046
FXUS63 KILX 300526
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
1226 AM CDT Wed Jul 30 2025

.KEY MESSAGES...

- A Heat Advisory remains in effect for central IL into this
  evening, and across southeast Illinois through Wednesday
  afternoon.

- Thunderstorms will develop along a slow-moving cold front
  Wednesday, bringing a risk of strong storms and torrential
  rainfall.

- Cooler and less humid air follows the frontal passage for
  Thursday into the weekend.

&&

.DISCUSSION...
Issued at 212 PM CDT Tue Jul 29 2025

Outflow from last night`s upper Midwest derecho had cleared the
entire CWA by late morning. Temporary north winds in its wake
mixed slightly lower dew points down to the surface, mainly low-
mid 70s, though still upper 70s along/south of I-70. So while
peak heat indices this afternoon are a few degrees lower than
yesterday, still looking at widespread 100-105, another dangerous
day for those vulnerable to heat stress.

Overall quiet weather is expected across the local area through
tonight. Have a weary eye to the northwest, where a couple
thunderstorm complexes have developed over northern IA today along
a sharp CAPE gradient. Convective allowing models have had a poor
handle on this, and though the downstream environment is less
favorable for organized convection, this will bear watching given
strong instability building across southern IA and resulting CAPE
gradient just to our NW late this afternoon and evening.

Shortwave energy entering the Plains this evening along a firming
frontal zone will likely develop another large MCS across eastern
NE and western IA, spreading into western IL after daybreak Wed. A
weakening low level jet and unfavorable diurnal timing should
cause these storms to dissipate as they move into the CWA. However
with increasing afternoon instability, festering clusters of
loosely organized storms appear likely, given 20-30 kt deep layer
shear. Isolated damaging wind gusts are the primary severe risk,
as noted by SPC`s Day 2 Marginal risk for all of central/SE IL.
Locally heavy rain will also be a concern given very high PWATS
near 2.2" (for reference 2.4" is the record high for ILX
soundings). HREF LPMM shows pockets of 2-3" 3-hour QPF Wed
afternoon and evening north of I-72, so a localized flash flood
threat exists, highlighted in WPC`s Day 2 Slight risk.

Heat will again be a concern Wed, though with lower confidence on
location than recent days due to increased cloud cover and
convective outflow from the north. Current gridded forecast shows
heat indices peaking at 100-105F as far north as a Taylorville to
Paris line. In collaboration with adjacent WFOs, extended the
current Heat Advisory for these areas through Wednesday afternoon.

The frontal zone gradually works southeast through the CWA Wed
night and Thu, with waves of showers and storms diminishing from
the north through time. Major pattern shift behind the front due
to amplifying upper ridging over the Rockies and a deepening
eastern CONUS trough. This to bring northwest upper flow to the
region, ushering Canadian high pressure into the Great Lakes
through this weekend, and a pleasant airmass we haven`t seen
since early June. NBM continues to advertise 75-80F highs Thu-Sat
with lows dropping into the upper 50s.

25

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1226 AM CDT Wed Jul 30 2025

Light winds under an exiting surface ridge of high pressure may
result in patchy MVFR fog this morning. However, thicker cirrus from
thunderstorm anvils off to our west/Northwest should limit this,
especially at western airfields. A challenging forecast lies
ahead with several rounds of showers/storms possible over the next
24 hours. The first looks to arrive by mid to late morning as it
spreads across the area through early afternoon. Beyond that
PROB30 groups continue to handle additional chances due to very
low confidence. Wind directions will move around a lot today, but
speeds should remain light aside from convectively enhanced winds.

NMA

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 7 PM CDT this evening for ILZ052-054>057-
061>063-066>068-071>073.

&&

$$