Severe Thunderstorm Warning 97, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
130 PM CDT Sat Aug 9 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- There is a slight risk of severe thunderstorms and excessive
  rainfall through early this evening. Strong to locally damaging
  winds and flash flooding in urban areas will be the primary
  concerns from Wood County to the lakeshore through about 8 pm.

- Showers and thunderstorms will have potential to bring the
  potential for locally heavy rainfall and urban flooding to
  parts of central and east central WI on Sunday and Sunday night.

- Gusty south winds and building waves will result in hazardous
  boating and swimming conditions on Lake Michigan through late this
  evening.

&&

.DISCUSSION...
Issued at 129 PM CDT Sat Aug 9 2025

Short Term...Tonight and Sunday

The latest RAP analysis and satellite/radar imagery show a cold
front draped from northeast Minnesota to far western Wisconsin to
northwest Iowa early this afternoon. The front is moving very
slowly as a potent upper-level low over the northern plains is
lifting northeast and winds aloft are moving parallel to the
front. Thunderstorms have been slowly moving for the most part
today, but a strong bowing segment is rapidly pushing east across
central Wisconsin. The primary forecast concerns are thunderstorms
and heavy rainfall as the slow-moving front slowly moves east.

Thunderstorms

The main show of thunderstorms will likely occur through late
afternoon as an MCV and bowing line segment race across central
and east-central Wisconsin. Localized damaging wind gusts and
perhaps a weak spin-up will be possible as this line segment
encounters a more buoyant airmass with ML CAPE of 1500 j/kg over
east-central Wisconsin this afternoon. Stratiform rainfall will
linger over northeast Wisconsin into the early to mid-evening
hours. The focus of nocturnal convection will then turn to
southern Wisconsin overnight as an outflow boundary or effective
front focuses thunderstorm activity south of the region. A second
round of showers and storms is indicated for Sunday as an MCV
slides into the region from the southwest. Diurnal instability of
1000-1500 j/kg is possible if widespread cloud cover doesn't
inhibit the heating curve. However, deep layer shear of 15-20
knots will likely make severe storms difficult to develop.

Heavy Rainfall

Heavy rainfall will remain a threat through early this evening.
Radar estimated rainfall has already reached over 2 inches over
Wood and southern Marathon counties. A corridor of 2-inch
precipitable water values remains across the region, which is
about 175% of normal. There is a slight risk of flash flooding
over parts of central to northeast Wisconsin. A Flood Watch
remains in effect over central Wisconsin until 5 pm and east-
central Wisconsin until 8 pm.

The main threat on Sunday will be heavy rainfall, particularly
after today’s heavy rains and persistent forcing along the front.

Marine

Persistent gusty south winds will cause waves to build to 4-
6 feet on Lake Michigan through 1 am Sunday. This will likely
result in hazardous boating conditions for small craft and
dangerous swimming conditions. A Small Craft Advisory and Beach
Hazard Statement has been issued.

Long Term...Sunday Night Through Saturday

The slow-moving cold front will continue to provide the focus for
showers and storms on Sunday night into Monday, mainly over
eastern Wisconsin. Instability looks limited during this period,
so severe weather is not expected. A stronger front will then dive
across the region on Tuesday, bringing an end to the storm chances
until later in the week. As deep layer flow turns to the southwest
once again, thunderstorm chances will return towards Thursday and
Friday.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1159 AM CDT Sat Aug 9 2025

A slow-moving cold front is expected to traverse the region over
the next 24 hours, bringing periods of showers and thunderstorms.
While the first round will continue through this afternoon, the
timing of subsequent rounds remains uncertain, with current
indications pointing towards Sunday morning as the most probable
period for another round of precipitation.

The primary concern for severe weather focuses on the east-
central Wisconsin TAF sites, specifically including Green Bay
(GRB), Appleton (ATW), and Manitowoc (MTW). Within the timeframe
of approximately 1900 UTC to 0100 UTC, there is a possibility of
severe thunderstorms. The main hazards associated with these
stronger storms include gusty winds in excess of 40 knots, small
hail, and reduced visibilities to IFR.

Following the departure of these thunderstorms to the south this
evening, the region is expected to experience a relatively quiet
period for the remainder of the night. Guidance suggests the
development of low stratus late tonight. This low cloud
development is projected to result in widespread visibility
reductions possibly reaching LIFR and ceilings reaching IFR
criteria. The most probable timing for these lower visibilities
and ceilings are from 0600 UTC and 1400 UTC.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 1 AM CDT Sunday for WIZ022-040-050.

Flood Watch until 5 PM CDT this afternoon for WIZ035>037-045.

Flood Watch until 10 PM CDT this evening for WIZ038>040-048>050.
&&

DISCUSSION.....MPC/MPC
AVIATION.......MPC

Hazardous Weather Outlook
National Weather Service Green Bay WI
130 PM CDT Sat Aug 9 2025

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-101830-
Vilas-Oneida-Forest-Florence-Northern Marinette County-Lincoln-
Langlade-Menominee-Northern Oconto County-Door-Marathon-Shawano-
Wood-Portage-Waupaca-Outagamie-Brown-Kewaunee-Waushara-Winnebago-
Calumet-Manitowoc-Southern Marinette County-
Southern Oconto County-
130 PM CDT Sat Aug 9 2025

This Hazardous Weather Outlook is for north-central and northeast
Wisconsin.

