591
FXUS63 KGRB 120451
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1151 PM CDT Fri Sep 11 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Chances for storms return late tonight into Saturday morning,
  mainly in north-central WI. Severe weather threat is very low,
  but brief gusty winds are possible.

- A round or two of heavy rain and storms is possible Monday into
  Tuesday. The severe weather threat is low.

- Gusty south-southwest winds will generate high waves along Lake
  Michigan this afternoon through Saturday morning, causing
  hazardous conditions to small craft and dangerous swimming
  conditions at Lake Michigan beaches.

&&

.DISCUSSION...
Issued at 228 PM CDT Fri Sep 11 2026

Shower/Storm Chances Tonight into Saturday...Dry conditions will
continue into the early evening hours, with only a stray shower or
storm possible near Vilas Co. Then, higher chances for showers
and storms will spread into central and northern WI (40-70%) late
this evening as a shortwave and cold front advance across WI. The
activity will outrun the better instability in the late evening,
with any instability over northern WI waning after midnight, so
the severe threat looks very low, but strong winds aloft could
lead to some gusty winds as the line weakens. Not much rain
expected with this activity either, with most spots seeing under a
quarter inch. By the time the initial area gets into eastern WI,
not much will be left other than maybe some sprinkles. Then as the
front completes its passage, a shower or storm will be possible
across far eastern WI through around noon, but forcing will be
limited and a weak cap will remain in place, so have only included
some slight chance PoPs over Door Co. Weak high pressure is then
forecast to move into the western Great Lakes bringing mainly dry
conditions for the remainder of the weekend. However, another weak
system could graze the southern counties with some clouds or
showers on Sunday.

Heavy Rain and Storm Potential Next Week...Ensemble and
deterministic models in fairly good agreement showing a strong low
pressure system and shortwave tracking across the northern Plains
early next week, which will usher in PWATs up to 2" (near the 99th
percentile of climatology). As the LLJ cranks up on Monday, a
widespread area of showers and storms will form to our southwest
and move into the area Monday afternoon into Tuesday morning, with
the exact timing still to be ironed out. Severe weather threat
looks low due to limited instability and a strong capping
inversion, but elevated instability and the mean flow also
briefly becomes more parallel with the boundary layer flow which
will promote training convection. This could lead to some heavy
rain and a soaking rain for many spots. Question is just how long
it will sit over our area and how many rounds of rain any one
location will see. NBM probs have lowered a little, down to
30-45% chance for greater than 2" of rain Monday into early
Tuesday, with the highest chances across central WI. WPC has
also shifted a Slight Chance for excessive rain a little to the
south. Will still need to monitor for heavy rain with the high
PWATs and possible training convection, but will not hit the
messaging too hard at this point and watch for trends.

Rest of the Forecast...questions remain on how far south the
boundary will get next week within the zonal flow over the Great
Lakes and if we will hit with additional showers and storms or if
high pressure wins out and we stay mainly dry. NBM brings low end
PoPs (20-40%), especially across the south, for much of the week,
which is basically just portraying the differences in location of
the boundary. Hopefully the picture gets a little clearer as we
get closer. If we were to get more bouts of heavy rain later in
the week, this could increase the overall flood threat and will
need to be monitored. Some cooler air will filter into the region
behind the system on Tuesday, with some chilly air in store if the
high wins out.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1151 PM CDT Fri Sep 11 2026

While high/mid clouds will prevail across the region at the start
of this TAF period, radar trends for upstream showers/storms,
paired with hi-res models, continue to indicate a window of -TSRA
from 07-10z Sat for RHI/AUW/CWA. Hi-res models indicate this line
of showers/storms, ahead of a cold front, weakening as it moves
eastward through the remainder of the night into Saturday morning.
However, kept PROB30 groups for -SHRA at GRB and ATW for now. An
area of MVFR clouds, and brief IFR cigs at RHI, is expected behind
the showers through midday Saturday. As the front exits the area
around midday Saturday, a stray shower will be possible over far
eastern WI, but VFR conditions will prevail through the remainder
of the TAF period following the frontal passage.

South-southwesterly winds around 8-12 kts will continue
overnight, then shift west-northwest Saturday morning, with gusts
to 20 kts. The west-southwest winds will subside into Saturday
evening. Southwest/west LLWS is expected overnight as winds
around 2000 ft increase to 35-40 kts.

&&

.MARINE...
Issued at 228 PM CDT Fri Sep 11 2026

No changes to the current marine/beach headlines. Winds and waves
continue to increase/build late this morning and early afternoon.
Most gusts are staying below 20 kts with waves building to around
4 ft at the mid-lake buoy off of Manitowoc. Expect winds and
waves to increase a little more this afternoon with gusts to 25
kts possible at times. A high swim risk will continue into
Saturday morning.

Another period of breezy southeast to south winds will lead to
increasing waves Monday into Tuesday. Additional Small Craft
Advisory or Gale Warning and Beach Hazard Statements will likely
be needed.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through Saturday afternoon for WIZ022.

Beach Hazards Statement until 10 AM CDT Saturday for WIZ040-050.
&&

$$

DISCUSSION.....Bersch
AVIATION.......Kruk
MARINE.........Bersch

NWS GRB Office Area Forecast Discussion