast along a baggy baroclinic zone. With the primary axis of instability now shifted toward the Ohio River Valley, any resulting precipitation should remain light, with a minimal risk of thunderstorms.

Although HREF CAM guidance varies, with some models depicting dry conditions, the mean HREF QPF suggests totals up to one- tenth of an inch near I-72, with up to one-quarter of an inch possible south of a Taylorville-to-Paris line.

Otherwise, a cooler and drier trend is taking shape today and Thursday as surface high pressure settles over the Great Lakes region. High temperatures may struggle to reach 70 degrees, while overnight lows drop into the upper 40s and lower 50s. Some forecast models also indicate that a lake breeze from Lake Michigan may penetrate as far inland as the I-74 corridor late this afternoon and again tomorrow, likely resulting in a cooler feel during the evening hours.

The period of dry weather will be short-lived. By Friday morning, a series of shortwave impulses is expected to move northward from the lower-Mississippi Valley, preceding a more significant trough moving through the central United States. This shift in the atmospheric pattern will push a surface front into central Illinois around midday Friday. Consequently, widespread showers are anticipated across the forecast area Friday afternoon and evening, driven by isentropic ascent and warm-air advection. While limited instability should prevent severe convective weather, high precipitable water (PWAT) values may lead to high rainfall efficiency. Forecasted rainfall totals remain uncertain; the 100-member LREF global ensemble shows a 25th-75th percentile range of 0.10 to 0.90 inches for our forecast area. While confidence in the occurrence of rain is high, the specific accumulation amounts among model guidance remain highly variable. Though, it is worth noting that this same guidance currently focuses the higher QPF across SE Illinois. As the front shifts northward through the region on Friday, temperatures are expected to surge this weekend, with highs reaching the upper 70s both Saturday and Sunday.

The main upper trough axis swinging through the Midwest may trigger additional scattered showers over the weekend. However, following the passage of the initial frontal zone on Friday, mid-level RH profiles appear significantly drier, resulting in substantially lower QPF for Saturday and Sunday.

Heading into next week, global deterministic models suggest the development of a Rex block over the Plains. The progression of the associated upper low will ultimately dictate rain and storm potential through early next week. Current indications suggest that areas south of I-72 are best positioned for rainfall as the low portion of the block pivots up the Mississippi Valley while the high-pressure side loiters over the Corn Belt. There is stronger model agreement regarding temperatures, with mid-to- upper 80s heat forecast to return by the middle of next week.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 1144 PM CDT Tue May 19 2026

A cooler, drier continental airmass is settling over the Great Lakes region behind a cold front. This will gradually shift the back edge of MVFR ceilings south of the central Illinois terminals overnight. Winds will generally remain northerly through Wednesday morning, shifting northeast prior to sunset.

ILX WATCHES/WARNINGS/ADVISORIES

None.