Casey, IL Weather

Key Messages

- Sunny mild days and cool nights persist across central and southeast Illinois through Monday, with highs in the 70s and lows in the 40s.

- A cold front moves across the region early next work week, though rain chances look pretty slim, with temperatures cooling a bit for middle of next week.

Discussion

Issued at 300 AM CDT Thu Oct 22 2026

A delightful stretch of fall weather is expected to continue across central/southeast IL through at least Monday with dry conditions, fair amount of sunshine, light winds and mild days. This bodes well for the fall harvest season in Illinois which is approaching 75% of crops (corn and soybeans) harvested.

A 1023-1025 mb high pressure ridge over the Great Lakes and into IL/MO was providing nearly clear skies and calm winds. Had a few patches of mid level clouds (8-9k ft bases) affecting mainly northern CWA since this past evening and dissipating as they moved se into central IL with a few patches over central and southern IN. Temps over CWA were generally in the 40s and lower 50s with BMI 55F and CMI 54F. Dewpoints were in the low to mid 40s. Aloft an upper level ridge was over the Great Plains while 558 decameter 500 mb low off the CA coast and 565 decameter 500 low (Subtropical Storm Josephine with 65 mph winds 245 miles south of Nantucket MA) was off the New England and mid Atlantic coast.

Not much change in the forecast into Monday as surface high pressure ridge stays near IL, and have strong mid/upper level ridge building into IL late this week as 500 mb heights to approach 588 decameters or higher on Sat afternoon into Sunday. Ample sunshine today with light ne winds (calm winds over the IL river valley) with highs in the mid 70s, with a few upper 70s from Peoria and Springfield west. Fair tonight with lows in the mid to upper 40s, coolest in eastern IL with patchy shallow ground fog near Wabash river valley overnight into early Fri morning. A fair amount of sunshine Friday with se winds less than 10 mph and highs in the low to mid 70s, coolest in eastern IL. Lows Fri night in the low to mid 40s eastern IL and 45-50F over the IL river valley from I-55 west.

Some increasing mid/high clouds during Fri night into Saturday though generally partly to mostly clear skies this weekend, with less cloud cover in southeast IL. SSE winds Sat and SSW on Sunday be generally staying less than 10 mph. Highs in the mid 70s Saturday and 75-80F on Sunday. The frontal boundary stays north of central IL on Monday with light SSW winds and mild highs in the mid to upper 70s, warmest from Springfield sw.

Deterministic medium range models show upper level trof moving into the central/northern Plains Mon/Tue while cold front slips southward into northern IL Monday and possibly into central IL Mon night and Tue. Brunt of models still keeping CWA fairly dry Mon night and Tue with qpf north of area. GFS is more aggressive with some light qpf northern CWA on Tue. The ECMWF-AI and ECWMF-ENS have been trending drier over central IL with its light qpf north/nw of CWA Mon night/Tue. Blended forecast currently is going dry over much of area thru Wed with just light pops 15% north of Galesburg and Lacon Tue morning. NBM highs Tue are in the mid to upper 60s from Quincy to Bloomington north and lower 70s south with mildest temps near 75F from highway 50 south over southern IL. Highs Wed in the mid to upper 60s, except near 70F from highway 50 south. A bit milder highs in the upper 60s/lower 70s Thu. A stronger wx system looks to move into the Midwest by next Thu possibly bringing next chance of showers if it gets this far south.

Aviation

Issued at 1240 PM CDT Thu Oct 22 2026

VFR conditions will persist through the TAF cycle as a ridge of high pressure maintains clear skies and light winds.

Ilx Watches

None.