Severe Thunderstorm Warning 8, NWS Milwaukee, WI

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1004 PM CST Mon Mar 6 2017

.UPDATE...

Storms are just now arriving in the western forecast area. Still
looks like the west has the best shot to see a few severe storms,
as meso models are trending weaker convection farther east. Temps
and dewpoints continue to slowly inch up though and shear remains
solid, so isolated severe threat could continue eastward. Will be
monitoring radar trends to consider expanding the watch later.

Storms should exit the east by 2-3 am, with cooling temps and clearing
skies behind the storms.

&&

.AVIATION/00Z TAFS/...

Storms are just now arriving in the western forecast area. Could
see a few severe storms, especially toward the western forecast
area. Strong winds are the primary threat of severe weather.
Storms will exit the east by 8-9Z.

VFR will return behind the storms as clouds clear out.

Will see near 30 knots of shear from the surface to 2 kft this
evening into tonight. Surface winds seem strong and gusty enough
though to leave out mention of wind shear in TAFs.

Mostly sunny and windy conditions are expected on Tuesday.

&&

.MARINE...

No changes to the Dense Fog Advisory or Gale Warning at this
time. Winds will become westerly later tonight behind a cold
front. These winds will be breezy, but likely sub gale levels. The
switch to offshore winds will also push the fog out of the area.

Gale Warnings will likely be needed again for Tuesday and
Wednesday as windy conditions are likely between low pressure to
the north and high pressure to the south.

&&

.PREV DISCUSSION... /Issued 556 PM CST Mon Mar 6 2017/

UPDATE...

Latest radar trends and mesoscale models suggest the storms might
be slowing down a tad, possibly coming in an hour later than
previously thought. Will continue to monitor trends and adjust the
forecast as needed. Otherwise, no change with the severe threat
for late evening into tonight.

AVIATION/00Z TAFS/...

Still expecting a line of thunderstorms to move through late this
evening into early tonight. Could see a few severe storms,
especially toward the western forecast area. Strong winds are the
primary threat of severe weather.

Low ceilings will hang around into the evening, but looks like
there could be some improvement west to east during the mid to
late evening hours per upstream observations. Currently seeing
mainly VFR ahead of the line of storms. If VFR conditions don't
return prior to the storms, they will return behind the storms as
clouds clear out.

Will see near 30 knots of shear from the surface to 2 kft this
evening into tonight. Surface winds seem strong and gusty enough
though to leave out mention of wind shear in TAFs.

Mostly sunny and windy conditions are expected on Tuesday.

MARINE...

Issued a Dense Fog Advisory per webcams. Dense fog is due to very
moist conditions for this time of the year over the chilly waters.
The fog will likely stick around until later tonight when winds
become offshore and a drier airmass begins to move in.

PREV DISCUSSION... /Issued 318 PM CST Mon Mar 6 2017/

TODAY AND TONIGHT...Forecast Confidence High.
A developing low pressure system is centered over the High
Plains with a warm front extending east across northern WI and a
cold front extending to the SW. Southern Wisconsin has been within
strong warm air and moisture advection throughout the day,
beneath overcast skies.

The low pressure system will continue to intensify as it moves to
the northeast. The deepening of the low will serve to enhance an
already strong pressure gradient across the region. As such, wind
shear vectors will also be quite strong as the potent cold front
extending from the low swings though southern Wisconsin late this
evening. The strong forcing, sufficient moisture, and modest
instability will be enough to initiate a line of thunderstorms this
evening. Guidance came in a bit slower with the fropa than in
previous runs, so slowed the timing of the most intense
precipitation.

Given the magnitude of the 0-6km (50kts) and 0-1km (50kts) shear
vectors, the potential for severe weather exists as the front
traverses the area. However, by the time storms arrive in southern
WI, the already limited instability will be depleted due to the
loss of diurnal heating. However, the strong forcing, shear, and
moisture are enough to warrant the slight risk in the far SW CWA and
marginal risk across much of the rest of southern Wisconsin.

TUESDAY THROUGH WEDNESDAY...Forecast confidence is high.

Strong gradient winds are expected through Wednesday, with a
diurnal lull Tuesday night. The deep surface cyclone lifting north
toward Hudson Bay, Canada, combined with ridging to the southwest,
will keep us in a tight gradient for a couple of days. Soundings
still show impressively deep mixing on Tuesday, potentially up to
10-12kft. We should see peak winds around mid afternoon. Winds
aloft are much stronger on Wednesday, though we only mix to 5kft,
but this will still potentially mix winds of 40-43kts from late
morning into the afternoon. Will hoist a wind advisory for Tuesday
alone at this point, with the expectation another one will be
needed for Wednesday.

