Hail in Wisconsin, August 24 to 25, 2020

Area Forecast Discussion
National Weather Service Green Bay WI
647 PM CDT Mon Aug 24 2020

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 225 PM CDT Mon Aug 24 2020

Main forecast issue centers around the anticipated convective
complex of thunderstorms that will move across central and east-
central WI tonight. Questions also linger on Tuesday regarding
potential for additional showers/storms that may develop during
the afternoon.

The 19Z MSAS surface analysis showed a cold front that stretched
from north-central WI southwest into southern MN. Weak high
pressure extended from northeast ND into northern MN. The radar
mosaic indicated scattered showers and thunderstorms that have
moved into west-central WI.

The cold front is forecast to slowly sag south into central WI
tonight and be the primary focus for showers and thunderstorms.
Despite a gradual loss of daytime heating, enough instability
(MUCAPES of 1K-2K J/KG) to be in place this evening along with
stronger shear of 35-45 knots, to produce strong to locally severe
storms generally along and south of Highway 29. Large hail and
damaging winds would be the primary threats. In addition, PW
values of 1.5-2.0 inches and dew points around 70 degrees ahead of
the front may produce very heavy rainfall with possible flooding
if thunderstorms train over the same area. The chance of showers/
storms over northern WI should dissipate overnight as the front
edges south. This may lead to fog development if enough breaks in
the clouds can occur. Min temperatures to range from the lower 50s
near the MI border (north-central WI), to the upper 60s across
east-central WI.

The cold front is forecast to stall between central and southern
WI on Tuesday and linger a chance of showers/few thunderstorms
over parts of central/east-central WI through morning hours. As
daytime heating takes place, cannot rule out a few showers/storms
to pop up again over parts of central/east-central WI. Areas north
of Highway 29 should see a decent amount of sunshine, less
humidity and slightly cooler temperatures. Look for max
temperatures to range from the upper 70s to around 80 degrees
north, lower to middle 80s south.

.LONG TERM...Tuesday Night Through Monday
Issued at 225 PM CDT Mon Aug 24 2020

Zonal flow will continue through the work week, with with a west
to east oriented frontal boundary lingering near the area. The air
mass will be very warm, moist and unstable, leading to several
periods of thunderstorm activity. Temperatures through this
period are expected to be much above normal through Thursday, but
daily readings will be dependent on the position of the frontal
boundary, any ongoing precipitation, and debris cloudiness from
overnight convection. Wednesday looks to to be the warmest day,
with highs reaching the lower 90s in central and east central WI.

The frontal boundary will lift north as a warm front Tuesday
night into Wednesday. Strong H8 WAA will become focused over
north/northeast WI overnight, and upper forcing with the RRQ of
an upper level jet will affect this same area. While isolated/
scattered convection may be found along the boundary in the
evening, the main activity is expected over the northeast half of
the CWA late Tuesday night into Wednesday morning, when the
dynamic forcing will be greatest. There are some timing differences,
with the GFS holding off any significant development until Wednesday
morning. Severe thunderstorms with large hail are possible, given
substantial elevated instability (H8 LI's -3 to -7 C) and strong
shear (bulk shear 40-50 kts, SRH 200-400). Heavy rainfall will
also be a concern, as PWATs will be in the 1.5 to 2 inch range.
The warm front may become stationary over northern WI later
Wednesday, leading to a continued threat of strong to severe
storms near the Upper Michigan border in the afternoon and evening.
Farther south, very warm mid-level temperatures (capping) should
suppress convective development.

The front will sag back to the south as a cold front later
Wednesday night into Thursday, and could result in another bout of
strong storms over the southern half of the CWA Thursday afternoon
and evening. The threat of showers and storms will continue until
a more significant Canadian cold front sweeps across the area
Friday night.

A cooler and drier Canadian air mass will return to the area for
the weekend, with temperatures near to a little below normal. As
the high shifts east early next week, southerly return flow will
bring the chance of precipitation back into the western Great
lakes region.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 641 PM CDT Mon Aug 24 2020

A cold front passing through northeast Wisconsin this evening,
will stall over central/southern WI on Tuesday. Expect scattered
showers and thunderstorms much of central and east-central
Wisconsin late this evening into the overnight hours. Gusty winds
and large hail are possible with the strongest storms. VFR
conditions will exist where no precipitation occurs. However,
vsbys could quickly drop to IFR under of the storms. Partial
clearing skies will occur late tonight across the north which may
lead to patchy fog and vsbys dropping into the IFR/MVFR range.

