NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 271125
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
625 AM CDT Fri Mar 27 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Cool with scattered snow showers today. Brief reduced visibility
  and quick minor snow accumulations are expected.

- Warming trend this weekend into early next week.

- Active weather pattern early to mid next week. Potential for
  thunderstorms and heavy rain, with lesser potential for minor
  snow and ice accumulations.

- Many rivers above bankfull into the weekend. Potential for at
  least minor flooding may increase next week.

&&

.DISCUSSION...
Issued at 250 AM CDT Fri Mar 27 2026

Snow showers today and active pattern next week are the main
focus points of the forecast.

High pressure building in from central Canada across the northern
Great Lakes leading to quiet start to the day. Northerly flow is
bringing lake clouds to Door County and the lakeshore, and most
recently into the Green Bay area. No flurries are noted though.

Watching shortwave upstream as this feature is already causing
snow from southern Manitoba to northwest MN. This wave arrives
during peak heating in our area, and low-level lapse rates will be
steep. Forecast soundings show strongest lift is within DGZ.
Though not a lot of snow will result, strongest snow showers late
morning through afternoon could be frisky as shown by modeled
reflectivity and vsby forecasts from CAMs. NAMnest and HRRR point
to far northeast WI, Door County and Fox Valley, lakeshore as
being where heavier snow showers will be this afternoon. Main
impact will be sharply reduced visibility less than 1SM and a
quick burst of snow. Though temps will be marginal, especially in
these areas, setup could allow quick cooling. If the more robust
guidance is correct, a few spots could be dealing with borderline
snow squall situation this afternoon and the snow squall parameter
points to such. Main factor holding that back is marginal temps,
so this will have to monitored as the day progresses. Certainly
could be day where we issue a few SPSs due to lower vsby with non-
zero chance of a Snow Squall Warning.

Transition day Saturday. Warmer than today, but decent amount of
clouds. GFS looks to be on its own showing another round of snow
showers north-central. Will discount that, for now. More significant
warming begins Sunday as high shifts east, putting area in return
flow. Onshore winds keep lakeshore cooler, but highs will return
to the 60s inland. Similar on Monday, though a gradient E-NE wind
could keep more of northeast WI to the Fox Valley, lakeshore on the
cooler side. Precipitation chances hold off until Monday night.

Active pattern still showing up for much of next week, though the
details are not certain. For the big picture look, low pressure(s)
forming over the central Plains on Monday will have a warm front
extending to the east, south of WI. Eventually though this warm
front lifts north, transporting deeper Gulf moisture and instability
into the western Great Lakes. One switch compared to last couple
days is colder air on Monday night is really shunted north, so
mainly liquid even all the way into northern WI. Small chances for
thunder as main elevated instability remains well to the southwest.
Better chances for thunder, maybe even the risk of stronger storms
along with possible heavy rain is Tuesday into Tuesday night.
ECMWF EFI has trended upward for its CAPE, shear forecasts compared
to previous runs that kept this focus mainly south. Can see this
in NBM temps as well which now have highs in the 60s farther north
into central WI and Fox Valley. We'll see if this occurs as it
can be a challenge to get the warm front that far north due to
colder flow off Lake Michigan. Guess the main takeaway is could
see some stronger storms close by or in our area on Tuesday. Given
the moisture into the system, locally heavy rain could occur as
well which could lead to hydro issues on rivers and even in an
areal sense for low-lying, poor drainage, urban areas.

At least right now, models have trended away from the wintry
aspect of these systems early in the week, but 32 degree line is
not that far away and looking at reasonable higher end scenarios
from ensembles points to some snow and ice accumulations over the
north. That said, current NBM probabilities for *any* snow or ice
accumulations Monday night through Wed morning stand at less than
10% where runs recent days showed values up to 30-40% at times, so
that trend is certainly noted.

Better agreement emerging in ECMWF idea from last couple days that
main low-level jet axis veers enough Wednesday into Thursday to
push main frontal zone south and east of forecast area. Current
pops still in chancy range Wednesday into Thursday, but could see
these lowering over time if the trends from ensembles continue.

Finally, though just beyond the scope of the current forecast,
we'll have to keep eye out for next Friday into Easter weekend as
GFS/ECMWF/Canadian and ensembles have been bouncing back and
forth with idea of another well developed system (with a wintry
component) shifting from the plains to the Great Lakes downstream
of well agreed upon large scale troughing over the western CONUS.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 623 AM CDT Fri Mar 27 2026

Lake stratocu clouds (MVFR) over eastern WI will scatter out through
mid morning as winds in the boundary layer shift from NNE to NNW.

Shroud of VFR clouds upstream into western WI will sweep across
all terminals late morning through the afternoon with scattered
light light snow showers or flurries. With daytime heating though,
snow showers could intensify from north-central to northeast WI this
afternoon. Have framed out the most likely time at RHI/GRB/ATW/MTW
with Prob30 groups when stronger snow showers may move through with
vsby down to IFR and gusty northwest winds to 25-30 kts. These
"windows" for the heavier snow showers are likely too long and
can be further refined through the day as confidence increases on
details. Overall, not completely sure these heavier snow showers
will materialize, so that is why just used a Prob30 for now.

Plan on improving conditions late this evening and overnight at
all TAF sites as skies become mostly clear and winds diminish.

&&

.HYDROLOGY...
Issued at 250 AM CDT Fri Mar 27 2026

Several rivers will remain above bankfull through this weekend
due to the recent melting snow along with the rain that fell on
Thursday. In addition, longer range ensemble river probability
forecasts point to handful of rivers potentially reaching minor
flood stage next week if we see thunderstorms and heavy rain early
in the week. This would especially be the case if the heavy rain
occurs over northern areas that will still have snow cover at that
point. Currently the highest probabilities for at least minor
flooding are showing up at points along the Menominee River, Wolf
River, Little Wolf River, and the Embarrass River.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......JLA
HYDROLOGY......JLA