Weavers Weather

898
FXUS63 KLOT 182335
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
535 PM CST Sun Jan 18 2026

.KEY MESSAGES...

- Fluffy steady snow will spread over the area late this
  afternoon and end before midnight. Untreated surfaces may
  become slick.

- An Arctic cold front will move across the area late this
  evening with west northwest winds gusting to 40 mph and
  tumbling temperatures.

- Bitterly cold conditions are expected Monday morning with wind
  chills of 20 to 25 below zero.

- A clipper system may bring accumulating snow to parts of the
  area Tuesday night into Wednesday morning.

- Another period of bitterly cold temperatures may arrive by
  Friday.

&&

.DISCUSSION...
Issued at 225 PM CST Sun Jan 18 2026

Tonight through Monday:

A potent mid-level wave currently over southeast Minnesota will
track southeastward late this afternoon and evening and bring a
round of light snow accumulations across the area. Outside of a
slight southward shift in the best forcing, no substantial
changes were made to the forecast through this evening.

Modest deep-layer forcing via the periphery of the left exit of
an upper-level jet and appreciable mid-level diffluence have
contributed to a decent snow shield aloft over the Upper
Mississippi River Valley early this afternoon. An embedded N/S
axis of weak isentropic ascent is also locally enhancing
snowfall rates aloft. However, moisture available remains a
limiting factor for a more impactful snow event, with PWAT
values as high as only 0.2". Upstream obs/radar support the
notion that existing dry air is eroding the leading edge of the
snow shield, but eventual top-down saturation is expected to
occur and result in a quick change in conditions at onset.
Thermo profiles in the bulk of the forced layer are on the cold
side of the DGZ, which should favor smaller and drier snowflake
generation through much of the event. Utilizing a SLR of 15-20:1
and consensus QPF of around 0.05" yields fluffy snow
accumulations of around 1" for much of the area. Given the
decent forcing in place, could still see some 2" amounts,
particularly if saturation occurs earlier and/or SLR values
surpass 20:1. The bulk of the snow will fall in the 4-10pm
window, with a given location likely seeing a 3-4 hour period of
more steady snow.

On the heels of the synoptic snow exiting to the east late this
evening, an arctic cold front will sweep across the area
generally in the 11pm-1am window. This will usher in rapidly
falling temps with WNW/NW gusts to 40-45mph. Some gusty snow
showers will also be possible with the front. With little
existing snow cover (around 2" along the WI state line and
Porter County to around 1" or less elsewhere) combined with
expected snowfall this evening of under 2" should limit the
availability for impactful blowing snow, but shallow blowing and
drifting snow are still expected.

Overnight, lingering stratus and strong CAA should produce
flurries with embedded narrow ribbons of snow showers efficient
in sharply knocking down visibility.

By daybreak Monday, the combination of temps around or slightly
above zero combined with the strong winds will result in wind
chill readings ranging from around -25F west to -15F to -20F
east. A Cold Weather Advisory is now in effect for the entire
area. Highs Monday will struggle to reach 10 degrees, with
maximum wind chills remaining solidly below zero even under
mostly sunny to partly cloudy skies.

Kluber

Monday night through next Sunday:

The persistent upper-level pattern characterized by deep
troughing across eastern North America and ridging along the
Pacific West will persist through the middle to end of the week,
if not longer. Our area will remain on the western side of the
aggregate eastern troughing and indeed within the highway for
periodic clipper systems and shots of Arctic air.

Ensemble model guidance remains in agreement that the next
clipper system will move into the Midwest in the Tuesday night
to Wednesday timeframe. At this point, ensemble guidance favors
the clipper tracking either directly over our area or just to
our north. Assuming this occurs, a quick hit of warm-air
advection should help temperatures climb toward the freezing
mark early on Wednesday before a swath of snow falls generally
near and north of the Wisconsin state line. Will note however
that confidence in the track of any clipper system more than 24
hours out is low, so adjustments in the forecast are all but
certain going forward.

