Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 171522 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1022 AM CDT SUN JUL 17 2016

.UPDATE...

SPC made a drastic change to the Slight Risk area for today due to
the morning convection. Only far southeast WI is included in the
Slight and Marginal risk area. This morning`s round of thunderstorms
produced around 2 inches in southwest WI, 0.5 to 1 inch in south
central WI, and up to a half inch in southeast WI. The leftover cold
pool and resultant stabilized air will take longer to destabilize
this afternoon, and the current thinking is that a full recovery is
not anticipated.

A latest HRRR model runs are now showing minimal convective activity
across southern WI this afternoon. There is still a chance for a few
thunderstorms to develop just ahead of a cold front that will be
tracking across WI this evening, but we are no longer expecting
these thunderstorms to become severe.

&&

.AVIATION/18Z TAFS/...

A period of MVFR cigs are possible through late morning in the wake
of the morning line of thunderstorms. Strong south winds with gusts
of 28 to 30 knots will diminish by late morning as well.

Mainly VFR conditions will return this afternoon, along with
somewhat gusty south to southwest winds. Gusts up to 25 knots are
possible.

The chance for thunderstorms just ahead of a cold front from late
afternoon to early evening has greatly diminished. Thus, I removed
the mention of thunderstorms from the TAFs. At this time, I do not
even have showers mentioned, but I will continue to assess precip
chances for the late afternoon in time for the 18z TAFs.

&&

.MARINE...

Strong south winds were a result of enhanced winds in the wake of
the thunderstorms that crossed southern WI and Lake Michigan this
morning. These strong winds will diminish by late morning.

However, expect elevated south winds to persist through late
afternoon due to a tight pressure gradient ahead of an approaching
cold front. A high-end Small Craft Advisory is in effect through
this evening.

Winds and waves will diminish tonight as the cold front moves
through and winds veer to the west and subside. There is now a much
lower chance for thunderstorms this afternoon/evening.

&&

.BEACHES...

Breezy south winds will persist through late afternoon due to an
approaching low pressure system and associated cold front. South
winds up to 30 mph will cause waves to build to 3 to 6 feet, with
highest waves affecting Sheboygan and Ozaukee county beaches due to
its geographic orientation into Lake Michigan. Will continue High
Swim Risk and Beach Hazard Statement in Sheboygan and Ozaukee
counties, with Moderate Swim Risk farther south. All beach goers
will need to keep up with the latest forecast because there is a
chance for thunderstorms late this afternoon into the evening.

&&

.PREV DISCUSSION... /Issued 329 AM CDT SUN JUL 17 2016/

TODAY AND TONIGHT... Forecast confidence - Medium.

Forecast focus on convection threat these periods.  Mesoscale
convective vortex showing up nicely in radar mosaic over southeast
MN around KRST.  This feature combined with strong push of warm air
and moisture advection due to 50kt low level jet producing
widespread convection across southern MN into northern IA. Weakening
trend expected with both features as they progress eastward this
morning across WI.  However still expect enough lift from moderate
moisture advection and MCV to carry some showers and storms across
srn WI this morning.  Currently getting very heavy rainfall in some
areas of northern IA and upstream NWS offices have issued Flash
Flood Watch for parts of MN/IA.

Hopefully some areas of southern WI will receive a bout of heavier
rainfall this morning, but not expecting flash flooding. Storm
motion is expected to increase to around 30 kts this morning but
Corfidi Vectors do show some slow motion around 5 to 10 kts early
this morning before increasing to 15 knots. One hour flash flood
guidance over 2 inches across all counties and all areas also have
experienced considerable dryness last week or so.  Both MSN and MKE
running around 1.5 inches below normal for the month. RAP and NAM
Flash Flood Factor becomes more progressive this morning over
southern Wi.  Hence will be keeping a close eye on morning rainfall
and may need to issue a Urban and Small Stream Flood advisory for
high rainfall rates, but flash flooding not expected.

