639
FXUS63 KGRB 121839
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
139 PM CDT Sat Sep 12 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- The first widespread frost of the season is expected across
  the north late Sunday night into early Monday morning. A
  few of the typical colder locations could drop to or slightly
  below freezing for a few hours.

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

- Hazardous conditions for small craft are likely Monday afternoon
  into Tuesday afternoon due to gusty southerly winds or high
  waves.

- High waves will lead to an increased risk of rip currents at
  Lake Michigan beaches Monday afternoon into Tuesday afternoon.

&&

.DISCUSSION...
Issued at 139 PM CDT Sat Sep 12 2026

A cold front moving across northeast WI this afternoon was
producing a band of thick cloud. As the front passes, skies
will clear with mostly sunny skies expected. Tranquil conditions
prevail tonight with a preview of fall like temperatures with lows
in the 40s to around 50. The expected fgen band for tonight will
pass to the south of the area. On Sunday, per coordination with
surrounding offices to the north and west, lowered high temperatures
a few degrees, especially across the north based on the latest
MET/MAV guidance. This will mean high temperatures will be mainly
in the 60s on Sunday, with a few lower 70s across east- central
WI. For Sunday night, high pressure centered across the area
combined with light winds and clear skies should bring the first
widespread frost of the season across the north. Some of our
colder spots could drop to or a few degrees below freezing for a
couple of hours around sunrise.

Strong low pressure across the northern plains will move northeast
into Canada with a trailing cold front approaching Wisconsin on
Monday. Clouds will be on the increase with rain arriving
during the afternoon for locations mainly west of the Fox Valley.
This in response to an increasing 850mb low level jet and warm
advection. Meanwhile, a wave of low pressure will move along the
front Monday night as it moves across the region. Precipitable
water near 2" are near the top of the charts for this time of
year. Some complexities to the forecast as the NBM probabilities
over an inch are 50-80% from central into northeast WI while LREF
probabilities are in the 20-50%. Highest probabilities in both
solutions are out towards Wausau and Wisconsin Rapids. The risk
of severe weather appears to stay just to our south. Any lingering
showers should end Tuesday morning across northeast WI.

The boundary should far enough south for Tuesday night into
Wednesday morning for dry conditions. Beyond that, there could be
a few rounds of showers and perhaps a few thunderstorms Wednesday
afternoon through Thursday. By Friday, the Canadian/ECMWF have a
wetter solution compared to the GFS. Below normal temps for Sunday
into Monday, then seasonable temps for the rest of the work week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1213 PM CDT Sat Sep 12 2026

A band of CIGS in the MVFR category will exit northeast WI
by/around 21z. VFR conditions expected through Sunday
afternoon. West to northwest winds this afternoon will
gust up to 20 knots. After a night of light winds,
west to northwest winds will gusts to around 20 knots late
Sunday morning through mid afternoon before gradually
diminishing towards sunset.

&&

.MARINE...
Issued at 139 PM CDT Sat Sep 12 2026

Another period of gusty southerly winds will lead to increasing
waves, along with an increasing risk of rip currents Monday into
Tuesday. A Small Craft Advisory or Gale Warning and Beach Hazard
Statements will likely be needed.

&&

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

&&

$$

DISCUSSION.....Eckberg
AVIATION.......Eckberg
MARINE.........Eckberg

NWS GRB Office Area Forecast Discussion