Severe Thunderstorm Warning 121, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
558 AM CDT Mon Jul 27 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Severe thunderstorms capable of producing damaging winds and
  isolated large hail are possible this morning, and again across
  northeast Wisconsin this afternoon. A Severe Thunderstorm Watch
  is in effect until 9 AM.

- Heat indices are forecast into the middle to upper 90s across
  central Wisconsin this afternoon.

- Gusty northerly winds will build waves from 3 to 5 feet on Lake
  Michigan south of Two Rivers this evening into Tuesday
  afternoon.

- A cold front passing through the region will bring a shift to
  northerly winds and relief from the high humidity for Tuesday
  through mid-week, with lower thunderstorm chances until late in
  the work week.

&&

.DISCUSSION...
Issued at 245 AM CDT Mon Jul 27 2026

The latest RAP analysis and satellite/radar imagery show a surface
low pressure centered over northwest Minnesota. A cold front extends
southwest across eastern South Dakota, while a warm front extends
southeast and across far northern Wisconsin. Elevated convection
continues across parts of northern Minnesota and northern Wisconsin
early this morning, situated on the cool side of the warm front.
The environment remains conditionally favorable for severe weather
across the region, with MUCAPE in 2000-3000 J/kg range and strong
deep-layer shear of 40 to 50 knots. While storms have struggled
to intensify over northern Wisconsin so far, a Severe Thunderstorm
Watch has been issued until 9 AM.

Low-level warm advection ahead of the southeast sliding surface
low is expected to generate additional storm development early
this morning. Most guidance continues to depict an increase in
storm coverage and eventual clustering or organization into one or
more squall lines, capable of producing damaging winds and
isolated large hail. While a very low probability, a weak spin up
along a more organized line segment is possible given favorable
0-3km wind shear. Confidence remains low with the evolution, as
the CAMS have a relatively poor track record over the past 24-36
hours.  These storms will likely exit northeast Wisconsin by mid
to late morning.

A lull in thunderstorm potential is expected late this morning
through early afternoon following the departure of the morning
convective cluster. Rapid destabilization is then forecast during
the afternoon under strong heating. Upwards of 2000 to 3000 J/kg
of CAPE could build near peak heating, primarily over east-central
Wisconsin. Deep-layer shear of 50 knots will support rapid storm
intensification if storms redevelop. The most probable window for
severe storms is from 2 PM to 6 PM.

Very warm and humid conditions will again push heat index values
into the middle to upper 90s across Wood, Portage, Waupaca, and
Waushara counties this afternoon. Heat indices in these areas may
briefly flirt with 100 degrees but duration will be short (1-2
hours). Therefore no Heat Advisory will be issued.

Behind the departing surface low, north winds will intensify
tonight with gusts of 20 to 25 mph. Skies will clear from north to
south, leading to a mostly sunny Tuesday. While temperatures will
remain near to slightly above normal on Tuesday, a much drier
airmass will bring welcome relief as humidity levels fall into the
lower 40s in the afternoon.

Long Term...Wednesday Through Sunday
High pressure will stick around into Wednesday, keeping conditions
dry and quiet across north-central and northeast Wisconsin.
Numerical models have trended slightly quicker with warm advection
returning late Wednesday, resulting in more ambitious shower
development for the second half of Wednesday through Thursday. The
next chance for widespread rain and thunderstorm activity will
arrive on Thursday night and linger at times into Saturday. Upper-
level winds are forecast to remain relatively light, which should
keep the severe weather risk low. Temperatures will remain at or
slightly above normal next weekend with high pressure building
back into the western Great Lakes.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 558 AM CDT Mon Jul 27 2026

A warm front and surface low over northern Minnesota will bring
potential for thunderstorms today. Clusters of showers and
thunderstorms extending from the Arrowhead of Minnesota into
northeast Wisconsin continue to move southeast along the warm
front. The primary threat through 17Z will be across far
northeast Wisconsin, particularly along the Upper Peninsula
border. If storms continue to organize, potential will increase
for hail and strong wind gusts north of a RHI to SUE line. Other
storms over northeast WI should exit by shortly after TAF
issuance. MVFR ceilings expanding along the front over northwest
Wisconsin could drift into KRHI and AUW for a few hours this
morning. Otherwise, predominant VFR conditions are expected
across central and northeast Wisconsin terminals.

A general lull of the thunderstorm activity is expected from late
morning through early afternoon before additional isolated to
scattered storms redevelop between 19Z and 23Z along and ahead of
the surface low. The highest probability for afternoon convection
will focus over east- central Wisconsin, potentially impacting
KGRB, KATW, and KMTW. Confidence on timing and spatial coverage of
showers and storms remains low, so PROB30 groups were added.
Behind the low, winds shift north to northeast with gusts to 20
kts. A period of MVFR ceilings is possible at all terminals this
evening before clearing to VFR after 08Z.

Outlook: High pressure brings widespread VFR conditions and
lighter winds Tuesday into Wednesday.

.KOSH...
Scattered to broken clouds with ceilings 3.5 to 4.5 kft could
impact OSH this morning, which eventually evolve into a cumulus
field with daytime heating. Low confidence that any storms will
impact OSH this morning.

As the surface low moves across northern WI this afternoon,
concern increases for thunderstorms development. Forecast
soundings show ample dry air that should keep coverage isolated.
Added a prob30 group for the most favored time frame for showers,
but held off adding thunder. Confidence is low due to the dry air.

