668
FXUS63 KGRB 050358
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
958 PM CST Tue Feb 4 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Snow will impact the area late Wednesday into Thursday morning.
  There is a 60-80% chance for at least 2" of snow north of Hwy
  29. Lower snowfall amounts are expected south of Hwy 29. A
  period of freezing drizzle is possible as the snow ends Thursday
  morning, which may create a glaze of ice on untreated roads and
  surfaces.

- Increasing westerly winds are expected Thursday afternoon into
  Friday morning with gusts of 30-40 mph, locally stronger gusts
  to 45 mph are possible from central WI to the lakeshore.

- Another round of accumulating snow is possible this weekend,
  with an area-wide chance of 50-70% for at least 2" of snow and a
  30-60% chance for greater than 4".

&&

.DISCUSSION...
Issued at 218 PM CST Tue Feb 4 2025

Short Term...Tonight and Wednesday

The low clouds across the north continue to erode this afternoon,
while mid and high clouds were on the increase from the west.
Temperatures were in the single digits above zero across portions
of central and north-central Wisconsin to the teens across
eastern Wisconsin.

For tonight, skies will be mostly cloudy across much of the
region. The only exception may be across the far north where there
may longer breaks in the clouds which will allow temperatures to
plummet as winds go light and variable. There will be a fairly
large range in temperatures from the single digits below to around
10 below zero across the far north to 10 to 15 degrees above zero
across east-central Wisconsin.

On Wednesday, high pressure will slide east of the area as the next
system approaches from the west. Low level winds turn to the east
by mid to late morning. Lake to 850mb temperature differences around
10C noted that would support light snow showers or flurries along
the Lake Michigan shoreline. Did add a chance of flurries for
late morning into the afternoon. For the rest of the area, there
is a chance of light snow during the mid to late afternoon across
portions of north-central, central and east-central Wisconsin. Any
light snow through late afternoon will be under an inch as the best
accumulating snowfall arrives Wednesday afternoon. High temperatures
were lowered a few degrees from the previous forecast with highs
mainly in the 20s.

Long Term...Wednesday Night Through Tuesday

A more active pattern is expected for the second half of this week
through the weekend. First period of impactful weather will come
Wednesday evening into Thursday morning as a round of snow and
potential freezing drizzle move across the region. Westerly winds are
then expected to increase Thursday afternoon with gusts up to 45 mph
possible. A brief period of quiet weather is expected Friday ahead
of another system that is progged to bring more accumulating snow to
the region Saturday into Sunday.

Snow/Ice Wednesday Evening through Thursday morning...A quick moving
shortwave in conjunction with an upper level left front jet quadrant
support an area of light to moderate snow across the upper Great
Lakes Wednesday evening through Thursday morning.  Snow is expected
to initially spread from southwest to northeast across the forecast
area as an axis of higher moisture and isentropic lift move over the
region. Light to moderate snowfall should then continue through the
overnight hours into Thursday morning. Snowfall rates are expected
to peak around 1"/hr at times, primarily across northern WI where
the strongest lift through the DGZ is expected. 12Z HREF probs show
a 25th-75th percentile spread of 1-3" across most of the region.
Expect areas across northern WI to be on the upper end of this range
if not a little higher as 12Z HREF localized probability-matched
mean shows a maximum in QPF, around.3", in this region. with SLRs
forecast to be around 15:1 this may result in localized amounts
around 4" in Vilas Co.

RAP forecast soundings do show the potential for snow to transition
over to freezing drizzle Thursday morning in the Fox Valley to the
lakeshore as the mid-level moisture gets stripped out of the column
and the saturate layer resides outside of the DGZ. Areas north and
west of the Fox Valley should remain mostly snow as thermal profiles
show colder profiles in those region. Impacts from the freezing
drizzle should be somewhat limited as the drizzle falls on fresh
snow, however, untreated roads may be slippery during the Thursday
morning commute.

Strong Winds Thursday afternoon...CAA and a tightening pressure
gradient will lead to increasing westerly winds Thursday afternoon
through Friday morning. NAM soundings suggest mixing to around 900mb
could bring down peak gusts of 30-40 mph with an isolated gusts to
45 mph possible. Strongest winds are generally expected from central
WI to the Fox Valley and along the lakeshore. There is the potential
for minor blowing snow, Thursday afternoon across, especially for
the more open areas in central WI. However, any frizzle drizzle
during the morning or slight melting of the top layer of snow during
the day may create a thing crust on top of the snow which would
limit any blowing snow. Stronger winds will also create hazardous
travel conditions for high profile vehicles on north-south oriented
roads.

Weekend Snow Chances...Long range ensembles continue to show signs
for more prolonged snowfall event Saturday into Sunday morning as an
upper trough moves over the upper Midwest. EFI of 0.6 during this
period suggest a slightly anomalous event, but likely not a record
setter. The system that will bring this snowfall is still over the
central Pacific. Details will need to be refined over the coming
forecast cycles.

Temperatures...Expect near to slightly below normal temperatures
through the extended period. Thursday night into Friday will be the
coldest night this week with wind chills falling into the negative 5
to negative 15 degree range. Another shot of cold air is expected to
arrive early next week, however, the extent of the cold is still
uncertain.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 958 PM CST Tue Feb 4 2025

VFR conditions will continue overnight, with middle and high clouds.
VFR should continue in most places through midday Wednesday, though
lake effect clouds with MVFR ceilings and snow flurries will move
inland from Lake Michigan in the afternoon. Light snow and IFR
conditions are likely Wednesday evening, especially north of a AUW
to ESC line, where a few inches are possible.

&&

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

&&

$$

DISCUSSION.....Eckberg/GK
AVIATION.......RDM