568
FXUS63 KLOT 290826
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
226 AM CST Sat Nov 29 2025

.KEY MESSAGES...

- A Winter Storm Warning remains in effect for the entire area
  through early Sunday morning.

- Periods of moderate to heavy snow will spread across the area
  this morning and continue into this evening producing
  hazardous travel conditions. The highest snowfall rates and
  worst conditions are expected this afternoon into early this
  evening.

- Accumulating light snow (70-80% chance) late Monday afternoon
  into Monday night.

- Well below normal temperatures will persist through next week.

&&

.DISCUSSION...
Issued at 226 AM CST Sat Nov 29 2025

Through Sunday Night:

No significant changes to the going forecast or reasoning.

Light snow continues to slowly spread into the area, saturating
the low levels. Once it begins, light snow will continue into
the morning hours and then increasing in intensity with periods
of moderate to heavy snow expected areawide through the
afternoon and into the early evening hours. Snowfall rates
during this time may approach 1 inch per hour. Southeast winds
will steadily increase through the morning hours with gusts into
the 30 mph range possible this afternoon. This will likely lead
to some blowing/drifting snow and expanded that mention across
the entire cwa. As the surface low pressure moves across the
northern part of the cwa this evening, warmer air will spread in
allowing temps to warm to near or just above freezing along and
southeast of I-55, allowing the snow to mix with or change to
some light rain or drizzle. By this time however, remaining qpf
amounts look rather light and while this may cut down on the
snowfall amounts, it may not make much difference for the snow
amounts. These warmer temps and possible mix should also end
the blowing/drifting snow potential.

As for qpf/snowfall amounts and snow ratios, no changes. Areas
southeast of a Pontiac to Valparaiso line will see the lowest
amounts, likely in the 5-9 inch range with areas northwest of an
Ottawa to Waukegan line seeing the highest amounts, with
perhaps a few areas reaching one foot across northwest IL.

After the low moves northeast of the area tonight, winds will be
shifting westerly, then northwesterly with cooler air spreading
back into the area. There will likely still be light snow or
snow showers falling overnight into Sunday morning and this snow
will be drier with some blowing/drifting snow possible again,
mainly across northwest IL. Though there may be a period of wind
gusts into the 30-35 mph range Sunday morning and blowing snow
may be possible wherever falling snow persists. It appears that
light snow will be ending from northwest to southeast across the
area Sunday morning with perhaps some flurries Sunday afternoon.

Lake effect snow may continue across Porter County Sunday
afternoon into early Sunday evening. Low confidence for how
long it may persist and for additional snowfall amounts and
while some headline extension may be needed for Porter County,
confidence is too low to make changes this morning. cms

Monday through Friday:
Issued at 255 PM CST Fri Nov 28 2025

The primary forecast focus beyond this weekend`s winter storm
is the increasing potential for another round of accumulating
snowfall during the Monday afternoon-Monday night. The multi-
model consensus this morning continues to advertise a secondary
shortwave dropping south through the Great Basin Sunday night
and eventually ejecting across the Central Plains on Monday as a
positively-tilted trough. This orientation would result in a
fairly progressive system overall, but intensifying mid-level
frontogenesis is forecast to result in an expanding region of
generally light snow across parts of our forecast area. A
significant north-south spread exists persists in the guidance
and ensemble output today, but in general, the favored location
for fgen-enhanced snowfall appears to be setting up somewhere
across the southeastern two-thirds of the forecast area.

Main concern during this period is that snow would be falling
into a cold airmass with surface temperatures in the upper teens
to mid 20s which would easily result in slick/hazardous travel
even with modest snowfall amounts. The other aspect that has our
attention is some degree of near-upright/convective instability
in recent model guidance above the main frontogenetic
circulations which could end up locally-enhancing precip rates.
At this time, liquid amounts are generally a quarter inch or
less which would support perhaps 2-4 inches of snowfall given
generally modest ascent through the DGZ and and cold surface
temperatures. Too much uncertainty at this point to pinpoint the
main threat area, but something we`ll be keeping a close eye on
over the coming days.

Increased cloud cover may end up tempering overnight lows/wind
chills a bit more than the currently-advertised NBM grids, but
cold conditions will nonetheless prevail next week. A
reinforcing shot of cold air is generally forecast to arrive
midweek as a roughly 1040 mb arctic high slides southward across
the central CONUS, perhaps with an additional round of snow or
at least flurries as the boundary layer saturates into the base
of a very deep dendritic growth zone.

Carlaw

&&

.AVIATION /06Z TAFS THROUGH 12Z SUNDAY/...
Issued at 1130 PM CST Fri Nov 28 2025

- Snow overspreads the region late tonight/early Saturday
  morning and continues through Saturday evening.

- CIGS and VSBYs will steadily deteriorate through Saturday
  morning. Periods of LIFR VSBYs are expected, particularly
  Saturday afternoon/early evening (localized VLIFR possible).

- Snowfall rates will average around 0.5"/hr but will peak
  around 1"/hr Saturday afternoon.

Tonight-Early Saturday morning:

Light snow/flurries may begin to move into the area as early as
6-8Z but it will take time for the snow to work through a
lingering dry layer. Because of this, opted to delay the onset
of MVFR -SN by an hour or two at all sites with the 3Z
amendments and have maintained those changes. VSBYs are expected
to steadily deteriorate to IFR (1-2 SM) as we approach daybreak
Saturday around 12Z (10Z at RFD). Expect steadily deteriorating
conditions through the remainder of the morning hours. Can`t
rule out occasional periods of LIFR VSBYs and IFR CIGs by mid-
late morning which may warrant TEMPO groups with later updates.

Light SE winds will gradually increase through the night with
gusts to 20-25kt expected by mid-late morning.

Saturday afternoon:

This is the window for the highest snowfall rates (up to 1"/hr)
and have accordingly maintained prevailing 1/2 SM VSBYs from
18-00Z. Localized dips to VLIFR also cannot be fully ruled out
but confidence remains too low for a formal TAF mention.

Saturday evening/night:

As the low center moves into the area winds will ease paired
with decreasing snowfall rates (0.25"/hr). This may also
coincide with a brief mix or full changeover to light drizzle
paired with lowering CIGs and VSBYs back down to LIFR to
potentially locally VLIFR. As the surface low moves through
overnight winds will return to southwest and then northwest,
becoming increasingly gusty again (gusts up to 20-25 kt) by
daybreak Sunday.

Petr

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Storm Warning until 6 AM CST Sunday for ILZ003-ILZ004-
     ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-ILZ019-
     ILZ020-ILZ021-ILZ023-ILZ032-ILZ103-ILZ104-ILZ105-ILZ106-
     ILZ107-ILZ108.

     Winter Storm Warning until midnight CST tonight for ILZ033-
     ILZ039.

IN...Winter Storm Warning until 6 AM CST Sunday for INZ001-INZ002.

     Winter Storm Warning until midnight CST /1 AM EST/ tonight for
     INZ010-INZ011-INZ019.

LM...Small Craft Advisory from 9 AM this morning to 10 PM CST
     Sunday for the IL nearshore waters.

     Small Craft Advisory from 9 AM this morning to 7 AM CST Monday
     for the IN nearshore waters.

&&

$$

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