361
FXUS63 KILX 201046
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
546 AM CDT Sun Sep 20 2026

.KEY MESSAGES...

- A Marginal Risk (level 1 of 5) of severe weather exists south
  of the I-72 corridor today. The primary risk will be isolated
  strong wind gusts during the afternoon and early evening.

- Much cooler weather will be on tap this week as high
  temperatures drop into the 60s everywhere north of I-70 Monday
  through Wednesday.

&&

.DISCUSSION...
Issued at 322 AM CDT Sun Sep 20 2026

A 25-30kt 850mb jet streak oriented from the Texas panhandle
northeastward to Iowa continues to provide the necessary fuel
for repeated clusters of convection from eastern Iowa across
northern Illinois early this morning. As expected, the bulk of
this activity is remaining north of the KILX CWA...with only
locations along/north of an Avon to El Paso line occasionally
being grazed. While the heaviest rainfall will stay to the
north, will need to keep an eye on a trailing line of
showers/thunder currently extending from southeast Iowa into
north-central Missouri. 00z CAMs have not handled the precip
particularly well: however, based on radar trends, it appears at
least scattered convection will push into the Illinois River
Valley toward dawn and approach I-55 by mid-morning. Given
the current set-up, have focused 60-80 PoPs along/north of I-72
this morning. Convective re-development will likely occur this
afternoon along the residual outflow boundary left behind by the
morning showers...with the most probable location of the
boundary being south of I-72. While most CAMs are largely dry,
think scattered thunderstorms will develop within the marginally
unstable/sheared environment during peak heating. 00z HREF
shows ensemble mean SBCAPEs of just 1500J/kg, but 0-6km shear of
around 30kt. While these parameters certainly do not point
toward widespread severe weather, think a few of the stronger
cells may be capable of gusty 50-60mph wind gusts between 2pm
and 8pm south of I-72. Areal coverage of the afternoon cells
will be low, with just 20-40 PoPs within the SPC Day 1 Marginal
Risk area.

Showers and thunderstorms will become a bit more numerous
across the southern half of the CWA tonight as a weak LLJ
interacts with the outflow/frontal boundary. Based on model
consensus, have focused highest PoPs of 50-60% south of I-72.
While the persistent front responsible for the disturbed weather
over the past few days drops south of central Illinois on Monday,
trailing upper-level energy will keep scattered showers in the
forecast before gradually tapering off and coming to an end by
Tuesday.

The main weather story for the week ahead will be the significant
pattern shift to much cooler temperatures. Highs will drop into
the 60s everywhere north of the I-70 corridor Monday through
Wednesday before slowly moderating back into the 70s by the end
of the week. The coolest night ahead still appears to be
Tuesday night when lows reach the lower to middle 50s. Even
cooler readings in the upper 40s are possible in favored low-
lying/rural spots as the 00z NBM indicates a 30-50% chance of
lows dipping below 50 degrees along/west of I-57...and a 60-70%
northwest of the Illinois River.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 546 AM CDT Sun Sep 20 2026

Clusters of convection continue to track across northern
Illinois into northern Indiana early this morning: however,
activity immediately upstream to central Illinois has weakened
considerably. 1030z/530am radar imagery shows a weakening line
of showers crossing the Mississippi River, and am expecting
those to primarily impact KPIA/KBMI over the next few hours.
Have removed all mention of thunder with this first round of
light precip. Later this afternoon, most models suggest
scattered re-development along residual outflow boundaries.
Exact location and timing of late day storms remains tricky, so
have continued the PROB30 groups for thunder at all sites. A
cold front currently across Iowa/Missouri will slowly pass early
this evening, bringing an end to the convection. Winds will
switch to NE and gust to around 20kt after FROPA. In addition,
all forecast model guidance shows ceilings lowering to IFR.

&&

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

&&

$$

KEY MESSAGES...Barnes
DISCUSSION...Barnes
AVIATION...Barnes