Once again, considerable uncertainty regarding potential convective
redevelopment during the afternoon and evening.  Short term guidance
not in very good agreement with regards to returning synoptic
forcing.  NAM takes enhanced lift from right entrance region of
strengthening upper jet across northern IL, while ECMWF more
across southern WI. GFS a blend of both solutions. Low level jet
continues to pivot off to the east and northeast as low level
winds turn more west to southwesterly across srn WI by the
evening. Second low level jet refires farther south across nrn
MO/srn IA into central and northern IL which could focus
convection in this area along outflow from morning activity. Due
to uncertainty, will continue chance pops this afternoon and
tonight and confine likely wording across southern tier for a few
hours in the evening.

MONDAY AND TUESDAY...Forecast Confidence...Medium

Surface high pressure will move overhead on Monday, slowly sliding
eastward and becoming centered over the eastern Great Lakes by
Tuesday evening. Upper ridging will begin to build in from the west
during this time period. This pattern suggests dry weather for both
Monday and Tuesday, though enough moisture/instability could creep
into the west for a shower/storm by later Tuesday night. Should see
temps within a couple degrees of normal values for both Mon and Tue.

WEDNESDAY THROUGH SATURDAY...Forecast Confidence...Medium

The surface high will continue to depart Wednesday and Thursday as a
weak trough approaches the region. Could see a wave or two ride
through the top of the mid/upper ridge in place, possibly bringing
some storms. Models not in great agreement with timing, placement,
or strength of individual waves, so not a ton of confidence in pops
at this moment.

The trough and surface boundary are expected to slide through
Friday, so kept precip chances going. Went dry Saturday, though
the latest ECMWF is showing another wave moving through the top
of the ridge, so uncertainty with precip chances continues into
the weekend.

Higher confidence for the second half of the week comes with
temps, as models are generally in good agreement for above normal
readings. Timing of clouds and precip chances with the weak waves
could certainly through a wrench in forecast temps for any given
day. Overall though, kept hot temps going, particularly Thursday
and Friday. The combination of 90+ temps and 70+ dewpoints could
result in heat indices approaching or exceeding 100 either or both
of those days.

AVIATION/12Z TAFS/...

A period of MVFR cigs and vsbys likely to accompany any tstorms that
affect TAF sites this morning.  Otherwise, mainly VFR conditions
should return later today after the scattered to numerous showers
and thunderstorms end later this morning.  However the chance for t-
storms will continue this aftn and evening before diminishing after
midnight.

MARINE...

Increasing south winds are expected as pressure gradient tightens
ahead of approaching cold front.  With a wind direction of mostly
southerly, occasional gusts to 25 knots are expected to develop this
morning. Hence will continue Small Craft Advisory today into this
evening.  Mariners should watch for a few storms later this morning,
with the chance returning during the afternoon and evening.  Winds
and waves will diminish tonight as the cold front moves through and
winds veer to the west and subside.

BEACHES...

Increasing south winds still expected this morning ahead of
approaching low pressure and cold front.  South winds of 10 to 20
mph will cause waves to kick up to 2 to 4 feet with 3 to 5 feet
waves affecting Sheboygan and Ozaukee county beaches due to its
geographic orientation into Lake Michigan.  Will continue High Swim
Risk and Beach Hazard Statement in Sheboygan county and add Ozaukee
county this morning, with Moderate Swim Risk farther south. If winds
become more south to southeast later this morning, areas farther
south could be elevated to High Swim Risk. All beach goers will need
to watch for thunderstorms this morning, with a chance this
afternoon into the evening as well.

&&

.MKX Watches/Warnings/Advisories...
WI...BEACH HAZARDS STATEMENT until 10 PM CDT this evening for WIZ052-
     060.

LM...SMALL CRAFT ADVISORY until 1 AM CDT Monday for LMZ643>646.

&&

$$

UPDATE...MRC
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Monday THROUGH Saturday...DDV



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