Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 140159
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
859 PM CDT Fri Apr 13 2018

.UPDATE...

Convection has started to blossom once again tonight as the low
level jet noses into the western portions of the area. Showers and
elevated thunderstorms will persist for much of the night.

Winds have come down a bit at this hour, but will increase again
late this evening into the overnight hours as the surface pressure
gradient tightens up further. Gusts around 40 MPH are expected
after midnight into the daytime hours on Saturday.

Overall, didn`t make much in the way of modifications to the
forecast for the rest of tonight and tomorrow. Still looks like
temperatures will mostly stay above freezing overnight, save for
the far northwestern portion of the forecast area--northwest of a
line from Loganville to Green Lake. A glaze to a tenth or so of
freezing rain will be possible across this area during the pre-
dawn hours Saturday morning.

Temperatures should then slowly fall to or below freezing for most
of the area as the day goes on Saturday. Precipitation type will
first transition from rain to freezing rain, but the low levels
may get cold enough to precipitation to eventually transition to
sleet, especially north of I-94. The exact timing of these
transitions will obviously have a significant impact on eventual
ice/snow/sleet accumulations. The forecast will be continuously
updated over the next 24 hours as new data is available, so be
sure to check back often for updates.

&&

.MARINE...

Winds have already reached gale force, and gusts will increase
further this evening and overnight. Gusts to 40 knots are expected
overnight, with gusts to 45 knots expected on Saturday.

Waves will continue to build across the nearshore, reaching 10 to
15 feet after midnight. These very high waves will continue
through Saturday evening. Waves should slowly diminish on Sunday
and Monday.

&&

AVIATION(00Z TAFS)...

Tonight:

Low ceilings are expected to persist overnight tonight.
Winds will increase from the northeast as well, with gusts to
30-40 knots overnight. Visibility will be variable, with
reductions due to a combination of fog and rain showers. Finally,
very strong winds right off the surface will lead to low level
wind shear.

Saturday:

Strong surface winds will continue on Saturday, along with the low
ceilings and low level wind shear. Winds are currently expected
to peak around mid day, with a few gusts possibly approaching 45
knots. In addition, colder air will filter into the area. This
will lead to precipitation transitioning from rain to a wintry mix
of snow, sleet (PL) and freezing rain. This should take place
during the afternoon hours, continuing into Saturday evening.

&&

PREV DISCUSSION... (Issued 355 PM CDT FRI APR 13 2018)

TONIGHT THROUGH SUNDAY...Forecast Confidence - Medium to High.

Quite the mixed bag of weather is expected over the next couple days
as strong low pressure moves through the region. Tonight will
feature mainly rain showers, with some thunder in the evening. As
temps cool off from the northwest, there could be some
snow/sleet/freezing rain northwest of Madison later tonight. Winds
will pick up overnight as well, with gusts of 40 to 45 mph by
morning.

The mixed precipitation will continue to sag southward during the
day Saturday as colder air filters in from the north. Mainly rain
will hold on through late afternoon toward the Illinois border.
Mainly freezing rain, sleet, and snow is then expected Sunday into
Sunday night, with some rain mixing in southeast during the day
Sunday.

Decided to go with a Winter Weather Advisory for all but southeast
portions of the forecast area. Milder temps will lead to more rain
and less snow/ice in the southeast. The main factors for going with
an advisory vs a warning are: mild ground temps which will make
icing difficult on pavement, long duration of the event (melting
will occur), and a lot of precip falling during the day Saturday and
Sunday (more melting likely). Model soundings were right on the edge
of sleet and freezing rain...so could end up seeing more sleet than
currently in the forecast.

Strong winds tomorrow could help bring down some tree branches given
enough icing. Went with a Wind Advisory for the whole area from 5 am
to 7 pm Saturday. Peak gusts of 40 to 50 mph are likely.

Prolonged period of onshore winds with a favorable fetch from the
East-northeast to northeast expected tonight into Sat night. Onshore
winds are expected to gust from 35 to as high as 45 knots at the
lakeshore and coastlines later tonight into Saturday night. With
Lake Michigan water levels running about a foot above the period of
record average, thinking there is an increased threat for lakeshore
flooding and erosion along the coastlines from Sheboygan south to
Kenosha.  Posted Lakeshore Flood Advisory to heighten the awareness
for this period.

SUNDAY NIGHT AND MONDAY...Forecast Confidence - Medium.

Lingering mid-level circulation and deformation will likely bring
some light snow to the area Sunday night. Colder air will be
funneling back into southern WI behind surface and 850H low
pressure moving through the central Great Lakes. However some
drying noted above the cloud bearing layer causing loss of ice
crystals. Surface temperatures are expected to fall into the mid
20s Sunday night so can not rule out a period of light freezing
rain or drizzle, changing over to -sn later Sunday night, tapering
off to flurries or ending on Monday. A light glaze and minor
accumulations of snow will be possible.

EXTENDED PERIOD...

MONDAY NIGHT THROUGH FRIDAY - Forecast Confidence...Medium.

Some recovery in temperature is expected early in the period as
short wave ridging results in a brief period of quiet weather around
Tuesday.  850H temps warm above freezing on Tuesday but cloud cover
and east to southeast winds will prevent much of a warm up.  Medium
range guidance in good agreement on another low pressure system
deepening over the tri-state area of IA/MN/Interests across the area should
check back often for updates tonight and tomorrow. WI later
Tuesday night into Wednesday. This system will move moving along a
tightening baroclinic zone and may bring another round of mixed
precip to southern WI during this period. ECMWF/GFS focus
strongest lift and heaviest QPF over central WI, possibly
affecting parts of northern CWA. The -sn should end Wednesday
night, with clouds and possible flurries lingering into Thursday.
Some recovery in temperature on Friday, but another low pressure
system will be poised to affect the area over the weekend. Climate
Prediction Center focusing on below normal temperatures into the
last days of April.


&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 5 PM Saturday to midnight CDT
     Sunday night for WIZ062>065-067>069.

     Wind Advisory from 5 AM to 7 PM CDT Saturday for WIZ046-047-051-
     052-056>060-062>072.

     Lakeshore Flood Advisory until 7 AM CDT Sunday for WIZ052-060-
     066-071-072.

     Winter Weather Advisory from 7 AM Saturday to midnight CDT
     Sunday night for WIZ051-052-058>060.

     Winter Weather Advisory from 1 AM Saturday to midnight CDT
     Sunday night for WIZ046-047-056-057.

LM...Gale Warning until 7 AM CDT Sunday for LMZ643>646.

&&

$$

Update...Boxell
Tonight/Saturday and Aviation/Marine...Boxell
Saturday Night through Friday...99



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