NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 181113
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
513 AM CST Thu Dec 18 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Mix of rain and freezing rain expected early this morning, then
  rain changing to snow this afternoon and evening. Snow squalls
  possible this afternoon and early evening, followed by a
  possible flash freeze. Significant travel concerns possible this
  afternoon and evening.

- Light snow possible Friday night into Saturday morning,
  especially over far northern Wisconsin.

- Periodic windy conditions and a chance of gales on Lake Michigan
  through Friday morning.

&&

.DISCUSSION...
Issued at 422 AM CST Thu Dec 18 2025

Short Term...Today...Tonight...and Friday

A strong low pressure system over northern Minnesota will track
over Lake Superior today then continue to western Quebec by
tonight. The region will initially be in the warm sector of the
low, with mainly liquid precipitation expected this morning. There
will be a window where freezing rain is possible this morning
before road temperatures warm up above freezing with probabilities
for freezing rain across north-central Wisconsin generally 10 to
30 percent. According to road temperature data and probabilities,
the greatest potential for this will be from 4 to 9 am north of a
line from Stevens Point to Athelstane. The rest of the region
should have warm enough road temperatures or a late enough onset
that freezing rain is not expected to be a concern.

As the low crosses Lake Superior this afternoon, an arctic front
will track across the area. Short-range guidance suggests
favorable conditions for snow squalls between mid and late
afternoon. Key ingredients include surface instability up to 75
J/kg, low-level frontogenesis, steep low-level lapse rates of 7-8
C/km, and strong forcing via the shortwave trough. Snow squall
parameter values between 2 and 6 in the NAM reflect this
potential. A flash freeze will also be possible as sub-freezing
temperatures spread west to east across wet roads through early
this evening. Light snow and minor accumulations will be possible
region-wide as the system departs tonight.

Long Term...Friday Night Through Wednesday

The extended forecast will bring another couple of fast moving
wintry systems to the region, the first of which will arrive
Friday into Saturday morning. This will be a fairly quick snowfall
for most of the region, the exception being across far north-
central in the lake effect snow, where on and off snow showers
could continue well into Saturday night. Snow totals with this
clipper are currently forecast to be relatively light, mainly due
to limited lift through the dendritic growth zone and the fast
moving nature of the system. Probabilistic guidance only brings a
50% chance of exceeding an inch of snowfall to areas north of a
line from Rhinelander to Iron Mountain, with a sharp cutoff
southwards. That said, a round of stronger winds does accompany
the snow, so some travel impacts will remain possible due to a
reduction in visibility through Saturday morning.

The next chance for snow will arrive along a warm front on Monday,
but there is some question on how much will reach the surface.
Soundings show upper levels saturate as the warmer air arrives
aloft but still a significant dry layer below, which may limit
snow reaching the surface. As a result, would currently expect
relatively low impact from the passage of this snow. Winds aloft
will be on the increase again however, but potential to mix to the
surface may be limited. Still, would expect a few gusts around 20
to 25 mph to be possible, with an increase likely if the
associated precipitation potential increases in subsequent
forecast cycles.

Temperatures will drop in the extended on Sunday behind the first
clipper, with highs generally in the teens, before coming back up
to more mild temperatures once the warm air arrives on Monday.
Highs are currently forecast to be in the upper 20s to middle 30s
in the middle of next week leading up to Christmas Day.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 513 AM CST Thu Dec 18 2025

Conditions varied from VFR across northeast and east-central
Wisconsin to MVFR across north-central central Wisconsin.
Increasing moisture will lead to lowering ceilings and the
development of light rain/drizzle from southwest to northeast.
There could be a brief period of freezing drizzle; however,
temperatures are solidly in the mid 30s so the impact would be
fairly minimal. Conditions will quickly drop to IFR/LIFR by
13Z-15Z as widespread rain and fog develop and begin to mix with
snow by mid to late morning.

A powerful arctic front will sweep through the region this
afternoon. This will trigger a transition from rain to snow, with
a period of snow squalls likely between 19Z and 23Z. These squalls
may produce brief LIFR visibilities and gusty winds. A flash
freeze is also possible as temperatures plummet behind the front.

Low-level wind shear is a significant concern this morning as a
45-55 kt southwesterly jet moves overhead at 2,000 ft. Surface
winds will be gusty from the south-southeast this morning,
veering west and remaining gusty behind the front this afternoon.

Light snow and gusty west winds will continue through this
evening. Up to 1 will be possible by the end of the TAF period.

&&

.MARINE...
Issued at 422 AM CST Thu Dec 18 2025

Models have come in more gusty this run, with winds at the top of
the boundary layer solidly in the middle to upper 30 knots with
a fairly shallow boundary layer of 950 mb. In addition, the wind
direction of southerly this morning means winds off the lake will
be unabated to the nearshore waters, especially along the Door
Peninsula where the direction is orthogonal to the shoreline.
Given winds are already gusting close to 30 knots just south of
the area, the potential is high enough for gales this morning to
go with a Gale Warning for the Lake Michigan nearshore areas given
the plethora of southward facing beaches.

Gales will again be possible tonight as winds turn northwest on
the backside of the departing low pressure system across the bay
and Lake Michigan nearshore waters. Although there will be a
window where Gales are not expected this afternoon, will continue
the Gale Warning through tonight instead of triple headlines along
the nearshore waters. Winds will then ease below gale force
Friday morning.

&&

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

&&

$$

DISCUSSION.....Kurimski/Uhlmann
AVIATION.......Kurimski
MARINE.........Kurimski