textproduct: Central Illinois

KEY MESSAGES

- An isolated shower or thunderstorm is possible in far southeast IL this afternoon, mainly over Lawrence county.

- After more seasonable temperatures and humidity levels early this week, expect very warm and more humid conditions to return to central and southeast IL during mid to late week. LREF has a 40-60% chance of heat indices reaching around 100 degrees or higher over the IL river valley Tue afternoon, and over much of central IL Wednesday afternoon with highs in the lower 90s. Heat indices in the upper 90s to around 100 look likely during the afternoon and early evening hours from Thursday through Saturday.

DISCUSSION

Issued at 300 AM CDT Sun Jul 12 2026

Short Term (Today through Monday Night):

The 08Z/3 am surface map shows weak 1015 mb low pressure over western tip of KY near the IL border with frontal boundary near the MO/AR border into southern KY. Meanwhile a weak 1021-1023 mb high pressure ridge was over central parts of WI and lower MI and extending into the southeast Ontario province. NE winds under 10 mph over central/se IL. Nearly clear skies over CWA with some patchy light fog/haze in eastern IL. Aloft a weak 586 decameter 500 mb low near the Ohio/KY border was embedded in an upper level trof from New Brunswick Canada sw across the Ohio river valley and into the mid MS river valley. Out West an expansive 500 mb high pressure ridge with 595-599 decameter heights was over the Rockies and nosing into the Northern Plains.

Some patchy shallow ground fog in eastern IL to lift by mid morning. Latest CAMs shows weak surface low pressure moving se into south central KY and north central TN later today, while high pressure ridge slowly settles down into the southern Great Lakes region. The upper level trof pivots se into the TN river valley. Brunt of it convection and deeper moisture will be southeast of CWA today. We just have a slight chance of showers and possible thunderstorms over Lawrence county this afternoon. Scattered cumulus clouds to develop in southeast IL later this morning and afternoon giving partly to mostly sunny skies, while just few cumulus clouds over central IL where sunny to mostly sunny skies expected. NE winds 8-15 mph and gusts to around 20 mph east of the IL river. Highs in the low to mid 80s, warmest from the IL river nw. Dewpoints in the 60s over central IL and lower 70s in southeast IL. Fair tonight with lows in the low to mid 60s.

High pressure ridge gets closer to central IL on Monday as frontal boundary pushes down into the northern Gulf Coast States. A fair amount of sunshine expected Monday with few cumulus clouds Mon afternoon over the Wabash river valley. The 500 mb ridge builds into the upper MS river valley and western Great Lakes on Monday with a 600 decameter 500 mb high over southern MN by sunset Monday. This will start our warm up as it builds closer to central IL with highs in the mid to upper 80s Monday, warmest over the IL river valley. Heat indices Monday afternoon around 90F in eastern IL and 90-95F west of I-57, highest over the IL river valley.

Long Term (Tuesday through Sunday):

The strong and large mid/upper level high pressure ridge will continue to dominate the Midwest and nosing into the Ohio river valley much of this week. The weak upper level low over the southern TN river valley Tue drifts westward into AR on Wed. Convection chances should stay south of CWA Tue and Wed with 20-30% pops in far southern/sw IL (south of I-64) Tue afternoon and Wed afternoon. Highs Tue in the upper 80s/lower 90s, warmest from I-72 north where heat indices Tue afternoon likely reach around 100F, with mid to upper 90s heat indices in southeast IL. Currently Wed appears to have highs in the lower 90s over much of CWA with heat indices in the upper 90s and lower 100s Wed afternoon, highest from I-72 north. NBM still appears to be suppressing dew points a bit too much, given the recent wet weather and evapotranspiration form mature crops (corn/soybeans). Dewpoints at least in the low to mid 70s expected Tue through at least Saturday. Heat indices in the upper 90s to around 100 degrees look likely each afternoon/early evening from Thu through at least Saturday and possibly higher.

The strong mid/upper level ridge retrogrades westward into the Central Plains and Rockies late this week with upper level troffing over the eastern Great Lakes, New England and mid Atlantic region. This puts IL in a Northwest upper level flow and may see some northern stream short waves/disturbances tracking into the Great Lakes and Ohio river valley from Friday into next weekend. Best chances of convection still appears to be northeast of central IL closer to the Great Lakes where there will likely be frontal boundaries, but we do have slight chances of showers/thunderstorms at times from Fri through next weekend.

The Climate Prediction Center (CPC) 8-14 Day Outlook July 19-25th has a 35-40% chance of above normal temperatures over IL. Precipitation is trending near normal, except around a 35% chance of above normal precipitation in east central and southeast IL.

AVIATION /12Z TAFS THROUGH 12Z MONDAY/

Issued at 550 AM CDT Sun Jul 12 2026

High pressure ridge over central parts of WI and lower MI and ridging into central Iowa, will settle into the southern Great Lakes region during tonight into Monday morning. This should provide fair weather to the central IL airports through 12Z/7 am Monday. A light fog/haze could occur until 13Z at DEC and CMI with 20% chance of MVFR vsbys. Otherwise, few to scattered cumulus clouds with 3-5k ft bases to appear between 14-15Z and dissipate by sunset. NNE to NE winds around 5 kts at dawn to be NE and increase to 7-12 kts after 14-15Z with few gusts of 14-19 kts possible over eastern airports (BMI, DEC and CMI). NE winds diminish back to around 5 kts at 00-01Z. CAMs are limited with patchy fog formation overnight and kept out of TAFs with somewhat drier air in place.

ILX WATCHES/WARNINGS/ADVISORIES

None.