868
FXUS63 KLOT 301740
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1140 AM CST Sun Nov 30 2025

.KEY MESSAGES...

- Accumulating snow to impact the Monday afternoon and evening
  commute and result in hazardous travel conditions.

- Well below normal temperatures will persist through next
  weekend with wind chills -5 to -15 possible Thursday and
  Friday mornings.

&&

.DISCUSSION...
Issued at 255 AM CST Sun Nov 30 2025

Short term challenge is how to handle headlines. Periods of
light snow will continue across northern IL and into northwest
IN through late morning and as temperatures cool, the snow will
become lighter/fluffy. Westerly winds will be gusting into the
30-35 mph range with some higher gusts possible this morning.
These conditions will result in some travel impacts but no
longer expecting warning level impacts and opted to replace the
winter storm warning with a winter weather advisory until noon
today for roughly areas along and north of I-80. Additional/new
snowfall from this point until it ends this morning will likely
be no more than one inch, with some areas possibly only seeing a
dusting of new snow accumulation. There remains uncertainty for
how long any lake effect snow may persist into Porter County
and the advisory may need to be extended there, but for now
opted to maintain the same expiration time of noon/18z. There
will remain a chance of flurries this afternoon.

With the new snow pack and light winds tonight, low temps could
really tank but there remains uncertainty for cloud cover with
both slowly eroding lower clouds and then increasing high/mid
clouds by daybreak Monday morning. Lows in the single digits
across northwest IL to lower/mid teens elsewhere look ok for
now, but changes may be needed based on cloud trends.

Attention then turns to the next accumulating snow that
continues to speed up, now arriving during early/mid Monday
afternoon. Ensemble support/agreement has steadily increased
over the past 24-48 hours and blended pops have steadily
climbed. Made additional upward changes to pops for Monday
afternoon/evening with this snow now looking to start just
before the Monday afternoon commute begins. With expected
cloudy skies on Monday, high temps may only climb into the 20s
allowing the snow to begin to stick when it begins falling. Qpf
amounts in the 0.2 inch to maybe 0.25 inch range with snow
ratios perhaps averaging 15:1 would yield 2-4 inches. While this
is on the low side of an advisory, with it falling during rush
hour, an advisory will need to be considered with later
forecasts for this time period. The snow will be ending from
west to east early Tuesday morning but with temperatures falling
back into the teens, any untreated surfaces will likely still
be slippery with at least some travel concerns for the Tuesday
morning rush hour.

A cold front is expected to move across the region Wednesday
with a chance of snow along/ahead of this cold front. Its
possible the snow may develop right over the cwa and timing
could also be for the Wednesday afternoon/evening commute.
Still quite a bit of uncertainty for this time period. High
pressure would then move across the area Thursday with the
potential for some very cold temps both Thursday and Friday
mornings, possibly subzero for at least parts of the area. Winds
might still be in the 5-10 mph range both mornings with the
lowest winds during the day Thursday, resulting in morning wind
chills both mornings possibly in the -5 to -15 range.

Still several days away, but will need to continue to monitor
another possible accumulating snow for Friday afternoon/evening
as there is growing ensemble support for this time period. cms

&&

.AVIATION /18Z TAFS THROUGH 00Z TUESDAY/...
Issued at 1140 AM CST Sun Nov 30 2025

Forecast concerns for the terminals...

- Diminishing winds and cloud cover this afternoon

- 15-20% chance for patchy fog late tonight, mainly west of the
  Fox Valley

- Period of accumulating snow Monday afternoon and evening
  resulting in IFR ceilings and visibilities


The early snow showers have concluded across northeast IL and
much of northwest IN as of 1730z. High pressure will begin to
build into the area later this afternoon/evening which will
allow winds to gradually diminish through the afternoon. In fact
as the surface high moves overhead tonight, many sites may
actually go light and variable with winds but the Chicago
terminals look to maintain a north-northwest direction.

That said, if the low stratus currently over southern MN erodes
this afternoon then conditions may become favorable for patchy
fog to develop late tonight into Monday morning. While the
stratus has shown some signs of eroding on recent satellite
trends, the expansive nature and the increasing cirrus to the
west do not offer sufficient confidence (15-20% chance) to
warrant the inclusion of patchy fog in the TAFs at this time.
If fog does develop tonight the near single digit to lower teen
temperatures will likely generate instances of freezing fog
especially for areas west of the Fox Valley.

Heading into Monday, any fog should erode by mid-morning with
cloud cover increasing through the day as our next storm system
begins to move into the area. As the system approaches winds
will turn south-southeasterly Monday afternoon with speeds
generally in the 6-8 kt range. The system will also bring
another period of accumulating snowfall to northern IL and
northwest IN starting around 19-20z and lasting through at least
midnight Monday night. While accumulations with this system will
be notably lower than what occurred this weekend (around 2-4
inches), the snow will be fairly steady and result in IFR
ceilings and visibilities Monday evening.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory until noon CST today for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ020-
     ILZ103-ILZ104-ILZ105-ILZ106-ILZ108.

IN...Winter Weather Advisory until noon CST today for INZ001-INZ002.

LM...Small Craft Advisory until 10 PM CST this evening for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CST Monday for the IN
     nearshore waters.

&&

$$

Visit us at weather.gov/chicago