717
FXUS63 KGRB 270428
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1028 PM CST Fri Dec 26 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Areas of fog and freezing fog across central to north-central WI
may create slippery conditions on untreated surfaces.

- Trends increasing for a minor to moderately impactful winter
weather system Sunday night through Monday morning.

- A surge of below normal temperatures is likely towards the New
Year`s time frame.

- Strong northwest winds gusting to 30 to 45 mph inland, and gale
  force gusts to 35 to 45 knots on Lake Michigan, are expected
  from late Sunday night through Monday evening.

&&

.DISCUSSION...
Issued at 254 PM CST Fri Dec 26 2025

Fog and Freezing Fog Potential Tonight:

Confidence is increasing for patchy to areas of fog across central
to north-central Wisconsin tonight. From western Waushara County
through Vilas County, visibility is likely (75%+ confidence) to
bottom out in the 0.25 to 0.5 mile range overnight. With surface
temperatures falling into the low 30s across this range, slippery
conditions may develop on untreated surfaces- includes roadways,
sidewalks and parking lots. Please use extra caution if traveling.

Sunday PM - Monday Winter Storm Potential:

The past two synoptic model run suites have significantly trended
upwards with a winter storm impacting our area... primarily north-
central. The driver for this winter storm is a rapidly intensifying
area of low pressure that ejects off the Rockies Saturday evening
and races northeastward- nearing the Chicagoland area by Sunday
afternoon. In these most recent model suites, the definition of
"bombogenesis"- when the pressure of a mid-latitude cyclone drops at
least 24mb within 24 hours. Perhaps aiding to recent model runs is
tracing this back to its source region on a 1.5 PVU anomaly map, it
is coming onshore along the Pacific NW today, so perhaps it is being
better sampled. This evening`s model runs may be very telling in the
sense of whether or not the intensification trends continue to
worsen, or if they "level off.

Temperature Influence: The temperature profile will be such that
ahead of this system, temperatures will be above freezing in our
area. And on the backside of this low, temperatures notably fall
below freezing... which would cause the rain --> snow transition.
This far out, it is tough to pin down when/where the cold backside
of this system will arrive in north-central Wisconsin. So any winter
weather headlines may need to be segmented... with north-central
locations starting earlier (maybe closer to 6 pm), and
northeastern/east-central WI locations starting later (maybe closer
to midnight). Simply put, if the warm air aloft lingers in
northeastern WI, there will not be enough hours of snow in NE WI for
accumulation much beyond 1 to 4 inches. And on the other side of
that coin... if cold air arrives in north-central WI earlier... then
north-central locations may receive closer to 1 foot of snow.
Overall, leaning conservative with total snow amounts at this point
in time until confidence increases with timing of the arrival of the
cold air on the backside of this low.

Wind Impacts:  It is very important to note the likelihood of wind
impacts. With an amped up such as this one is seemingly trending to
be, strong winds would be very plausible. If this system plays out
as is being currently modeled, accompanying wind gusts would range
in the 30 mph to 40 mph during periods of snow. Nearly immediately
on the backside of this system as the cold air takes over and rain
transitions to snow, there would be an area of large dendrites. In
conjunction with 30 to 40 mph wind gusts, visibility would easily
fall to 1 mile or less.

Headlines:  For now, have issued a Winter Storm Watch for our
northern counties from Sunday late afternoon through Monday morning.
The timing may change as confidence increases on when the rain -->
snow transition would occur. And the coverage area may also expand
southward/southwestward if trends continue.

In addition, strong northwest winds may gust to 30 to 45 mph inland,
with gale force gusts reaching 40 to 45 knots on Lake Michigan. The
cold and strong northwest flow will likely boost snowfall totals
across north central Wisconsin and possibly Door County through
Monday.

Cold air arriving middle to late next week...

Confidence increasing in a secondary surge of cold air arriving
behind this system sometime towards the second half of next week. As
of now, minimum wind chill values look to bottom out in the negative
10 to negative 20 degree range, with actual air temperatures
bottoming out in the single digits below zero. So not record-setting
cold by any means, but any outdoor events focused around the New
Year`s may be impacted by this cold. With temperatures in this
range, frostbite could occur within 30 to 45 minutes.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1028 PM CST Fri Dec 26 2025

IFR/LIFR status has developed over central and northern WI along
with areas of patchy MVFR fog this evening. Cigs have remained MVFR
across east-central WI. More blanket IFR/LIFR conditions are
expected to develop overnight. IFR vsbys are also expected tonight,
mainly in and around the Wisconsin River Valley as areas of fog
develop. With temperatures falling a few degrees below freezing
tonight across northern WI freezing fog is possible at RHI. There is
lower confidence in fog further east so went with TEMPO groups at
ATW and GRB for periods of MVFR fog early Saturday morning.

Flying conditions will be slow to improve Saturday morning, however,
forecast soundings do show enough heating/warm advection to lift fog
into a IFR/MVFR status deck by late morning. There is a ~20% chance
that patchy areas off freezing drizzle could develop Saturday
afternoon, mainly across northern WI. Confidence in freezing drizzle
occurring at any TAF is too low to include with this issuance.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Sunday afternoon through Monday morning
for WIZ005-010>013.
&&

$$

DISCUSSION.....Kotenberg
AVIATION.......GK

NWS GRB Office Area Forecast Discussion