Forecast Discussion for GRB NWS Office
FXUS63 KGRB 072254

Area Forecast Discussion
National Weather Service Green Bay WI
454 PM CST Thu Dec 7 2023

Updated aviation portion for 00Z TAF issuance

Issued at 313 PM CST Thu Dec 7 2023

SHORT TERM...Tonight and Friday

Main forecast concerns to be on small chance for drizzle or
freezing drizzle to develop over northern WI later tonight,
followed by extent of clouds and temperatures for Friday.

The 19Z MSAS surface analysis showed an area of low pressure over
western ND with a cold front extended southward into the central
Plains and a warm front extended east-southeast through southern
sections of MN and WI. Visible satellite imagery indicated patches
of mid-level clouds over northeast WI with clear skies farther to
the west and south.

The warm front is forecast to slowly lift north tonight with
eventual south winds beginning to tap gulf moisture. As
temperatures slowly drop and dew points rise, expect low clouds to
develop along with patchy fog after midnight. The question then
becomes whether any precipitation will develop. Forecast soundings
still show dry air aloft, thus drizzle/freezing drizzle would be
the precipitation type if it does form at all. Most models stay
dry, but feel that northern WI may see this mixed precipitation so
have added this potential to the forecast. Min temperatures are
forecast to bottom out in the lower 30s north, middle to upper 30s
south late this evening, then slowly rise overnight as cloud cover
develops. As temperatures do moderate toward daybreak, any
freezing drizzle would become drizzle.

Any drizzle should end by mid-morning Friday as the warm front
lifts farther north through Upper MI. Patchy fog could also linger
until mid-morning before mixing out. Southwest winds and warmer
air will continue over the area on Friday, however forecast
soundings show a pretty stout inversion that be tough to break. If
clouds hang tough, it will be hard for temperatures to
significantly warm. Even if the low clouds mix out, middle and
high clouds are forecast to arrive in the afternoon. For now, have
max temperatures ranging from the lower to middle 40s over north-
central WI, to around 50 degrees across east-central WI.

LONG TERM...Friday Night Through Thursday

The main focus remains on the system to impact the area Friday
night through Saturday night, bringing a mix of rain and snow.

There has been some back and forth on whether there will be one
main wave, or two separate waves which generate precip Friday
night through Saturday night. Latest runs are on the two wave
scenario. Lift generated from the first approaching shortwave
Friday night into Saturday morning, along with proximity to the
LFQ of the upper jet, will allow precipitation to begin.
Temperatures Friday night will initially be in the middle 30s to
lower 40s, resulting in nearly all rain at precip onset as it
spreads in from the south. Temperatures cool Saturday morning
starting in the north. This will lead to a transition to snow as
the second shortwave moves through mid-morning through Saturday
night. QPF amounts during the snow portion of the event have
lowered, which has resulted in slightly lower snow totals in this
most recent forecast update. The potential for 2 inches or more
is highest across far north-central Wisconsin, but these
percentages are down to 10 to 30 percent. Potential for 4 inches
or more is now zero. Across the rest of the area, a trace to 1
inch is the most likely scenario.

Cooler air will filter in behind this system; however, readings
will still be near normal for early December. High temps from
Sunday through Wednesday will range from the middle 20s to middle
30s, low temps will be in the teens and 20s.

Precipitation chances look low through the rest of the long term
forecast. A clipper system moves across Canada Wednesday and
Thursday. Right now, any associated precipitation remains north of
the Wisconsin border, but will need to monitor in case the track
drifts any farther south.

.AVIATION...for 00Z TAF Issuance
Issued at 438 PM CST Thu Dec 7 2023

VFR conditions are expected across the area this evening.
Overnight, the models are depicting low clouds in the MVFR
or IFR category or lower to develop from 08z to 11z and linger
into Friday morning. Along with the low clouds, there may be
some patchy drizzle as well, possibly could be freezing drizzle
from KRHI on northward. Low level wind shear will develop this
evening and continue into Friday morning, generally from 200 to
220 degrees at 30 to 35 knots. CIGS should gradually improve late
Friday morning and afternoon.





NWS GRB Office Area Forecast Discussion