Behind the low, winds will shift to the north or northeast and
become gusty for a time. Gusts to 15-20 kts seem reasonable. The
north winds could also bring a brief period of MVFR ceilings
before skies clear overnight.

&&

.MARINE...
Issued at 245 AM CDT Mon Jul 27 2026

A cold front sagging south across the region will bring a risk of
severe thunderstorms to Green Bay and Lake Michigan this morning
and again this afternoon, posing a hazard to mariners. Behind the
front, a tightening pressure gradient will cause northerly winds
to increase to 15 to 25 knots tonight into Tuesday. Waves will
build to 3 to 5 feet on the Lake Michigan nearshore waters south
of Two Rivers, and a Small Craft Advisory will be issued. Winds
and waves will gradually subside Tuesday afternoon as high
pressure builds in from the north.

&&

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

&&

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

Hazardous Weather Outlook
National Weather Service Green Bay WI
249 AM CDT Mon Jul 27 2026

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-280800-
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-
249 AM CDT Mon Jul 27 2026

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

.DAY ONE...Today and Tonight

Strong to severe thunderstorms and locally heavy rainfall are
possible at times through this afternoon. Damaging winds, large
hail, and urban and small stream flooding will be the primary
hazards.

Heat index values may reach the middle to upper 90s over parts of
central Wisconsin this afternoon.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

The chance of thunderstorms will return late in the work week.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report any wind damage or hail to the
National Weather Service in Green Bay.

LMZ521-522-541>543-280800-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
249 AM CDT Mon Jul 27 2026

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

.DAY ONE...Today and Tonight

Strong to severe thunderstorms are possible at times through this
afternoon. Any storms could pose a hazard to mariners.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Conditions hazardous to small craft are expected south of Two
Rivers tonight through Tuesday afternoon.

The chance of thunderstorms will return late in the work week.

MPC

Special Weather Statement
National Weather Service Green Bay WI
913 AM CDT Mon Jul 27 2026

WIZ005-010-271500-
Vilas WI-Oneida WI-
913 AM CDT Mon Jul 27 2026

...A STRONG THUNDERSTORM WILL IMPACT NORTH CENTRAL ONEIDA AND VILAS
COUNTIES UNTIL 10 AM CDT...

At 913 AM CDT, Doppler radar was tracking a strong thunderstorm near
Winchester, or 34 miles northwest of Eagle River, moving southeast at
50 mph.

HAZARD...Wind gusts up to 50 mph and penny size hail.

SOURCE...Radar indicated.

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

The strong thunderstorm will be near...
  Winchester around 915 AM CDT. Rice Creek Natural Area around 920 AM
  CDT. Boulder Junction around 925 AM CDT. Johnson Lake Barrens
  Natural Area around 935 AM CDT. Eagle River around 955 AM CDT.

Other locations impacted by this strong thunderstorm include
Manitowish Waters, Van Vliet Hemlocks Natural Area, High Lake Natural
Area, Nixon Lake Natural Area, Trout Lake, Sayner, Star Lake, Upper
Buckatabon Springs Natural Area, St Germain and Conover.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

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 4590 8983 4598 8997 4598 8993 4630 8993
      4627 8976 4609 8905 4570 8952
TIME...MOT...LOC 1412Z 298DEG 42KT 4617 8987

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...50 MPH

JM

Special Weather Statement
National Weather Service Green Bay WI
915 AM CDT Mon Jul 27 2026

WIZ022-040-271500-
Door WI-Kewaunee WI-
915 AM CDT Mon Jul 27 2026

...A STRONG THUNDERSTORM WILL IMPACT SOUTHERN DOOR AND NORTHWESTERN
KEWAUNEE COUNTIES UNTIL 10 AM CDT...

At 915 AM CDT, Doppler radar was tracking a strong thunderstorm 9
miles northeast of Bay Shore Park, moving east at 35 mph.

HAZARD...Wind gusts up to 40 mph and penny size hail.

SOURCE...Radar indicated.

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

The strong thunderstorm will be near...
  Sherwood Point Light around 945 AM CDT. Sturgeon Bay Ship Canal
  Light around 950 AM CDT. Whitefish Point around 955 AM CDT.

Other locations impacted by this strong thunderstorm include
Shoemaker Point, Duvall, Dyckesville, Namur, Brussels, Rosiere,
Kolberg, Maplewood, Forestville and Carnot.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Monitor the weather situation closely and be alert for threatening
weather conditions.

&&

LAT...LON 4466 8775 4471 8777 4486 8765 4498 8718
      4489 8714 4489 8715 4488 8714 4486 8715
      4476 8725 4476 8726 4475 8728 4469 8731
      4465 8775
TIME...MOT...LOC 1414Z 257DEG 29KT 4475 8771

MAX HAIL SIZE...0.75 IN
MAX WIND GUST...40 MPH

KS

Preliminary Local Storm Report
National Weather Service Green Bay WI
941 AM CDT Mon Jul 27 2026

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

0904 AM     Hail             4 NE Eagle River        45.94N 89.17W
07/27/2026  E1.50 Inch       Vilas              WI   Public

            Report from mPING: Ping Pong Ball (1.50
            in.).

0939 AM     Hail             4 SE Crandon            45.52N 88.85W
07/27/2026  E1.00 Inch       Forest             WI   Public

            Report from mPING: Quarter (1.00 in.).

0938 AM     Hail             3 NE Brussels           44.77N 87.59W
07/27/2026  M1.00 Inch       Door               WI   Public

&&

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