Special Marine Warning 13, NWS Green Bay, WI

Area Forecast Discussion
National Weather Service Green Bay WI
706 PM CDT Mon Jul 6 2020

Updated aviation portion for 00Z TAF issuance

.SYNOPSIS...
Issued at 218 PM CDT Mon Jul 6 2020

Remaining rather hot and humid with scattered thunderstorms at
times through Friday, then a little cooler and much less humid
next weekend.

A fairly typical summertime upper pattern was in place across
North America. The subtropical ridge was stretched out from the
Atlantic to the southwest CONUS, with a weakness in the ridging over
the Gulf States. To the north, a modestly strong fairly low-
amplitude belt of westerlies was located from the Pacific
Northwest across the far northern CONUS and southern Canada.
The current pattern will persist for a few more days, then an
upper anticyclone will consolidate within the ridge over the Four
Corners region. As the anticyclone expands north and nudges the
westerlies over western North America northward into Canada,
troughing will gradually increase over the eastern CONUS. The
result will be a northwest upper flow across the forecast area by
the weekend.

The upper pattern favors very warm and humid conditions
for several more days, then the humidity will return to more
comfortable levels and temperatures will drop back closer to (but
probably still a little above) normal as the upper flow turns
northwest late in the week and during the weekend. Precipitation
amounts are likely to vary considerably in time and space. When
considering the precipitation averaged across the whole area and
totaled for the entire period, the overall pattern probably
supports near to slightly above normal rainfall.
&&

.SHORT TERM...Tonight and Tuesday
Issued at 218 PM CDT Mon Jul 6 2020

The main forecast challenge remains on precipitation trends right
through Tuesday afternoon as several weather features combine with
daytime heating/humid conditions persist.

The 19Z MSAS surface analysis showed a weak cold front that
stretched from north-central MN southwest into southeast SD.
Otherwise, the surface features over the Great Lakes were rather
diffuse. Daytime heating, combined with a mid-level shortwave and
several outflow/lake breeze boundaries, had generated scattered
convection across much of WI this afternoon.

Ongoing convection will dissipate somewhat by mid-evening as we
lose daytime heating. However, the approach of the cold front,
coupled with another mid-level shortwave, will allow for
additional showers/thunderstorms to move through the forecast area
into the overnight hours. We will continue to watch for stronger
storms into this evening as shear increases a bit, especially
across northern WI. Exactly how far south the cold front can get
will determine how long to hang on precipitation chances
overnight. Northern WI should begin to dry out, but central/east-
central WI may be close enough to the front such that chance pops
would need to be carried well into the early morning hours. Min
temperatures to range from the lower to middle 60s north-central
WI, to around 70 degrees east-central WI.

The cold front is forecast to stall somewhere over southern WI on
Tuesday. Meanwhile, models show a shortwave trough to move into
the western Great Lakes region Tuesday afternoon. CAPE values
reach 1-2K J/KG during the afternoon with weak shear at 20-25
knots. Plenty of low-level moisture still in the vicinity with dew
points in the 60-70 degree range (highest central/east-central)
and PW values at around 1.5 inches over east-central WI.
Anticipate at least scattered showers/thunderstorms to develop,
primarily south of Highway 29. Northern WI will still see a chance
of showers/storms, but this activity to be more spotty in nature.
Do not expect the severe risk to be above marginal based on the
weak shear. Small hail, gusty winds and heavy rain will be
possible. Max temperatures to range from the lower 80s north-
central, upper 80s east-central WI (cooler lakeside).

.LONG TERM...Tuesday Night Through Monday
Issued at 218 PM CDT Mon Jul 6 2020

Diurnally driven convection on Tuesday could linger past 00Z, so
added slight chance PoPs for the evening. Diurnal destabilization
will probably support some convection on Wednesday, though
coverage will be limited by a lack of large scale support as
ridging shifts through the area. Stuck with the standard
initialization grids which had slight chance PoPs across north-
central Wisconsin, though may need to expand those to other areas
as the lake breeze or other local effects may be sufficient to
kick off isolated storms.

The potential for more widespread convection will be higher
Wednesday evening through Thursday evening as a frontal boundary
drops south into the area and a significant shortwave crosses the
region. Some of the ingredients for a more substantial severe
storm threat appear to be in place, though the latest runs of the
models don't appear especially ominous. The severe risk will
probably depend on smaller scale details of the pattern which are
still difficult to ascertain this far in advance.

Precipitation chances will be minimal Friday into the upcoming
weekend as the northwest upper flow develops and the reservoir of
very moisture rich air get shunted southwest of the area.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 704 PM CDT Mon Jul 6 2020

A couple broken bands of showers and a few embedded thunderstorms
will continue to slowly weaken this evening as they move east
across central and eastcentral Wisconsin. Brief MVFR cigs and
vsbys may accompany some of the embedded stronger cells.
Thunderstorm outflow racing out ahead of the eastern most band may
impact GRB and ATW TAF sites around 01 UTC with a wind shift to
the northwest and gusts to around 25 to 30 kts.

