Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 242040

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
340 PM CDT TUE MAY 24 2016

.TONIGHT AND WEDNESDAY...Forecast Confidence Is Medium.

Scattered showers and some thunderstorms have moved northeast of
Sheboygan and Port Washington, out over Lake Michigan. Additional
scattered showers were moving northeast through portions of the
forecast area. They were being helped along by a confluent low level
boundary, as well as a passing weak 500 mb vorticity maximum and
some weakly focused 850 mb warm air advection. Mesoscale models have
this area of showers gradually shifting east of the area by the
early evening hours.

Adjusting dew points on area forecast soundings from synoptic models
downward, and upward on some of the mesoscale models, gives 500 to
800 J/kg of tall, skinny mean layer CAPE into early evening. Given
the lack of focused upward vertical motion, mentioned just isolated
thunder into this evening. Deep layer shear is around 20 knots at
best, so not anticipating anything severe.

HRRR and other mesoscale/synoptic models look rather dry for the
rest of tonight and even into early Wednesday morning, with a lack
of forcing for upward vertical motion over the area. Cut back the
pops somewhat tonight, and may need further trimming or removal
later on.

Main issue later tonight into Wednesday morning will be fog
potential over the area. Dew points will gradually hold steady or
slowly rise tonight into Wednesday morning, then rise Wednesday
afternoon. Models have been too high with dew points for awhile in
general, so lowered consensus blend values several degrees.

Still, upper 50s northeast to lower 60s southwest dew points look
reasonable for later tonight into Wednesday morning. Light winds
during this time should allow for patchy fog to develop across most
of the area, best bet in the north and east. Onshore winds Wednesday
afternoon may keep the fog going near the lake. Dense fog is not out
of the question, but will hold off for now until better confidence
in higher dew point values can be found.

Continued to trend higher with pops later Wednesday morning into the
afternoon southwest to northeast across the area. Models agree on a
500 mb shortwave trough moving northeast into the area during this
time. Southerly flow continues at 850 mb, with moisture continuing
to steadily flow into the area. This should be enough to bring
decent chances for showers and storms. Some uncertainty here, as
best forcing for ascent is northwest and south of the area.

Adjusted area forecast soundings suggest mean layer CAPES around
1000 J/kg with 20 knots or so of deep layer shear. Marginal risk for
severe is in the western portions of the area, which looks
reasonable given the better dew points there. Clouds may keep highs
a bit cooler than currently forecast inland, with onshore winds
keeping lakeshore areas quite a bit cooler.


Ongoing convection will begin to wind down from southwest to
northeast during the evening as short wave energy and surface low
move away to the northeast, but still expect a few showers and
storms to fire with southerly winds impinging on a trailing thermal
boundary that stalls somewhere over southern Wisconsin/northern

Expect a break in the precipitation for a time Thursday morning into
the afternoon as the boundary lifts northward, but differing timing
among the models leads to at least slight chance PoPs through the
day. 925 mb thermal ridge builds over the state, with 20C to 24C 925
mb temperatures in place by 00Z Friday. Blended temperatures in the
mid-80s may not be warm enough if the middle of the day is dry with
some sun breaking through.


Low-level winds back and increase as 500 mb wave moves out from the
4-corners region into the central Plains, deepening the 500 mb
trough Thursday night into Friday. Focus of the forcing with the low-
level winds is mainly to the west Thursday night, shifting east
Friday with lift aided by weak short wave energy. Again not
expecting all day showers/storms but low confidence to remove rain
chances for any one period. Temperatures will remain above normal.


After a short wave trough lifts through the region Saturday into
Sunday, a subtle change to the pattern as a 500 mb low begins to
consolidate over the nw U.S/sw Canada and short wave energy becomes
less active into the Upper Midwest, focusing more back to the
Plains. However broad lee trough over the Plains keeps warm, and
at times moist, flow into the region through the extended, with
precipitable water values hovering around 1 inch. The resulting
instability seems to be the main reason for the diurnally-driven
periods of showers and storms in the models...especially Monday
and Tuesday since there is no obvious strong trigger for
convection. Temperatures will remain a good 7F to 10F above



Scattered showers are expected to continue moving northeast across
the area into early this evening, before moving to the east of the
area. There may be a few thunderstorms as well during this time, but
timing and placement of storms will be tough to pinpoint with some
uncertainty in areal coverage. For now, will just mention vicinity
thunder in TAFs into early this evening. The southeast sites may end
up dry.

The rest of tonight into early Wednesday morning may end up dry
across the area. Main issue will be low clouds and fog developing
later tonight into Wednesday morning, especially at the eastern
sites. Continued to mention ceilings around or below 2000 feet later
tonight at Milwaukee and perhaps Kenosha, with visibilities down to
1 mile. Dense fog is possible during this time at these sites, but
will leave out of TAFs for now due to uncertainty. The other sites
should see visibilities down to around 3 miles with ceilings above
2000 feet.

Better shot for more widespread showers and thunderstorms comes
Wednesday afternoon, as a warm front moves north toward the area.
May see a gradual increase in areal coverage of these showers and
storms during the afternoon hours, though some uncertainty remains
here with this. Visibilities and ceilings may drop to or below
alternate minimums in any of the storms. Fog may linger into the
afternoon at Milwaukee and Kenosha as well with onshore winds, but
left out for now due to uncertainty.



Higher dew points gradually moving into the region tonight, and
lingering into the upcoming weekend, will encounter the cooler
waters of Lake Michigan. Light winds later tonight into Wednesday
morning may allow for fog to form over the waters. Continued patchy
fog wording for now later tonight into Wednesday, though stronger
wording may be needed as the higher dew points work into the area.
Dense fog is possible at times during this period, and may need
advisories at times.


.MKX Watches/Warnings/Advisories...


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