Gurnee, Illinois Weather Forecast Discussion

632
FXUS63 KLOT 250746
AFDLOT
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
246 AM CDT Thu Sep 25 2025
.KEY MESSAGES...
- Lake effect showers expected, becoming more focused along the
  Indiana nearshore late morning/early afternoon.
- Drier conditions are expected to end the week as temperatures
  inch back into the 80s over the weekend.
&&
.DISCUSSION...
Issued at 246 AM CDT Thu Sep 25 2025
An impressive cloud shield is seen on recent satellite imagery
draped southeast of Interstate 55. It is associated with higher
moisture content closer to a surface low in the Ohio River
Valley gradually drifting east. Meanwhile, very weak warm
advection has allowed for a ribbon of mid level moisture to
develop into a narrow corridor of stratus clouds over the
central part of the forecast area, with mostly clear skies
elsewhere.
Lake water temperatures are still in the 60s with recent ACARs
soundings analyzing 850 mb temperatures around 10C creating a
10-15 degree temperature difference creating limited to modest
lake induced instability. Surface winds remain out of the
northeast over the water this morning. Lake effect showers have
already cropped up on radar this morning and are drifting into
northern Cook and Lake County Illinois. Lake effect showers will
continue through the morning but become increasingly more
focused over northwest Indiana as winds turn northerly and
eventually northwesterly late morning/early afternoon. As
instability diminishes in the late afternoon, showers chances
will subside.
Taking a step back, synoptically speaking there is a long wave
upper level trough draped over the western Great Lakes whose
axis spans from Oklahoma City, OK to western Quebec with a
closed low over Michigan`s mitten (as analyzed on SPCs meso
page). The upper level ridge over the Rocky Mountains will
slowly drift eastward through the rest of the week as the trough
moves east and its closed low sinks down to the southeast part
of the CONUS. A drier airmass will move in behind the departing
trough. Depending how much clearing happens and if winds become
weak enough tonight, there is a nonzero chance for some patchy
fog developing. The best chances would be for parts of northwest
Indiana away from the lake shoreline (especially for areas that
get some of today`s lake effect showers); however, with some
uncertainty on wind and cloud trends, it was kept out of the
forecast for now, but may be reconsidered in this afternoon`s
forecast package.
Before the previously mentioned ridge moves in this weekend, mid
range guidance is starting to pick up on a weak mid level wave
that would move southeastward out of Manitoba toward Grand
Rapids, MI late Thursday night through Friday. Model soundings
are looking too capped and dry to merit any mention in the PoPs
at this time. However, these models are suggesting a surface
front could develop and come racing southward down the Lake
Michigan shoreline which could drop temperatures from the low
80s down to the 70s and even 60s in its wake. Confidence
in the front making it to northern Illinois is low presently,
so no changes were made to the forecast that the NBM provided.
DK
Saturday through Wednesday Night:
As the ridge moves over the western Great Lakes this weekend, it
will usher in higher pressure and a drier air mass.
Temperatures will gradually creep back into the mid 80s to
locally upper 80s in the western CWA early next week. While a
weak cold front is still expected to swing through the area late
Sunday into Monday, the lack of moisture and cold air with it
look to offer little change to the forecast. However, the front
will allow winds to favor a more easterly direction and make it
more favorable for daily lake breezes to move onshore Monday,
Tuesday, and Wednesday. Thus temperatures near the lake these
days will be a bit cooler in the low to mid-70s.
DK/Yack
&&
.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1227 AM CDT Thu Sep 25 2025
Pockets of MVFR cigs will be possible this morning, with the
greatest chances near the lake. At GYY, light lake effect
showers may develop in the vicinity, but have pushed the timing
back closer to daybreak. The low-level flow will back to the
northwest this afternoon which should shunt any lingering
precipitation east of the terminal.
Winds will largely be northwesterly this morning, but will turn
northeasterly, first at GYY and then at MDW and possibly ORD.
Confidence in the NE wind shift timing is lowest at ORD, and
it`s conceivable this wind shift struggles to make it fully
through the airfield.
Tonight into Friday morning: winds will ease and trend towards
light and variable. With clearing skies, there is some potential
for BR/FG development, mainly near GYY and perhaps DPA, but just
beyond the end of the current TAF windows.
Carlaw
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement until 7 AM CDT this morning for ILZ006-
     ILZ103-ILZ104.
IN...Beach Hazards Statement until 1 PM CDT this afternoon for
     INZ001-INZ002.
LM...Small Craft Advisory until 7 AM CDT this morning for the IL
     and IN nearshore waters.
&&
$$
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NWS LOT Office Area Forecast Discussion