645
FXUS63 KGRB 201718
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1118 AM CST Sat Dec 20 2025

.KEY MESSAGES...

- Light snow this morning over northern WI, with the highest
  accumulations near 2" near the MI border. Chance (30-50%) of
  light snow or a light wintry mix over central and east-central
  WI with snow accumulations under a half inch.

- Gusty west winds of 30-40 mph late this morning and afternoon
  will create some blowing/drifting snow, especially on north-
  south roads.

- Next round of light snow (wintry mix?) arrives Sunday evening
  into Monday.

- Below normal temps arrive tonight into Sunday, then above normal
  readings for most of next week.

&&

.DISCUSSION...
Issued at 327 AM CST Sat Dec 20 2025

The latest clipper system will quickly traverse the region today,
with another surge of arctic air behind it. After a very impressive
virga show on radar through the overnight hours, light snow/flurries
will continue to expand and become heavier early this morning
across northern WI, with a round of moderate to briefly heavy snow
after 10-11z, as a couple rounds of strong FGEN moves through.
Still looking like a quick 1-2" snow event for locations along and
north of Hwy 8 (Probs of 1" of snow over 90% near the MI border,
but quickly decrease to 30% as you work toward Hwy 29). But some
dry air will likely cut into totals in most locations. As the
front and FGEN sink south later this morning, a brief burst of
precip is possible across east-central WI, but models are not in
great agreement whether the forcing and overcome the dry air.
Think the dry air will mostly win out, but a short period of
precip is possible, with HREF probs of at least 0.01" above 50%.
So will continue with 30-50% PoPs but keep QPF under 0.05". All
snow is expected across the north as profiles will remain cold
enough. However, as you work south, a warm nose initially between
800-750mb then a secondary nose around 900mb will lead to a little
mixed precip (freezing rain or sleet) if we can sufficiently
saturate. Any freezing rain would freeze on any untreated roads as
road temps remain below freezing. The freezing rain threat looks
to decrease after 9am as the colder air aloft arrives. Any precip
looks to exit by 18z, with lingering lake effect snow showers over
far north-central WI late this afternoon into tonight with only
minor accumulation.

Winds will turn to the west behind the front and become gusty as
winds at 900mb peak around 50 kts early this afternoon. Expect
surface gusts of 30-40 mph this afternoon (a few locally higher),
slowly diminishing this evening. The gusty winds will create some
drifting snow of the newly fallen snow, especially on north-south
roads.

Next chance for precip arrives on Sunday evening into Monday as a
strong push of WAA arrives from the southwest. Looking like mainly
snow for the majority of the event. There is an initial period
with a small warm nose aloft, but it looks like that will be
erased as the column cools/saturates, so will not have any
freezing rain mentioned Sunday night. However, as we lose some of
the mid-level moisture and ice production, there is a chance of
some freezing drizzle mixing in as the precip ends on Monday.
Temps could also warm sufficiently to change some of the precip to
rain or drizzle over the south on Monday. Minor winter impacts
are possible due to the snow and freezing drizzle.

Temps ahead of the front today will climb into the upper 20s to
low 30s across eastern WI, with temps falling quickly behind the
front into the single digits and teens by early evening. A cold
night is on tap tonight with lows in the single digits above/below
zero for most location, with wind chills between -5 and -20.
Sunday will be cold with highs mainly in the teens to around 20.
Temps jump back above normal for the rest of the week with highs
mainly in the 30s, with some 40s looking more and more likely on
Christmas Day.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1118 AM CST Sat Dec 20 2025

Westerly winds will increase to 15 to 25 kts with gusts up to 35
kts this afternoon and evening as a cold front moves through.
Winds will slowly diminish overnight and will subside to under
10 kts on Sunday for most areas under the influence of high
pressure.

The highest chances for MVFR ceilings and snow showers will be
across north-central Wisconsin into tonight. There is a lower
probability (20 to 40%) for patchy MVFR ceilings for a time
later this afternoon and evening with the arrival of the colder
air. Despite the gusty winds, confidence was not high enough to
mention any visibility reductions from drifting/blowing snow.

&&

.MARINE...
Issued at 327 AM CST Sat Dec 20 2025

Southwest winds gusting to 30 kts (with an isolated gale gusts)
will continue this morning, then shift to the west this afternoon
behind a cold front. As the better mixing arrives with the
strongest push of cold air advection this afternoon/evening, gale
force gusts are expected. Waves up to 12 feet are expected on
Lake Michigan, then will subside to 3-6 feet as winds become
offshore. On the bay, some ice coverage will limit wave action,
with ice-free areas seeing waves up to 6 feet. Current start
times for the Small Craft Advisory and Gale Warning look to be in
good shape. The Gale Warning might need to be extended by a couple
hours or a short Small Craft Advisory may be needed after the
gale expires to allow winds and waves to subside.

Ice floe threat will be present for a time this morning due to the
south winds and some ice cover on the bay, but as winds turn to
the west, the ice floe risk should decrease.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...None.
MARINE...Small Craft Advisory until 3 PM CST this afternoon for LMZ521-
     522-541>543.
     Gale Warning from 3 PM this afternoon to midnight CST tonight
     for LMZ521-522-541>543.

&&

$$

DISCUSSION...Bersch
AVIATION...JM
MARINE...Bersch

NWS GRB Office Area Forecast Discussion