433
FXUS63 KILX 110709
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
209 AM CDT Fri Sep 11 2026

.KEY MESSAGES...

- Dense fog will reduce visibility to a quarter mile or less
  across portions of central Illinois through mid-morning.
  Drive with caution and allow extra stopping distance.

- Isolated showers and possibly a brief funnel cloud or two are
  possible this afternoon and evening south of I-72, but the
  overall severe storm threat is very low.

- Summerlike heat returns this weekend with highs approaching
  90 degrees in parts of central Illinois, followed by periodic
  chances for thunderstorms next week along a stalled front.

&&

.DISCUSSION...
Issued at 201 AM CDT Fri Sep 11 2026

...Dense Fog This Morning...
Early this morning, surface high pressure centered over lower
Michigan extends southwestward into central Illinois. Light and
variable winds, combined with clearing skies from the west, have
set the stage for strong radiational cooling. Given the influx
of low-level moisture from recent rainfall, dense fog has
developed in several areas. As the ridge axis shifts eastward
over the next several hours, a developing southeasterly pressure
gradient may act to displace or dissipate the fog from east to
west. In the interim, a Dense Fog Advisory remains in effect for
portions of central Illinois, specifically from the lower
Illinois River Valley eastward through Springfield. Will monitor
observational trends closely for any needed expansions through
mid-morning.

...Upper Low This Afternoon and Evening...
Water vapor imagery early this morning reveals a potent mid-
level vort max digging southeastward across Oklahoma and
Arkansas. Model guidance suggests this wave will close off at
500mb as it lifts northeastward across southern Missouri and
into southern Illinois by late this evening and overnight.
Strong differential cyclonic vorticity advection (dCVA) ahead of
this feature will peak over central and southern Illinois mid-
to-late this afternoon. This forcing for ascent will align with
the right-entrance region of a modest 70-kt upper-level jet
streak, interacting with a weakly unstable environment. The GFS
is advertising MLCAPE values near 500 J/kg across central
Illinois by Friday afternoon. However, forecast soundings depict
elongated, `skinny` CAPE profiles, which should limit updraft
strength. Combined with negligible deep-layer shear, the overall
severe threat remains very low. In fact, weak updrafts may
struggle to grow deep enough to support lightning. Despite the
low severe risk, the proximity of the closed upper low does
present a conditional threat for funnel clouds. The RAP
highlights a few pockets of non-supercell tornado parameters
around 1-3 grazing our southern CWA border, though the primary
focus for this activity remains closer to the core of the low
within the LSX forecast area.

...Saturday and Sunday...
By Saturday, the closed upper low is projected to open into a
trough as it slowly moves eastward along the lower Ohio Valley.
A few lingering light showers are possible east of I-57, but the
vast majority of central Illinois will remain dry. To the
northwest, a cold front will advance across the Upper Midwest on
Saturday. An associated thermal ridge, characterized by 850mb
temperatures of 18-20C, will surge across central Illinois ahead
of the front. This will support a quick rebound in temperatures,
with widespread highs in the upper 80s and a few locations
hitting 90. As the front stalls over the region on Sunday, a
sharp thermal gradient will develop across the local area. Highs
north of the Illinois River are forecast to sit around 80,
while southern areas south of I-70 soar into the lower 90s.
While a few light showers or sprinkles cannot be ruled out near
the front, a prominent 700mb warm nose will keep deep convection
capped.

...Monday through Wednesday...
An active and unsettled weather pattern is anticipated for the
first half of next week. A high-amplitude upper-level wave is
progged to lift from the Pacific Northwest across the Canadian
Rockies Sunday night into Monday. In response, a deep surface
low will develop and trek from the Canadian Prairies toward
Hudson Bay between Monday and Tuesday. An associated warm front
will lift across the Great Plains Sunday night, acting as a
focus for nocturnal convection. Some decaying activity could
linger into portions of central Illinois as the warm front lifts
northward through the area on Monday. A better opportunity for
widespread showers and thunderstorms arrives Tuesday into
Wednesday as the trailing cold front pushes into and stalls
across the Midwest. A sharp north-to-south temperature gradient
will establish itself across the CWA, with highs ranging from
the upper 70s north to the lower 90s south. This period will
require close monitoring for potential severe weather, as the
upper-level jet dips into the Great Lakes, boosting deep-layer
shear across the stalled boundary.

...Thursday and Friday...
Unsettled weather looks to persist late next week as the
baroclinic zone is progged to linger across the Midwest, serving
as a focus for daily precipitation chances. Model solutions
begin to diverge regarding the exact placement of this frontal
boundary by Thursday and Friday; the GFS lifts the front
northward into the Great Lakes, whereas the ECMWF and GEM keep
the boundary stalled directly over the Midwest. While details
regarding timing and location remain low-confidence, the primary
takeaway is that daily chances for showers and thunderstorms
will continue near the front. Temperatures will remain highly
dependent on the front`s position, but current guidance
suggests a range from the 70s north to the upper 80s or low 90s
south.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1210 AM CDT Fri Sep 11 2026

Dense fog has developed over west-central Illinois and will expand
into central parts of the state through this morning. Highest
confidence in visibility falling below 1 mile is at western
terminals (KPIA, KSPI), with more transient development east of
there. Fog should improve by 13/14Z, parting way to light south-
southeast winds through the remainder of the day.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM CDT this morning for ILZ040-
047>051.

&&

$$

KEY MESSAGES...Deubelbeiss
DISCUSSION...Deubelbeiss
AVIATION...NMA