Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 191501 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1001 AM CDT FRI AUG 19 2016

.UPDATE...

A trough of low pressure continues to slowly approach from the
west today. This will likely result in additional convective
development this afternoon after the current precip winds down.
Already seeing some storms develop along a low level boundary to
the west. The HRRR has been pretty consistent in developing storms
this afternoon, though is struggling with the current development
to the west.

Given the extent of rain at this moment along with clouds through
the region, bumped forecast high temps down a bit. Will not take
much filtered sunshine to warm things up though, so still kept
highs into the 80s.

&&

.AVIATION/18Z TAFS/...

There should be a brief lull in precip behind the current rainfall
late this morning into early afternoon. Already seeing development
to the west though, and the HRRR has been persistent in bringing
more storms to the forecast area this afternoon.

Low pressure will finally move on through tonight and Saturday,
likely bringing more rounds of showers and storms to southern
Wisconsin. Lower ceilings and visibilities are probable at times
as the low and associated precip move through.

&&

.MARINE...

Showers and a few rumbles of thunder will linger through the morning
as the weak WAA and frontogenesis forcing it moves out of the area.
After a brief lull in precipitation early in the afternoon, there is
a chance that thunderstorms refire later in the day and move toward
Lake Michigan. The best precip chances will be on Saturday as a
strong low pressure system moves into the region.

Winds today should only gust up to 20 kts, but as the low approaches
on Saturday, we should exceed small craft criteria. Thus, a Small
Craft Advisory will likely be needed tomorrow for wind gusts up to
25 kts.

&&

.PREV DISCUSSION... /Issued 337 AM CDT FRI AUG 19 2016/

SHORT TERM...

TODAY AND TONIGHT...Forecast Confidence Is Medium.

The main focus in the near term is with convection chances. As of
3am, the main surface warm front arches northeast from a low in
southeast South Dakota to near the Twin Cities on southeast into
southwestern Wisconsin.  The first round of convection that rolled
through southwest/south central Wisconsin did help to drop dew
points into the low/mid 60s though those should rebound quickly
today with the south winds picking up in the warm sector.  The main
forcing for any convection this morning is from the low level
jet/moisture transport which the 19.07z RAP analyzed as being
strongest along and south of the boundary in southern
Minnesota/southwest Wisconsin. The nose of the LLJ has led to a main
band of convection going through eastern Minnesota and far western
Wisconsin with more scattered/isolated convection developing in
southern Wisconsin. Current expectations is that this focus will
shift north/east of southern Wisconsin through the morning hours and
diminish in coverage as the forcing weakens with the LLJ weakening.
Some brief heavy rainfall is possible along with some small hail,
but widespread severe weather is not expected.

Going through today/tonight, the focus for any forcing is non-
existent, so any development will likely hinge on any leftover
boundaries or by hitting peak heating this afternoon/evening.  As
far as severe potential goes, the wind profile from the surface on
up to the mid levels looks fairly weak going through tonight with
the LLJ not looking as strong, so there shouldn`t be much in the way
of storm organization.  The instability should rebound today with
temps getting into the upper 80s and sfc dew points getting into the
upper 60s/low 70s. Given the weak wind profile, the main storm mode
should be pulse storms which could briefly go strong or produce some
locally heavy rain with an MCS unlikely due to there being a weaker
LLJ tonight.

LONG TERM...

SATURDAY... Forecast confidence is medium.

An amplified upper trough will be situated over western MN at 12Z
Sat morning. A relatively strong shortwave will dig through the base
of the trough Sat morning and slide northeast into the U.P. of
Michigan by 00Z Sunday. The ECMWF and GFS are fairly similar in the
strength, track and timing of the associated surface low, and have
been showing a strengthening trend the last couple of runs. This
means winds are trending a little stronger with this system.

The NAM continues to develop a very strong low over MN/WI and is
much slower bringing the system across the Great Lakes than the
GFS/ECMWF as a result. The regional Canadian model also develops a
strong low, but moves it along quicker than the NAM.  The deep lows
that the Canadian and NAM models show are characteristic of a fall
system. The GFS and ECMWF ensembles do not support a strong low
solution, so we are continuing to shy away from the NAM scenario.

The surface cold front will track from western WI Sat morning to
eastern WI by mid afternoon. There should be some instability ahead
of the front, although model soundings are showing tall, skinny
CAPE. The shear will be strong near the front. There is a marginal
risk for severe storms at this time.

Expect showers to taper off from west to east behind the cold front
Saturday late afternoon/evening. Most models have the precip out of
southern WI by early Saturday evening.

Saturday will begin warm and muggy. There is a lot of uncertainty
about cloud cover, but expecting southeast WI to have a chance to
warm up to around 80 before the precip arrives. Cooler and drier air
will work its way into the region later Saturday night.

SUNDAY... Forecast confidence is medium.

Cyclonic flow will linger over the Great Lakes through Sunday night
leading to steep low level lapse rates, plenty of cloud cover, a
chance for light showers, and temperatures topping out in the lower
70s. Winds will be a little brisk out of the northwest during the
afternoon. Dewpoints will drop into the mid 50s, bringing more
comfortable conditions. Sunday night lows are expected to fall into
the lower 50s inland from Lake Michigan.

MONDAY AND TUESDAY... Forecast confidence is medium.

Ridging and warmer air will begin making a comeback on Monday and
continue into the middle of next week. The GFS continues to bring
some warm air advection precip to southern WI Monday night, but the
forcing looks like it will be just north of the MKX area.

WEDNESDAY THROUGH FRIDAY... Forecast confidence is medium.

The next best chance for showers and weak storms will be Wed into
Thu. The GFS is faster than the ECMWF with bringing a shortwave into
southern WI. This looks like a short duration precip event, 12 hours
or less, but the chance is spread out over two days due to timing
differences. Friday and Saturday look dry at this time. Temperatures
will be on the rise through the week as this system approaches.

AVIATION/12Z TAFS/...

The main focus is on any chances for rain/storms today into tonight.
Confidence in the timing of when they may occur is low, but there
could be a few isolated showers/storms early this morning with
another round possible later this evening/tonight.  Conditions
should mainly be VFR, though some brief drops to MVFR can not be
ruled out with any storms that roll through.

MARINE...

Winds will be picking up out of the south today and could become
gusty up to around 15-20kts.  Winds should then back off a bit until
Saturday when a stronger cold front moves through the lake.
Southerly winds will shift around to the west and become gusty to
25kts with a small craft advisory likely to be needed going into
Sunday.

&&

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

$$

UPDATE...DDV/BSH
TODAY/TONIGHT AND AVIATION/MARINE...Halbach
Saturday THROUGH Thursday...MRC



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