NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 310447
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1047 PM CST Tue Dec 30 2025

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 811 PM CST Tue Dec 30 2025

Widespread snow is shutting down over central Wisconsin, but radar
and obs show the snow is continuing over eastern WI, including the
Fox Valley. Snow has been quite fluffy and efficient with SLRs
over 20:1 the entire time. Snow amounts over 3 inches were
reported in southern Winnebago County this evening. As of 6pm, we
had nearly 2 inches at our office near the Green Bay airport.
Back edge of snow is pressing east-southeast and will reach the
Fox Valley by 10p. Heavier radar echoes over 20dbz suggesting
snowfall rates of at least 0.5"/hr have faded over the last 2
hours.

Other aspect of this system has been some freezing drizzle that
for the most part has remained southwest of central Wisconsin.
Could see a bit of freezing drizzle as the snow ends late this
evening, especially south of highway 10. Another wave of light
freezing drizzle has developed upstream northeast MN into the
Duluth vicinity, now pushing into northwest WI. Not sure if this
will hold together as it slides into central WI, but enough
evidence upstream to add a mention overnight across central WI and
perhaps reaching the southern portions of the Fox Valley late
tonight. Confidence on how the freezing drizzle evolves overnight
is low.

&&

.KEY MESSAGES...

- A clipper system brings a round of fluffy snow through this
  evening. An inch or less is likely for most, with 1 to 2 inches
  expected in the Fox Valley, bayshore and lakeshore areas as well
  as across the lake effect snow belt in north-central Wisconsin.
  Minor travel concerns are expected.

- An arctic cold front will bring additional light snow on
  Wednesday, with a dusting to a half inch anticipated in most
  areas. A couple inches of snow will be possible in Vilas County
  due to lake-effect.

- Wind chills as cold as 15 to 25 below zero are possible New
  Years Eve night into the morning on New Years Day.

&&

.DISCUSSION...
Issued at 210 PM CST Tue Dec 30 2025

First Round of Snow: A fast moving Clipper system is currently
bringing a swath of light snow and flurries to the region late
this afternoon. Although moisture is meager, snow ratios are
fairly high (upper teens) with fairly good dynamics in the form of
a mid level PV anomaly and left-front quad of a 110 knot upper
level jet. The high snow ratios and dynamics should lend
themselves to most areas getting around a half inch of snow, with
the Fox Valley, bayshore and lakeshore areas could get 1 to 2
inches. This will produce slick roads, especially in eastern
Wisconsin, for the evening commute.

Arctic Cold Front Snow: An arctic cold front will move into
northern Wisconsin late tonight, then drop south through the rest
of the region during the day on Wednesday. As this occurs,
conditions will become more favorable for lake-effect snow
(northwest winds and increasing instability over western Lake
Superior with delta T values around 20) in north-central
Wisconsin, with accumulations of 1 to 3 inches possible in Vilas
County. Despite the arrival of a dry arctic air mass, will keep
POPs higher than NBM (30-50%) given fairly strong dynamics with
the frontal passage, increasing frontogenesis, a mid-level short-
wave and the left-front quad of a 135 kt jet streak. Outside of
the lake-effect region, only expecting a dusting to a half inch
of powder in most areas.

Brief Period of Cold: A fairly strong push of cold air arrives in
the wake of the arctic front, with 800 mb temperatures dropping
to 18 to 23 below zero Celsius across the region later Wednesday
into Wednesday night. The combination of surface temperatures
falling into the single digits below zero (except near Lake
Michigan) and persistent northwest winds will result in wind
chills of 15 to 25 below zero late Wednesday night into Thursday
morning. These cold temperatures would likely impact any
activities late New Years Eve into the morning hours of New Years
Day. Cold Weather Advisories may eventually be needed for roughly
the northwest half of the forecast area. Some moderation in
temperatures is expected Thursday into Thursday night as incoming
cloud cover prevents temperatures from tanking overnight, which
will mean wind chill values will only fall to around 10 below zero
across central and north-central Wisconsin Thursday night into
Friday morning.

Rest of the Forecast: No significant precipitation events are
expected for the rest of the extended forecast period. After the
brief shot of arctic air, a gradual moderate in temperatures is
expected, with highs reaching the 20s by Sunday/Monday.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1042 PM CST Tue Dec 30 2025

Light snow has ended over eastern WI. Patchy freezing drizzle
could occur over central WI late tonight, but this is a very low
chance and will leave out of this set of TAFs. Otherwise, rest of
tonight will feature transient clouds with any cigs MVFR to lower
VFR. A few flurries may occur at times over far north-central WI.

Snow may move back into RHI around daybreak Wednesday as an
Arctic front arrives from the north. As the front moves through,
another round of light snow (vsby mostly VFR, but as low as MVFR
portions of central WI) would occur from mid morning through mid
afternoon, before tapering off by late afternoon as the front
shifts south. Cigs on Wednesday will be mainly MVFR. Skies clear
out by Wednesday evening, except over north-central WI where lake
effect clouds and a few flurries will linger.

Winds will be from the W-NW with speeds of 10 knots or less
the rest of tonight. Northwest winds on Wednesday then increase
to 10 to 20 knots as the Arctic front moves through. Winds will
diminish late Wednesday evening.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE.........JLA
DISCUSSION.....Kurimski
AVIATION.......JLA