041
FXUS63 KGRB 050351
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
951 PM CST Wed Dec 4 2024

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 909 PM CST Wed Dec 4 2024

As the strong pressure rise/fall couplet moves across the Lower
Peninsula of Michigan, winds have subsided some over east-central
Wisconsin. There were some gusts to around 45 mph at Austin-
Straubel Airport in Green Bay and Wittman Field in Oshkosh
between 7-8 pm, but there has been an overall decreasing trend
over the past 1-2 hours, possibly associated with minor decreases
of low level lapse rates. As a result, have ended the Wind
Advisory over east-central Wisconsin. The Wind Advisory over Door
County continues as planned since wind directions are favorable
for strong wind gusts.

No changes to the Winter Storm Warning over Vilas county. LES
parameters (overlap of 1000-850mb winds and 850-700mb RH) look to
peak late this evening into the first half of the overnight.

We received numerous reports of black ice and slippery roads
earlier this evening after the snow showers ended. Suspect a
gradual improvement will take place tonight as roads get treated,
but some untreated secondary roads may remain slippery for
Thursday morning commute.

&&

.KEY MESSAGES...

- Brief, heavy snow showers will continue to track across east-
  central and northeast Wisconsin through late this afternoon.
  These heavy snow bursts will bring visibility to a quarter
  miles or less, accompanied by strong winds, and make for a 15 to
  60 minute window of significant travel impacts.

- Lake effect snow showers will bring 2 to 5 inches of snow in
  most of Vilas County this evening and overnight. Amounts of 8 to
  10 inches are possible in the northwest part of the county. Snow
  combined with strong winds will create hazardous travel into
  Thursday morning.

- Increasing northwest winds and cold temperatures are expected to
  result in wind chill values of 0 to 10 degrees below zero late
  tonight into Thursday morning.

&&

.DISCUSSION...
Issued at 347 PM CST Wed Dec 4 2024

Short Term...Tonight and Thursday

Focus is on the near-term forecast and heavier snow bands embedded
within the broader scale snow event.

As of 20Z surface low pressure was located in south-central
Ontario with a strong cold front extended to the southwest, which
was bisecting the GRB forecast area, located from roughly Iron
Mountain to east of Wisconsin Rapids at 20Z. Satellite imagery
shows the convective nature of the snow along the front.
Additional forcing from a potent midlevel shortwave and LFQ of an
upper jet is also present.

Low level lapse rates of 8.5 C/km or higher are evident along the
front, with a snow squall parameter around 3.0 (anything above
1.0 is considered noteworthy). As a result, have seen a lot of
embedded heavier snow showers within the broader area of light
snow. Brief visibility drops of 1/2 mile or less have been
observed upstream in central and western Wisconsin. Will continue
to track these showers as they move east into the Fox Valley and
east-central Wisconsin during the late afternoon. Specifically
reaching snow squall warning criteria is uncertain, as
visibilities must technically drop below 1/4 mile with sub-
freezing ground temperatures. However, regardless of if this
criteria is met, rapidly deteriorating conditions are likely for
anywhere from 15 to 60 minutes in many areas. Following the heavy
snow bursts, light snow and flurries will continue through mid-
evening, with minor additional accumulations..

After the front/heaviest snow comes through, winds will remain
strong and gusty through early tonight. Most locations will gust
up to 40 mph, but could be closer to 45 mph along the Lake
Michigan lake shore where there is stronger mixing. Therefore, a
Wind Advisory is in effect here this evening into Thursday
morning.

Meanwhile, the strong NW winds over Lake Superior will allow for
lake effect snow across mainly Vilas County into Thursday morning.
A Winter Storm Warning remains in effect until 6 AM Thursday.
Accumulations will range from 2 to 5 inches in most of Vilas
County, but up to 8 to 10 inches in the northwest part of the
county. Most of this will be before 6AM, with minor light snow
showers or flurries lingering into early afternoon.

On Thursday, conditions will generally trend quieter, with
decreasing clouds and winds. Wind chills Thursday morning will
range from about 0 to 10 below, and then improve into the positive
teens in the afternoon.

Long Term...Thursday Night Through Wednesday

Main highlights from this forecast period revolve around a roller
coaster of temperatures and the next chance for precipitation
sometime between late Sunday and Tuesday.

Temperatures...Cold Canadian air and high pressure will reside over
the area Thursday night into Friday, leading to below normal
temperatures. Thursday night`s lows will range from the single
digits above zero in central and north-central WI to the low to
middle 10s in eastern WI. Although winds will be light, wind chills
as cold as the single digits above and below zero are anticipated
into early Friday morning. High temperatures on Friday will also be
below normal with highs ranging from the upper teens to middle 20s.
Strong return flow will shift into the area late Friday and lift
warming air back into the region. Temperatures will gradually warm
into the 40s by Sunday and continue on Monday for most locations.
Cooler air drops back into the area late Monday into Tuesday,
causing temperatures to fall back to the 20s and 30s.

Precipitation...Generally dry conditions are expected for much of
the extended. One of the exceptions is some light snow late Friday
into Saturday, but these showers should stay confined to the
WI/Upper MI border. The other exception is associated with a clipper-
like system that may bring widespread precipitation sometime between
late Sunday and Tuesday. Given the warmer temperatures, the
precipitation would start out as rain before switching to a
rain/snow mix and eventually to all snow sometime on Monday.
Precipitation amounts appear to be light, so the impact level should
stay low.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 951 PM CST Wed Dec 4 2024

Behind a dynamic shortwave trough and cold front, a mix of VFR and
MVFR flight conditions (for ceilings) prevail across the region.
IFR conditions will persist over Vilas county within heavy lake
effect snow shower activity until early Thursday morning. Central
and east- central WI should see a clearing trend take place around
late morning to early afternoon, but far northern WI will likely
have to wait until mid to late afternoon for clearing.

Strong northwest winds will gradually subside tonight and
Thursday. A Wind Advisory remains in effect over Door County until
12z. As surface winds subside, a brief period of low level wind
shear is possible late overnight into Thursday morning.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 6 AM CST Thursday for WIZ005.

Wind Advisory until 9 AM CST Thursday for WIZ022.
&&

$$

UPDATE.........MPC
DISCUSSION.....KLJ/Kruk
AVIATION.......MPC