167
FXUS63 KLOT 291903
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
203 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 /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1228 PM CDT Fri Aug 29 2025

- 20-30 percent chances for light/vfr shra/sprinkles late
  tonight into Saturday morning

There are no significant aviation weather concerns. VFR cloud
cover will gradually increase this afternoon and evening as a
disturbance currently in Wisconsin pushes southeastward into the
region. Virga appears probable this evening/overnight, along with
some chances for periodic sprinkles/very light showers. Given
fairly limited moisture depth in forecast soundings and
anticipated overall low impacts, left a precip mention out of
the 18z TAFs although a mention could be needed in future
updates.

Otherwise, SCT-BKN VFR clouds will persist into Saturday
afternoon. East/northeast winds around 10 knots with occasional
gusts will continue at the lake-adjacent terminals today, with
light/variable winds inland eventually turning southeasterly
late this afternoon and evening. Light SE winds under 10 kts
will then prevail on Saturday.

Carlaw

&&

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

&&

$$

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