Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 251812 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
112 PM CDT WED MAY 25 2016

.UPDATE...

Main 500 mb shortwave trough is expected to slide northeast
through the area later this afternoon and early this evening. Some
focused 850 mb warm air/moisture advection also shifts through the
area, with the surface warm front sliding slowly northward this
evening.

These features should bring a broken line of showers and
thunderstorms east northeast through the area. HRRR model develops
this activity over south central Wisconsin between 20Z and 22Z
Wednesday, then exits the far east between 02Z and 04Z Thursday.
The WRF/ARW also shows development, but over southeast Wisconsin.
Other mesoscale models are mainly dry. Used the HRRR timing in the
forecast, as it has been pretty good with trends so far today.

SPC has entire area in a marginal severe risk, which implies
isolated severe storms possible. Given the mean layer CAPEs to
around 1000 J/kg, and deep layer shear of 20 to 30-plus knots,
could see an isolated severe storm.

Other issue to watch is slow movement of storms, which may drop
heavy rainfall in a short period of time. This would bring minor
street flooding possibilities in urban and low lying areas.

Onshore winds will keep areas in the northeast and far eastern
counties quite a bit cooler than the lower to mid 80s well inland
this afternoon.

&&

.AVIATION/18Z TAFS/...

Expect a broken line of showers and thunderstorms to move east
northeast across TAF sites between 20Z Wednesday and 03Z Thursday.
This activity may be on and off during this period. VFR category
conditions will prevail, though may see visibilities down to fuel
alternates in any showers/storms. Brief gusty winds and small hail
may occur as well. Easterly winds are expected at the eastern
sites this afternoon, and southeast winds at Madison.

Should see mainly quiet weather for most of the rest of tonight
into Thursday across TAF sites. There are outside chances for
showers and storms, but not enough confidence to mention in TAFs
at this point.

There should be a period of fog and low clouds across the area
later tonight into Thursday morning. May see ceilings down to or
even below 1000 feet above ground level between 09Z and 15Z
Thursday, with visibilities down to around 2 miles. Some
uncertainty here with the timing and how low ceilings and
visibilities will get.

&&

.MARINE...

A Marine Dense Fog Advisory continues for Sheboygan to Port
Washington until 21Z this afternoon. Webcams there continue to
show dense fog, and this may need to be extended into tonight if
the fog lingers. The rest of the waters do not show much in the
way of fog, but should increase tonight with higher dew points and
warmer air moving back into the area.

The fog should linger through the upcoming weekend, as warm and
moist air lingers over the region. May see some dense fog at
times, as the moist airmass lingers over the cool lake waters.

&&

.PREV DISCUSSION... /Issued 350 AM CDT WED MAY 25 2016/

SHORT TERM...
TODAY AND TONIGHT...Forecast Confidence - Medium.

Patchy fog should thin and dissipate fairly rapidly early this
morning.  However early morning sunshine should give way to
increasing mid-high clouds from the southwest associated with
incoming mid-level short wave trof and increasing warm air
advection.  Upstream vigorous short wave extends from south central
SD southeast into eastern NE/KS vicinity will continue to move
northeast today.  High precipitable waters already in place, between
1-1.25 inches.  However even deeper mid-level rh located upstream
will accompany short wave as it progresses northeast.  Although nose
of developing low level jet remains west of the area, combination of
increasing warm air and moisture advection along with axis of short
wave trof moving through should produce scattered to numerous
showers and tstorms across the CWA this afternoon and early evening.
Bulk shear later in the day looks more impressive than yesterday,
reaching around 35 kts with MUCape climbing to 1-2k joules. Marginal
risk covers western half of CWA which seems reasonable, with Slight
risk at the WI/IA border.  That may need to be scooched slightly
eastward into far western CWA as aftn shear in this area pushing 40-
45kts.  SPC SSEO showing a few spots of Updraft Helicity over 25
m2/s2 in the west at 21z.

