textproduct: Central Illinois

KEY MESSAGES

- A cooler weather pattern will remain in place the remainder of the week, and high temperatures for the start of May will be about 10 to 15 degrees below normal.

- There is about a 30-50% chance of temperatures cool enough for frost formation Friday night, mainly north of I-72, posing a risk for tender young vegetation.

- After this morning's rain exits eastern Illinois, additional showers through Thursday will be fairly scattered (about a 20-30% chance) and light.

DISCUSSION

Issued at 230 AM CDT Wed Apr 29 2026

The Big Picture:

The cooler weather pattern will remain in place the remainder of the week. Water vapor imagery this morning shows a broad upper low pattern stretching from Ontario to northwest Minnesota, and the synoptic models show this pattern settling over the Great Lakes. Some warmup is anticipated during the weekend into early next week, as the low becomes more centered south of Hudson Bay. However, the CPC 6-10 day temperature outlook does favor below normal temperatures for next week, likely to arrive more toward the second half of the work week.

Short Term (through Friday):

Overnight showers should largely be east of the Illinois border by the morning commute, as a shortwave pushes east of the area. However, within the broader pattern, additional shortwaves will pivot southeast across the western Great Lakes the next few days. With steep low level lapse rates each afternoon, at least some isolated showers should develop. Much of it this afternoon would be more associated with a wave swinging across Minnesota, with some showers potentially as far south as Danville. Better chances will accompany a shortwave dropping southeast across Illinois Thursday afternoon and evening. However, low level moisture with this system is fairly meager, with NAM and GFS soundings rather dry below 5,000 feet. 20-ish PoP's seem reasonable at this point, and added some to Thursday afternoon and evening. Some adjustment may eventually be needed for Friday as well, but more model variance suggests holding off at this time.

Longer Term (Friday Night through Tuesday):

Frost concern remains for Friday night, with LREF probabilities of lows 36F or colder about 30-50% near the I-74 corridor and southeast to near Terre Haute. Will continue to mention areas of frost for about the north half of the forecast area. After that, the upper low finally gets far enough east to allow for some warmer air to spread back into the area. NBM guidance brings highs back to near 70 across the Illinois River Valley by Sunday, with highs 70-75 degrees prevailing Monday and Tuesday.

High pressure will keep the first part of the weekend dry, but as the upper low gets reestablished over Ontario and Quebec, we'll get back into a pattern of fast moving shortwaves dropping southeast across the Great Lakes. This will bring periodic chances of showers early next week, though nothing that would favor severe weather.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/

Issued at 522 AM CDT Wed Apr 29 2026

VFR conditions will generally prevail the next 24 hours, though there is a bit of a visibility restriction around KCMI that will persist through about 12-13z. In general, ceilings will be 6kft or higher, but clouds are expected to thin as the day progresses. Northwest winds will increase to near 15 knots by late morning and remain elevated through sunset, before diminishing this evening.

ILX WATCHES/WARNINGS/ADVISORIES

None.