Special Weather Statement, NWS Milwaukee, WI

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
546 PM CDT Fri Jul 21 2017

.UPDATE...
The best CAPE gradient remains right along our southern tier of
counties, south into Illinois. Farther to the north we have decent
elevated action going on, but the severe threat should stay close
to where the watch is. The atmosphere is very tropical with PWs
in the 2-2.2inch range. Very efficient rainfall process. Urban and
low lying areas could see flooding tonight, even north of the
watch area by 1 or 2 tier of counties.

&&

.AVIATION(00Z TAFS)...

Fairly steady thunderstorms moving through southern Wisconsin this
evening. A mix of MVFR/IFR conditions in the heavier rain. Once
the rain moves off toward midnight, we get into a very light flow
regime that will likely lead to IFR CIGS/VSBYS due to very high
moisture in the low levels. Severe storms should remain along the
WI/IL line with heavy rain expected a few tier of counties north
of there. Improving conditions, with respect to cigs/vsbys will
occur later Saturday morning.

&&

.PREV DISCUSSION... (Issued 341 PM CDT Fri Jul 21 2017)

SHORT TERM...
Rest of Today and Tonight...Forecast Confidence Medium.

Removed Marquette Co from the Flash Flood Watch since the axis
of heavy rainfall has shifted south. Heavy rain is the main
concern with the greatest threat across far southern WI. Rainfall
with isolated thunderstorms are expected to continue across
southern WI. The low level jet has strengthened to around 35 knots
pointing into southwest WI where the 850 baroclinic zone is
located. Models show the LLJ strengthening to 40 knots this
evening when moisture transport is maximized. See Hydrology
section for more info.

The surface boundary and outflow is across Iowa and northern
Illinois. Activity has fired up north of this boundary but this
activity will likely end up south of WI. Cape and shear will
increase this evening so we'll have to see if anything can fire
upstream in Minnesota this evening. If it does, we can still
expect some severe weather.

After midnight the low level jet pivots to the east and slides south
of the state. PWs drop as this forcing leaves the region and precip
should wind down during this time.

Saturday...Forecast confidence Medium.

PWs decrease slightly early Saturday morning but remain high, around
1.5, during the day. Low pressure will move along the WI/IL border
on Saturday. Not too excited and thunderstorm chances tomorrow. Cold
air advection will be in place and the low level thermal boundary
will have shifted south of the state. There will be some surface
convergence after it moves through. Cape looks to be over 1000-2000J
with 35-40 knots of shear so if something get going we could see
some isolated severe storms.

LONG TERM...
Sunday through Thursday...Forecast Confidence High

Small chances for thunderstorms linger into Sunday with a shortwave
moving through. Most areas will be dry. High pressure will sink into
the region bringing dry weather Monday and Tuesday. Temperatures
will also be cooler with less humidity on northwest winds. Tuesday
night surface low pressure will move across southern Canada
dragging a cold front and some precip with thunderstorm possible.
Behind this system high pressure will briefly nudge in. Low
pressure will approach from the southwest later in the week and a
baroclinic zone will be draped southwest of the state. This
system has potential to bring more rain to southwest wi later in
the week. Beyond this it looks like high pressure will set
bringing quiet weather.

AVIATION(21Z TAFS)...
Showers with a few lightning strikes will continue to move across
southeast WI. Another batch of showers with heavy rain at times
will move in this evening. Thunderstorms are possible during this
time. Mainly VFR conditions are expected through tonight, except
for with thunderstorms. Fog is likely again tonight with weak
winds and plenty of moisture in place. MVFR or lower ceilings will
develop over central WI Saturday morning and sag toward southern
WI.

MARINE...
Showers are expected through the night. Fog is possible after
midnight. Thunderstorm chances increase this evening with strong
winds the main threat. North winds will increase Sunday night and
Monday but are expected to remain below small craft levels.

HYDROLOGY...
12Z DVN sounding showed PW of 1.9 with a freezing level of 14kft.
This is a favorable environment for efficient rainfall. The GFS and
NAM show values up to 2.5 this evening. This is when moisture
transport is maximized on a 40 knot jet. A 850 baroclinic zones lies
across southwest WI with mean layer from out of the west. Forward
propagating corfidi vectors of 20 knots are parallel to this
boundary and flow allowing for training storms. WPC precip
discussion notes the info is nearly double the mean wind which may
lead to backbuilding. The question is where this will set up,
closer to the surface boundary, the 850 boundary, or somewhere in
between.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Flash Flood Watch through Saturday morning for WIZ056>058-
     062>072.

LM...None.
&&

Update...Davis
Tonight/Saturday and Aviation/Marine...Marquardt
Saturday Night through Friday...Marquardt

Hazardous Weather Outlook
National Weather Service Milwaukee/Sullivan WI
606 PM CDT Fri Jul 21 2017

WIZ046-047-051-052-056>060-062>072-222315-
Marquette-Green Lake-Fond Du Lac-Sheboygan-Sauk-Columbia-Dodge-
Washington-Ozaukee-Iowa-Dane-Jefferson-Waukesha-Milwaukee-
Lafayette-Green-Rock-Walworth-Racine-Kenosha-
606 PM CDT Fri Jul 21 2017

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

.DAY ONE...Tonight

Thunderstorms are expected through the overnight hours. Repeated
rounds of storms over the same area will produce heavy rain that
would affect the already high rivers. A flash flood watch is in
effect for all but east central WI. There is a Slight Risk of
severe weather for far southern Wisconsin. Damaging winds, large
hail and even a tornado are possible.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

There is a small chance of thunderstorms Saturday and Sunday, and
again Tuesday night into Wednesday.