.DAY ONE...Tonight

There is a slight risk of severe thunderstorms across much of
northeast Wisconsin. A few severe storms with damaging winds and
torrential rainfall will be possible, especially in parts of east-
central Wisconsin, including the Fox Valley through early
evening.

Conditions will also be favorable for heavy rainfall over parts
of central and east-central Wisconsin. A Flood Watch has been
issued through 8 PM for forecast rainfall amounts of 1 to 3
inches with localized amounts up to 4 inches possible.

There is an increased risk of rip currents on Lake Michigan
beaches through this evening. A Beach Hazards Statement has been
issued.

.DAYS TWO THROUGH SEVEN...Sunday through Saturday

Additional rounds of thunderstorms will be possible Sunday into
Monday especially over the southeast half of the forecast area.
While the threat of severe storms is fairly low during this
period, there is potential for torrential rainfall and urban
flooding in parts of central and east central Wisconsin.
Additional thunderstorms will be possible at times during the
end of the next work week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this afternoon and this evening.

LMZ521-522-541>543-101830-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
130 PM CDT Sat Aug 9 2025

This Hazardous Weather Outlook is for portions of northwest Lake
Michigan and the waters of Green Bay.

.DAY ONE...Tonight

Gusty south winds and high waves will likely result in conditions
hazardous to small craft through this evening. A Small Craft
Advisory has been issued for the Lake Michigan nearshore waters.

There will be a chance of thunderstorms through late tonight. The
stronger storms will be capable of producing gusty winds and
torrential rainfall. Any thunderstorms that develop will pose a
threat to mariners.

.DAYS TWO THROUGH SEVEN...Sunday through Saturday

Thunderstorms will be possible at times from Sunday through
Monday, and at times at the end of next week. Any thunderstorm
could pose a threat to mariners.

MPC

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Preliminary Local Storm Report
National Weather Service Green Bay WI
1259 PM CDT Sat Aug 9 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1210 PM     Hail             De Pere                 44.45N 88.05W
08/09/2025  M0.50 Inch       Brown              WI   Public

&&

Special Weather Statement
National Weather Service Green Bay WI
100 PM CDT Sat Aug 9 2025

WIZ073-074-091845-
Southern Oconto County WI-Southern Marinette County WI-
100 PM CDT Sat Aug 9 2025

...STRONG THUNDERSTORMS WILL IMPACT SOUTHERN MARINETTE AND SOUTHERN
OCONTO COUNTIES THROUGH 145 PM CDT...

At 1259 PM CDT, Doppler radar was tracking a cluster of strong
thunderstorms near Oconto, or 15 miles northwest of Bay Shore Park,
moving northeast at 35 mph.

HAZARD...Wind gusts up to 40 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor hail damage to vegetation is
         possible.

This strong thunderstorm will be near...
  Oconto around 105 PM CDT.

Other locations impacted by this storm include Little Suamico,
Cullen, Abrams, Brookside, Stiles, County Line, Harmony, Peshtigo,
Sobieski, and Pensaukee.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with this storm and may lead to
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4494 8759 4490 8778 4486 8777 4470 8792
      4467 8797 4474 8816 4512 8782 4498 8757
TIME...MOT...LOC 1759Z 225DEG 30KT 4482 8796

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...40 MPH

JLA

Special Weather Statement
National Weather Service Green Bay WI
144 PM CDT Sat Aug 9 2025

WIZ031-036-037-091915-
Waupaca WI-Shawano WI-Portage WI-
144 PM CDT Sat Aug 9 2025

...STRONG THUNDERSTORMS WILL IMPACT EAST CENTRAL PORTAGE...WAUPACA
AND WESTERN SHAWANO COUNTIES THROUGH 215 PM CDT...

At 144 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Amherst to Waupaca. Movement was northeast
at 45 mph.

HAZARD...Wind gusts up to 50 mph.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects.

Strong thunderstorms will be near...
  Waupaca around 150 PM CDT.

Other locations impacted by these storms include Fitzgerald Corners,
Rural, Schmidt Corner, Split Rock, Northport, Scandinavia, Sheridan,
Northland, Nelsonville, and Ogdensburg.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

Torrential rainfall is also occurring with these storms and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 4426 8917 4451 8938 4477 8900 4440 8873
      4434 8874
TIME...MOT...LOC 1844Z 233DEG 39KT 4452 8923 4433 8909

MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH

JLA

Preliminary Local Storm Report
National Weather Service Green Bay WI
200 PM CDT Sat Aug 9 2025

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0145 PM     Tstm Wnd Dmg     Waupaca                 44.34N 89.06W
08/09/2025                   Waupaca            WI   Law Enforcement

            Tree branches down.

&&