Severe Thunderstorm Warning 42, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
750 PM CDT Fri Aug 11 2023

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 248 PM CDT Fri Aug 11 2023

Main concern is on thunderstorm potential this evening.

As of 19Z all but a few light showers had departed the area from
the morning convection, with pockets of clear skies, but clouds
were mostly still scattered to broken. Even so, SBCAPE values
ranged from about 800 to 1800 J/kg across the forecast area,
highest in central Wisconsin, lowest near the Upper Michigan
border. Farther west, an area of convection was developing across
central MN associated with a mid-level shortwave and jet streak.
This will be the main focus for this evening.

Ahead of this, some isolated, mid-afternoon light showers were
starting to pop up across the CWA as of 1930Z, driven by
instability and weak WAA. While the instability is there, don't
think the forcing will be strong enough to get much going out of
these. Some brief rain, and maybe a few lightning strikes will be
the main concern.

The complex across central MN is expected to reach the western CWA
around 01Z. While this complex will likely grow over the next few
hours, by the time it reaches the GRB forecast area instability
will start to wane and becoming elevated. The area with the
greatest potential for severe storms is central Wisconsin between
about 01Z to 04Z, with damaging winds and large hail the main
threats. After that time severe potential looks low. However, rain
and non- severe storms will continue to track across the area,
focused mainly south of Hwy 29. After 07Z most of this activity
will depart.

The rest of the night...Some clearing across the southern CWA, but
clouds and fog are possible across the north, possibly dense fog
in spots. Lows will range from the middle 50s to lower 60s.

Saturday...Overall, should be a quiet and pleasant day. Clouds
will be more persistent across northern Wisconsin, with a few
stray instability showers possible in the afternoon. Highs will
range from the upper 60s across far northern Wisconsin, to the
low 80s in the Fox Valley.

.LONG TERM...Saturday Night Through Friday
Issued at 248 PM CDT Fri Aug 11 2023

A low pressure system developing across the upper Mississippi
Valley will bring the next chance for rain to the region Sunday
afternoon into Monday night. This will be a slow moving system
with strong dynamics and several rounds of rainfall expected
during this period. The rain will start Sunday afternoon across
central and north-central Wisconsin, then spread east Sunday
night. The system will occlude Sunday evening and slowly track
across the western Great Lakes region Monday with lingering wrap
around moisture Monday night as the system tracks off to the east.
Instability with this system will be fairly limited, which will
limit overall severe potential. However some strong storms are
possible Sunday evening given the strong dynamics and decent bulk
shear values in place. The system is on track to provide a
widespread rainfall of over an inch across all of the area during
this period.

After a dry period on Tuesday another low pressure system and
attendant cold front could bring the chance for additional showers
and thunderstorms during the middle part of the week. Once this
system clears the area dry weather is then expected for the end of
next week. Other than below normal temperatures on Monday,
temperatures during the week are expected to more or less be
around normal for this time of year.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 750 PM CDT Fri Aug 11 2023

Isolated to scattered showers and a few storms will continue over
parts of eastern WI this evening, with a large cluster of storms
pushing across central WI. This cluster will race across east
central WI this evening, bringing brief lower CIGs and VSBYs and
gusty winds. Included thunder for AUW/CWA/ATW but held off on
GRB/MTW and will wait to see if the northern edge holds its line
or drops south. The storms will exit by 04-05z with only lingering
showers possible in north central WI overnight. Low clouds and fog
is also expected, mainly over north central WI overnight with some
IFR/LIFR conditions likely. More uncertainty in central WI.

Mainly dry conditions are expected on Saturday, but spotty showers
are possible, with a mix of low, mid and upper clouds. Northwest
winds will gust up to around 20 kts, possibly higher if we can mix
a little higher than expected.
&&

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

SHORT TERM.....KLJ
LONG TERM......Kurimski
AVIATION.......Bersch

Hazardous Weather Outlook
National Weather Service Green Bay WI
250 PM CDT Fri Aug 11 2023

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-122000-
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-
250 PM CDT Fri Aug 11 2023

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

.DAY ONE...Tonight

Thunderstorms are expected to arrive in central Wisconsin this
evening, around 8:00 PM. These storms could be strong or severe
and produce damaging winds and hail. There is only a marginal
threat of severe storms elsewhere during the evening.

Fog development is possible across northern Wisconsin tonight,
some of which could become dense.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

Thunderstorms are possible Sunday and Monday. Some of these storms
may become strong Sunday evening.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

LMZ521-522-541>543-122000-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
250 PM CDT Fri Aug 11 2023

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

.DAY ONE...Tonight

Scattered thunderstorms are possible this evening. Some storms
could produce strong winds during the evening.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

Thunderstorms are possible Sunday and Monday. Any thunderstorms
could pose a hazard to mariners.

KLJ/Kurimski

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