948
FXUS63 KILX 311655
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1155 AM CDT Mon Aug 31 2026

.KEY MESSAGES...

- Hot and mostly dry weather is forecast through mid week, with
  afternoon heat indices peaking above 100 degrees in west-
  central Illinois today and areawide Tuesday through Thursday.

- A Heat Advisory is posted from this afternoon through
  Thursday afternoon southwest of Marshall, Woodford, McLean,
  Champaign and Edgar counties.

&&

.DISCUSSION...
Issued at 345 AM CDT Mon Aug 31 2026

Main weather story this week will be the late season heat wave,
with afternoon heat indices reaching the upper 90s to around 100
today and Friday and 100-105 Tuesday through Thursday. We
expanded the heat advisory ne to Stark, Peoria, Tazewell, Logan,
DeWitt, Piatt, Douglas, Coles and Clark counties from this
afternoon through Thu afternoon. We may eventually need to
expand the heat advisory further ne over the remainder of CWA
(Marshall, Woodford, McLean, Champaign, Edgar and Vermilion
counties) from Tuesday through Thursday.

The 08Z/3 am surface analysis shows 1020-1022 mb high pressure
over the Appalachians and mid Atlantic States. Meanwhile a
frontal boundary extended from near the MN and Dakotas border
into central Nebraska. A light SSE flow of warm and rather humid
air mass was over IL. 3 am temps were in the upper 60s to mid
70s while dewpoints were in the low to mid 60s. Patches of
mid/high clouds were in eastern IL and from Galesburg to Decatur
ne and more widespread clouds in ne and northern IL where
scattered showers were from Lacon to Hoopeston northeast and
tracking ESE. A 30-45 kt sw low level jet extended from central
KS ne over eastern Iowa, central/se WI and nw IL and helping
support these showers. As sw low level jet wanes during the
morning, these showers and isolated thunderstorms north of I-74
should diminish. Strong 500 mb high pressure ridge over the mid
MS river valley to build northward with 500 mb heights rising to
or above 594 decameters over CWA. 850 mb temps to rise to 22-24C
this afternoon and warmest over western CWA. Skies to become
partly to mostly sunny today over central/se IL and SSW winds
10-15 mph and gusts to around 20 mph to bring in the heat with
highs 90-96F (warmest south of I-70 and from Springfield sw).
Heat indices this afternoon peak in the upper 90s to around
100F, warmest readings near or just above 100F over western CWA
and from highway 50 south in southeast IL.

Nocturnal low level jet to our north/nw tonight could spark some
convection overnight into Tue morning but should stay along and north
of I-80. GFS model is an outlying with convection getting as far
south as I-72 late tonight and Tue morning. The strong
mid/upper level ridge stays near IL Tue/Wed with temperatures
getting a bit higher into the 90s over CWA and afternoon heat
indices 100-105F (peaking around Wed). Will likely need to
expand heat advisory further ne over rest of CWA during mid
week. Mid/upper level ridge flattens on Thu and could see 20-30%
chance of convection getting into northern/ne CWA by Thu
morning. Highs Thu in the lower 90s ne CWA and mid to upper 90s
sw CWA with afternoon heat indices 100-105F.

Forecast models continue to show 500 mb high pressure ridge
retrograding westward into the Central Plains and MO valley late
this week and this weekend with IL getting into a nw and
possibly more unsettled flow. NBM has slight chances of
convection over much of CWA overnight Thu night and Fri and
again overnight Fri night and Sat. May see higher chances of
convection during this time frame but too difficult to pin down
in this pattern that far out. Does look like the heat wave eases
slightly late this week into the weekend with more clouds
expected and possible convection chances. Highs Fri in the lower
90s with afternoon heat indices in the upper 90s to near 100F.
Highs of 85-90 on Sunday/Monday with dry weather expected as
upper level heights rise again over IL with ridging from the
Central Plains.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1155 AM CDT Mon Aug 31 2026

VFR conditions are expected through the 18z TAF period. Breezy,
south-southwest winds this afternoon will lessen this evening to
less than 10 knots overnight.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT Thursday for ILZ027>029-036-037-
040>044-047>056-061>063-066>068-071>073.

&&

$$

KEY MESSAGES...07
DISCUSSION...07
AVIATION...Copple