Decatur, IL 62523 Weather

Key Messages

- Dry and mild weather is expected through this weekend along with a fair amount of sunshine and fairly light winds. Highs will climb into the 70s with lows in the 40s and lower 50s today through Sunday.

Discussion

Issued at 315 AM CDT Tue Oct 20 2026

Delightful fall weather will likely continue through at least early next week across central and southeast IL. The 08Z/3 am surface map shows large 1031 mb high pressure over eastern Ontario Province and ridging SSW across the Great Lakes region and IL/IN. Aloft a mid/upper level ridge was over the MS river valley with cutoff upper level lows/trof off the mid Atlantic Coast and West Coast/CA. Nighttime Microphysics satellite imagery shows a swirl of scattered to broken mid/high clouds over central and southern IL, and more widespread high clouds in southern/sw IL. Temperatures not as cool as past few nights, with current mercury levels in the 40s, ranging from 38F at NWS Lincoln to 51F at the Bloomington airport and 50F at Peoria airport. Light to calm winds with dewpoints in the low to mid 40s, with a few spots having upper 30s at Lincoln and Lacon.

Surface high pressure strengthens to ~1033 mb as it drifts eastward into Quebec by sunset while still ridging back over IL and upper level ridge staying over IL. Strong subsidence over IL today, with high clouds decreasing during this morning, lasting longest in southeast IL where partly to mostly cloudy skies early this morning gives way to sunny skies by late morning. With dewpoints a bit higher and with light to calm winds and high clouds decreasing, could see patchy shallow ground fog early this morning near rivers/creek beds and other water areas but coverage limited and whatever fog develops will lift quickly after sunrise. Highs today in the lower 70s with very light winds with high pressure ridge overhead. Fair tonight with lows 40-45F. Little change with weather on Wed as surface and upper level ridge stay over IL. Some clouds increasing over the IL river valley/western CWA on Wed but still a fair amount of sunshine Wed. Temps 1-2 degrees warmer with highs 70-75F and very light to calm winds.

Another high pressure drifts eastward across southern Ontario Wed night and pushes a weakening cold front southward into the southern Great Lakes by early Thu morning and will have little affect on our weather with nearby high pressure ridge and light ne flow developing over CWA on Thu. Ample sunshine Thu with highs in the low to mid 70s. The large high pressure system strengthens to 1036 mb or stronger as it moves over PA/NY by Saturday morning and stays near the mid Atlantic States through the weekend and surface ridging sw into the lower MS river valley pinching off gulf moisture from returning to IL. Circulation around high pressure gives a light se flow on Friday with sunny skies, and highs in low to mid 70s. Strong mid/upper level ridge into the Eastern Plains on Friday shifts east into IL on Saturday ensure dry and mild weather. A bit stronger SSE winds Saturday and some increasing clouds overnight Fri night into Saturday as skies become partly cloudy. SW winds on Sunday with partly sunny skies and highs in the mid to upper 70s.

GFS model is most aggressive with pushing a cold front and some rain chances se into central IL late Monday afternoon and Monday night while GEM and Ecmwf models keep CWA dry as system weakens since moving into strong mid/upper level ridge from the OH/TN river valleys into the Southeast States. Highs 70-75F over central/se IL Mon and upper 60s nw of the IL river but if front is slower to move in would likely be warmer there too. Temps cool closer to seasonable levels next Tue/Wed.

The Climate Prediction Center (CPC) 6-10 Day Outlook for Oct 25-29th has 50-60% chance of above normal temperatures over IL and 35-45% chance of below normal precipitation (especially southeast IL). CPC 8-14 Day Outlook for Oct 27-Nov 2 has 55-60% chance of above normal temperatures over central/se IL and 35-45% chance of above normal precipitation (especially in western IL). As of Oct 18th, Illinois has 63% of corn harvested and 66% of soybeans harvested, running 5% ahead of schedule. Generally looks like favorable weather conditions into next week for the 2nd half of harvest season. Given the dry and mild weather pattern for at least next week, and developing moderate drought in southeast IL, some fire weather concern with possible field fires. Though lighter winds and RH's staying above critical thresholds should help limit field fires.

Aviation

Issued at 612 AM CDT Tue Oct 20 2026

VFR conditions will prevail at all TAF sites next 24hrs with few cirrus and clear skies. Winds will remain light and variable under high pressure.

Ilx Watches

None.