360
FXUS63 KGRB 132306
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
506 PM CST Sat Dec 13 2025

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Bitterly cold arctic air with wind chills as low as 20 to 30
  degrees below zero will remain dangerous through Sunday morning
  for most areas. A Cold Weather Advisory is in effect for all of
  northern and central Wisconsin (except Door County).

- A warming trend develops Tuesday and Wednesday, followed by a
  potent system that brings the potential for a wintry mix, rain,
  fog, and strong winds Wednesday night into Thursday.

&&

.DISCUSSION...
Issued at 218 PM CST Sat Dec 13 2025

The latest RAP analysis shows low pressure spinning north of Lake
Superior while arctic high pressure is building southeast from the
northern Plains to the mid-Mississippi Valley. Scattered cumulus
clouds developed near the U.P. border around midday, but otherwise,
skies have been mostly clear across the region so far today. Lake
effect snow showers and clouds streets have mostly remained north of
the U.P. border so far today. Scattered clouds are pushing south
across northern Minnesota and northwest Ontario, but high relative
humidity profiles in model soundings suggest there should be more
clouds than are currently present. Have therefore lowered cloud
cover for the rest of the afternoon. Current wind chills early this
afternoon range from 15 below to 25 below zero. Focus of this
forecast remains on the bitter cold wind chills and subsequent cold
weather headlines.

Bitter Cold Temperatures and Wind Chills:

Arctic high pressure will gradually slide south across the northern
Mississippi Valley tonight. On the eastern flank of this arctic
high, the core of the arctic airmass will drop southeast across
Wisconsin tonight. Low level wind trajectories will gradually be
veering, which is supportive of lake clouds and light snow showers
pushing south from the western U.P. and into far northern WI. There
is low confidence in how quickly this occurs and how far south the
clouds reach. Considering the bias of model RH fields in arctic
airmasses, errored on the lower coverage side. This impacts
temperatures and wind chills, and consequently, lowered min temps
and wind chills across far northern WI. This puts all of northern
Wisconsin (except for Door County) into Cold Weather Advisory
criteria (20 below to 30 below) into the evening. Guidance insists
on rising temps overnight and can see parts of the Cold Weather
Advisory cancelled prior to expiration (6 am for the north). Over
central WI, minimum wind chills of 30 below to 35 below are
expected, which falls just shy of Extreme Cold Warning criteria.
Temperatures should warm quicker on Sunday morning than this morning
with wind chills rising above advisory criteria in the 9-10 am
timeframe across central and east-central WI. Otherwise, expect
mostly sunny skies with highs ranging from the middle single digits
over central WI to the upper teens over far northeast WI.

High pressure shifting east across the Ohio Valley will promote
return flow developing on Sunday night. Southwest winds will become
breezy which will maintain low wind chills generally 5 below to 15
below zero. Shouldnt see much fall in temperatures while
statistical guidance actually shows surface temps undergoing a slow
warming trend at some locations.

Light Wintry Precipitation Late Sunday Thru Tuesday:

Guidance continues to show weak clipper energy producing light
snow after midnight on Sunday night into early Monday morning over
far northeast WI. Chances reach up to 40% near the U.P. border.
Perhaps up to one half inch of snow will be possible. Light snow
from additional clipper systems look to remain north of the area
on Tuesday and Tuesday night.

Mid-Week System and Warming Trend:

Then will be monitoring a potential fast moving and potent cyclone
crossing Lake Superior on Wednesday night into Thursday. This system
has trended stronger over the past 48 hours of ensemble runs.
Critical thickness values are projected to lift north of the Upper
Peninsula border by Wednesday evening. Probability of 850mb temps
reaching above freezing range from 60-90%. Surface dewpoints are
expected to rise above freezing over the southern parts of the area
on Wednesday night. Probabilities range from 60-80%. Therefore a
wintry mix looks possible on Wednesday night. Liquid precip will
have potential to freeze after sunset as the ground will be very
cold. Dense fog will also have potential to develop over the
southern parts of the area. Behind the system, colder air will
return, but there is quite a large spread in regards to how cold the
airmass will be. There is higher confidence of windy weather on
Thursday in the cold advection part of the cyclone. 925mb winds are
currently in the 90-95th percentile. Light snow and minor
accumulations will also be possible region wide. Another system
could impact the region late Friday into Saturday.

By Tuesday, there is a greater than 80% chance that highs will
top 32F across the entire forecast area. Global ensembles favor
these more moderate temperatures sticking around into Thursday.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 506 PM CST Sat Dec 13 2025

Mainly VFR conditions through the TAF period thanks to a bitterly
cold arctic airmass across the region. Light snow showers will be
possible at times over northern Vilas and Door Counties that
could produce MVFR ceilings and brief IFR to MVFR visibilities.
In general, trended more optimistic with ceilings tonight due to
the dry arctic airmass.

W-NW winds of 10-15 knots with gusts of 20-25 knots will occur at
times through the weekend.

Low level wind shear will be possible late tonight into Sunday
morning over parts of north-central and northeast WI that may
impact RHI and GRB.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Cold Weather Advisory until 6 AM CST Sunday for WIZ005-010>013-
021-073-074.

Cold Weather Advisory until 10 AM CST Sunday for WIZ018>020-030-
031-035>040-045-048>050.
&&

$$

DISCUSSION.....MPC
AVIATION.......Kurimski

NWS GRB Office Area Forecast Discussion