373
FXUS63 KGRB 231955
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
155 PM CST Tue Dec 23 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- A wintry mix is possible late Wednesday afternoon into Wednesday
  evening along and south of the Highway 29 corridor. Slippery
  travel conditions will be possible.

- Confidence continues to increase for a more impactful period of
  mixed wintry precipitation late Thursday night through Friday
  morning. Icing will be the primary threat north and west of the
  Fox Valley.

- A significant cooling trend will arrive late this weekend, with
  high temperatures falling into the single digits and teens by
  Monday.

&&

.DISCUSSION...
Issued at 155 PM CST Tue Dec 23 2025

The latest RAP analysis and satellite/radar imagery show low
pressure passing over northern Ontario, with a shallow cold front
currently tracking across northeast Wisconsin. Behind this front,
a shallow polar airmass is supporting a field of low stratus
around 1000 ft agl, which is poised to move into far north-central
Wisconsin this afternoon. Upstream, high pressure is centered
over eastern North Dakota, while mid-level clouds are streaming
into the northern Mississippi Valley ahead of warm advection aloft
occurring over the northern Plains. Forecast concerns revolve
around the icing potential late tonight, Wednesday afternoon and
evening, and Thursday night into Friday.

Light frozen precipitation potential tonight and Wednesday: High
pressure will build into the region this evening, leading to light
and variable winds and a period of good radiational cooling
before high clouds increase. Guidance suggests some fog potential
over far north-central Wisconsin as lows drop to around 10
degrees. As warm advection arrives aloft, weak frontogenesis is
expected in the 850-700mb layer. Deep saturation will be difficult
to achieve in the lowest 2 km, and a dry wedge below 800mb should
limit freezing drizzle chances. Therefore, backed off on freezing
drizzle chances as support is limited. However, a brief light
wintry mix of snow and sleet is possible near the U.P. border
early Wednesday morning. A secondary surge of more robust low-
level saturation (up to 850-800mb) arrives late Wednesday
afternoon and evening. Light drizzle or freezing drizzle looks
possible during this time, particularly along and south of the
Highway 29 corridor where surface temperatures will be near
freezing. While minor travel impacts are possible given
temperatures in the low to mid 30s, this period will need to be
monitored for slippery spots.

Wintry mix and icing potential Thursday night and Friday:
Christmas Day looks pleasant with high pressure at the surface
providing sunny skies and seasonable temperatures in the upper 20s
and 30s. Attention then turns to a strong warm advection event
late Thursday night into Friday morning. Height falls over the
Plains will lead to the development of a 30-40 kt low-level jet,
advecting moisture into the region. A pronounced warm nose
centered around 800mb will push wet bulb zero temperatures above
freezing south of a Rhinelander to Sturgeon Bay line. While
thermal profiles would suggest snow over north- central Wisconsin,
transient deep saturation may lead to the loss of ice crystals and
periods of freezing drizzle. Farther south and east, marine-
modified air off Lake Michigan should keep surface temperatures
near to above freezing in the Fox Valley and lakeshore.
Therefore, the greatest threat for icing is expected north and
west of the Fox Valley, where probabilities of ice accumulations
currently sit around 50-70 percent. The threat will shift north
Friday morning as the atmosphere warms, with precipitation ending
by mid- afternoon.

Temperature trends through Monday: Following the departure of the
late-week system, much colder air is forecast to arrive by the end
of the weekend. Ensemble guidance shows a deep northern stream
trough digging into the north-central U.S., allowing an arctic
airmass to spill into the Great Lakes. High temperatures will
trend significantly colder towards the end of the period, with
single digits and teens expected for highs by Monday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1101 AM CST Tue Dec 23 2025

Primary concerns in the short term involve LLWS this afternoon
and potential for light frozen precipitation and fog late tonight.

Low level wind shear will impact KRHI/KAUW/KCWA through
approximately 23z as a 35-40 kt jet persists at 2000 ft agl. At
the surface, gusty west to northwest winds to 20 kts will subside
early this evening as high pressure builds in and winds become
light/variable.

A brief period of low MVFR ceilings (1100-1400 ft agl) could move
into north- central WI for a time this afternoon. Otherwise, mainly
VFR conditions prevail through the evening with passing mid and
high clouds.

However, low level moisture increases overnight as warm advection
arrives aloft. Guidance suggests a period of fog and low stratus
development at KRHI after 08z, with visibilities potentially
dropping to 1-2SM and ceilings to LIFR/IFR. Added a tempo group
for the KRHI TAFs. Additionally, a brief 1-2 hour window of light
snow or freezing drizzle is possible near the U.P. border early
Wednesday morning, though dry air below 800mb may limit
accumulation. Confidence remains low enough to exclude a mention
at the KRHI TAFs.

Confidence is high for VFR conditions elsewhere through 18z
Wednesday.

Outlook: MVFR ceilings and potential for a light drizzle will move
into central and east-central WI late Wednesday afternoon into the
evening.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC

NWS GRB Office Area Forecast Discussion