596
FXUS63 KGRB 150637
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
137 AM CDT Tue Sep 15 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Light to moderate rain will exit by mid to late morning,
  followed by breezy west winds gusting 20 to 30 mph this
  afternoon.

- Hazardous marine conditions with gale-force gusts on Green Bay
  and Lake Michigan will transition to Small Craft Advisories
  later this morning. A dangerous rip current risk along Lake
  Michigan beaches will continue through this afternoon.

- A stronger system brings widespread rain late Friday into
  Saturday, with a 40 to 50 percent chance of rainfall exceeding 1
  inch across much of north-central and northeast Wisconsin.

&&

.DISCUSSION...
Issued at 133 AM CDT Tue Sep 15 2026

A potent surface low pressure system centered over southern
Manitoba early this morning is tracking northeast toward Hudson
Bay, pulling a cold front eastward across Minnesota while a warm
front lifts northward into Iowa. Aloft, a strong 50 to 60 knot
low-level jet directed into northeast Wisconsin has generated
widespread showers and scattered embedded thunderstorms early
this morning. Latest radar imagery and surface observations
confirm a swath of 1 to 3 inches of rain, with localized reports
exceeding 3 inches, extending from Portage and Waushara counties
northeastward into Outagamie and Brown counties. Although local
county dispatch reported no widespread flooding overnight, radar
estimates and private weather stations indicated rainfall rates
exceeding 6-hour flash flood guidance, maintaining a localized
urban and small stream flooding risk early this morning. Will
maintain the Flood Advisory for east-central WI until expiration.
As the low- level jet veers eastward, the heaviest precipitation
is shifting south and east of the area.


Light to moderate rain today through Wednesday Night...
Light to moderate showers along with isolate storms will linger
through mid to late morning until the cold front sweeps across the
area. Additional rainfall amounts up to 0.50 inches will be
possible across east- central and northeast WI. Strong boundary
layer mixing behind the front will yield clearing skies and breezy
west winds this afternoon, with frequent gusts of 20 to 30 mph
expected before winds diminish rapidly near sunset.

Surface high pressure building across the northern Great Lakes
will bring dry and tranquil weather for tonight and Wednesday.
Radiational cooling beneath clear to partly cloudy skies and light
winds will promote the formation of patchy ground fog late
tonight into early Wednesday morning, particularly across far
northern Wisconsin. High temperatures Wednesday will be
seasonable, reaching the upper 60s to low 70s. As the frontal zone
slowly returns north Wednesday night, elevated warm advection
will bring a 30 to 50 percent chance of light showers to central
and east- central Wisconsin. However, moisture availability is
modest and elevated instability reaches only 100 to 200 J/kg,
keeping the probability of rainfall exceeding 0.50 inches under 10
to 20 percent in the southern Fox Valley, with no heavy rain
impacts anticipated.

Widespread rain late Friday into Saturday...
A more dynamic weather system is forecast to impact north-central
and northeast Wisconsin late Friday into Saturday as a shortwave
ejects from the western United States trough. Supported by a 40
to 50 knot low-level jet and precipitable water values rising to
around 1.70 inches (roughly 95 percent of seasonal normal),
widespread showers and embedded thunderstorms will spread across
the region. Model guidance indicates a 40 to 50 percent
probability for 24-hour rainfall amounts to exceed 1 inch across
much of the area from Friday night through Saturday morning.
Elevated instability remains limited with Most Unstable CAPE
generally under 500 J/kg, keeping the severe thunderstorm risk
low. Forecast predictability decreases markedly Sunday into Monday
depending on how quickly the main western trough moves eastward,
but lingering mid-level energy will maintain a 20 to 30 percent
chance of showers through Sunday.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 133 AM CDT Tue Sep 15 2026

Rain and scattered thunderstorms, some with heavy rain, will
gradually end from northwest to southeast overnight into early
Tuesday morning. VFR CIGS will steadily fall into the IFR/MVFR
category from west to east through the overnight. Some fog may
form late north-central, including at RHI. Conditions will
gradually improve to VFR by Tuesday afternoon.

Concerning winds, south to southeast winds with gusts 20-30 kts
are expected at times through the night as winds veer southwest.
Low-level jet up to 50 kts will be present most of the night,
leading to LLWS at all TAF sites. The cold front will push across
the area late tonight into Tuesday morning, with gusty west winds
lingering behind it into Tuesday afternoon. Winds will become
light on Tuesday evening.

&&

.MARINE...
Issued at 133 AM CDT Tue Sep 15 2026

Hazardous marine conditions remain present early this morning with
gale force gusts measured at Sheboygan Light to the northern Lake
Michigan buoy. These gale force gusts look mainly confined to Lake
Michigan. Southerly wind gusts up to 35 knots will subside
through early morning as the cold front approaches and the
pressure gradient relaxes somewhat. Gales will expire by 7 AM CDT,
giving way to Small Craft Advisories across all nearshore waters
through the afternoon as winds shift west at 15 to 25 knots.
Additionally, residual high wave action along Lake Michigan
beaches will create a high risk of dangerous rip currents through
this afternoon, supporting an active Beach Hazards Statement for
the shoreline of Door, Kewaunee, and Manitowoc counties.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement through this evening for WIZ022.

Beach Hazards Statement through this afternoon for WIZ040-050.

MARINE...Gale Warning until 7 AM CDT this morning for LMZ521-522-
     541>543.
     Small Craft Advisory from 7 AM this morning to 4 PM CDT this
     afternoon for LMZ521-522.
     Small Craft Advisory from 7 AM this morning to 7 PM CDT this
     evening for LMZ541>543.
&&

$$

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