082
FXUS63 KGRB 091832
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
132 PM CDT Wed Sep 9 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Gusty west winds up to 35 mph this afternoon will subside early
  this evening, yielding quiet and seasonable weather tonight
  through Thursday as high pressure moves across Wisconsin.

- Chances for thunderstorms return on Friday night into Saturday
  morning, though the severe weather threat is low.

- Potential for heavy rainfall and thunderstorms increases Sunday
  into Monday as a stronger low pressure system tracks near the
  region, though forecast uncertainty remains high.

&&

.DISCUSSION...
Issued at 131 PM CDT Wed Sep 9 2026

RAP analysis indicates a cold front dropping into southeast
Wisconsin early this afternoon, with surface high pressure
centered over the northern Plains steadily building eastward
toward the western Great Lakes in its wake. West winds behind the
departing cold front have become gusty early this afternoon, with
widespread gusts between 25 and 30 mph and occasional peak gusts
reaching 35 mph across north-central Wisconsin. A Small Craft
Advisory remains in effect for the Bay of Green Bay and Lake
Michigan nearshore waters north of Sturgeon Bay through 7 PM CDT
due to these gusty winds and building wave action.

Gusty Winds Today and Fog Potential Tonight...
Wind gusts will subside rapidly early this evening as boundary
layer mixing wanes and surface high pressure slides into the
state. A dry airmass accompanying the surface high, combined with
modest boundary layer winds, will limit fog formation overnight
despite clear skies and modest surface winds. Tranquil conditions
will prevail through Thursday under high pressure, with scattered
fair- weather cumulus developing late Thursday morning with bases
between 4000 and 5000 feet. High temperatures on Thursday will
remain near seasonal norms in the 70s.

Thunderstorm Potential Friday Night and Saturday...
The weather pattern becomes more active heading into the end of
the work week as shortwave energy lifts northeast across the
northern Plains into south-central Canada. This shortwave will
push a cold front across Wisconsin late Friday night through
Saturday morning. Ahead of the boundary, a narrow moisture channel
will advect into the region, pushing precipitable water values up
to 140 to 150 percent of normal. Despite respectable synoptic
dynamics and moisture, the risk for organized severe weather
appears low. Model sounding profiles display a significant capping
inversion centered around 800 mb, which should limit surface-
based convection. While elevated instability of 600 to 800 J/kg
exists above the cap, instability diminishes significantly with
eastward extent late Friday night into Saturday morning.
Consequently, scattered thunderstorms and rain showers are
expected along and ahead of the front, but severe weather is not
anticipated.

Thunderstorm and Heavy Rainfall Potential Sunday and Monday...
Forecast attention turns to the Sunday into Monday timeframe as
the frontal boundary returns north as a warm front. A wave of
surface low pressure is forecast to track northeast along the
front, with the latest guidance showing the low passing across
northwest Wisconsin. Guidance spread remains rather large
regarding the precise surface low track and timing, leading to low
confidence in the exact details. However, dynamic forcing aloft
combined with excessive moisture transport bringing precipitable
water values approaching 200 percent of normal creates a signal
for heavy rainfall. The Extreme Forecast Index highlights
Wisconsin for potential heavy rain, with probabilities for greater
than 1 inch of rainfall reaching 40 to 50 percent over north-
central Wisconsin. This widespread precipitation would offer
beneficial moisture to drought-stricken areas across far northern
Wisconsin. Should the low track across northwest Wisconsin as
advertised, portions of the forecast area could enter the warm
sector, allowing Most Unstable CAPE to reach 1000 to 1500 J/kg if
sufficient surface heating occurs. This potential setup would
favor a risk for severe thunderstorms, though overall confidence
remains low given the extended timeframe.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1217 PM CDT Wed Sep 9 2026

Behind a cold front, west winds will remain gusty at 20-30 kts
this afternoon across all terminals (KGRB/KATW/KMTW/KAUW/KCWA/KRHI),
subsiding early this evening. Otherwise, VFR conditions are
expected through the TAF period. High pressure moving across the
state will bring a dry airmass, keeping the fog risk low tonight.
Scattered fair-weather clouds with ceilings around 4000-5000 ft
AGL will develop late Thursday morning.

Forecast confidence is high for VFR conditions and wind trends.

&&

.MARINE...
Issued at 131 PM CDT Wed Sep 9 2026

The Small Craft Advisory remains on track to expire at 7 PM today
due to gusty west winds. Another Small Craft Advisory and Beach
Hazards Statement will likely be needed from Friday afternoon
through Saturday morning for gusty south winds to 30 kts and waves
3-6 ft.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......MPC
MARINE.........MPC

NWS GRB Office Area Forecast Discussion