THURSDAY...Forecast confidence is medium.

The GFS and the ECMWF are looking fairly dry for Thursday, but
there is an area of warm advection associated with a very weak mid
level trough that swipes by and they do suggest some light qpf
potential, mainly during the afternoon. The Canadian-GEM is likely
overreacting and generating quite a bit of precip.

FRIDAY AND SATURDAY...Forecast confidence is medium.

There continues to be model uncertainty with low pressure
development over the central/northern plains that dives southeast
with time, eventually tracking well south of Wisconsin. We could
see some light snow arrive Friday afternoon through Saturday
afternoon with some light snow accumulations. Temps will be close
to thresholds and could mix for a time with rain during the peak
warmth of the afternoons. This doesn't look like it will have any
big impact at this point.

SUNDAY...Forecast confidence is medium.

High pressure should return and bring dry weather for the end of
the weekend.

AVIATION/18Z TAFS/...
Primary concerns are thunder timing and low level wind shear this
evening. Slowed down thunder timing overnight per high res
guidance. Around the time the storms come though, winds at 2kft
ramp up to around 50 kts. I am expecting gusts at the surface to
be around 30kts as the storms come though, so chose to leave llws
out of TAFs at this time.

MARINE...
Strong winds will continue over Lake Michigan this evening and
tonight as a cold front swings through southern Wisconsin. Gusts
should be just above gale force criteria. Winds will swing around
to the southwest and calm somewhat after the frontal passage. Then
very deep mixing and continued strong gradient flow will
reintensify winds Tuesday and Wednesday. Certainly a SCA, and
potentially another Gale Warning will be required each of those
days.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Wind Advisory from 8 AM to 6 PM CST Tuesday for WIZ046-047-051-
     052-056>060-062>072.

LM...Dense Fog Advisory until 3 AM CST Tuesday for LMZ643>646.

     Gale Warning until 3 AM CST Tuesday for LMZ643>646.

&&

UPDATE...DDV
TONIGHT/Tuesday AND AVIATION/MARINE...BSH
Tuesday NIGHT THROUGH Monday...Davis

Hazardous Weather Outlook...Updated
National Weather Service Milwaukee/Sullivan WI
1007 PM CST Mon Mar 6 2017

WIZ046-047-051-052-056>060-062>072-072130-
Marquette-Green Lake-Fond Du Lac-Sheboygan-Sauk-Columbia-Dodge-
Washington-Ozaukee-Iowa-Dane-Jefferson-Waukesha-Milwaukee-
Lafayette-Green-Rock-Walworth-Racine-Kenosha-
1007 PM CST Mon Mar 6 2017

This Hazardous Weather Outlook is for portions of east central
Wisconsin, south central Wisconsin, and southeast Wisconsin.

.DAY ONE...Tonight

A cold front will bring widespread showers and scattered
thunderstorms to southern Wisconsin tonight. There is a marginal to
slight risk for severe thunderstorms across the southwest two-thirds
of the forecast area. A Severe Thunderstorm Watch is in effect for
western portions of the forecast area until 2 am. Strong and
damaging straight-line winds are the main threat.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Windy conditions will then prevail in the wake of the cold front
for Tuesday and Wednesday. West to southwest winds will gust to
35 to 45 mph. A wind advisory is in effect for Tuesday and will
likely be needed for Wednesday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will be needed this evening into tonight.

LMZ643>646-072130-
Sheboygan to Port Washington WI-
Port Washington to North Point Light WI-
North Point Light to Wind Point WI-
Wind Point WI to Winthrop Harbor IL-
1007 PM CST Mon Mar 6 2017

This Hazardous Weather Outlook is for portions of Lake Michigan.

.DAY ONE...Tonight

A Gale Warning is in effect until 3 AM tonight. Breezy south
winds will prevail overnight with gale force southerly wind gusts
expected. A cold frontal passage will then occur after midnight
with brisk westerly winds afterward. Scattered thunderstorms are
expected tonight.

Moist conditions for this time of the year over the chilly waters of
Lake Michigan will result in areas of dense fog into late tonight.

.DAYS TWO THROUGH SEVEN...Tuesday through Monday

Brisk westerly winds will continue Tuesday and Wednesday. Gale
force wind gusts are possible during this time.

DDV

www.weather.gov/mkx