textproduct: Central Illinois

KEY MESSAGES

- Frost will be likely across areas generally east of the IL river through 9 am as temperatures dip into the low to mid 30s by dawn. A frost advisory remains in effect until 9 am cdt from McLean, Logan and Sangamon counties east. Patchy frost is possibly in eastern IL overnight and early Monday morning with lows in the mid to upper 30s.

- Temperatures will begin a warming trend this week. Highs today in the mid to upper 60s, will climb into the mid 70s to lower 80s from Thursday into next weekend.

DISCUSSION

Issued at 300 AM CDT Sun Oct 18 2026

The 08Z/3 am surface analysis shows 1035 mb high pressure over the upper Ohio river valley (southeast Ohio, western PA and northern WV) and ridging sw into the mid MS river valley including southeast IL. Nearby high pressure ridge providing clear skies across IL, with light south to SE winds in central IL and near calm winds in southeast IL. Temperatures were in the mid 30s to around 40F at 3 am, with Robinson, Marshall and Paris close to freezing. Dewpoints were in the low to mid 30s and this is how cool some areas will likely get by dawn east of the IL river valley. Will continue the Frost Advisory until 9 am for central/eastern CWA from McLean, Logan and Sangamon counties east where frost will be more widespread, while patchy frost over the IL river valley.

High pressure to settle over New England and the mid Atlantic States by sunset and continue to ridge back into IL through Monday. Southerly winds increase some today especially northern/nw CWA with gusts 15-20 mph by afternoon. Ample sunshine today with nearby surface high pressure along with mid/upper level ridge over IL (500 mb heights over 585 decameters). Milder and seasonable highs in the mid to upper 60s. Seasonably cool night ahead tonight with lows in the upper 30s to around 40F, with mid 30s possible near the IN border. Patchy frost possible in eastern IL later tonight and early Mon morning, though less coverage than early this morning. High/cirrus clouds to increase from the west late Mon morning into Monday afternoon, though still a fair amount of sunshine. Dry atmosphere continues to modify with highs Monday in the upper 60s and lower 70s. Lows Mon night in the upper 30s and lower 40s, coolest in eastern IL.

Another large high pressure system moves eastward from Ontario across Quebec Province on Tue/Wed while ridging into IL and continues fair/dry weather. Highs 70-75F on Tue and a few degrees warmer Wed, in the mid 70s. Lows Tue night in the low to mid 40s, coolest in eastern IL again. Yet another high pressure system moves eastward over the northern Great Lakes Thu and into southeast Canada and New England late this week while ridging toward IL. Meanwhile have strong mid/upper level ridge building over IL late this week. These two features to ensure dry weather with warmer temperatures with highs in the mid 70s to lower 80s from Thu through next Sunday.

The Climate Prediction Center (CPC) 6-10 Day Outlook for Oct 23-27th has a 65-75% chance of above normal temperatures over central and southeast IL, with a 40-50% chance of below normal precipitation. This bodes well for the fall harvesting which is more than half way complete over Illinois. CPC 8-14 Day Outlook for Oct 25-31st has a 60-70% chance of above normal temperatures and precipitation trending near normal, except trending slightly below normal (33-40%) near the Indiana border.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 600 AM CDT Sun Oct 18 2026

VFR conditions will prevail at all TAF sites next 24hrs with clear skies expected. Winds will be light and variable early this morning, then become south at around 10 kts. Light and variable return for the evening hours.

ILX WATCHES/WARNINGS/ADVISORIES

Frost Advisory until 9 AM CDT this morning for ILZ038-042>046- 051>057-061>063-066>068-071>073.