950
FXUS63 KILX 292302
AFDILX

Area Forecast Discussion...Updated Aviation
National Weather Service Lincoln IL
602 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- There is a very low (15%) chance central and southeast Illinois
  exceeds 1 inch of rainfall over the next 7 days, and only a
  medium (40%) chance of exceeding one-quarter inch. Source(s): NBM
  (13z) and LREF (00z) QPF.

- There is a low (25%) chance for thunderstorms next Wednesday,
  and severe weather is not anticipated at current time.

- At least some signal for near-record low temperatures is
  emerging for late next week, particularly in the Thursday/Friday
  timeframe.

&&

.DISCUSSION...
Issued at 211 PM CDT Fri Aug 29 2025

A non-zero chance for rain exists both today and Saturday, especially
in west-central Illinois, due to lingering surface convergence
near a weakly-forced, high-arching, backdoor cold front. Satellite
analysis shows an expanding cumulus field along this boundary,
and the latest HREF output suggests a 20-30% chance of scattered
showers developing in this convergence zone. The chance of a
thunderstorm is very low (10%) with Mean HREF surface-based CAPEs
offering around 500 J/kg through late afternoon. A similar weather
pattern is expected for tomorrow. Otherwise, most areas will
remain dry today and through the holiday weekend as an atmospheric
blocking pattern keeps surface high pressure anchored over the
Great Lakes, ensuring quiet weather.

The pattern changes fairly dramatically by the middle of next
week as the polar jet stream buckles over the Canadian Prairies
and sends a pronounced 500-mb trough southward into the Great
Lakes. Model guidance is still exhibiting notable spread in the
evolution of this digging trough, with guidance split between two
scenarios. Scenario A (GEFS/GEPS) features a faster, shallower
500-mb wave that keeps the cold core further north, while Scenario
B (EPS) highlights a slower, deeper 500-mb wave that would result
in faster mid-level flow, stronger deep-layer shear, a stronger
cold frontal passage, higher convective potential, and more QPF.
Leveraging cluster analysis, which links together similar
solutions among all 100 ensemble members (50 EPS, 30 GEFS, and 20
GEPS), we see that there is a slight nod towards Scenario B.

To expand further upon next week`s setup, it is worth noting that
the ensembles may be camouflaging what could be a double-dip in
the jet stream and a pair of cold fronts rather than just one.
Some global deterministic guidance (e.g. GFS, ECMWF AIFS) suggests
this could be the case, with a cold front pushing through on
Wednesday, and again on Friday. Despite the changing pattern,
moisture return ahead of the fronts will remain poor. The
persistent, amplified trough positioned over the eastern half of
the U.S. will continue to impede Gulf moisture from surging
northward. This is evident in both the NBM (13z) and LREF (00z)
data sets, which both reveal very low probabilities (15% chance
or less) of exceeding 1 inch of rain over the next 7 days.
Temperatures on the back side of these fronts is still somewhat
uncertain and dependent on how the upper trough evolves, but there
is still a signal in the global guidance (e.g. GFS, ECMWF) of sfc
dewpoints tanking into the 30s by Thursday. If this signal holds,
then overnight temps could dip into the lower 40s and challenge
record lows.

MJA

&&

.AVIATION...  (For the 00z TAFs through 00z Saturday Evening)
Issued at 602 PM CDT Fri Aug 29 2025

A weak front is draped from west-central to southeast IL this
evening. A few showers have developed along the boundary, but will
largely stay south of the airfields before they come to an end in a
couple hours. Winds will be light overnight as they gradually veer
from the northeast to southeast by Saturday morning. There is a low
chance (20%) for a scattered shower once again tomorrow afternoon,
but chances remain too low to include at this time.

NMA

&&

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

$$