Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 200330
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1030 PM CDT FRI AUG 19 2016

.UPDATE...The west-east line of convection from Iowa County to wrn
Waukesha County lines up along a zone of 925 mb frontogenesis.
This zone of frontogenesis and storms will gradually lift nwd as
the 925-850 mb sly flow develops nwd during the overnight. Another
area of showers and tstorms over ne IA will move into the wrn CWA
after midnight, although this area of rainfall may not hold
together through the night. Additional areas of showers and
tstorms are expected though as a lead shortwave trough moves into
S WI by 12z Sat. A north-south band of showers and storms will
move ewd through S WI in the morning with another expected with
the cold frontal passage in the afternoon.

&&

.AVIATION/06Z TAFS/...Scattered to numerous showers and tstorms
will continue over S WI tonight and Saturday. Stratus clouds of
1-3 kft will form over south central WI during the early morning
hours of Sat with mvfr vsbys from light fog or rainfall. Low cigs
will also form over the SE WI TAF sites but may not develop until
the morning daylight hours. The low cigs will then remain over S
WI for much of the day with some improvement during the
afternoon. Low cigs and low vsbys expected within any showers or
storms.


&&

.MARINE...A small craft advisory is in effect from Sat afternoon
into Sunday morning for breezy swly winds becoming breezy wly
winds by Sat evening. Waves will build to 3 to 4 feet Sat
afternoon into the evening.


&&

.PREV DISCUSSION... /Issued 302 PM CDT FRI AUG 19 2016/

SHORT TERM...

TONIGHT AND SATURDAY...Forecast Confidence...Medium

Showers and storms continue to fire to the west/southwest this
afternoon along the CAPE gradient. Forecast instability trends into
early evening along with mesoscale model simulated radar suggest the
best chance for storms will be in the south half of the forecast
area late afternoon into early evening. Storms do look possible
across the entire area though.

After the first round of storms winds down mid/late evening, there
could be a lull into the first part of the night. Activity should
pick up in the western forecast area later in the night as the
trough approaches from the west. Widespread showers and storms are
then expected Saturday as deepening low pressure lifts northeast
through southern Wisconsin. Should see this activity wind down west
to east during the late afternoon as best instability and deeper
moisture shift eastward with the departing low.

Due to the expected clouds and precip, kept temps close to a blend
of model 2 meter temps for tonight and tomorrow.

SATURDAY NIGHT AND SUNDAY...Forecast Confidence...Medium

The upper level trof will scoot past the area Sunday, leaving
Wisconsin firmly within NW flow by midday on Sunday. Little to no
upper level divergence is evident in the guidance as the jet wraps
wound the base of the trof and moves through the area. At 500 mb,
the base of the trof moves from just west of WI at 00z Sunday to
Lake Michigan by 12z. This does bring a shot of DCVA in the late night
and early morning hours. Additionally, there appears to be a
subtle shortwave embedded on the back side of the trof that will
slide into WI around 00z Monday.

In the lower levels, the low pressure center over northern
Wisconsin/Lake MI at 00z Sun quickly moves off to the
northeast, taking much of the precipitation with it. Behind the
low, much of WI will be in in NW flow, with ample CAA through at
least 12z Sunday, before tapering off during the day. That CAA
will result in steep low level lapse rates throughout the day. In
terms of moisture, 700 mb should be mostly dry as soon as the low
moves off Sat night, but moisture appears to linger through much
of the day Sunday at 850 and 925. Given these moist lower levels,
steep low level lapse rates, and the embedded shortwave at 500 mb,
decided to keep slight chance of showers in the east through the
daytime hours on Sunday.

LONG TERM...

SUNDAY NIGHT THROUGH TUESDAY...Forecast Confidence...Medium

NW flow will dominate the upper levels before ridging moves over the
state on Tuesday. In the lower levels, high pressure will pass south
of the state on Monday, flipping winds around to the southwest.
There will be a relatively tight temperatures gradient along the
axis of the ridge extending north from the high, so we should start
to see some WAA by Monday afternoon. Additionally, much of the
guidance has got a slug of moisture riding along that ridge at
700mb, and the GFS is even painting some precip across northern
WI Mon night and Tues morning. Have left the precip out of this
time period given the GFS is the only model showing accums. SW
flow will continue into Tuesday, allowing warmer and more humid
conditions to build back into the region.

TUESDAY NIGHT THROUGH FRIDAY...Forecast Confidence...Medium

Beginning Tuesday night, another low pressure system will begin
to impact the region. A shortwave immediately upstream of the
upper level ridge will move in Tues night and Wed morning as the
low in the lower levels develops over the central plains. The low
will move towards Wisconsin, before passing the state some time on
Thurs. This will bring precipitation chances from Tuesday night
through at least Thursday. High pressure looks to take over by
Friday, which will translate into very nice weather for the
weekend.

AVIATION/00Z TAFS/...

Still seeing storm development to the west this afternoon and
expecting this to continue into late afternoon within the
instability gradient. Based on the current CAPE analysis and latest
mesoscale models, seems the best chance for storms late afternoon
into early evening will be in the southern half of the forecast
area.

Could see a lull in widespread activity from late evening into the
night, with showers/storms picking back up in the west later in the
night as the trough approaches. Showers and storms are then expected
across the forecast area on Saturday as the low and associated cold
front move through. The activity will likely wind down from west to
east later in the afternoon.

Lower ceilings and visibilities are probable at times through
tomorrow...mainly during the rounds of precip.

MARINE...

South to southwest winds ahead of an approaching cold front will
become gusty by Saturday afternoon. West to northwest winds will
then remain gusty behind the cold front Saturday evening into Sunday
morning. Decided to issue a small craft advisory from early Saturday
afternoon to mid-morning on Sunday. Gusts to 25 knots are likely
through this period.

Waves will be highest Saturday afternoon and early evening in the
northern marine zones due to the southerly winds. The highest waves
will then be confined toward open waters for the remainder of the
advisory as winds become offshore.

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...SMALL CRAFT ADVISORY from 1 PM Saturday to 10 AM CDT Sunday for
     LMZ643>646.

&&

$$

UPDATE...Gehring
TONIGHT/Saturday AND AVIATION/MARINE...DDV
Saturday NIGHT THROUGH Friday...BSH



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