386
FXUS63 KILX 270531
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1231 AM CDT Sun Jul 27 2025

.KEY MESSAGES...

- A medium probability (15-40% chance) of flash flooding exists
  today and tonight. A Flash Flood Watch is now in effect for
  portions of central Illinois where an additional 1 and 4 inches
  of rainfall is forecast.

- A Heat Advisory is in effect along and south of a Jacksonville
  to Danville line today. The oppressive heat will spread back
  northward across all of central Illinois Sunday through Tuesday
  as heat index values once again reach 105-115.

- A low probability (5-15% chance) of severe weather exists north
  of the I-70 corridor today...with the primary risks being
  scattered damaging wind gusts and large hail.

&&

.DISCUSSION...
Issued at 1246 PM CDT Sat Jul 26 2025

Radar and satellite analyses show a decaying Mesoscale Convective
Vortex (MCV) moving across northern Illinois, with two outflow
boundaries pushing south across central Illinois. These
boundaries have mostly converged and eroded near a line extending
from roughly Jacksonville to Gibson City. North of this boundary,
conditions may remain stable enough to prevent new convective
development this afternoon. Near and south of the boundary,
CAPE/shear profiles are supportive of strong-to-severe storms and
the potential for urban and small stream flooding.

Many areas in west-central and north-central Illinois have already
received multiple inches of rainfall in the past 24 hours, with
rates exceeding 1-2 inches per hour. Given a similar air mass near
and south of the residual outflow this afternoon, additional heavy
rainfall pockets are anticipated into this evening across portions
of central and southeast Illinois.

Otherwise, the dangerous heat has continued into this afternoon,
with areas within the Heat Advisory already displaying heat index
values between 97-107 F even despite increasing cloud cover.

By Sunday, a robust heat dome will extend northward into central
Illinois, shifting the effective surface boundary out of our area
and reducing upper-level flow and deep-layer shear. While boundary
layer conditions will remain moderately unstable Sunday afternoon,
especially near and south of the I-72/Danville corridor, within a
wide area of very high PWATS (> 2 inches), the poor deep-layer
shear suggests somewhat limited convective coverage and intensity.
The primary concern will be torrential rainfall from any
developing multi-cell clusters in the vicinity of a remnant
outflow, wherever it evolves.

Our posture on heat headlines have largely remained unchanged,
with the current heat advisory most likely needing an
extension/expansion across the region through Wednesday. While
forecast guidance has persistently highlighted Monday and Tuesday
as the hottest days of the period, some concern lingers regarding
the evolution of upstream convection each of those days. This
potential has come into better focus with this morning`s suite of hi-
res guidance, where all of the HRRR, 3km NAM, ARW, and FV3 all
depict decaying convection entering northern/central portions of
Illinois by Monday morning. This convective debris could be enough
to thwart an upgrade to an Extreme Heat Warning on Monday, at least
for a good chunk of our area. As a result, we will likely take a
more conservative day-to-day approach with heat headlines, extending
and expanding the current Heat Advisory as needed based on trends.

A major pattern change still looks on track to occur Wednesday
into Thursday, with significantly cooler and drier conditions
forecast by the back half of next week.

MJA

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1231 AM CDT Sun Jul 27 2025

A healthy cluster of thunderstorms is ongoing south of a Pittsfield
to Taylorville line late tonight, with this activity expected to
gradually spread east. Aside from a few isolated showers/storms it
appears that the majority of this will stay south of the
terminals, with PROB30 groups only mentioned at KSPI and KDEC.
Further north, fog development appears likely overnight with near
term guidance showing visibilities dropping as low as 3-5 SM
mainly at KPIA, KBMI, and possibly KCMI. Winds will be rather
light through the period aside from any increases with storms.
South winds overnight will veer to the southwest later this
morning with speeds below 10 kts. There is a low chance for
isolated shower/storm activity Sunday afternoon, but the higher
chances look to stay south of the airfields.

NMA

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 11 AM this morning to 7 PM CDT this evening
for ILZ027-029-031-036>038-040>043-047-048.

Flood Watch through this afternoon for ILZ031-037-038-041>048-
050>053.

Heat Advisory until 7 PM CDT this evening for ILZ044>046-049>057-
061>063-066>068-071>073.

&&

$$