Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 240036 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
736 PM CDT Thu Mar 23 2017

.UPDATE...

Area of elevated convection moving east through the area, being
driven by strong/focused 850 mb to 700 mb warm air advection and
low level jet nose. Not a lot of elevated CAPE, but enough with
the strong upward vertical motion and effective layer shear to
produce hail. We had a few 1 inch diameter hail reports in Iowa
and Lafayette Counties with the initial storms, with several
reports of small hail since then across the Madison area and
points south.

Expect these storms to continue east across the rest of the area
this evening, exiting the east by 10 pm or 11 pm, as the focused
warm air advection and low level jet pivot across the area. The
strongest storms could still bring isolated hail to 1 inch in
diameter, along with cloud to ground lightning and brief heavy
rainfall.

There should be a lull in precipitation later on this evening and
overnight/Friday, as the area gets into the warm sector and the
best upward vertical motion focuses north and west of the area. We
should get into rain again later Friday into Friday evening, as
low pressure moves to the south of the area.

&&

.AVIATION(00Z TAFS)...

Broken line of thunderstorms will continue to move east through
the area this evening, exiting the eastern areas between 10 pm and
11 pm. Look for isolated hail to 1 inch in diameter, along with
cloud to ground lightning, brief heavy rainfall and gusty winds
to around 30 knots. Visibility values may drop to 1 to 2 miles as
well, with ceilings around 2000 feet.

There should be a lull in the precipitation later tonight into
most of Friday. Ceilings should rise to above 3000 feet, with
visibilities above 6 miles during this period. Could even see some
clearing in the far southern counties at times as well.

Gusty south to southeast winds this evening should weaken somewhat
and become more light and variable later tonight into Friday
morning. Northeast winds should then develop and become gusty
later Friday into Saturday night, as low pressure passes by to the
south.

&&

.MARINE...

Extending the Small Craft Advisory for areas south of North Point
Lighthouse until 1 am Friday morning, matching the one for the
north half of the nearshore waters. Gusty south to southeast winds
are lingering, with gusts to around 30 knots at times. Elevated
waves above 4 feet should subside by 1 am Friday morning. These
winds should weaken later tonight into Friday.

Another Small Craft Advisory will be needed for later Friday into
at least Saturday night, as low pressure passes by to the south.
Gusty northeast winds are expected during this period, with high
waves developing with the onshore fetch.

&&

.PREV DISCUSSION... (Issued 325 PM CDT THU MAR 23 2017)

TONIGHT AND FRIDAY - Forecast Confidence...Medium.

A complex situation is playing out across the northern plains. A
weak warm front is pushing northeast through Iowa and Illinois while
a secondary boundary stretching from north central IA into NE Kansas
also pushes to the NE. Near the intersection of these two
boundaries, a small cluster of thunderstorms have developed and have
been pushing across northern Iowa though the afternoon. Meanwhile, a
large dry slot has developed between the two frontal features.

High res guidance has a very poor handle on all of these features,
but given current trends and set up of the atmosphere, am expecting
the cluster of thunderstorms to gradually weaken before making it
to our western CWA. Shortly after those showers and storms arrive,
the warm front will push through the area. We can expect at least a
slight chance of precip as these features move through the area.

Guidance is in good agreement that the warm front will stall out in
central Wisconsin, but there is quite a bit of noise regarding how
much moisture will remain in place to the south of the front. Most
guidance keeps much of the moisture in the vicinity of the front, so
am expecting broken to occasionally scattered clouds in the southern
half of the CWA.

The warm front will stay to the north of the CWA though the night
before it begins to slowly creep southward tomorrow. As it moves
south, am expecting cloud coverage and precip chances to increase
into the afternoon. MU CAPE looks limited through at least the early
afternoon, so chose to leave thunder out until after 21z. Before the
front moves into our area, we can expect broken to scattered clouds
in our south along with moderately strong southerly winds. This will
result in very warm temperatures in the southern half of the CWA,
perhaps breaching 70 in some locations.

FRIDAY NIGHT THROUGH SUNDAY - Forecast Confidence...Medium to
High.

More widespread precipitation threat expected Friday night into
Saturday morning as approaching low pressure system still
undergoing minor strengthening.  Impressive layer Q-vector
convergence of 20 to 30 units brushes southern WI Fri night along
with layer frontogenetical forcing for a time.  Short term guidance
trending slightly south with axis of heavier precipitation
during this period.  Will continue highest pops Friday night
into Saturday morning, then trend slowly downward.  However
occasional light rain or drizzle will likely continue into
Sunday as low pressure weakens and gets nudged eastward later in
the weekend as weak convergence and low level deformation lingers
across the area along with plentiful low level moisture.  Fog threat
will increase as boundary layer winds weaken Saturday night into
Sunday.  Will continue to mention thunder threat as well Friday
night when strongest synoptic scale forcing is expected along with
nearness of southward moving boundary.

EXTENDED PERIOD...

SUNDAY NIGHT THROUGH THURSDAY - Forecast Confidence...Medium.

Unsettled weather looks to continue through early next week.
Secondary weakening short wave over central Plains trending
toward more northerly track and may bring more light rain back
to southern WI on Monday and Monday night. Cool ENE surface wind
flow to continue so cooler by the lake for much of the period.  More
amplified 500H pattern sets up for several days as upstream long
wave trof moves across the western CONUS, and resulting large scale
ridging builds across the Great Lakes and upper midwest.  Around mid-
week, upstream trof wl get nudged eastward into the central CONUS,
eventually returning rain chances to the Great Lakes Thu into
Friday.  ECMWF and Canadian more bullish in spreading rain back into
srn WI on Thursday, while GFS holds off for 24 hours.  WPC Blend
has more confidence in faster solution so wl spread chance pops back
in for Thursday.  Warmer Low level thermal structure favors rain
for the expected precipitation events during the period.

AVIATION (21Z Taf Update)

Warm front continues to approach the area from the southwest.
Scattered showers and isolated thunderstorms have developed along
the front, along with some MVFR to occasionally IFR cigs. As the
front passes through the region in the late afternoon and evening,
most guidance has the cigs improving and the precipitation
dissipating. However, models do not currently have a good handle on
the complex unfolding situation, so uncertainty in the forecast is
high. It seems like a good bet the MVFR cigs will reach at least to
MSN as the front passes later this afternoon, and perhaps farther
east toward evening. Meanwhile, LLWS remains likely though the
overnight hours.

MARINE...

Winds should begin to diminish this evening as the pressure gradient
gradually weakens. Accordingly, SCA expiration looks to be on
schedule. After a brief period of weaker winds overnight and into
tomorrow morning, offshore winds will ramp back up in the early
afternoon, especially in the south. Another SCA may be needed for
this time.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 1 AM CDT Friday for LMZ645-646.

     Small Craft Advisory until 1 AM CDT Friday for LMZ643-644.

&&

$$

Update...Wood
Tonight/Friday and Aviation/Marine...BSH
Friday Night through Thursday...MBK


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