297
FXUS63 KILX 040955
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
455 AM CDT Mon Aug 4 2025

.KEY MESSAGES...

- Residual smoke from wildfires will linger over central Illinois
  the next few days, though much of the time the greatest
  concentrations will remain aloft.

- There is a low (20-30%) chance for scattered showers and
  thunderstorms this afternoon. Severe weather is not anticipated,
  but there could be a few innocuous funnel clouds.

- A warming trend will push afternoon temperatures into the upper
  80s by the end of the week.

&&

.DISCUSSION...
Issued at 147 AM CDT Mon Aug 4 2025

Early morning water vapor imagery shows a compact upper-level low
over the Mid-Mississippi Valley, which is expected to linger over
central Illinois for the next few days due to a split-flow regime.
Beneath it all, a subtle surface trough has moved into eastern
Illinois, increasing dewpoints to the mid-60s. This influx of
moisture and convergence near the surface trough axis is expected
to lead to widely scattered showers and storms this afternoon,
particularly near and east of I-55.

A more exciting prospect is the potential for funnel clouds, with
the synoptic pattern appearing quite favorable for their
development today and tomorrow under the upper-level low. All the
necessary ingredients are expected to align: steep low-level lapse
rates will form this afternoon beneath partly sunny skies, and
sufficient surface vorticity and low-level CAPE will develop near
the surface trough axis. The funnel cloud narrative is supported
by mesoscale models, with both the NAM12 and RAP13 indicating NST
parameter values exceeding 1 by the afternoon.

By Wednesday, the upper low will open and shift eastward due to
strong shortwave energy moving across the Central Plains. This,
along with another shortwave reaching the Pacific Northwest, will
push the upper ridge axis towards the Mid-Mississippi Valley. As a
result, temperatures will steadily rise to the mid-to-upper 80s by
mid-week.

Rain chances appear minimal for the latter half of the week,
despite the return of warmer and more humid conditions. The jet
stream is expected to be displaced north of our area, and a
blocking pattern seems likely to persist until at least Friday.
Global deterministic models indicate that it wont be until
Saturday or Sunday that a northern stream shortwave and its
associated cold front will move through the Midwest, breaking down
the ridge and potentially bringing rain back to central Illinois.
Right now, our blended (NBM) and multi-model ensemble (LREF)
guidance suggest low/medium (20-50%) chances for rain this
weekend. These probabilities are likely tamped down by notable
timing/placement differences. Anecdotally, I would expect for the
weekend rain probabilities to increase in the coming days.


MJA

&&

.AVIATION...  (For the 12z TAFs through 12z Tuesday Morning)
Issued at 448 AM CDT Mon Aug 4 2025

VFR conditions will persist through this TAF period as surface
high pressure remains anchored just north of the regional
terminals. Widely scattered thunderstorms remain a possibility
later this afternoon, particularly between 18z-00z.  Both
confidence and coverage remain low enough to favor a PROB30 for
TSRA, and not a TEMPO group.

Low-level winds will maintain its east component through late
tonight, with speeds between 3-8 kts.

MJA

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$