textproduct: Central Illinois

KEY MESSAGES

- Chances of rain showers have increased for this afternoon and evening (40-60%). While amounts should be relatively light, some gusty winds will accompany the heavier showers. Additional showers are expected Friday afternoon, though confidence is lower (20% chance).

- While frost remains a concern for Friday night, additional cloud cover introduces some uncertainty.

- The overall weather pattern the next week will favor temperatures below normal, with only Sunday and Monday reaching near climatological normals (low 70s for early May).

DISCUSSION

Issued at 215 AM CDT Thu Apr 30 2026

The Big Picture:

Early morning water vapor imagery continues to show an upper low over Lake Superior, with the next in a series of shortwaves dropping southeast across the Dakotas and Minnesota. The projected upper pattern to start May has not significantly changed, with the upper low dominating the Great Lakes region before lifting northeast this weekend, only to be followed by additional lobes of low pressure expanding over south central Canada next week. As a result, temperatures generally will remain on the cooler side for this time of year, with a brief warmup for Sunday and Monday.

Short Term (through Saturday):

With the series of upper waves dropping southeast, rain chances are a concern for today, and Friday to a lesser extent. Have boosted PoP's for this afternoon and evening with the wave moving through, and they are now in the 50-60% range west of I-55 this afternoon and east of there in the evening. However, forecast soundings show the cloud bases being relatively high (5000-7000 feet) with considerable dry air below that, so accumulations should be relatively modest. The large inverted-V signature would suggest some gusty winds with the heavier showers, and a few rumbles of thunder are possible given the steep low level lapse rates. A similar scenario may unfold on Friday, though with the upper wave lagging behind a bit, will only go with 20% chances for now near/west of I-55.

Frost potential remains a concern, mainly on Friday night. Will keep a mention of areas of frost from about Galesburg-Paris northeast. However, cloud cover may be more of an issue, as the broader upper trough will be swinging across the state. The coolest weather will be associated with this trough, with highs Friday and Saturday mainly in the mid to upper 50s over a good chunk of the forecast area.

Long Term (Sunday through Wednesday):

Once the upper trough shifts eastward, we'll get a southerly flow setting up to start the new week. High temperatures return to the lower 70s west of I-55 Sunday, and 70s will be common Monday over the region. The upper pattern shifts more into a split flow, as an upper low drops into California as the Canadian troughing digs south. Synoptic models show our area caught in the middle, with extended rain chances from Monday into midweek. LREF Grand Ensemble shows probabilities of more than a half inch of rain peaking around Tuesday night and Wednesday, in the 40-50% range. Temperatures ease back again as the Canadian trough deepens and digs into the mid and upper Mississippi Valley.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1220 PM CDT Thu Apr 30 2026

An upper level disturbance is digging across the mid/upper Mississippi Valley early this afternoon with scattered light and high-based showers spreading SE from IA into IL. There could be some gusty winds and brief MVFR visibility in and near the showers as they move across central IL this afternoon and evening, otherwise VFR conditions are expected through the period. A modest SW Breeze in place this afternoon will set up out of the NW tonight then veer to northerly during the day Friday.

ILX WATCHES/WARNINGS/ADVISORIES

None.