Heat index values in the lower to middle 90s are forecast across
mainly southwest portions of the area Saturday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

LMZ643>646-222315-
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-
606 PM CDT Fri Jul 21 2017

This Hazardous Weather Outlook is for portions of Lake Michigan.

.DAY ONE...Tonight

Thunderstorms are expected tonight. Gusty winds and hail are
possible.

.DAYS TWO THROUGH SEVEN...Saturday through Friday

There is a small chance of thunderstorms Saturday and Sunday, and
again Tuesday night into Wednesday.

www.weather.gov/mkx

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Special Weather Statement
National Weather Service Milwaukee/Sullivan WI
708 PM CDT FRI JUL 21 2017

WIZ062-067-068-220045-
Green-Lafayette-Iowa-
708 PM CDT FRI JUL 21 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT EASTERN LAFAYETTE AND
GREEN COUNTIES...

At 707 PM CDT, radar indicated strong thunderstorms were located
along a line extending from near Blanchardville to 8 miles north of
Nora to Warren. Movement was east at 35 mph.

Winds in excess of 30 mph and pea size hail are possible with these
storms.

Locations impacted include...
Monroe, Brodhead, New Glarus, Brooklyn, Monticello, Albany, Argyle,
Blanchardville, Somers, Wiota, Dayton, South Wayne, Browntown,
Gratiot, Juda, Jordan Center and Woodford.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

A severe thunderstorm watch remains in effect until midnight CDT for
south central Wisconsin.

LAT...LON 4251 9006 4290 8984 4286 8984 4285 8937
      4265 8937 4250 8946
TIME...MOT...LOC 0007Z 269DEG 30KT 4284 8979 4258 8994 4249 8999

HENTZ

Special Weather Statement
National Weather Service Milwaukee/Sullivan WI
712 PM CDT FRI JUL 21 2017

WIZ070-072-220045-
Walworth-Kenosha-
712 PM CDT FRI JUL 21 2017

...A STRONG THUNDERSTORM WILL AFFECT SOUTHERN WALWORTH AND
SOUTHWESTERN KENOSHA COUNTIES...

At 711 PM CDT, a strong thunderstorm was located over Sharon, or near
Harvard, moving east at 35 mph.

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

The storm has shown a slight weakening trend.

Locations impacted include...
Lake Geneva, Twin Lakes, Williams Bay, Genoa City, Walworth,
Fontana-On-Geneva Lake, Sharon, Darien, Powers Lake, Como, Pell Lake,
Bohners Lake, Allens Grove, Bassett, Delavan Lake, New Munster and
Slades Corners.

Heavy rainfall is also occurring with this storm, and may cause
localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

LAT...LON 4259 8878 4263 8830 4261 8830 4261 8823
      4250 8822 4249 8876 4249 8878
TIME...MOT...LOC 0011Z 269DEG 29KT 4250 8867

HENTZ

Special Weather Statement
National Weather Service Milwaukee/Sullivan WI
750 PM CDT FRI JUL 21 2017

WIZ057-063-068-220115-
Green-Columbia-Dane-
750 PM CDT FRI JUL 21 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHEASTERN GREEN...
SOUTHEASTERN COLUMBIA AND DANE COUNTIES...

At 749 PM CDT, radar indicated strong thunderstorms were located
along a line extending from near Poynette to Waunakee to 6 miles
northwest of Belleville. Movement was east at 25 mph.

Winds in excess of 30 mph and pea size hail are possible with these
storms.

Locations impacted include...
Madison, Sun Prairie, Fitchburg, Middleton, Stoughton, Waunakee,
Verona, Oregon, McFarland, Monona, Windsor, Columbus, Marshall,
Deforest, Cottage Grove, Poynette, Belleville, Deerfield, New Glarus
and Fall River.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4287 8978 4320 8957 4344 8936 4338 8901
      4314 8901 4285 8922 4284 8937 4268 8937
TIME...MOT...LOC 0049Z 292DEG 21KT 4335 8933 4317 8948 4291 8965

HENTZ

Special Weather Statement
National Weather Service Milwaukee/Sullivan WI
815 PM CDT FRI JUL 21 2017

WIZ063-064-068-069-220145-
Green-Rock-Jefferson-Dane-
815 PM CDT FRI JUL 21 2017

...A LINE OF STRONG THUNDERSTORMS WILL AFFECT NORTHEASTERN GREEN...
WESTERN ROCK...EASTERN DANE AND WESTERN JEFFERSON COUNTIES...

At 814 PM CDT, radar indicated strong thunderstorms were located
along a line extending from Sun Prairie to near Belleville. Movement
was southeast at 30 mph.

Winds in excess of 30 mph and pea size hail are possible with these
storms.

Locations impacted include...
Madison, Sun Prairie, Fitchburg, Stoughton, Oregon, McFarland,
Monona, Windsor, Lake Mills, Edgerton, Evansville, Marshall,
Waterloo, Brodhead, Cottage Grove, Belleville, Deerfield, New Glarus,
Shorewood Hills and Cambridge.

Torrential rainfall is also occurring with these storms, and may
cause localized flooding. Do not drive your vehicle through flooded
roadways.

LAT...LON 4279 8964 4328 8928 4328 8921 4323 8901
      4320 8901 4320 8888 4316 8875 4252 8921
TIME...MOT...LOC 0114Z 300DEG 25KT 4320 8924 4283 8952

HENTZ