textproduct: Central Illinois

KEY MESSAGES

- Seasonal and mostly dry weather is expected through Tuesday.

- The next chance for showers and storms arrives Wednesday. Some of these storms could be strong to marginally severe.

DISCUSSION

Issued at 243 AM CDT Mon Aug 24 2026

Upper analysis has the middle Mississippi Valley positioned under northwest flow with strong upper ridging over the southwest US and a closed low impacting the northeast US. Surface high pressure over central IL early this morning has kept skies mostly clear and winds light. Temperatures as of 2 am have dropped into the upper 50s to low 60s with dewpoint depressions ranging from 0 to a couple degrees. Because of this, patchy low lying fog will be possible through about sunrise. Otherwise, seasonal and mostly dry weather is expected through Tuesday with high temperatures today and tomorrow expected to be in the upper 70s to middle 80s.

By Wednesday, a mid-level shortwave will track through the southern Canadian provinces and into the northern Great Lakes Region, sending a cold front through Illinois. This will bring our next chance for showers and storms. Out ahead of the front, temperatures will climb well into the 80s with steady moisture return bringing dewpoints back into the upper 60s to low 70s. Moderately strong instability is expected to develop by Wednesday afternoon with seasonally strong shear around 30 kts nearest to the front. Forecast soundings depict inverted-V T/Td profiles, implying evaporative cooling could rapidly send parcels toward the surface and locally increase winds. A capping inversion will be in place most of the day, but will erode by late afternoon/early evening as the front approaches and lapse rates steepen. Although the better forcing will be displaced to our north, a few strong to marginally severe storms could develop late Wednesday afternoon and evening, posing a threat for damaging wind gusts and isolated large hail.

Northwest flow remains largely in place through late this week, transitioning to zonal by the weekend. A few weak shortwaves rippling through the upper flow may spark occasional spotty showers through the end of the week, though most will stay dry. Longer range guidance shows a more defined wave/front moving through the Midwest states sometime between Saturday night and Sunday, which could bring another chance for showers and storms. Temperatures will remain seasonable through the end of the week, then turn warmer later this weekend into early next week with the NBM showing upper 80s to near 90 degree highs.

AVIATION /12Z TAFS THROUGH 12Z TUESDAY/

Issued at 540 AM CDT Mon Aug 24 2026

Surface high pressure will keep winds light and variable through today, becoming easterly later tonight. Patchy fog may impact the terminals through about 13Z this morning and again overnight tonight mainly at northern airfields (KPIA, KBMI, KCMI). High clouds will increase in coverage today, with a period of diurnal cumulus also expected from late morning through afternoon.

ILX WATCHES/WARNINGS/ADVISORIES

None.