Severe Thunderstorm Warning 22, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
Issued by National Weather Service Milwaukee/Sullivan WI
400 PM CDT Thu May 15 2025

.KEY MESSAGES...

- Marine Dense Fog Advisory for the nearshore areas of Lake
  Michigan through the early evening. A Small Craft Advisory

- A broken line of strong thunderstorms will cross northern WI
  between 4 and 9 PM today. Some severe storms are likely with
  the passage of a cold front. All hazards possible over central
  WI and large hail possible over eastern WI.

- Another period of showers and weak storms expected Friday with
  some potential for gusty winds with some of these
  showers/storms.

&&

.DISCUSSION...
Issued at 304 PM CDT Thu May 15 2025

The Rest of this Afternoon through Friday Night:

A broken line of cellular storms has broken out, currently from
Eau Claire down to Madison WI. This is line is expected to
develop further and ramp up in intensity this evening. Hail and
gusty winds are expected, owing to SBCAPE around 2500 J/kg amid
effective shear around 40 knots. A couple tornadoes also look
possible, given effective SRH values around 200 m2/s2 over much
of NE WI, and an effective warm front parked from the Fox
Valley up through Marathon and Lincoln County. The peak timing
for storms looks to be from 5pm through 8pm this evening as the
broken line moves northeast. A Tornado Watch is out from now
through 10pm over much of our CWA.

Storms will quickly move through and a dry punch aloft will
clear out skies fairly quickly behind the storms. There will be
a bit of a lull overnight, but tomorrow, enhanced mixing will
lead to gusty southwest winds with some scattered gusts to 40
mph. A secondary shortwave pivoting around an upper level low
and lingering moisture will squeeze out some more scattered
thunderstorm activity in the afternoon. Very dry low levels and
the high based nature of the storms will cause the potential for
gusty winds with any storms that get established enough in the
environment.

Saturday through Wednesday

The upper low will linger into Saturday. Cooler conditions are
expected due to clouds and the cooler air aloft and highs will
top out in the low to mid 60. Diurnally driven scattered
showers may occur through the day. This upper low should move
east on Sunday, restoring relative high pressure, but clouds
will likely linger along with cooler temperatures as winds will
come around to northeasterly. By late in the extended period, a
large low pressure system is expected to approach the upper
Midwest Monday into Tuesday, bringing a prolonged period of
showery rain and clouds to the area. Winds will remain
northeasterly off of the lake, keeping our CWA cool with highs
in the 50s.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 304 PM CDT Thu May 15 2025

Current conditions still largely remain VFR across the CWA with
SCT to CLR conditions most everywhere save for areas from west
of KGRB to KCWA where BKN040 is largely present. A line of
storms currently present, arching from KMSN to KMSP, and this
line should continue to develop and move northeast between now
and 03z this evening. These storms will feature gusty winds, and
large hail. Following storms, skies are expected to remain
clear overnight as a dry slot moves in, with mostly clear winds.

VFR ceilings return tomorrow afternoon with sfc wind gusts
becoming strong out of the southwest to 35 knots in spots. There
may be additional scattered thunderstorm development in the
afternoon with gusty winds being the primary threat.

&&

.MARINE...
Issued at 304 PM CDT Thu May 15 2025

Marine dense fog will continue into this evening until
thunderstorms and a front pass during the early evening hours. A
small craft advisory will also continue into tonight on
southeast winds. Following the passage of the front, winds
should ease for a time overnight and then come around to
southwesterly by tomorrow at dawn. Gusty southwesterly winds are
then expected to pick up leading to a potential second period of
Small Craft Advisory conditions during tomorrow afternoon.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...None.
MARINE...Dense Fog Advisory until 7 PM CDT this evening for LMZ521-522-
     541>543.
     Small Craft Advisory until 1 AM CDT Friday for LMZ522.
     Small Craft Advisory until 11 PM CDT this evening for LMZ542-
     543.

&&

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

Hazardous Weather Outlook
National Weather Service Green Bay WI
Issued by National Weather Service Milwaukee/Sullivan WI
308 PM CDT Thu May 15 2025

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-162015-
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-
308 PM CDT Thu May 15 2025

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

.DAY ONE...Tonight

A line of strong thunderstorms will cross northern WI between 4
and 9 PM this afternoon into tonight. Severe storms are likely
with all hazards possible over central WI and large hail possible
over eastern WI.

.DAYS TWO THROUGH SEVEN...Friday through Thursday

Gusty southwest winds up to 45 mph are possible for the Fox
Valley on Friday. Showers and another round of storms may bring
gusty winds Friday afternoon.

Thunderstorms may return Tuesday into Wednesday of next week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed this afternoon and evening. Your
reports are appreciated.

LMZ521-522-541>543-162015-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
308 PM CDT Thu May 15 2025

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

.DAY ONE...Tonight

A Marine Dense Fog Advisory remains in effect through the early
evening.

Small Craft Advisory in effect this afternoon through much of the
evening for the southern portion of the Bay of Green Bay as well
as in the nearshore from Sturgeon Bay to Sheboygan.

Thunderstorms are expected this afternoon and evening. Some of
the storms could become severe. The primary hazard will be large
hail.

.DAYS TWO THROUGH SEVEN...Friday through Thursday

Hazardous conditions for small craft are possible Friday through
Saturday due to high winds, particularly for Lake Michigan
nearshore waters.

Preliminary Local Storm Report
National Weather Service Green Bay WI
621 PM CDT Thu May 15 2025

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

0615 PM     Hail             2 E Evergreen           44.84N 89.61W
05/15/2025  E1.00 Inch       Marathon           WI   Public

            Report from mPING: Quarter (1.00 in.).

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
622 PM CDT Thu May 15 2025

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

0615 PM     Hail             2 E Evergreen           44.84N 89.61W
05/15/2025  M1.00 Inch       Marathon           WI   Public

            Report from mPING: Quarter (1.00 in.).

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
625 PM CDT Thu May 15 2025

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

0624 PM     Rain             2 S Plover              44.43N 89.54W
05/15/2025  M1.09 Inch       Portage            WI   Public

            1.09 inches of rain from 5:45 to 6:20PM and
            still moderate rain falling.

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
652 PM CDT Thu May 15 2025

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

0620 PM     Hail             2 E Evergreen           44.84N 89.59W
05/15/2025  M1.25 Inch       Marathon           WI   Public

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
655 PM CDT Thu May 15 2025

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

0650 PM     Hail             2 WSW Amherst Junction  44.46N 89.35W
05/15/2025  E1.50 Inch       Portage            WI   Public

&&

Preliminary Local Storm Report
National Weather Service Green Bay WI
659 PM CDT Thu May 15 2025

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

0600 PM     Hail             1 N Stratford           44.81N 90.08W
05/15/2025  M0.70 Inch       Marathon           WI   Trained Spotter

            Reported on slack from trained spotter.

&&