Flood and Lakeshore Flood in Wisconsin, April 28 to 29, 2020

Area Forecast Discussion
National Weather Service Green Bay WI
1049 PM CDT Tue Apr 28 2020

Updated aviation portion for 06Z TAF issuance

.SYNOPSIS...
Issued at 259 PM CDT Tue Apr 28 2020

A raw day with gusty north winds, chilly temperatures, and
occasional light rain tomorrow, then a warming trend for the end
of the week and the weekend.

The upper flow across North America will undergo rapid
amplification the next few days as a deep, sharp upper trough
develops just east of the area. The amplified pattern won't last
long as the flow is expected to begin trending back toward zonal
by the start of the weekend.

Temperatures will be well below normal tomorrow, then warm to
above normal by the weekend. Readings will likely drop back to AOB
normal for next week. The cyclone associated with the developing
upper trough will be a good precipitation producer, so the total
precipitation for the week is likely to be AOA normal.
&&

.SHORT TERM...Tonight and Wednesday
Issued at 259 PM CDT Tue Apr 28 2020

The models still seem to be struggling with the evolution of the
precipitation field with the developing cyclone. That may be
related to the fact that several significant but distinct pieces
of middle and upper level energy get wrapped up into the upper
trough as the system forms. Water vapor satellite imagery shows
the individual vorts and speed maxes nicely, but there still
doesn't seem to be any clear cut trend toward things merging
together on the imagery. For this reason, was somewhat hesitant to
lean too heavily on the details of the model solutions (several
of which want to place a distinct minimum in the precipitation
right across the forecast area) and based the forecast more on
what would typically be expected on the western flank of a
deepening cyclone. That basically meant carrying higher PoPs and
QPF into Wednesday, and pulling down temperatures on Wednesday.

The Lakeshore Flood Advisory still looks on target, with at least
minor flooding anticipated along the shore of the Bay in Brown and
Oconto counties. Given the stronger winds we now have in the
forecast, the potential for the flooding to shift into northwest
Kewaunee and southwest Door counties as winds back NNW on
Wednesday has increased. Will add these areas to the Lakeshore
Flood Advisory, but delay the start time there since they aren't
as susceptible to flooding on NE winds.

.LONG TERM...Wednesday Night Through Tuesday
Issued at 259 PM CDT Tue Apr 28 2020

The main highlights for the long term period will be the
continuination of precipitation Wednesday night into Thursday, and
then the sharp warmup into the weekend, as temperatures head well
above normal.

Wednesday night through Thursday...The upper-level cutoff low is
expected to slowdown over northern Illinios and Indiana, making
its way over Michigan. As it slows, ample wrap around moisture
will be over the area, keeping rain in place overnight for a good
portion of eastern Wisconsin. The low will strengthen during this
time, keeping strong gusty winds in place across the region into
Thursday afternoon. The persistent northerly flow will likely
once again pose a flooding concern for shorelines along the bay of
Green Bay. Some light rain will likely continue across eastern
Wisconsin through Thursday afternoon, before a quieter period
arrives once more.

Rest of the extended...An upper level ridge arrives Thursday night
into Friday, which will bring back dry conditions into the early
weekend. Southerly flow will pick up quickly Friday, which will
bring a good chance of above normal temperatures by the weekend,
with highs in the 60s Friday and possible lower 70s Saturday. A
shortwave will move across the region Saturday morning, bringing
with it a slight chance for rain. With high pressure blocking the
gulf moisture during this time, this system will be somewhat
moisture starved. Given the timing and relatively low chance for
precipitation, kept thunder out of the forecast for now, but a few
rumbles may be possible. Cooler air will return towards the
beginning of next week, bringing highs back down closer to normal
in the upper 50s. A few additional chances of rain are possible
towards the middle of next week as well.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1046 PM CDT Tue Apr 28 2020

Conditions will continue to vary wildly overnight from LIFR to VFR
at times as showers and isolated thunderstorms affect the TAF
sites during the overnight hours. Will continue to amend TAFs as
thunderstorms affect the TAF sites, however activity appears to be
waning. Vsbys are expected to improve through the day on
Wednesday to VFR as the heaviest rain ends, with cigs improving
to MVFR. Gusty low level winds will bring LLWS at times with
strong winds above the surface.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Lakeshore Flood Advisory from noon to 10 PM CDT Wednesday for
WIZ022-040.

Lakeshore Flood Advisory until 10 PM CDT Wednesday for WIZ039-
073-074.
&&

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Uhlmann
AVIATION.......Kurimski

Hazardous Weather Outlook
National Weather Service Green Bay WI
304 PM CDT Tue Apr 28 2020

WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074-292015-
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-
304 PM CDT Tue Apr 28 2020

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

.DAY ONE...Tonight

There is a chance of thunderstorms tonight, especially over
central and east central Wisconsin. The storms are not expected to
be severe, but could produce small hail and gusty winds.

Gusty northeast winds tonight could result in lakeshore flooding,
especially along the bayshore from Marinette to Oconto to Green
Bay.

.DAYS TWO THROUGH SEVEN...Wednesday through Tuesday

Additional shoreline flooding and erosion along the shores of the
Bay of Green Bay are possible Wednesday and Wednesday night as
strong gusty winds increase across the area.

.SPOTTER INFORMATION STATEMENT...

Spotters are requested to report any occurrences of lakeshore
flooding to the National Weather Service in Green Bay.

LMZ521-522-541>543-292015-
The Bay of Green Bay south of a line from Cedar River MI to Rock
Island Passage-Lake Michigan from Washington Island to Sheboygan-
304 PM CDT Tue Apr 28 2020

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

.DAY ONE...Tonight

Dense fog is possible at times, and will pose a hazard to
navigation on the lake and bay.

Conditions hazardous to small craft are likely tonight, as strong
northeast winds develop.

.DAYS TWO THROUGH SEVEN...Wednesday through Tuesday

Conditions hazardous to small craft are likely Wednesday and
Thursday. A few gale force gusts are possible Wednesday.

Skowronski/Uhlmann