As long as the stalled front is in the vicinity, a few showers and
thunderstorms may develop throughout the day Tuesday, but mainly
in the afternoon hours. While VFR conditions to be most
prevalent, vsbys could drop into the MVFR category under any
precipitation. Additional chances of showers and storms will
linger into Tuesday night as the front lifts northward as a warm
front, again, some of those storms could become strong to severe
late Tuesday night.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM.....Kallas
LONG TERM......Kieckbusch
AVIATION.......Cooley

Hazardous Weather Outlook
National Weather Service Green Bay WI
232 PM CDT Mon Aug 24 2020

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-251945-
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-
232 PM CDT Mon Aug 24 2020

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

.DAY ONE...Tonight

There is a slight risk of severe weather over mainly central and
east-central Wisconsin. Large hail, damaging winds and torrential
downpours will be possible.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Thunderstorms will be possible at times through the work week.
Another severe threat may occur over north-central and northeast
Wisconsin Tuesday night into Wednesday. Large hail and heavy
rainfall will be the main threats.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed tonight. Spotters are asked to
report any hail, strong winds or rainfall over one inch.

LMZ521-522-541>543-251945-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
232 PM CDT Mon Aug 24 2020

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

.DAY ONE...Tonight

Isolated strong to severe storms are possible late tonight,
mainly south of Sturgeon Bay. Gusty winds and hail are possible
with the strongest storms.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Thunderstorms will be possible at times through the work week.
Another round of strong to severe storms will be possible Tuesday
night into Wednesday, especially north of Sturgeon Bay. Any
storms that develop will pose a hazard to boaters.

Kallas/Kieckbusch

Special Weather Statement
National Weather Service Green Bay WI
751 PM CDT Mon Aug 24 2020

WIZ030-035-036-250130-
Wood WI-Marathon WI-Portage WI-
751 PM CDT Mon Aug 24 2020

...SPECIAL WEATHER STATEMENT...

At 751 PM CDT, Doppler radar was tracking a strong thunderstorm over
Spencer, or 19 miles northeast of Neillsville, moving east at 35 mph.

Pea size hail and winds in excess of 30 mph will be possible with
this storm.

Locations impacted include...
Marshfield, Mosinee, Spencer, Knowlton, Stratford, Biron, Hewitt,
Sherry, Auburndale and Rudolph.

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.

Persons in campgrounds should consider seeking sturdy shelter until
this storm passes.

&&

LAT...LON 4487 9031 4479 8966 4444 8975 4459 9032
TIME...MOT...LOC 0051Z 286DEG 38KT 4474 9029

Cooley

Special Weather Statement
National Weather Service Green Bay WI
830 PM CDT Mon Aug 24 2020

WIZ030-035-036-250215-
Wood WI-Marathon WI-Portage WI-
830 PM CDT Mon Aug 24 2020

...SPECIAL WEATHER STATEMENT...

At 830 PM CDT, Doppler radar was tracking a cluster of strong
thunderstorms near Marshfield, or 21 miles northwest of Wisconsin
Rapids, moving east at 35 mph.

Pea size hail and winds in excess of 35 mph will be possible with
this storm.

Locations impacted include...
Marshfield, Mosinee, Knowlton, Biron, Hewitt, Sherry, Auburndale,
Vesper, Rudolph and Junction City.

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.

Persons in campgrounds should consider seeking sturdy shelter until
this storm passes.

&&

LAT...LON 4471 9031 4478 8959 4441 8965 4448 9031
TIME...MOT...LOC 0130Z 278DEG 22KT 4461 9015

Cooley

Special Weather Statement
National Weather Service Green Bay WI
850 PM CDT Mon Aug 24 2020

WIZ035-036-250230-
Wood WI-Portage WI-
850 PM CDT Mon Aug 24 2020

...SIGNIFICANT WEATHER ADVISORY FOR WOOD AND PORTAGE COUNTIES UNTIL
930 PM CDT...

At 850 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from 13 miles west of Stevens Point to near
Pittsville. Movement was east at 40 mph.

Pea size hail and winds in excess of 40 mph will be possible with
these storms.

Locations impacted include...
Stevens Point, Wisconsin Rapids, Marshfield, Whiting, Amherst,
Pittsville, Babcock, Lake Wazeecha, Plover and Stockton.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

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.

Persons in campgrounds should consider seeking sturdy shelter until
these storms pass.

&&

LAT...LON 4449 9032 4468 9018 4468 8923 4424 8931
      4425 9032
TIME...MOT...LOC 0150Z 275DEG 40KT 4460 8980 4440 9023

Cooley

Special Weather Statement
National Weather Service Green Bay WI
916 PM CDT Mon Aug 24 2020

WIZ030-031-036-037-250315-
Waupaca WI-Shawano WI-Marathon WI-Portage WI-
916 PM CDT Mon Aug 24 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN PORTAGE...
SOUTHEASTERN MARATHON...NORTHWESTERN WAUPACA AND WEST CENTRAL SHAWANO
COUNTIES UNTIL 1015 PM CDT...

At 916 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Mosinee to near Whiting. Movement was east
at 35 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Stevens Point, Weston, Rib Mountain, Mosinee, Bevent, Wittenberg,
Rothschild, Stockton, Schofield and Knowlton.

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.

Persons in campgrounds should consider seeking sturdy shelter until
these storms pass.

&&

LAT...LON 4493 8915 4443 8904 4453 8960 4491 8991
TIME...MOT...LOC 0216Z 271DEG 15KT 4485 8976 4450 8952

Cooley