By 06Z the activity should push out of the area followed by some
patchy ground fog over parts of central and northcentral Wisconsin
where a bit more rainfall occurred.

Generally VFR conditions should prevail after 12 UTC Tuesday, with
perhaps a few isolated showers or thunderstorms redeveloping after
18 UTC in the vicinity of a weak cold front, especially south of
Interstate 29. Confidence too low on coverage and location to
explicitly mention in 00Z TAFs.

&&

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

SYNOPSIS.......Skowronski
SHORT TERM.....Kallas
LONG TERM......Skowronski
AVIATION.......ESB

Hazardous Weather Outlook
National Weather Service Green Bay WI
222 PM CDT Mon Jul 6 2020

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-071930-
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-
222 PM CDT Mon Jul 6 2020

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

.DAY ONE...Tonight

Scattered thunderstorms are expected through mid-evening. A few
of the storms could be severe, with isolated damaging wind gusts,
hail, and torrential rainfall.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Hot and humid weather will continue through Thursday. Be sure to
stay hydrated and safe in the heat.

Isolated to scattered thunderstorms are expected at times through
the rest of the work week. The strongest storms will be capable
of producing briefly gusty winds and torrential rainfall.
Conditions may be favorable for severe storms on Thursday. Be sure
to monitor later forecasts for more detailed information.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to forward any reports of wind damage,
hail, or rainfall totals over an inch to the National Weather
Service in Green Bay.

LMZ521-522-541>543-071930-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
222 PM CDT Mon Jul 6 2020

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

.DAY ONE...Tonight

Isolated thunderstorms are expected through mid-evening. Any of
these storms may pose a hazard to boaters.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Isolated to scattered thunderstorms are expected at times
through the rest of the work week. Any thunderstorms that develop
will pose a hazard to boaters on the lake and bay.

Kallas/Skowronski

Special Weather Statement
National Weather Service Green Bay WI
748 PM CDT Mon Jul 6 2020

WIZ073-074-070115-
Southern Oconto County-Southern Marinette County-
748 PM CDT Mon Jul 6 2020

...A STRONG THUNDERSTORM WILL AFFECT SOUTHERN MARINETTE AND CENTRAL
OCONTO COUNTIES...

At 746 PM CDT, a strong thunderstorm was located 8 miles north of
Oconto, or 13 miles southwest of Marinette, moving northeast at 20
mph.

Winds in excess of 30 mph and pea size hail are possible with this
storm.

Locations impacted include...
Marinette, Menominee, Oconto, Peshtigo, Porterfield, Coleman,
Harmony, Cullen and County Line.

LAT...LON 4491 8751 4496 8758 4494 8759 4493 8754
      4493 8771 4490 8777 4486 8777 4484 8789
      4506 8804 4523 8773 4517 8774 4511 8766
      4509 8759 4514 8760 4514 8759 4508 8752
      4497 8758 4492 8751 4495 8744 4493 8743
TIME...MOT...LOC 0046Z 247DEG 18KT 4501 8789

EB

Special Weather Statement
National Weather Service Green Bay WI
748 PM CDT Mon Jul 6 2020

WIZ073-074-070115-
Southern Oconto County-Southern Marinette County-
748 PM CDT Mon Jul 6 2020

...A STRONG THUNDERSTORM WILL AFFECT SOUTHERN MARINETTE AND CENTRAL
OCONTO COUNTIES...

At 747 PM CDT, a strong thunderstorm was located 8 miles southeast of
Pound, or 12 miles west of Marinette, moving east at 20 mph.

Winds in excess of 30 mph are possible with this storm.

Locations impacted include...
Oconto, Peshtigo, Porterfield, Harmony, Cullen and County Line.

LAT...LON 4483 8796 4510 8800 4522 8773 4521 8773
      4520 8774 4517 8774 4515 8770 4514 8769
      4499 8764
TIME...MOT...LOC 0047Z 261DEG 17KT 4503 8788

EB

Special Weather Statement
National Weather Service Green Bay WI
808 PM CDT Mon Jul 6 2020

WIZ045-070145-
Waushara-
808 PM CDT Mon Jul 6 2020

...STRONG THUNDERSTORMs WILL AFFECT WAUSHARA COUNTY...

At 807 PM CDT, strong thunderstorms were located 8 miles west of
Plainfield, or 16 miles southeast of Wisconsin Rapids, moving east
at 25 mph.

Winds in excess of 40 mph and half inch hail are possible with this
storm.

Locations impacted include...
Wautoma, Redgranite, Plainfield, Napowan Scout Camp, Silver Lake,
Pine River, Dakota, Mount Morris, Saxeville and Wild Rose.

LAT...LON 4398 8960 4424 8960 4424 8905 4398 8898
TIME...MOT...LOC 0107Z 269DEG 20KT 4419 8967

EB

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