Severe Thunderstorm Warning 64, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
703 PM CDT Mon Aug 26 2024

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Heat indices around 100 this evening will ease off the rest of
  the night. Impactful heat continues on Tuesday for some, when
  heat indices may reach 95 to 100 over parts of central Wisconsin
  and the Fox Valley.

- There is a slight risk of severe thunderstorms through Tuesday.
  At this time, it appears the greatest risk will occur after
  midnight tonight through early Tuesday morning. Damaging winds
  will be the primary concern. Another round is possible Tuesday
  afternoon into Tuesday evening; however, confidence is lower for
  this second round.

- Temperatures will be at or below normal starting Wednesday.

- Rain and thunderstorm return late Thursday into Friday.
  Probabilities of getting at least 1 inch of rain range from
  20-50%.

&&

.DISCUSSION...
Issued at 347 PM CDT Mon Aug 26 2024

Short Term...Tonight and Tuesday

The latest RAP analysis and satellite/radar imagery show a strong
mid-level ridge axis centered from the mid-Mississippi Valley,
across Wisconsin, to Lake Superior early this afternoon. With
daytime heating, a widespread cumulus field develop over central
and north-central Wisconsin by late this morning. Temperatures
have warmed into the middle to upper 80s. Combined with dewpoints
in the middle 70s, heat indices are reaching into the middle to
upper 90s. Looking upstream, a cold front is draped across western
to north-central Minnesota.

Satellite imagery shows shallow cumulus clouds developing across
northern Wisconsin this afternoon as a substantial capping
inversion exists between 750 mb and 800 mb. Upstream
thunderstorms are developing across Minnesota, which is progged
to track through the area later tonight. CAMs models are still
all over the place, with some models developing storms across
north-central Wisconsin later this evening, while others wait
until the thunderstorms across Minnesota develop further and ride
the ridge in place across the western Great Lakes region. Given
the substantial capping inversion in place, the later scenario
with the ridge riders seems mostly likely. That being said, the
model discrepancies do not lend a high level of confidence to the
forecast. Any storms that do develop will likely be organized
into a line, taking advantage of 1500-3000 J/kg of MUCAPE, with
straight line winds being the main severe weather threat.

Any storms that track through late tonight could linger well into
Tuesday morning, depending on the CAMs model. The forecast for
Tuesday is even more murky as lingering cloud cover would likely
mute high temperatures, whereas any clearing would pose a threat
for afternoon thunderstorms as instability soars to 1500 to
2500 J/kg. If there is enough clearing and instability, all forms
of severe weather will be on the table given steep low level
lapse rates and surface based convection as the cold front sweeps
through the area. That being said, lingering cloud cover would
likely keep the severe weather threat to a minimum. If there is
enough clearing, high temperatures will likely get into the low
90s with heat index values well into the 90s and approaching
100 degrees. Given the uncertainty regarding this cloud cover,
will not extend the Heat Advisory into Tuesday at this time.

Long Term...Tuesday Night Through Monday

Lots of uncertainty at the start of the long term period beginning
00Z/Wed. Many CAMs show precip/thunderstorms south or east of the
area by this time; however, recent runs of the NAMNest in
particular show another round of convection Tuesday evening. Given
the surface front will still be departing, and a 500mb wave has
yet to clip far northern Wisconsin, will carry chance/likely PoPs
Tuesday evening, and then gradually lower PoPs into Wednesday
morning, hanging around longest in northern WI. Instability will
theoretically wane Tuesday evening, but given the complex nature
of everything to happen before this time, severe storms could
still be possible, especially north.

The cold front will be past the area by Wednesday, bringing
cooler and slightly less humid air to northeast WI. High temps on
Wednesday will range from the upper 60s to upper 70s, coolest in
far north- central Wisconsin.

Rain/thunderstorm chances return Thursday afternoon into Friday
ahead of an approaching shortwave and frontal system. Timing is
not certain, but the current depictions show the best timing is
overnight, which would be less favorable for strong or severe
thunderstorms. Pwats climb as high as 2.0 inches which will bring
a heavy rain threat. Precip-free days appear most favorable from
midday Friday into next Monday; although some weak shortwave
energy could produce some spotty showers this weekend.

Temperatures will be near normal Thu-Sat, and then fall a few
degrees below normal Sun-Mon. This generally means highs in the
upper 60 to low 80s, and lows in the 40s and 50s.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 657 PM CDT Mon Aug 26 2024

Focus through Tuesday afternoon is on thunderstorm potential.
Quiet at this time. Isolated storms stretch from northwest WI to
western Upper Michigan, but these should remain north of RHI.
Cluster of storms over central MN just west of MSP are poised to
push into western WI 01z-03z. If these hold together they would
reach western TAF sites (CWA, AUW and RHI) after 05z, then make
it to east-central WI TAFs after 09z. Have shaped updated TAFs
this way for now. Brief IFR conditions will occur during
thunderstorms. Given how humid it is already, mainly MVFR cigs
and/or vsby would likely linger a few hours even after the storms
exit. No thunderstorm wind gusts highlighted at this time, but
will monitor as the evening progresses and add them if needed.

Once this round of storms moves out 11z-13z Tuesday, there
remains questions on whether more storms will form during peak
heating of the day as there may be a lot of debris clouds around
in wake of the storms. Even so, there will be abundant instability
present ahead of cold front and maybe enough time for recovery to
develop additional storms mid to late afternoon. For now, placed
a small mention of storms in the western TAFs closer to the cold
front.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT this evening for WIZ018-020-030-031-
035>039-045-048-049-074.
&&

DISCUSSION.....Kurimski/KLJ
AVIATION.......JLA

Hazardous Weather Outlook...UPDATED
National Weather Service Green Bay WI
912 PM CDT Mon Aug 26 2024

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-280215-
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-
912 PM CDT Mon Aug 26 2024

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

.DAY ONE...Tonight

A line of severe storms is expected to shift into central
Wisconsin by midnight and sweep across much of the area through
the early morning hours. Damaging wind gusts to 60 mph will be
the primary threat. Brief, but torrential downpours will accompany
the storms as well. Severe thunderstorm watch 653 is in effect
until 4 am Tuesday morning.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Impactful heat and humidity will continue on Tuesday, though heat
indices are expected to be slightly cooler.

Additional strong to severe storms are possible Tuesday afternoon
and evening, but development is uncertain due to potential impacts
from the the storms that occur later tonight into early Tuesday
morning.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed late this evening and overnight.

LMZ521-522-541>543-280215-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
912 PM CDT Mon Aug 26 2024

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

.DAY ONE...Tonight

A line of strong to severe storms are expected after midnight.
The primary hazard will be damaging winds. Brief heavy rain will
also accompany the storms. Severe thunderstorm watch 653 is in
effect until 4 am Tuesday morning.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Strong to severe storms may be possible Tuesday afternoon and
evening, but development is uncertain due to potential impacts
from the the storms that occur later tonight into early Tuesday
morning. Any storm will pose a threat to mariners.

More thunderstorms are possible Thursday night and Friday morning
which would pose a hazard to mariners.

JLA

Preliminary Local Storm Report
National Weather Service Green Bay WI
1034 PM CDT Mon Aug 26 2024

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

1030 PM     Tstm Wnd Gst     1 N Colby               44.92N 90.30W
08/26/2024  E50 MPH          Marathon           WI   Trained Spotter

            Spotter estimated winds of 40 to 50 mph and
            also recorded pea size hail. Torrential
            rainfall was also occurring with poor
            visibilities.

&&

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