Granite Peak

000
FXUS63 KGRB 151707
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1207 PM CDT Tue Sep 15 2026

Updated aviation portion for 18Z TAF 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 18Z TAF Issuance
Issued at 1206 PM CDT Tue Sep 15 2026

Gusty westerly winds and higher VFR conditions will prevail this
afternoon in the wake of a departing cold front. Some diurnally
driven cumulus may bring conditions down to MVFR at times across
north-central and central Wisconsin.

High pressure will bring light winds and clearing skies tonight,
as any diurnally driven cumulus dissipate across the region. The
clear skies and light winds will bring some patchy fog across the
region late tonight, particularly the north-central and central
Wisconsin TAF sites. LIFR VSBYs are most favored at KRHI after 
08Z (kept TEMPO), with patchy MVFR/IFR fog at KAUW/KCWA. VFR will
prevail at KGRB/KATW/KMTW.

Once the fog burns off Wednesday morning, VFR conditions and light
winds will prevail on Wednesday.

&&

.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 until 7 PM CDT this evening for WIZ022.

Beach Hazards Statement until 4 PM CDT this afternoon for WIZ040-
050.
&&

$$

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