676
FXUS63 KILX 290842
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
342 AM CDT Sat Aug 29 2026

.KEY MESSAGES...

- A late season heat wave is forecast to impact central and
  southeast IL for the upcoming week starting Sunday. Daily
  heat indices are projected to reach around 100 Monday
  afternoon, 100-105F Tuesday through Thursday and upper 90s to
  around 100 Friday.

- Precipitation chances are low for the next several days,
  though an active storm track is forecast just to our north
  for much of next week.

&&

.DISCUSSION...
Issued at 330 AM CDT Fri Aug 28 2026

1023 mb high pressure over the eastern Great Lakes and ridging
sw into IL and providing fair skies with some thin cirrus clouds
especially western and northern IL. Patchy shallow ground fog
noted near the Wabash river valley, with Robinson airport down
to 1.5 miles (varying from 1/4 to 5 miles) and Paris having a
light fog/haze at 5 miles. The latest CAMs are more aggressive
with fog formation in eastern IL where pockets of dense fog in
east central IL from I-57 east through 12Z-13Z. Though fog
currently not as widespread as HRRR and RAP13 are forecasting so
mentioned patchy fog in eastern IL until 8 am with areas of fog
near the Wabash river/Indiana border.

An MCS over eastern SD, nw Iowa and central/sw MN will affect
Iowa and WI with showers/thunderstorms today with a weakening
outflow boundary moving se into the IL river valley during this
afternoon. HRRR was more aggressive with scattered showers
during mid/late afternoon nw of I-55 though drier lower levels
will likely dissipate these with sprinkles possible northern/nw
CWA this afternoon. We will see increasing mid/high clouds from
the west/nw during today with few-scattered cumulus clouds also
forming by midday/afternoon. South to SSE winds 5-15 mph today
with few gusts 15-20 mph at midday and afternoon. Highs 83-88F
today, coolest ne of I-74 where more clouds expected today.

Warm advection/isentropic lift increases tonight into Sunday
morning, as a warm front lifts ne across CWA overnight into
Sunday morning. Warm front to be near the WI/IL border by sunset
Sunday, with our CWA likely staying in warm sector much of the
upcoming week. We have slight chance of convection over Knox
and Stark counties overnight into early Sunday morning. Lows
overnight 65-70F and mildest over the IL river valley.

Main weather story will be the extended heat wave to impact
central and southeast IL much of the upcoming week. 500 mb
heights of 588-590 decameters this morning to increase to
594-596 decameters Monday through Wed High confidence remains
in a late season thermal ridge amplifying across the Mid-
Mississippi Valley for much of next week. Deterministic and
ensemble guidance align on 500 mb heights swelling to 593-596
dam, with 850 mb temperatures ranging between +22C and +24C.
Extreme Forecast Index (EFI) values from the ECMWF range between
0.80 and 0.85 for max temperatures Monday through Wednesday and
only slightly lower late this week. A stronger mid/upper level
ridge near central IL would keep us hotter along with the "ring
of fire" with convection from MCS`s to generally stay north of
central IL. Highs Sunday in the upper 80s/lower 90s and low to
mid 90s Monday with heat indices peaking around 100F Mon
afternoon, warmer over western CWA. Tue and Wed appear to be the
hottest days with highs in the mid to upper 90s with areas from
Springfield to Lawrenceville getting close to 100F. Afternoon
heat indices likely reach 100-105 and may be close to heat
advisory criteria then. The last time Springfield reached 100
or higher was July 31, 2012 when it was 101 and we were also in
a severe drought much of that summer. The Globe EF1 for ILX CWA
shows 0.90 Monday, 0.97 Tue, 0.99 Wed and 0.94 Thu.

As upper level ridge starts to flatten and retrograde west late
this week, we could see low convection chances starting Thu and
going into Labor Day Weekend. Still hot on Thu with highs in the
lower 90s from I-74 ne (pm heat indices around 100) and upper
90s over SW CWA and southeast IL (pm heat indices 100-105).
Highs by next Saturday and Sunday (Sep 5-6th) in upper 80s and
lower 90s which is still about 10 degrees warmer than normal for
early September.

The Climate Prediction Center (CPC) 8-14 Day Outlook for Sep
5-11 has around 60% chance of above normal temperatures over
central/se IL with precipitation trending near normal. CPC Week
3-4 Outlook for Sep 12-25 (release Aug 28) has equal chances of
above and below normal temperatures and precipitation.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1216 AM CDT Sat Aug 29 2026

Upstream thunderstorms across the central and northern Plains
will result in an increase in mid- and high-level cloudiness
prior to 12z.

Short-term model guidance is hinting at scattered, high- based
showers moving across the central Illinois terminals between
18z-00z. Low-level dry air will likely prevent these showers
from reaching the ground in most areas, but virga and the
effects of evaporative cooling could result in gustier surface
winds during this period. We have therefore added a mention of
15-20 kt gusts in the TAFs through the afternoon and early
evening hours. Winds will primarily be from the south and
unidirectional with height throughout this TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

KEY MESSAGES...07
DISCUSSION...07
AVIATION...MJA