245
FXUS63 KLOT 300003
AFDLOT

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

.KEY MESSAGES...

- Periods of snow are expected through the evening and overnight
  hours 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.

&&

.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 /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 603 PM CST Sat Nov 29 2025

- Periods of SN to continue overnight with TEMPO LIFR VSBYs
  most favored through ~2Z.

- Period of LIFR CIGs likely overnight (~4-9Z) beneath center of
  surface low.

- Gusty SE winds ease under the low center overnight and turn
  gusty WNW in its wake.

Widespread snowfall continues across the area this evening.
There have been occasional gaps within the broader region of
snow which has helped lead to temporary improvements in VSBYs
and CIGs. However, LIFR VSBYs will remain possible for the next
couple of hours under any of the patches of locally higher
snowfall rates (~0.5"/hr).

Confidence on the end time of snow remains fairly low, with
areas south of I-80 (and the terminals) most favored to see an
earlier end. Farther north it could very well snow through the
remainder of the overnight hours, and have accordingly opted to
make limited changes to snowfall trends. Nevertheless, VSBYs
are expected to gradually improve through the night with
decreasing snowfall rates resulting in additional accumulations
up to around 2-3".

The center of the surface low is projected to move right across
the area overnight which will lead to a 3-5 hour period of
lighter winds and CIG reductions likely back to low-end IFR to
LIFR (~4-9Z). 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.

There remains a signal for a narrow band of snow and/or lake
effect to move across far NE/IL into NW IN in the morning on
Sunday. Confidence in how far west this ends up on the Illinois
side remains low, but it felt prudent to include a mention with
this update, so have introduced TEMPO groups for ORD/MDW/GYY
(PROB30 for DPA) to account for this.

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 until 10 PM CST Sunday for the IL
     nearshore waters.

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

&&

$$

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