551
FXUS63 KILX 202325
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
625 PM CDT Mon Jul 20 2026

.KEY MESSAGES...

- Air Quality: Smoke will thin this evening and tonight before
  a cold front brings slightly higher smoke levels once again
  Tuesday, keeping air quality in the moderate category.

- Severe Weather: Thunderstorms are expected tonight into
  Tuesday. While uncertainty remains regarding how far south
  the main line of storms will track, any severe storm could
  produce damaging winds and locally heavy rain.

- Late Week Outlook: Drier and slightly cooler conditions
  arrive Wednesday and Thursday, followed by a 20% to 30% chance
  of storms returning Friday.

&&

.UPDATE...
Issued at 624 PM CDT Mon Jul 20 2026

Bow echo across Iowa has been pushing southeast the last few
hours, and is approaching the Quad Cities this hour. Severe
Thunderstorm Watch was recently issued for areas from about I-55
northwest. WoFS model guidance is in decent agreement with
pushing this line into our northern CWA (Galesburg-Lacon), but
is a little more sketchy on how far southeast it may make it.
SPC mesoanalysis does have a fairly tight CAPE gradient over
western Illinois at this hour, though it will work its way
eastward with time. PoP`s were updated earlier to increase rain
chances over the northwest half of the forecast area for this
evening.

&&

.DISCUSSION...
Issued at 203 PM CDT Mon Jul 20 2026

Air Quality and Smoke:
Smoke stemming from wildfire activity across Canada and the
Upper Midwest continues to persist across portions of the Great
Lakes and Midwest. Recent HRRR near-surface smoke guidance
points toward a slight improvement in smoke concentrations as
prevailing south/southwesterly flow overspreads the region,
effectively shunting the plume northward. While EPA data
indicates PM2.5 levels remain unhealthy for sensitive groups
today, we anticipate a period of improvement this evening and
overnight. As a cold front approaches tomorrow, smoke levels may
see a slight increase behind the front, keeping AQI levels in
the moderate category.

Severe Weather Outlook: Tonight and Tuesday:
A cold front currently bisecting Minnesota is projected to push
southeast across central Illinois overnight. Ahead of this
feature, a decaying cluster of thunderstorms is tracking
southeast, though southward propagation along the instability
gradient--currently situated near our western CWA border--has
kept the most robust activity just outside our region. We
anticipate these storms will continue to weaken as they become
outflow dominant.

Looking ahead, convective re-development is expected late this
afternoon across the Upper Midwest, with these storms
subsequently tracking southeast into central Illinois late this
evening and overnight. A highly favorable parameter space for
severe weather remains in place ahead of the front; latest RAP
advertises MLCAPE values of 3000-4000 J/kg combined with 40-50
kt of deep-layer shear to our northwest, supportive of severe
convective development upstream. The cold front continues to
trend slightly slower, which implies that most of central
Illinois will see storm arrival well after peak heating.

A modest southwesterly low-level jet will develop this evening,
assisting in advecting instability into central Illinois. While
mean steering flow generally drives storms from the west-
southwest to east-southeast, Corfidi vectors suggest southward
propagation into the region of better instability and LLJ
forcing. However, confidence regarding the southernmost extent
of this propagation remains low. Convective allowing models
(CAMs) exhibit a significant spread; the HRRR suggests severe
storms may skirt the I-74 corridor, whereas more robust
solutions like the FV3 drive a solid line south to the I-70
corridor. We are currently discounting the NAMNest solution,
which misses the local area entirely, as an outlier, but it
further illustrates the uncertainty of the forecast.

The uncertainty in the evolution of tonights convection
snowballs into Tuesday, leading to low confidence in the precise
position of the effective cold front where storms are expected
to redevelop. Strong instability is anticipated ahead of the
front, and while redevelopment of storms near the I-70 corridor
remains possible, the majority of models now favor this activity
developing further south. Regardless of the exact location of
midday redevelopment Tuesday, an attendant severe weather threat
persists.

Extended Forecast: Wednesday through the Weekend:
The remainder of the work week, beginning Wednesday, will be
characterized by drier air and slightly below-normal
temperatures. A strong Canadian high-pressure system will spread
southeast across the Midwest, keeping highs generally in the
low to mid 80s with no notable precipitation chances through
Thursday. A signal for warm advection-driven storms exists for
Thursday night off to our west, which may move into portions of
central Illinois on Friday (20-30% chance). A warming trend will
commence next weekend as the surface ridge axis shifts to our
east, allowing for a return of warmer southerly flow.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 624 PM CDT Mon Jul 20 2026

Currently watching a bow echo of severe convection moving
southeast out of Iowa, and KPIA has the best chance of being
impacted, likely in the 01-02z time frame. Some uncertainty with
the southeast extent of this line, so PROB30 mentions will
address areas further southeast. A cold front is expected to
move through the area toward 12z and shift winds to the
northwest, and some gusts over 20 knots are likely by early
afternoon.

The area of smoke and haze has been diminishing from west to
east, though some MVFR visibilities will linger at KCMI and KDEC
for another couple hours.


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Air Quality Alert until midnight CDT tonight for ILZ027>031-
036>038-040>057-061>063-066>068-071>073.

&&

$$

KEY MESSAGES...Deubelbeiss
UPDATE...Geelhart
DISCUSSION...Deubelbeiss
AVIATION...Geelhart