NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 031144
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
544 AM CST Tue Dec 3 2024

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- A clipper system will bring a few inches of light snow to
  northern Wisconsin late this afternoon into Wednesday.

- Another round of snow Wednesday will bring some light snowfall
  to most, with enhanced lake effect snowfall across north-central
  Wisconsin.

- Increasing northwest winds and cold temperatures are expected to
  result in wind chill values of 5 to 10 degrees below zero late
  Wednesday night into early Thursday morning.

&&

.DISCUSSION...
Issued at 409 AM CST Tue Dec 3 2024

Short Term...Today...Tonight...and Wednesday

The short term forecast will mainly be focused on the passage of
an upper level trough, which will bring some snow to most of the
region and may bring a return or lake effect snow to the northern
snow belts. Winds accompanying the passage of the trough will also
be on the increase.

Snow/Wind Trends...
A passing upper trough will bring snowfall to the region starting
this evening as warm air advection ahead of the main trough
passes over the region. This initial round will primarily affect
areas along the Upper Peninsula border and the northern portion of
Door County while areas in central to east- central Wisconsin see
dry conditions prevail. Probabilistic guidance suggests a good
(70%+) chance of snow mainly north of a line from Rhinelander to
Menominee through Wednesday morning, with a sharp gradient south
of this line. Highest amounts accompanying this first wave range
around 1-2 inches, limited mainly to areas along the Upper
Peninsula border. Despite the relatively low snow amounts, wind
gusts accompanying the snow will increase to around 25 to 30 mph,
which will help lower visibility in any clear areas across the
north.

Coverage of snow will decrease briefly time mid-morning Wednesday
before spreading over the rest of the area Wednesday afternoon
and evening as colder air arrives behind the upper trough.
Moisture along the cold front will be fairly limited so most of
the region will likely only see a dusting of snow but areas in the
far north will see lake enhancement kick back on as winds shift
northwest aloft. Combined with Delta-T values still in the 20+
range and a decent mixed layer under the inversion, a fairly
sharp gradient in snow totals for the northwoods in the snow belt
regions is likely in the works. Probabilistic guidance supports
this with around 30-50% chance of any accumulations (>0.1 inches)
across central to east- central Wisconsin and almost no chance
(<10%) of more than an inch outside of northern Door County and
areas near the UP border in Vilas County. Winds accompanying this
second round of colder air will be stronger as well, with gusts up
to 30 to 40 mph over land and 35 to 45 mph over the Bay of Green
Bay and Lake Michigan. All together, little to no travel concerns
are expected for most of the region from snowfall but wind may
still cause visibility restrictions in open areas during the
evening commute. Travel impacts from snow and wind will be greater
in the northwoods and the Upper Peninsula Wednesday afternoon and
evening, so anyone traveling that way during this period will
want to watch road conditions.

Temperatures...
The warmer air ahead of the trough will bring low temperatures up
a few degrees compared to last night and will bring high
temperatures into the middle 20s to lower 30s for the area
Wednesday. Then, as colder air arrives, expect temperatures to
rapidly fall Wednesday, heading for lows in the single digits and
low teens for most Wednesday night.

Long Term...Wednesday Night Through Monday

Extended forecast quiets down a bit following the passage of
Tuesday/Wednesday's clipper system, with next chances for
widespread precip not arriving until later this weekend. Lake
effect snow will be possible across north-central Wisconsin behind
the clipper, although dry air entrainment will play a role in
limiting snowfall amounts.

Lake effect snow chances... Some lake effect/enhancement will be
possible across north-central Wisconsin behind the cold front on
Thursday as 850 mb winds take on a more north/northwest trajectory
and CAA ramps up. However, dry air entrainment (10th percentile
PWATs) and low inversion heights over Lake Superior may put a
damper on lake effect potential during this time.

Temperatures/winds... Increasing winds look to be a concern late
Wednesday into early Thursday as the pressure gradient tightens
up along the back edge of the departing clipper and mixing
increases behind the cold front. Surface gusts between 35 and 40
mph will thus be possible during this time, mainly across central
Wisconsin where current probabilistic guidance shows a 60 to 70
percent chance of exceeding 34 knot (39 mph) gusts. Given strong
CAA regime, suspect that winds may even have potential to
overperform. Wind chills will likewise tank to 5 to 10 degrees
below zero, locally lower, as a surge of cold Canadian air
arrives from the northwest. No cold weather headlines are
currently anticipated.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 543 AM CST Tue Dec 3 2024

Ceilings will likely vary between IFR and MVFR again this morning
and possibly into the afternoon as a low stratus deck remains in
place across the region. There will be a chance for a few areas to
see scattered sky cover in the afternoon which would briefly
improve conditions but timing was too uncertain to add to the TAF
especially as low clouds return quickly tonight. A clipper system
will bring light snow to the region but should predominantly
impact areas in northern Wisconsin through Wednesday morning,
which will only be KRHI at this time.

Winds will be on the increase today, with gusts up to 20 to 25
knots by the evening and early overnight hours. Some stronger 40
knot winds will also be around just off the surface, bringing LLWS
to the TAF period overnight.

&&

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

&&

$$

DISCUSSION.....Uhlmann/Goodin
AVIATION.......Uhlmann