779
FXUS63 KLOT 051931
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
231 PM CDT Fri Sep 5 2025

.KEY MESSAGES...

- A series of storm systems moving through the northern Great
  Lakes will reinforce fall-like conditions through the
  weekend.

- Generally dry and warmer weather is expected next week.

&&

.DISCUSSION...
Issued at 231 PM CDT Fri Sep 5 2025

Through Saturday Night:

The partly to mostly cloudy, cool and breezy conditions this
afternoon will give way to mostly clear, calm, and chilly
conditions tonight. Our forecast lows are generally in the
lower to mid 40s away from Chicago and the immediate Indiana
lakeshore, where upper 40s to lower 50s are expected.

Saturday will again feature breezy westerly winds (developing by
the late morning), albeit not to the extent of today. Most
locations will top out in the mid to upper 60s Saturday
afternoon, with a few spots in central IL up around 70F. A
fairly robust short-wave will dive southeast on the southwest
periphery of northeastern North American troughing Saturday
afternoon and evening. Despite the re-blossoming of strato-Cu,
forecast soundings appear too dry across the local area along
with an inversion around 10 kft AGl to support shower development.
Farther north into Wisconsin, isolated to scattered showers are
favored. If any of these showers approach far northern Illinois
from the mid afternoon into the early evening, they should tend
to dissipate, though we can`t rule out a few spotty sprinkles.

Expansive high pressure will overspread the mid and upper MS
Valley Saturday night, resulting in another clear and chilly
overnight period. Lows by early Sunday should be similar to
early Saturday, if not a degree or two cooler in spots. Both
tonight and Saturday night appear to be decent candidates to
have patchy shallow fog near ponds, streams/rivers, and over
fields, though the ingredients don`t look to be in place for any
impactful fog.

Castro

Sunday through Friday:

Upper level low pressure spinning over Hudson Bay and northern
Quebec is progged to gradually fill and drift northeast late
this weekend into early next week, with the larger scale long-
wave trough axis shifting east of the forecast area. This will
allow aforementioned expansive surface high pressure to spread
east across the forecast area Sunday into Monday, maintaining
dry weather characterized by cool nights (lows in the 40s again
Sunday night-early Monday). Sunday afternoon may not end up much
warmer than Saturday, though with sunny skies and lighter winds,
it`ll feel warmer. As the surface high drifts east on Monday,
modest return southerly flow, warm air advection, and ample
sunshine will enable a nice warm-up into the low-mid 70s, with
a few upper 70s plausible.

Farther to our west, ensembles continue to depict a cut-off low
slowly drifting from the eastern Pacific into the West Coast
and downstream ridging and warm advection gradually spreading
toward the central CONUS into mid-week. Downstream of the ridge
axis, ensemble guidance does depict a mid-level short wave
tracking across the upper Midwest/northern Great Lakes region
Tuesday into early Wednesday, with a corresponding axis of warm
advection and modest moisture return mainly north and northwest
of the immediate forecast area from IA into MN/WI. Blended NBM
guidance does swipe far northwest and northern IL with some
slight (<20%) pops late Monday night through Tuesday night,
which doesn`t appear unreasonable. Forecast soundings indicate
deeper moisture north and northwest of the area, with increasing
dry air in lower levels farther to the south/southeast of the
IL/WI border. This continues to suggest little in the way of
substantial rainfall potential with this system.

A cold front associated with the upper Midwest short-wave is
currently forecast to push across the area late Wednesday, with
surface high pressure building across the northern Great Lakes
region behind it on Thursday. Following highs in the upper 70s
to around 80F on Tuesday and upper 70s to above normal mid 80s
on Wednesday (aside from shoreline cooling), more pronounced
east and northeast low-level winds off of the Lakes are in store
Thursday and Friday. This will bring the footprint of cooler
highs in the low-mid 70s farther inland, though solidly above
normal temps (near 80F to lower 80s) will continue well inland.
Guidance is in generally good agreement however, in continuing
to spread the mid-upper level ridge east across the Plains/Corn
Belt through the end of the week, downstream of the upper
trough moving ashore out west. This portends generally dry
weather persisting through next weekend.

Ratzer/Castro

&&

.AVIATION /18Z TAFS THROUGH 00Z SUNDAY/...
Issued at 1235 PM CDT Fri Sep 5 2025

Winds will remain mostly out of the west through the current TAF
period. Wind gusts this afternoon expected between 20 to 25
knots. Gusts should taper off as the sun sets, but return
tomorrow late morning with gusts around 20 knots through the
afternoon. Stratocu will remain VFR through the afternoon with
decreasing cloudiness tonight. VFR stratocu will then redevelop
again tomorrow.

DK

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...Beach Hazards Statement through late tonight for INZ002.

LM...Small Craft Advisory until 10 PM CDT this evening for Winthrop
     Harbor IL to Burns Harbor IN.

     Small Craft Advisory until 4 PM CDT Sunday for Burns Harbor to
     Michigan City IN.

&&

$$

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