Looking toward the end of the week, ensemble guidance is
trending toward another clipper system moving into the region
followed by the southward surge of the Polar Vortex into the
Great Lakes. The EPS in particular is bullish with 51-member
mean low temperatures reaching double-digit below zero values
near the Wisconsin state line Saturday morning, some 30 to 40
degrees below normal for this time of year. Would have to think
the southward displacement of the low- level baroclinic zone
would shift any big precipitation-makers well south of our area
by the weekend, though we`re not out of the woods, yet.
Regardless, the Friday through Sunday timeframe is trending
toward being bitterly to even dangerously cold across the
Midwest/Great Lakes region.

Borchardt

&&

.AVIATION /00Z TAFS THROUGH 06Z TUESDAY/...
Issued at 535 PM CST Sun Jan 18 2026

Key aviation messages:

- Period of steady, but mainly light, snow this evening.
  Periodic dips to IFR vsbys. Activity diminishes through about
  06z.

- Arctic front arrives with a strong and gusty northwest wind
  shift overnight and tumbling temperatures.

- Increasing concern for convective snow showers along the
  front. Low confidence on exact placement, but potential exists
  for brief but sharp vsby reductions under 1 sm and wind gusts
  near 35-40 kts.

- Intermittent flurries/shsn likely to persist overnight and
  possibly through Monday morning.

Steady, light snow will continue this evening with periodic IFR
vsbys. This activity is expected to diminish through late this
evening. An arctic cold front will sweep across the region later
tonight (about 04-05z at RFD, 06-08z through the Chicago-area
terminals) with a notable northwest wind shift with gusts near
30-35 kts. Temperatures will plummet into the single digits
through the late overnight behind the front.

Upstream radars indicate the presence of convective snow showers
along the front stretching from near Minneapolis, southeastward
into eastern Iowa. This activity may push across the terminals
later this evening, and have introduced TEMPO groups with lower
vsbys to account for this. Brief vsby reductions (30 minutes or
less) near or under 3/4 sm will be possible at times if more
robust individual SHSN move across a particular area, but this
is not possible to indicate with confidence and specificity at
this range.

Otherwise, flurries/light snow showers will continue off-and-on
through the night and potentially through Monday morning.
Current TAFs indicate a return to VFR around midday, but it`s
entirely possible that MVFR cigs remain entrenched or redevelop
through the day.

Carlaw

&&

.MARINE...
Issued at 225 PM CST Sun Jan 18 2026

The gale warning remains in effect from midnight tonight into
Monday morning for all of the IL and IN nearshore waters.

A heavy freezing spray warning remains in effect for the
nearshore waters east of Gary, IN.

A strong arctic cold front will move across the area tonight,
bringing a period of gale force winds between 35 and 40 knots.
These strong winds will slowly diminish on Monday with gales
ending across the IL nearshore Monday morning and then across
the IN nearshore Monday afternoon. Very cold temperatures will
spread across the area behind this cold front and combined with
the high waves, heavy freezing spray is expected across parts of
the IN nearshore waters, mainly east of Gary, IN. Offshore winds
and a decent amount of ice formation along the Illinois
nearshore over the past day precludes the inclusion of a Heavy
Freezing Spray Warning west of Gary, IN.

cms/Kluber

&&

.HYDROLOGY...
Issued at 126 PM CST Sun Jan 18 2026

Area hydrographs and ice spotter reports confirm that ice
continues to develop and spread across areal rivers. Localized ice
jams are already present along the Rock and Des Plaines rivers.
Continued cold temperatures tonight and Tuesday will cause ice
to continue growing.

After a brief warm-up in temperatures to above 20 degrees on
Wednesday, another push of bitterly cold temperatures may arrive
as early as Friday. As a result, the threat for ice jams
including localized flooding will increase further toward the
end of the week.

- NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Cold Weather Advisory from 3 AM to noon CST Monday for ILZ003-
     ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-ILZ012-ILZ013-
     ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-ILZ103-
     ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...Cold Weather Advisory from 3 AM CST /4 AM EST/ to noon CST /1
    PM EST/ Monday for INZ001-INZ002-INZ010-INZ011-INZ019.

LM...Gale Warning from midnight tonight to noon CST Monday for
     Winthrop Harbor IL to Gary IN.

     Gale Warning from midnight tonight to 3 PM CST Monday for Gary
     to Burns Harbor IN-Burns Harbor to Michigan City IN.

     Heavy Freezing Spray Warning from midnight tonight to 9 PM CST
     Monday for Gary to Burns Harbor IN-Burns Harbor to
     Michigan City IN.

&&

$$

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