977
FXUS63 KILX 241933
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
233 PM CDT Fri Jul 24 2026

.KEY MESSAGES...

- A Heat Advisory is in effect west of the I-57 corridor Sunday
  afternoon through Monday evening as heat index readings peak
  above 105 degrees.

- There is a 15-30% chance for severe weather along and
  northeast of a Lacon to Paris line on Monday as a cluster of
  thunderstorms potentially grazes central Illinois to the
  northeast.

&&

.DISCUSSION...
Issued at 233 PM CDT Fri Jul 24 2026

**** A Few Showers Tonight into Saturday Morning ****

18z/1pm surface analysis shows a nearly stationary frontal
boundary extending from near Kansas City into the Tennessee
River Valley. A short-wave trough dropping southeastward out of
the Upper Midwest is currently interacting with the boundary to
produce clouds and a few radar echoes across central Illinois.
Despite the radar presentation, only a few light sprinkles have
reached the ground in spots...as the 12z KILX upper air sounding
indicated ample dry air below 600mb. Forecast soundings show the
atmosphere slowly moistening from the top-down, which will
eventually allow showers to become more numerous late tonight
into Saturday morning before the short-wave sinks into the Ohio
River Valley. Most CAMs suggest scattered sprinkles this
afternoon, followed by a lull in precip until late tonight when
the 850mb jet streak modestly increases to 20-30kt. Scattered
showers will develop...mainly along/south of a Rushville to
Lawrenceville line. May even see a rumble of thunder or two as
MUCAPEs reach 1000-1500J/kg. Once the wave passes, short-wave
ridging in its wake will lead to an end to the light showers by
midday Saturday, followed by a partly to mostly cloudy and dry
afternoon.


**** Typical Summertime Heat Returns ****

Upper ridging currently centered over the Desert Southwest will
build northeastward early next week: however, its progress will
be curtailed by a deep low over Hudson Bay. Pieces of energy
pivoting around the low will drop into the eastern Great Lakes
and New England...maintaining the northwesterly flow pattern
across the Midwest. As upper heights rise, temperatures will
climb into the upper 80s and lower 90s on Sunday, then into the
lower to middle 90s on Monday. With dewpoints rising back into
the 70s, heat index readings will reach 100 degrees or higher
across the entire CWA by Sunday afternoon. Things get a little
more interesting on Monday as a convective complex impacts parts
of the region. Confidence on the exact track/timing of the
complex remains low, but the synoptic pattern and early signs
from some of the longer-range CAMs such as the RRFS suggest the
storms may only graze central Illinois to the northeast. This
could potentially send an outflow boundary W/SW and impede
heating across the E/NE KILX CWA on Monday. The 00z Jul 24 LREF
backs up this theory as it shows only a 20% chance or less of
heat index values exceeding 105 degrees east of the I-57
corridor Monday afternoon. As such, decided to issue a Heat
Advisory across all locations west of I-57 for Sunday afternoon
through Monday evening. Future shifts may opt to expand the
advisory further east across part or all of east-central
Illinois depending on convective trends.


**** Severe Weather Potential Sunday Night into Monday ****

The latest convective outlooks from SPC have pulled the severe
weather risk area a bit further northeast than previously
thought. Despite rising upper heights, the flow across the
Midwest/Great Lakes will remain northwesterly. As such, will
need to keep a close eye on the track/timing of short-wave
troughs cresting the ridge, then digging southeastward through
the Great Lakes. Its still too early to pinpoint this process:
however, the 06z/12z RRFS offers an early glance at a potential
scenario featuring a wave triggering a storm cluster across
central Wisconsin late Sunday night dropping southeastward
across Lake Michigan into northern/central Indiana Monday
morning. Previous runs of the RRFS showed this convection
directly impacting the NE KILX CWA around Champaign/Danville:
however, the 12z run is further east and much less impressive.
Even if the initial storm cluster completely misses central
Illinois to the northeast, the residual outflow boundary could
serve as the focus for convective re-development across the E/NE
CWA Monday afternoon/evening. With SBCAPEs in excess of
3000J/kg and 0-6km bulk shear of 30-40kt, any cells that form in
this environment will be capable of damaging wind gusts and
large hail and perhaps a couple tornadoes. Stay tuned to later
forecasts for additional details.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1248 PM CDT Fri Jul 24 2026

Despite a pronounced dry layer below 600mb as evidenced by the
12z KILX upper air sounding, a weak short-wave is generating
enough lift to trigger scattered sprinkles/very light showers
along/north of I-72 early this afternoon. Have included VCSH
accordingly. NAM/RAP forecast soundings show ceilings gradually
dropping from around 10,000-12,0000ft down to 4,000-5,000ft
toward sunset. As the wave traverses the area, the HRRR/RAP
suggest ceilings lowering to MVFR late tonight into Saturday
morning as showers become a bit more numerous. Based on the
latest HRRR output, have opted to maintain VCSH at the I-74
terminals, but have gone with prevailing -SHRA at KSPI/KDEC
after 11z/12z. The showers will drop south of the terminals
toward midday, followed by a return to VFR conditions by
Saturday afternoon.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Sunday to 9 PM CDT Monday for
ILZ027>031-036>038-040>044-047>054-061.

&&

$$

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