Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 241802 AAA
AFDMKX

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

.UPDATE...

Scattered showers are moving northeast through western and central
portions of the forecast area, associated with a passing weak 500
mb vorticity maximum and some weakly focused 850 mb warm air
advection. Several mesoscale models have these showers shifting
northeast through the area this afternoon, with the HRRR being the
closest to reality so far today.

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 mean layer CAPE this afternoon into early
evening. So, continued the thunder mention as well. Deep layer
shear is around 20 knots at best, so not anticipating anything
severe. The southeast counties may remain dry until early this
evening.

HRRR and other mesoscale models look rather dry for the rest of
tonight, so may have to trim back pops. Middle clouds helping hold
down temperatures a bit in the area, so may need to adjust them
downward in spots. Still looks to reach the upper 70s to lower 80s
in most areas. Onshore winds along the lake will keep cooler
temperatures there.

&&

.AVIATION/18Z TAFS/...

Scattered showers are expected to continue moving northeast across
the area this afternoon, before ending early this evening. There
should 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 this afternoon into early this evening.

Tonight may end up dry across the area, with the main issue being
low clouds and fog developing later tonight into Wednesday
morning. Continued to mention ceilings around or below 2000 feet
later tonight at Milwaukee and Kenosha, with visibilities down to
1 mile. May see dense fog develop at times later tonight into
early Wednesday morning at these sites, as winds become light. The
other sites should see visibilities down to 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.
Should see a gradual increase in areal coverage of these showers
and storms during the afternoon hours. Visibilities and ceilings
may drop to or below alternate minimums in any stronger storms.
Fog may linger into the afternoon at Milwaukee and Kenosha as
well, but left out for now due to uncertainty.

&&

.MARINE...

Higher dew points moving into the region tonight into the rest of
the week will encounter the cooler waters of Lake Michigan. Light
winds later tonight into Wednesday morning may allow for areas of
fog to form over the waters. Dense fog is possible during this
time, and a Dense Fog Advisory may be needed in later forecasts
for this period. The fog may persist at times into this weekend,
with the warm and humid airmass over the cooler waters lingering.
Dense fog may be possible at times into the weekend as well.

&&

.PREV DISCUSSION... /Issued 330 AM CDT TUE MAY 24 2016/

TODAY AND TONIGHT...Forecast confidence - Medium.

We know it had to happen eventually.  Blocking high pressure ridge
that had been bringing beautiful, dry weather to southern Wi has
finally been nudged farther eastward into the central Great Lakes.
Our region will now be under the influence of persistent west to
southwest steering flow this period, and through the end of the
week.  This southwest steering flow will usher deeper column
moisture into the area today.  Expect surface dewpoints to increase
into the 50s to around 60 today as column precipitable water more
than doubles to around 1-1.25 inches.  These increasing southwest
winds are carrying a mesoscale convective eddy currently located in
central IA to the northeast.  Short term guidance not handling this
very well as showers and a few tstorms continue to develop and move
northeast.  For now have chance pops in my west early this morning,
but if trend continues, will be bumping up to scattered or possibly
numerous wording.  Spread chance pops across entire CWA later this
morning and afternoon.  Any convection from this morning`s passing
eddy may leave boundary draped across the area. MUCapes are expected
to climb into the 1-2k range with around 30 kts of bulk shear.
Marginal risk seems appropriate this aftn and eve as isold severe
appears possible.

Starting out warmer today and with periods of thinner mid-high
clouds, bumped up high temperatures several degrees, mainly for
inland areas.  Wl keep lower chance pops for the overnight hours as
weak frontal boundary slides south into parts of southern WI and
elevated instability remains. However chance definitely lower
than today as weak short wave ridging spreads across the area, and
low level jet refocuses farther west in the plains. Will need to
watch for fog development near the lake as winds turn onshore
later tngt.

WEDNESDAY AND THURSDAY...Forecast Confidence...Medium

The front is expected to lift northward through the forecast area
Wednesday, likely bringing showers and thunderstorms with it.

It will likely be somewhat cooler most places Wednesday with the
front slowly making progress back into the area. Coolest temps
will be near Lake Michigan under east winds. Would not be
surprised at some fog lingering into Wed in the east given the
onshore winds and higher dewpoints over the cooler water.

SPC has cut back on the Marginal Risk for severe storms for Wed,
with only the southwest forecast area highlighted at this time.

It is starting to look mainly dry on Thursday, as model soundings
are fairly capped. Cut back pops to slight chances most places
during the day. With 925 mb temps of 22-24 C per most guidance,
could be a pretty warm day. Bumped temps up a bit, but not as high
as 925 mb temps would suggest due to some uncertainty with
timing/placement of the front and associated convection.

THURSDAY NIGHT THROUGH MONDAY...Forecast Confidence...Medium

Shortwave energy along with a surge of deeper moisture should
result in more rounds of showers/storms from Thursday night
through Saturday.

Kept chance pops for Sunday and Monday, but overall moisture will
be less and there is not a real obvious trigger for convection
during this period. Still can`t rule out a few storms though given
the expected instability and precipitable water values hanging on
at 1 to 1.25 inches.

Above normal temperatures will likely continue late in the week
and into early next week.

AVIATION/12Z TAFS/...

Thicker cloud cover is expected today as deeper column moisture and
weak short wave low pressure pass through this morning. Atmosphere
becomes unstable this morning so possible a few storms could briefly
affect taf sites.  More scattered t-storms expected this aftn and
evening which would have a better chance of affecting eastern taf
sites.  Cigs should remain mostly vfr.  Later tonight a weak front
will sag south into parts of central and southeast Wi and may bring
some lower mvfr cigs to taf sites.

MARINE...

Mariners will need to watch for late morning and afternoon
thunderstorms as deeper moisture and atmospheric low pressure
ripples move into the western Great Lakes today.  The threat for
showers and thunderstorms will continue tonight as a weak frontal
boundary slips south across central into southern Lake Michigan.
The more humid air mass and lighter winds near the front may
result in areas of fog tonight into Wednesday. Lake temperatures
are in the upper 40s to middle 50s. With the humid air remaining
place through the end of the week, fog will be a concern each day.

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...None.
&&

$$

UPDATE...Wood
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Wednesday THROUGH Monday...DDV



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