220
FXUS63 KLOT 291111
AFDLOT

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

.KEY MESSAGES...

- Dangerous swimming conditions will persist at southern Lake
  Michigan beaches through at least this morning and possibly
  into this afternoon.

- Comfortable conditions for outdoor activities are expected
  through the Labor Day holiday weekend, with the warmest
  afternoon temperatures on Sunday and Labor Day (Monday).

- Following our next decent chance (40-50%) of showers and
  storms with a strong cold front Wednesday, a substantial cool-
  down is expected for the second half of next week.

&&

.DISCUSSION...
Issued at 330 AM CDT Fri Aug 29 2025

Through Tonight:

A region of 1020-1025 mb surface high pressure centered over
central Ontario will slowly drift southward across the Great
Lakes today. The associated anticyclonic flow will result in
onshore flow persisting through the day today, likely keeping
high temperatures near the lakeshore at or below 70F while
inland locations warm into the 70s amidst generally partly
cloudy skies within a fairly dry air mass. This onshore flow has
also led to dangerous swimming conditions being observed at
southern Lake Michigan beaches, with 3-7 ft wave heights noted
in overnight buoy readings. While the winds over Lake Michigan
have diminished (and will continue to gradually diminish with
time), dangerous waves and the threat for rip currents should
persist through at least this morning before also gradually
coming down as the day goes on. Based on the latest wave model
data, it`s possible that the going Beach Hazards Statement may
be able to be dropped before its current 4 PM CDT end time, but
opted to leave its end time untouched for now given that it is
not uncommon for high, choppy wave action to persist longer
than depicted in wave model forecasts.

In other news, modest warm air advection/isentropic ascent has
allowed for a batch of convective showers to flourish along the
periphery of a ribbon of weak instability in the Upper
Mississippi River Valley early this morning. Divergence within
the right entrance region of an upper-level jet streak and weak
DPVA should provide some additional forcing support with time
and allow for this shower activity to persist in some capacity
as it trickles towards the Illinois-Wisconsin state line,
though an increasingly drier air mass with southeastward extent
will make it difficult for at least this initial wave of
showers to survive into our CWA. The odds of precipitation
occurring here should increase a bit tonight as the main axis of
warm air advection/isentropic ascent slides into the area.
While dry air will continue to be an inhibiting factor for
precipitation, there is a fair amount of support across the
latest suite of hi-res guidance in the attendant mid-level cloud
deck being deep enough to support hydrometeors. Forecast
soundings suggest that the sub-cloud layer should not be
insurmountably deep and dry to prevent raindrops from reaching
the ground if they were to be present, so have introduced some
slight chance PoPs across our northern CWA tonight/early
Saturday morning to reflect the increased possibility of
sprinkles or light rain showers being observed here.

Ogorek


Saturday through Thursday:

The Holiday Weekend is setting up to be a pleasant one across the
area as surface high pressure remains dominant across the Great
Lakes. The main chances for diurnal showers or storms in this
pattern will be largely be displaced to our west, particularly
for Sunday and Monday. Saturday is also looking to be largely dry
for the area, though we will have to keep on eye on the potential
for a few lingering showers during the day, particularly across
northwestern IL. Temperatures through the weekend should top out
in the mid 70s Saturday under partly cloudy skies, then warm into
the upper 70s to near 80 for inland areas Sunday and Monday. Tuesday
is then largely looking to be a carbon copy of the weather on
Monday.

A large and anomalously deep upper trough and strong cold front
is expected to move across the area midweek. The current timing of
this strong system is favored to present the local area with the
next best chance for more widespread showers and storms on
Wednesday. Following the passage of this cold front, breezy
northwest winds are expected to usher in a very cool airmass
(more typical of mid-October) for the second half of the week.
Forecast highs are currently in the lower-mid 60s next Thursday!

KJB

&&

.AVIATION /12Z TAFS THROUGH 18Z SATURDAY/...
Issued at 611 AM CDT Fri Aug 29 2025

There are no significant aviation weather concerns through the
period.

Surface high pressure will settle across the Great Lakes today
into tonight. This will foster persistent northeasterly surface
winds up around 10 kt through the daylight hours today.
Otherwise, generally VFR conditions are anticipated.

A weather disturbance will move towards the area tonight into
early Saturday. While this looks to result in a lower VFR cloud
deck across the area, there will also a low (~20%) chance for a
few widely scattered light showers tonight into Saturday
morning. However, given that the probability is currently rather
low and any impacts will be limited, we have opted to leave a
formal mention out of the 12Z TAFs.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 4 PM CDT this afternoon for
     ILZ006-ILZ103-ILZ104.

IN...Beach Hazards Statement until 4 PM CDT this afternoon for
     INZ001-INZ002.

LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL
     nearshore waters.

     Small Craft Advisory until 10 AM CDT this morning for the IN
     nearshore waters.

&&

$$

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