NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 072358
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
558 PM CST Wed Jan 7 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Dense freezing fog possible tonight into Thursday morning,
  especially across central and north-central Wisconsin. Slippery
  travel possible.

- Rain and snow expected late Thursday afternoon into early Friday
  morning. Chance for at least 1 inch of snow highest over
  northern WI (30-50%), but locally higher amounts could occur if
  switch from rain to snow occurs earlier.

- 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 late Friday night into Saturday night.
  Chances for at least 2 inches of snow across the entire area
  range from 30-60%. However, the spread from low-end to high-end
  snow amounts is very high with this system.

&&

.DISCUSSION...
Issued at 234 PM CST Wed Jan 7 2026

Fog potential tonight into Thursday morning...
Stratus and some fog have persisted into early this afternoon.
Satellite and obs show a bit of scattering out upstream with
partial clearing into parts of central WI. Does seem that any
clearing into the evening will just be replaced with more stratus
and fog overnight tonight, which will last into Thursday morning.
Saw patchy dense fog earlier today and that was with mostly cloudy
skies, so could see more widespread dense fog later this evening,
through the night and lasting into Thursday morning. Given the fog
and temperatures that will be back below freezing, another night
of freezing fog is likely, especially central and north-central.
Will keep this message going in the HWO as this again could lead
to slippery travel into the morning commute as we saw earlier
today.

Thursday and Thursday night Low Pressure System...
Southern stream, moisture laden system (as evidenced by higher
EFI/SOT values and PWATs that will likely be over the max for the
date per SPC PWAT climo) is on track to arrive central WI to
southern Fox Valley by late Thursday afternoon. Precipitation
spreads north and west quickly early on Thursday evening. Rainfall
amounts of at least 0.5 inch are likely for all areas, with
chances of over 1 inch increasing to 35-50% for the Fox Valley to
the lakeshore, which is up from 20-30% 24 hr ago. Other
experimental guidance suggests an inch is pretty achievable. Ptype
will be an issue over northern WI on Thursday 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 wx 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 on Thursday night.

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 yesterday, 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
12z runs bear this out with GFS, ECMWF showing more phasing and
keeping moist cyclonic flow in play longer, thus more precip 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 high and even
more so than yesterday. For example at GRB, from the NBM the 25th
percentile is 0 inches while the 75th percentile is 9 inches. 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 WI. 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 00Z TAF Issuance
Issued at 558 PM CST Wed Jan 7 2026

LIFR/IFR ceilings held tough across parts of the area during the
afternoon hours, but other locations saw the lower clouds exit for
a time with VFR conditions prevailing. This mix of LIFR/IFR and
VFR conditions will continue early this evening, with the LIFR/IFR
clouds, along with areas of fog, expanding through the early
overnight hours. Some VLIFR conditions are expected at times,
especially north/west of the Fox Valley, either with 100ft
ceilings and/or 1/4SM vsbys. Models hinting at some improvements
in the conditions at GRB/ATW/MTW late tonight into Thursday
morning, but remained pessimistic on any clearing until closer to
12z. A period of VFR/MVFR conditions are expected for a time
Thursday morning/afternoon, then conditions deteriorate again as a
large area of rain spreads north into the area by Thursday
evening.

Winds will under 10 kts through the TAF period, shifting from the
south tonight to the east/northeast Thursday afternoon/evening.
Some low-end LLWS will be possible late tonight as winds at 2000
ft climb to 25-35 kts. Winds aloft will be highest toward the Fox
Valley and lake shore, so have included LLWS in the GRB/ATW/MTW
TAF, but have not included elsewhere. Another period of LLWS is
possible Thursday evening as northwest winds.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION.....JLA
AVIATION.......Bersch