112
FXUS63 KLOT 300516
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1116 PM CST Sat Nov 29 2025

.KEY MESSAGES...

- Periods of snow are expected overnight mainly near and north
  of I-80 leading to continued hazardous travel conditions.

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

- Well below normal temperatures will persist through next week.

&&

.UPDATE...
Issued at 951 PM CST Sat Nov 29 2025

Just made a couple of tweaks to the forecast grids and our
going headlines based on observational trends this evening.
Everything is still, however, more or less playing out as
expected, and our forecast expectations still essentially remain
the same for the remainder of the night.

The only change to the going Winter Storm Warning was to cancel
the warning for Livingston, Ford, Iroquois, and Benton counties
ahead of schedule now that the threat for additional snow
accumulations has largely ended there with temperatures warming
above freezing and the system`s dry slot passing overhead,
resulting in the cessation of precipitation in some areas and a
transition to more of a drizzle or light rain in other areas.
The center of the surface low was analyzed near the Quad Cities
at 900 PM CST/0300Z, and the east-northeasterly track that it
is expected to take along the I-88 corridor and into the
northern part of the Chicago metro should keep most of any
accumulating wrap-around snowfall north of these areas tonight.
This also applies to Newton and Jasper counties in northwest
Indiana, but opted to keep the original 06Z warning expiration
time for these counties since snowfall was still ongoing there
at the time of our evening product push.

All other locations in our forecast area could still pick up a
few tenths to a couple of inches of additional snowfall (highest
amounts farther north) through the overnight hours, so have
left the Winter Storm Warning unchanged for the northern 2/3rds
of our CWA. However, the incoming overnight shift may be able to
cancel at least part of the warning early wherever observational
trends are supportive of such a decision.

Ogorek

&&

.DISCUSSION...
Issued at 219 PM CST Sat Nov 29 2025

Through Monday:

Large scale ascent is peaking across the region with our storm
system in full swing at this hour. Persistent, broad UVVs on
the order of 10-15 ubar/second through a 4-6 kft thick DGZ near
and north of I-80 has really helped improve snowflake quality
and resultant SLRs since noon, and this will continue through
the rest of the day, supporting snowfall rates around one half
to, intermittently, one inch per hour.

A notably more convective look to the satellite and radar has
recently taken place across central Illinois where 500-600 mb
lapse rates are steepening ahead of the northward-advancing
dryslot. This has allowed for the development of some embedded
lightning strikes where large scale forcing and the steepest
lapse rates intersect. As a result, wouldn`t be totally
surprised to see a flash near our far south (southern Ford to
Benton counties) during the 3pm-6pm timeframe, along with a
period of briefly very heavy snowfall rates into the 1-2
inch/hour range in that same time window. Latest trends and
guidance suggest the main potential area for these higher rates
will set up in the vicinity of a Gibson City to Paxton line, but
this will be a short window.

The system dryslot will impinge quickly on our locales south of
the Kankakee River Valley through this evening. This will
gradually result in the loss of cloud ice and will transition
lingering precipitation to very poor-quality snow, if not even
flipping things entirely to drizzle late this evening and into
the early overnight. Temperatures will be slowly warming to at
to just above freezing as this occurs, limiting the potential
for any icing impacts. Some additional light snow will be
possible as the low departs very early Sunday morning.

Farther to the north, it looks like we should hold onto just
enough saturation colder than about -10 C that things should
stay all snow north of about I-80. Here, snowfall rates will
diminish through the evening, with just another 2-3 inches of
snow expected overnight.

West to northwesterly winds will steadily increase overnight as
the surface low pulls away, and some gusts could possibly push
40 mph south of I-80. With the warming temperatures, not sure
this will be enough to worsen any blowing snow threat, so
continued to leave this out of the gridded forecast but do
continue a mention west of the Fox Valley Sunday.

Continue to see a signal for one last batch of snow Sunday
morning in association with a trough axis that will push south
out of Wisconsin after 5-6 AM. This feature looks to be pretty
progressive, so will limit residence time, but this could end up
squeezing another quick inch or two of snow near and north of
about I-90 before precip shuts off by mid-late morning. Some
modest lake effect could persist across parts of NE Porter
county through mid afternoon, but the flow largely looks to
shift westerly enough to push the main focus east of our region.
Will continue to keep an eye on this, but at this time, no
plans for headline extensions.

Carlaw


Monday Night through Saturday:

Focus will be on a quick hitting snow event for Monday afternoon
and evening. This system is still developing off the Pacific NW
and dig into the Great Basin and then to the central Rockies by
early Monday. Model guidance depicts additional shortwave
forcing emanating out of the Canadian prairies in a largely
positive to neutrally tilted trough. The degree to which this
northern energy strengthens will play a role to the degree of
impacts from the snow in this event, particularly for areas
north of I-80. The left exit region of an increasing upper jet
will promote a decent area of lift, which will allow an area of
snow to expand across most of the area Monday afternoon. Any
strengthening frontogenetical circulation, albeit transient,
could also translate to higher impacts away from the currently
favored region for elevated snowfall totals which is along and
southeast of I-55, where the low level mass response will be
focused.

Probability matched mean QPF is consistent with the ensemble
envelope of 0.1 to 0.2 inches of QPF, highest southeast, with
less than 0.1" northwest of the Chicago area. This would
translate to a light snowfall toward Rockford to 3" along and
southeast of I-57. While forcing is modest, an increasing
dendritic growth zone could promote a bit fluffier snow than
this past weekend. There are certainly some details to be worked
out here, but a quick hitting impactful snowfall seems on tap
for the Monday afternoon and evening commute where many will be
back at work following the holiday.

KMD

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 1115 PM CST Sat Nov 29 2025

- Periods of -SN overnight with MVFR to occasional IFR VSBYs.

- Low-end IFR to LIFR CIGs expected through ~9Z.

- Strong west to northwest winds develop late tonight through
  Sunday AM (gusts to 25-30kt).

- Burst of -SHSN Sunday AM with a 1-2hr period of IFR
  conditions between 12-16Z.

Light snow continues late this evening across the terminals with
visibilities in the 1-2 SM range. VSBYs are expected to
gradually improve through the night at the Chicago area
terminals (potentially remaining lower toward RFD for longer).

The center of the surface low is beginning to move into the
area. As it does so, winds will continue to ease with CIGs
lowering back down to low-end IFR to potentially LIFR. Account
for this in TEMPO groups from 6-9Z. In the wake of the
departing surface low, winds then ramp back up out of the west
northwest with gusts in the 25-30 kt range expected through
Sunday morning. Can`t rule out some patchy blowing snow during
this time as well.

There remains a signal for a narrow band of snow and/or lake
effect to move across northern IL into northwest IN in the
morning on Sunday. Have maintained TEMPO groups for ORD/MDW/GYY
and added DPA, with a PROB30 for RFD due to lower confidence on
the westward extent.

Winds ease and MVFR CIGs scatter out toward late afternoon
Sunday with increasing high clouds ahead of our next winter
system.

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-ILZ103-ILZ104-ILZ105-ILZ106-ILZ107-
     ILZ108.

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

     Winter Storm Warning until midnight CST tonight for INZ010-
     INZ011.

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

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

&&

$$

Visit us at weather.gov/chicago