182
FXUS63 KGRB 081130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
530 AM CST Thu Jan 8 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Dense fog and freezing fog expected this morning with slippery
  travel possible. A Dense Fog Advisory has been issued.

- Rain and snow expected late this afternoon into early Friday
  morning. Chance for at least 2 inches of snow highest over
  northern Wisconsin (30-50%), but locally higher amounts could
  occur if switch to snow occurs earlier. A Winter Weather
  Advisory has been issued tonight for far northern Wisconsin.

- Where rain falls on melting snow and frozen ground and frozen
  rivers there is a potential for minor flooding in low-lying and
  poor drainage areas and also along rivers. There is a potential
  for ice jams as well.

- Another system expected Saturday and Saturday night. Chances for
  at least 2 inches of snow across the entire area range from 40-80%.
  However, the spread from low-end to high-end snow amounts is
  very high with this system.

&&

.DISCUSSION...
Issued at 234 AM CST Thu Jan 8 2026

Dense fog and freezing fog this morning...

Stratus and dense fog have persisted and expanded across the
region overnight into early this morning. In addition,
temperatures near or below freezing has caused freezing fog across
the region, which is making untreated roadways and surfaces
slippery. Models indicate this dense fog will last through a good
portion of the morning, definitely through the morning commute,
before lifting north later this morning. Therefore, will issue a
Dense Fog Advisory for the entire area given the high impact this
morning. Expiration times will follow the model trends of clearing
with 15Z across the southern 2 tiers of counties and 18Z further
north where the fog will linger.

Low Pressure System This Afternoon Through Friday Morning...

Southern stream, moisture laden system (as evidenced by higher
EFI values and PWATs that will likely be over the max for the
date per SPC PWAT climo) is on track to arrive central Wisconsin
to the southern Fox Valley by late this afternoon. Precipitation
spreads north and west quickly early this evening. Rainfall
amounts of at least 0.5 inch is expected for all areas, with
chances of over 1 inch increasing to 50-70% for the Fox Valley to
the lakeshore, which is up from 15-20% 12 hours ago. Precipitation
types will be an issue over northern Wisconsin this evening, with
soundings then switching to snow by midnight. Soundings are quite
isothermal, so will not take much warming/cooling to push precip
to only snow or only rain.

If the switch to snow occurs quicker to take advantage of heavier
QPF lifting in, several inches of wet, heavy snow could occur
north of Tomahawk to Iron Mountain. This is what is shown by some
deterministic models (using a 10:1 ratio) which indicate
localized amounts over 6 inches. Freezing rain not out of the
question as well, though lower probability. WPC super ensemble
snow and ice plumes show the sharp gradient from central WI to
north-central WI from only rain to ice and snow potential. Means
of the plumes point to rain instead of snow being primary weather
type during the heaviest QPF, even in the north. The plumes and
NBM ensemble data is certainly a lower contrast to what some of
the deterministic models continue to show. Again, will all depend
on how quick the change from rain to snow occurs tonight. Recent
model and probabilistic data has come in a bit higher with
snowfall amounts this run, due to the slightly sooner changeover,
with 2 to 4 inches of snow across the far north tonight. Given the
model trends will issue a Winter Weather Advisory for the farthest
northern counties as the trend has been for more snow each run.

Away from the winter concerns, hydro concerns remain present with
the rain falling on top of snow, frozen ground and mostly frozen
rivers. Low-lying and poor drainage areas will be most
susceptible to minor flooding. But, with the increasing flow
making it into area rivers, also could see minor river flooding
and potential for ice jams. Will continue to message this in HWO.
Later flood watch is not out of the question, though right now as
long as rainfall amounts don`t come up too much, based on similar
events with similar rainfall in the past, the overall flooding
impacts look minor. This would especially true if the swath of
heaviest rain occurs Fox Valley eastward as snow depth (0-
2 inches) and resulting snow water equivalent is less compared to
areas of central WI and north-central WI. That said, we will have
to keep close eye on ice jam flooding potential Thursday evening
into Friday as any ice jam can lead to locally higher impacts
nearby.

Saturday and Saturday night Low Pressure System...

As alluded to in previous forecasts, extent of phasing between
northern stream and southern stream shortwaves, and even more
specifically with the jet streaks involved, with weekend system is
tough to determine this far out and will have big impact on how
much snow occurs over the region. Even a cursory glance though
GFS, ECMWF and Canadian 00z runs bear this out with GFS, ECMWF
showing more phasing and keeping moist cyclonic flow in play
longer, thus more precipitation and snow. Meanwhile, Canadian ties
up main QPF in leading jet and shows minimal precip over the
area. This is why spread from 25th to 75th percentile for snow
amounts remains very broad, although less broad than yesterday.
For example at GRB, from the NBM the 25th percentile is 1 inch
while the 75th percentile is 9 inches. In addition, probabilistic
data continues to inch upward with the chance for 2 inches or more
of snow increasing 10-20% from yesterday, sitting at 40-80%. What
we do know that primary ptype will be snow and there still is a
rough signal that highest snow amounts from this system occur over
northeast WI including Door County into east-central Wisconsin.
Will continue to message this system in HWO. Beyond late Saturday
night, still looks colder with only minor snow chances into early
next week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 530 AM CST Thu Jan 8 2026

VLIFR/LIFR conditions were ubiquitous across the region this
morning with dense fog and freezing fog. There were also pockets
of MVFR/VFR noted as clearing lifts north. This clearing will
continue working its way north through the morning, with a period
of VFR/MVFR conditions are expected for a time later this
morning/afternoon, then conditions deteriorate to IFR/LIFR again
as a large area of rain spreads north into the area by this
evening. The rain will mix with snow at AUW/CWA and likely change
over to all snow at RHI this evening. Plowing operations will
likely be needed at KRHI by Friday morning with a few inches of
snow expected.

Winds will be under 10 kts today, shifting from the south this
morning to the east/northeast this afternoon/evening. Gusts to
around 20 kts are possible this evening. Some low-end LLWS will
be possible this morning with winds at 2000 ft at 25-35 kts.
Winds aloft will be highest toward the Fox Valley and lake shore,
so have kept LLWS in the GRB/ATW/MTW TAFs, but have not included
elsewhere. Another period of LLWS is possible this evening as
winds turn to the north/northwest.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until noon CST today for WIZ005-010>013-
018>022-030-031-073-074.

Winter Weather Advisory from 9 PM this evening to 6 AM CST
Friday for WIZ005-010>012.

Dense Fog Advisory until 9 AM CST this morning for WIZ035>040-
045-048>050.
&&

$$

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

NWS GRB Office Area Forecast Discussion