Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 161713
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1213 PM CDT Sat Sep 16 2017

.UPDATE...

The very warm and dry forecast for this afternoon remains on
track. The rain should stay west of the area into the early
evening hours. The convection across Iowa is developing in an
increasingly unstable atmosphere ahead of the main trough/frontal
system approaching from the west. Although some of this initial
convection could bring a chance for rain to areas west of Madison
early this evening, it will likely fall apart in deference to the
more organized stuff expected to form along the sfc to 850mb
frontal boundary over central Iowa this evening. That main line
will push into southern Wisconsin after midnight, but will be
weakening as we lose the diurnal instability. So, best chances for
rain will be west of Madison, while the southeast may not see
anything if this line completely falls apart before getting there.

&&

.AVIATION(18Z TAFS)...

VFR conditions are generally expected through the TAF period.
A line of scattered showers and a few thunderstorms should spread
west to east across southern Wisconsin after midnight, exiting to
the southeast by or shortly after sunrise on Sunday. This activity
will be along an approaching cold front. The line of showers will
be weakening and falling apart as it approaches southeast
Wisconsin late tonight. We could see some patchy MVFR CIGS in the
wake of the front Sunday morning.

&&

.PREV DISCUSSION... (Issued 926 AM CDT Sat Sep 16 2017)

UPDATE...

The showers just west of the forecast area are drying up rapidly,
so pulled the very small mention of showers this morning west of
Madison.  Look for a dry and very warm day.

MARINE...

The small craft advisory was left in effect north of Milwaukee,
only due to the fact that we may see some gusts to around 25 knots
this afternoon in the advisory area. And, those gusts would
likely be closer to shore due to the stable conditions expected
over the lake. Air temps in the lower and mid 80s combined with
water temps in the lower to mid 60s will produce the stable
conditions over the water, making it tougher for gusts to mix
down. The southerly wind fetch will produce 2 to 4 foot waves.

PREV DISCUSSION... (Issued 642 AM CDT Sat Sep 16 2017)

UPDATE...

The line of showers/scattered thunderstorms over Minnesota and
Iowa will weaken as they push east, with only a chance of high
based showers as they approach south central Wisconsin.

AVIATION(12Z TAFS)...

VFR conditions are expected to prevail through the day. Will see
mid level clouds at times, but otherwise mostly clear skies will
persist. IFR fog in the sheboygan area due to moisture off Lake
Michigan. Expect this to dissipate quickly.

The line of showers/scattered thunderstorms over Minnesota and
Iowa will weaken as they push east, with only a chance of high
based showers as they approach south central Wisconsin.

A cold front will bring showers/isolated thunderstorms late
tonight, especially south central Wisconsin. Some MVFR cigs/vsbys
with this line, south central sections.

PREV DISCUSSION... (Issued 336 AM CDT Sat Sep 16 2017)

SHORT TERM...

Today And Tonight...Forecast Confidence Is Medium.

A strong upper shortwave over the northern high plains will bring
a strengthening southwest flow over southern Wisconsin, as the
shortwave pivots into south central Canada. Upper level divergence
increases tonight.

The 850 mb low level jet is affecting mainly the northwest half
of Wisconsin early this morning, with isolated elevated showers
brushing our far north areas. The jet moves northeast and weakens
today, and increasing again a little tonight.

A southerly low level flow is expected to be keep things
unseasonably warm this period, as wind gusts increase today with
surface heating and low level steeper lapse rates. Low pressure
and an associated cold front will remain to our west today. We
will remain within the warm sector, with 925 temps reaching the
lower 20s Celsius. So highs will be in the 80s, with some cooler
temps evolving as onshore component takes shape.

CAPE values increase to 1500 Joules/kg northwest areas this
afternoon, but with a fairly strong cap.

Much of the better mid level forcing pivots off to our north
tonight, though some lift is associated with the low level forcing
associated with the surface/850 cold front. CAPE values decrease
as the cap weakens. Expect mainly showers with just a chance of
thunderstorms, mainly south central Wisconsin later tonight.

Sunday Through Monday Night...Forecast Confidence Is Medium.

Models are in decent agreement with pushing the cold front
southeast through the area Sunday morning, exiting in the
afternoon. A 500 mb vorticity maximum slides east northeast
through the area during the morning, providing some differential
cyclonic vorticity advection. There is some lingering moisture per
area forecast soundings, with rather low values of mean layer
CAPE.

Kept PoPs for showers with slight chances for thunderstorms going
in the morning across the area, with PoPs hanging on in the far
southeast counties in the afternoon. May be able to remove these
afternoon PoPs in later forecasts, if dry look for Sunday
afternoon continues. Warm temperatures continue, with 70s across
the area. Highest will be in the far southeast areas ahead of the
cold front.

Things look dry for Sunday night across the area, with high
pressure sliding east across northern Wisconsin. A southwesterly
low level jet then transports more moisture into the region Monday
into Monday night. There is disagreement with where the low level
jet will be Monday night, with several models shifting it back to
the west of the region.

A 500 mb vorticity maximum slides east northeast through the area
Monday afternoon and evening, providing some upward vertical
motion. There may be some upper divergence from the right rear
quadrant of a jet streak as well on Monday. Continued the upward
trend with PoPs for Monday into Monday night. Mild temperatures
should continue, with somewhat cooler readings near Lake Michigan
Monday with onshore winds.

LONG TERM...

Tuesday Through Friday...Forecast Confidence Is Medium.

Models are generally showing the main 500 mb negatively tilted
shortwave trough sliding northeast through the northern Plains and
Minnesota Tuesday into Wednesday. Southern Wisconsin remains in
southwest flow, and continues through the week, with a large
anticyclone at 500 mb developing over the Middle Mississippi River
Valley.

At the surface, models try to bring a warm front north into the
area Tuesday night. They then differ with timing in trying to
bring the tail end of a cold front through the area between
Wednesday and Wednesday night. There is not a lot of upward
vertical motion besides the frontogenesis response with this
system. Thus, kept mainly low PoPs across the area Tuesday into
Wednesday night. Mild temperatures look to continue.

Southerly flow returns to the area later in the week, with some
warm air advection bringing warm temperatures back into the area.
kept some PoPs for showers and storms, though best chances may
reside in northern Wisconsin closer to the surface warm front.
Still some time to let models try and sort this system out.

AVIATION(09Z TAFS)...

A few showers will move through areas northwest of Madison over
the next couple hours, with dry weather then returning for the
remainder of the night into Saturday.

VFR conditions are expected to prevail through the day Saturday.
Will see high clouds at times, but otherwise mostly clear skies
will persist. Should be enough wind in the lower levels tonight to
limit any fog development.

MARINE...

Persistent south to southeast winds will keep waves in the 2 to 3
foot range through Saturday night. Could see a few waves pushing
4 feet, along with wind gusts to 25 knots, especially near Port
Washington north. As a result, will issue a Small Craft Advisory
this afternoon and early evening that area. Offshore winds will
result in lower waves for Sunday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 9 PM CDT this evening for LMZ643-644.

&&

$$

Update...Davis
Today/Tonight and Aviation/Marine...Davis
Sunday THROUGH Friday...Wood



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