066
FXUS63 KLOT 300452
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1152 PM CDT Mon Sep 29 2025

.KEY MESSAGES...

- Dry and unseasonably warm daytime conditions through next
  weekend.

&&

.UPDATE...
Issued at 847 PM CDT Mon Sep 29 2025

Forecast largely on track, the only real adjustment this
evening was to expand the area of fog mention some in the grids
and to introduce areas of dense fog in the northern Chicago
suburbs. Higher dewpoints advected inland across northeast IL in
the wake of the lake breeze Monday afternoon. Clear skies, calm
winds, and the increasingly long night should set the stage for
strong radiational cooling, well below the cross over temps
across northeast IL, particularly the northern suburbs. Seems
pretty likely that a dense fog advisory will be needed before
the night is over, especially northern suburbs.

While dense fog can`t be ruled out in the city of Chicago, I
suspect that the urban heat island will probably spare the
city from the greater dense fog threat.

No other changes made to forecast.

- Izzi

&&

.DISCUSSION...
Issued at 136 PM CDT Mon Sep 29 2025

Blue skies abound across much of the forecast area this
afternoon. The exception is southeast of I-57 where weak
instability has allowed for some mid level cumulus to
develop. With an upper level ridge remaining firmly in place
through much of the week, unseasonably warm and dry conditions
are expected to prevail. Temperatures can be expected in the 80s
inland, but persistent east-northeast flow will help keep the
lake shoreline in the mid to upper 70s tomorrow through
Thursday. As winds turn back to the south-southwest on Friday,
temperatures will once again rise into the upper 80s, with low
to mid 80s near the lake setting up a warm and dry weekend.

Returning momentarily to tonight: clear skies, light onshore
winds and a stout inversion are expected overnight. Localized
patchy shallow fog may crop up in traditional low-lying areas.
For now, the best chances look to be to the north in Wisconsin,
so the only formal mention patchy fog in the forecast is in Lake
(IL) and McHenry Counties.

The upper level ridge is projected to slowly move east this
weekend with an upper level trough moving toward the western
Great Lakes Saturday night into Sunday. There is still some
discrepancies between models in the exact track of the trough
into early next week, but many are showing a more northward
track through Canada. There was already low confidence in the
chances for precipitation early next week in the last forecast
package, and it seems that models are trending lower with PoPs
more focused north of Illinois. Any chances for meaningful
precipitation seems low which could further exacerbate drought
conditions, at least in the foreseeable future.

DK

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 1152 PM CDT Mon Sep 29 2025

Key messages for the 06Z TAF period:

* At DPA and GYY, BR possible overnight into early Tuesday

NE winds will remain light through the night and pick up to
around 10 kt mid-late morning.

Vsby reductions due to BR will be possible overnight into early
Tuesday, primarily at GYY and DPA. Otherwise, expect VFR
through the period.

Doom

&&

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

&&

$$

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