Synoptic scale forcing associated with short wave moves off to the
northeast during the evening, however unstable atmosphere will
persist through the night and both NAM and GFS show weaker moisture
flux convergence returning later in the night.  Hence need to hold
onto chance pops for after 06z.

Afternoon convection will likely deposit some briefly heavy
rainfall, potentially amounts of over 1.0 inch in one hour resulting
in some ponding of water and minor street flooding.  NAM Corfidi
Vectors suggesting moderate to slower storm motion and storm motion
less than 10 m/s for a time.  With deeper warm cloud depth and a
period of stronger 925-850mb moisture convergence this aftn, these
storms will need to be watched closely for heavy rainfall.  Will
address in HWO.

LONG TERM...

THURSDAY... Forecast confidence is medium.

Thursday might end up being hot and humid with quiet weather.
Southern WI will be in between shortwaves, with one exiting to our
northeast Thu morning and the next arriving Thu night.

925mb temps will be increasing to 21 or 22C by Thu afternoon. This
would yield max temps toward the mid 80s, although sunshine will be
necessary. The NAM brings remnants of an MCS through northern IL. If
this happens and southern WI stays under widespread cloud cover for
much of the day, then the max temps in the mid 80s is overdone.

There will be no focused low level jet (LLJ) or warm air advection
with the shortwave Thu night, so kept chances for storms on the
lower side.

FRIDAY THROUGH SATURDAY... Forecast confidence is medium.

Friday will bring the next good chance for showers and
thunderstorms. The closed upper low over the southwest states will
progress northeast into the upper Midwest through Saturday. Repeated
waves of vorticity advection, a steady feed of moisture from the
Gulf and the LLJ directed into southern WI support one or more
rounds of convection during this period. Expect CAPE to be around
1000 j/kg or less, but the warm profile is showing tall, skinny
CAPE. Shear will continue to be around 20 kts. These conditions
support thunderstorms with the potential for a few to grow strong.

SUNDAY THROUGH MONDAY... Forecast confidence is medium.

The weakening upper trough will slide through northern WI on Sunday
and the corresponding surface low will track across Lake Superior.
The GFS is slower to move the trough out of the area than the ECMWF,
so it hangs on to precip chances a little longer.

We will transition into a temporary zonal flow pattern for Memorial
Day. There is little in the way of upper level forcing to support
precip chances, and the GFS looks way overdone with its qpf.
Southern WI will still be in the mild air mass, so expect
temperatures in the lower 80s.

TUESDAY THROUGH WEDNESDAY... Forecast confidence is medium.

A mid level shortwave will make its way across the northern Plains.
This will bring another chance for showers and storms to southern
WI. Mild temperatures with southerly flow will continue until this
system moves through the area.

AVIATION/12Z TAFS/...

Fog will continue to affect the KUES area due to light winds and
Tuesday rainfall.  Still need to be cautious about some low clouds
in the vicinity of weakening front affecting eastern taf sites this
morning.   Otherwise, mid-high clouds this morning will give way to
scattered afternoon and early evening t-storms.  An isolated severe
storm will be possible along with brief heavy rainfall.  Cigs may
flirt with MVFR levels during precipitation but should return to VFR
for a time tonight, however confidence lower due to lingering low
level moisture and increasing boundary layer winds.  Enough
convergence to possibly generate some stratus along with areas of
lighter fog.

MARINE...

Weak frontal boundary sagging south across near shore waters will
result in variable winds early this morning turning more e to
northeast.  Some patchy fog may develop due to lighter winds
associated with front and more humid air in place.  Sfc dewpoints
for now only a few degrees higher than water temp so not expecting
widespread dense fog, at least today.  Increasing southerly winds
should pull higher dewpoints across cooler Lake MI waters tonight
and Thursday, increasing the threat for more widespread dense fog.
Mariners should be on the lookout for scattered late aftn and eve
storms over the near shore waters. Gusty winds with storms may
approach 30-35kts.

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...DENSE FOG ADVISORY until 4 PM CDT this afternoon for LMZ643.

&&

$$

UPDATE...Wood
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Thursday THROUGH Tuesday...DDV



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