098
FXUS63 KLOT 292343
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
643 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- A pleasant pattern will continue through the holiday weekend
  with only a low (20%) chance for showers this evening and
  tonight.

- An early fall storm system may move through the Great Lakes
  region toward the middle to end of next week accompanied by a
  shot of well below average temperatures.

&&

.DISCUSSION...
Issued at 203 PM CDT Fri Aug 29 2025

Through Friday:

Showers continue to move southeastward through Wisconsin ahead
of a low-amplitude trough propagating around a sprawling upper-
level low centered over far southern Quebec. While the showers
may tend to weaken as they move into Illinois (owing to a pocket
of dry mid-level air), new showers may develop overnight over
the general region as the upper-level trough swings overhead.
Low-end PoPs (20% chance) seem appropriate for the regime,
which should not amount to more than a few hundreds of rain at
any given location. With that said, a batch of mid-level clouds
associated with the trough should limit radiational cooling
overnight, so opted to lean in warm guidance and feature low
temperatures generally in the mid to upper 50s.

A surface high pressure system centered over the central Great
lakes will continue to dominant the prevailing pattern through
the holiday weekend and into early next week. As a result,
confidence is high that a relatively tranquil pattern will
prevail with low humidity levels, light (northeasterly) winds,
seasonable to seasonably cool temperatures, and little to no
chances for meaningful rainfall.

Ensemble model guidance continues to provide an unusually strong
signal for a polar trough to scream southeastward from the Beaufort
Sea toward the Great Lakes during the middle to end of next
week. As the trough approaches, would expect at least some
moisture return and low pressure development to take place ahead
of the southeastward-surging cold front, supporting the next
opportunity for rainfall (Wednesday timeframe). Thereafter,
robust cold air advection should lead to a notable cool down
Thursday into Friday (EPS ensemble 850mb IQRs fall entirely
below +5C by Friday). Highs may struggle to climb out of the low
to mid 60s both Thursday and Friday, and overnight lows may
make a run for the lower 40s (if not colder). All hope is not
lost however as ensemble model guidance shares a similarly
strong signal for temperatures to rebound into the 2nd week of
September presumably as ridging becomes established behind the
departing troughing.

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 643 PM CDT Fri Aug 29 2025

Aviation forecast concerns for the 00Z TAFs:

- A couple of periods of VFR SHRA possible (20-30% chances)
  into Saturday morning.

A pair of mid-level disturbances will track SE across the region
tonight into Saturday morning, each of which may bring a period
of scattered VFR SHRA to the area. Current radar depicts a
west-east oriented band of SHRA drifting SSE across far northern
IL in association with the first disturbance. These are moving
into drier air, with a noted dissipating trend as they spread
into the terminals. Have covered this with a couple hour period
of VCSH early this evening, as they continue dissipate across
the area. The second disturbance approaches late tonight and
will increase SHRA chances again into early Saturday morning.
SHRA should come to an end around 12Z for RFD and by 14Z or so
for the Chicago metro sites. While a brief MVFR cig/vis combo
can`t be completely ruled out beneath a shower, prevailing VFR
conditions are expected through the period. Lightning threat
looks to remain quite low across the terminals, being higher
west of the area into eastern IA.

Otherwise, surface high pressure is expected to persist across
the Great Lakes region, maintaining light E-NE winds across the
area through the period. Lingering VFR cigs Saturday should
scatter out by evening.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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