226
FXUS63 KGRB 170454
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1054 PM CST Thu Jan 16 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- An arctic airmass remains on track to arrive this weekend.
  Widespread dangerously cold wind chills of 25 to 35 degrees
  below zero, locally colder, appear likely during the early
  morning hours Sunday through Tuesday. Expect cold weather
  headlines to be forthcoming.

&&

.DISCUSSION...
Issued at 248 PM CST Thu Jan 16 2025

Short Term...Tonight and Friday

Gusty northwest winds will subside this evening as a ridge of high
pressure tracks through the western Great Lakes. A weak mid level
shortwave may bring some flurries to northern Wisconsin late
tonight as it tracks through the region. Lows tonight are expected
to range from the middle teens across the north, to around 20
across central and east-central Wisconsin.

Gusty winds will resume Friday as a cold front tracks through the
region. Surface winds will be southerly early Friday morning,
turning southwest late in the morning, and eventually westerly
Friday afternoon. As the cold front moves through the region there
will not be much moisture; however, model soundings indicate there
could be enough low level moisture to produce some
drizzle/freezing drizzle or flurries depending on how deep the
moisture is. The chance for precipitation will be low (10-20%)
but there is enough of a signal in the soundings to include it in
the forecast. The timing of the precipitation, during the day when
the sun is up, should help mitigate impacts from freezing
drizzle. Highs on Friday are expected to mainly be in the 30s.

Long Term...Friday Night Through Thursday

Main focus from this forecast period is the continued strong signal
for bitter cold temperatures and dangerously cold wind chills
associated with an Arctic airmass prevailing from Saturday through
Wednesday. Periods of light lake-effect snow showers in far north-
central WI are also anticipated throughout this forecast period, but
impacts will be minor.

Temperatures/wind chills...Following the cold frontal passage on
Friday, an anomalously cold airmass will begin to spread its Arctic
air over the region for the weekend. The signal remains strong for
the Arctic airmass to stick around through at least Tuesday.
Although this airmass is abnormal, it will not be extreme enough to
threaten record temperatures. However, it is still the coldest
airmass the region has seen thus far this winter season. This bitter
cold air will pair with light-moderate northwest winds to create
dangerously cold wind chills throughout this time frame as well,
especially in the overnight/morning hours. Probabilities for wind
chills less than -30 are solidly 60-95% for almost the entire
forecast area for early Monday morning and early Tuesday morning.
Probabilities for wind chills less than -35 are 35-65% for central
and north-central WI early Monday morning and 30-75% across almost
the entire area early Tuesday morning. Point is, cold weather
headlines will be needed, but depending on the location and which
day, there is some question if the headline will be a warning or
advisory. Temperatures begin to bounce back on Wednesday as ridging
builds over the region.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1054 PM CST Thu Jan 16 2025

Mainly VFR conditions overnight, though brief MVFR will be possible
over northern WI. An approaching cold front will result in light
snow or flurries developing across the area on Friday, though
temps will be warm enough for the precip to be in form of sprinkles
or a mix of rain/snow. Cigs on Friday start off VFR, but will
drop to MVFR over northern WI by midday and in the afternoon
across central WI. VFR cigs should hold from the Fox Valley to the
lakeshore (GRB/ATW/MTW), even through the end of the TAF period.

Winds will be the other issue. A strong low-level jet arrives
late tonight and persists into much of Friday ahead of the cold
front. There will be a stronger low-level inversion though, so it
may take until later in the day for strongest gusts to reach the
sfc. Thus, LLWS is expected late tonight through Friday morning
as the low-level jet increases to 40 to 50 knots from the south-
southwest. Better mixing late morning into the afternoon will
support sfc wind gusts to around 25 kts across most of the area.

&&

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

&&

$$

DISCUSSION.....Kurimski/Kruk
AVIATION.......JLA