553
FXUS63 KGRB 041750
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1150 AM CST Wed Dec 4 2024

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- A strong upper level disturbance will bring snow showers during
  the late morning and early afternoon hours as it moves across
  the area. Some of these snow showers could be briefly heavy,
  and produce slick roads and poor visibility. Snow accumulations
  of a dusting to a half inch are expected in most places.

- Lake effect snow showers later today and tonight could produce 3
  to 6 inches in most of Vilas county, with 8 inches or more
  possible in the northwest part of the county. Northwest winds
  gusting to 35 mph will produce considerable blowing and drifting
  snow and hazardous travel conditions.

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

&&

.DISCUSSION...
Issued at 410 AM CST Wed Dec 4 2024

Short Term...Today...Tonight...and Thursday

Light to moderate snow will end early this morning across far
northeast Wisconsin as a shortwave exits the region.

A strong upper low dropping south from western Ontario to Lake
Superior will produce strong upper diffluence, steepening lapse
rates and push a cold front across the region today. Conditions
look favorable for brief, narrow bands of snow showers from late
this morning through the afternoon. The snow squall forecast
parameter suggests there is potential for brief but heavy snow
squalls that can cause dangerous travel conditions. Northwest
winds will gust to 40 mph behind the front, and produce blowing
snow where there is any accumulation.

The snow showers should end by evening over all but far northcentral
Wisconsin, where lake effect snow will intensify. Lake induced
CAPE of over 500 J/kg are forecast by the convective allowing
models with extreme instability due to the cold temperatures aloft
and the unseasonably mild lake waters. Snow accumulations of 3 to
6 inches are likely across Vilas county, with 8 inches or more in
the northwest corner of the county. The gusty winds will produce
considerable blowing and drifting snow and very difficult travel.
Wind gusts will also be quite strong near Lake Michigan, with wind
gusts to 50 mph possible across far northern Door county
overnight.

The lake effect snow should diminish Thursday, with clearing skies
expected during the day. Highs will be mostly in the 20s, with
wind chills in the single numbers and teens.

Long Term...Thursday Night Through Tuesday

Quieter weather is anticipated for the extended through much of
the weekend, along with a surge of warmer temperatures. Eyes then
turn towards the next potential system Sunday into Monday.

Thursday evening through Sunday...Ample cold air will follow on
the heels of the light snow from the short term on Thursday, which
will drive low temperatures for Thursday night into the single
digits for much of central and north-central Wisconsin, and into
the low teens near the Fox Valley lakeshore. Wind chills will dip
below zero overnight, which will be some of the coldest
conditions we`ve seen so far this season, but are still unlikely
to merit a headline. As winds shift towards the south during the
day Friday, strong return flow will push some warmer temperatures
back into the region for the weekend, with highs in the 30s
Saturday and in the middle 40s on Sunday. This period will be
predominantly dry, but some weak lake effect snow will still be
possible late Friday afternoon and evening before winds shift.

The next weather system...Long range guidance shows another
clipper system crossing the region Sunday evening into Monday,
bringing back some widespread precipitation. With temperatures
still ranging from the 30s to 40s during the day at the surface, a
mix of rain and snow will be possible with this system, with snow
being the dominant precipitation across the northwoods and rain
for the Fox Valley. Despite this, precipitation amounts are
expected to be relatively light, so impacts are expected to be
low, even with snow.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1150 AM CST Wed Dec 4 2024

The main aviation concern through this afternoon is the potential
for brief, heavy snow showers within the lighter snow passing
through. All TAF sites are expected to get some snow this
afternoon as a cold front approaches from the northwest. Embedded
within this, conditions are favorable for some localized, heavier
bands of snow to develop which would bring rapidly increasing snow
intensity, lowered visibility to 1/2SM or less, and strong winds
to 35+ kts. Exactly where these bands setup is difficult to
pinpoint. The most likely locations are from central into east-
central Wisconsin from 18-22Z. Included TEMPO groups in the TAF
update to highlight the best timing at each location. The
duration of any intense snow would be 30 to 60 minutes.

Meanwhile, light snow will be occurring across the area this
afternoon and evening, accompanied by lowered visibility of 1 1/2
SM to 6SM. W/NW winds will also increase with gusts of 30 to 40
kts possible through early tonight. Winds subside a bit overnight
and Thursday morning, but this is also when LLWS increases at
2kft.

Locations north of KRHI will get into heavier lake effect snow
this evening and overnight, resulting in a longer period of
MVFR/IFR flying conditions

Some improvement to flight conditions late Thursday morning and
afternoon as there is partial clearing of clouds and wind gusts
subside to around 20 kts.

&&

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

Wind Advisory from 6 PM this evening to 9 AM CST Thursday for
WIZ022.

Wind Advisory from 6 PM this evening to 6 AM CST Thursday for
WIZ040-050.
&&

$$

DISCUSSION.....RDM/Uhlmann
AVIATION.......KLJ

NWS GRB Office Area Forecast Discussion