566
FXUS63 KGRB 151150
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
650 AM CDT Sat Mar 15 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Strong south to southwest winds of 40-50 mph are highly likely
  (60-90% chance) today across the Fox Valley, bayshore, and
  lakeshore. A Wind Advisory is in effect.

- Ice floes are possible on the bay today due to the gusty winds.

- A potent storm could bring substantial precipitation totals
  during the middle of next week. Rain, snow and a wintry mix are
  possible at times with this system.

&&

.DISCUSSION...
Issued at 413 AM CDT Sat Mar 15 2025

Short Term...Today...Tonight...and Sunday

Active weather to start the weekend but things quiet down on
Sunday. Above normal temps continue this morning/early afternoon,
then fall back toward normal tonight into Sunday.

Precipitation / Storm Trends: Band of showers and storms will
continue to shift/exit to the northeast through the area early
this morning. Surface gusts have decrease through the overnight
hours as nocturnal stabilization has won out. While surface/mixed
layer CAPE is nil, some gusty winds up to ~35 mph will be possible
with the stronger showers/storm as the 40 kts winds partially
make it down to the surface. As the vertically stacked low
pressure tracks towards western Lake Superior this morning, an
area of moisture will wrap around the low, bringing an area of
precip back into central and north central WI later this morning
and into part of the afternoon. Looking like mainly rain, but
some flakes could mix in late this afternoon as the colder air
arrives over north central WI. The dry slot should keep things
mainly dry further east. As the low exits into Canada this
evening, the precip will end over northern WI. A secondary low
pressure system will track into Lower Michigan late tonight into
Sunday, possibly bringing some light snow to far eastern WI.
Consensus is to keep any accumulating snow just to our east, but
any westward jog to the precip shield would bring some light snow
into far eastern WI. Have continued with some chance PoPs over
the far east, along with very minor accumulations.

Winds: Limited instability/mixing and lack of any significant CAA
will hold winds down through the early morning hours (outside of
any stronger shower), but with the arrival of the dry slot,
better mixing and an increasing pressure gradient, winds will pick
up quickly this morning. RAP/HRRR/NAM forecast soundings continue
to show winds of 40-50 kts aloft to mix into across eastern WI,
but have backed off slightly. This is likely why HREF probs of 45+
mph wind gusts have come down a bit, but still are 60-90%. Will
continue with the Wind Advisory with gusts to around 45 mph are
still expected, with gusts to ~50 mph possible if we can mix a
little deeper. Winds will decrease this afternoon as winds aloft
and mixing decrease. Northwest winds will gust to around 25 mph on
Sunday.

One other thing to note is areas of dust currently across Iowa.
The strong winds in the dry slot could spread this dust towards or
into the area today. Some lower visibilities were reported with
the dust, so if skies do turn a little hazy, this would be the
likely cause.

Temps: It will not be as warm as yesterday, but another above
normal day is expected with morning or early afternoon highs
ranging from the 50s to low 60s, warmest in the dry slot across
eastern WI. CAA really kicks in tonight with much colder temps
arriving. Lows will drop into the teens over north central WI and
into the 20s to around 30 across eastern WI. The quick shot of CAA
pushes through Sunday morning with WAA already beginning by the
afternoon, but it will be colder with highs in the 30s to low 40s.

Long Term...Sunday Night Through Friday

The main focus of the extended period will be the next active
weather system that could cross the Great Lakes region late
Tuesday night through Wednesday.

Southerly flow will increase again early in the work week,
bringing back above normal temperatures and moisture towards the
western Great Lakes. The increased warm air advection in
conjunction with the arrival of an upper shortwave will spin up
the next low pressure system that will cross into the region from
Nebraska to Illinois. This track keeps the surface warm front
stalled across central Wisconsin, which will favor a mix of
precipitation from snow across far northern Wisconsin to a mix and
then rain as the intrusion of warm air in the lower levels
increases with proximity to the warm front. The good news is that
surface temperatures closer to the warm front may also stay above
freezing, so while mixed precipitation may make roads slick,
freezing precipitation remains less favored. Probabilistic
guidances shows around a 20% chance of ice accumulation across the
area north and west of the Fox Valley. As we get into the daytime
hours of Wednesday, the low will start to pull off to the east,
bringing through much colder air and changing over precipitation
to snow for the rest of the region by the mid to late afternoon.
Accumulating snowfall is then expected across the region from
Wednesday evening through Thursday morning, with the heaviest
period of snowfall being that Wednesday evening to early overnight
period. Overall signal for snow does show that this has the
potential to be a significant wintry system, with the probability
of exceeding 6 inches in the 50-70% range in areas north of a line
from Wausau to Iron Mountain and also 40% across the Fox Valley.
The ultimate snow potential for this system will be greatly
influenced by when rain changes to snow, which in turn will be
sensitive to the track the low takes in the days leading up to
this event. Winds on the back side of this system may also be
gusty, which will increase any travel impacts from snow due to
limited visibility. Suffice to say, Tuesday night through early
Thursday will be a period to watch for travel impacts.

Relatively quiet conditions are expected outside of this period of
active weather during the middle of the week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 650 AM CDT Sat Mar 15 2025

A mix of MVFR and VFR conditions are expected through the TAF
period. Brief IFR conditions are expected early this morning due
to low clouds near Lake Michigan (MTW) then possibly later today
across central and north central WI due to low clouds and rain
showers associated with a low pressure system pulling away from
the region. A few flakes could mix in across north central WI
(RHI) late this afternoon and evening. The Fox Valley will remain
VFR most/all the day as they will remain in the dry slot.

Have added some 6SM haze to the eastern WI TAF sites as some smoke
and/or dust as spread all the way from New Mexico, Oklahoma and
Texas into the Great Lakes in the dry slot of the intense low
pressure. The sky will likely be hazy at times today.

LLWS will remain possible early this morning where surface winds
have not begun to gust. After sunrise, the threat for LLWS will
end as south surface winds become very gusty (30 to ~40 kts)
through early afternoon. Winds will diminish later this afternoon
into tonight.

&&

.MARINE...
Issued at 413 AM CDT Sat Mar 15 2025

Southeast winds will veer south this morning then southwest this
afternoon. After a lull in the stronger winds early this morning,
increased mixing and stronger winds aloft are likely to produce
gale force gusts from mid-morning to mid-afternoon. Winds will
decrease this afternoon and evening. A Small Craft Advisory is
currently in effect with a Gale Warning starting at 10am.

Ice conditions continue to deteriorate on the bay due to recent
warm temperatures and gusty winds. Latest satellite imagery
showing much of the ice was shifted westward on Friday due to the
gusty southeast winds, along with other cracks and areas of open
water across the central/southern bay. As gusty winds veer to the
south/southwest, favorable conditions for shifting ice and ice
floes will continue today.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 4 PM CDT this afternoon for WIZ022-038>040-
048>050-073-074.
&&

$$

DISCUSSION.....Bersch/Uhlmann
AVIATION.......Bersch
MARINE.........Bersch

NWS GRB Office Area Forecast Discussion