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National Weather Service Green Bay WI
1145 AM CST Sat Dec 3 2016

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 316 AM CST Sat Dec 3 2016

Although shortwave ridging will keep the weather dry across the
area today and tonight, abundant low level moisture will keep
clouds in place across the western Great Lakes. The abundant
cloud cover and lack of appreciable advection of warm or cold air
will mean temperatures will stay right around where they have
been the last few days, with little diurnal range anticipated.

Things change quite a bit on Sunday as a large upper level low
seen on water vapor imagery over Baja California spins off a piece
of energy and ejects it northeast today. This energy will develop
into a mid level trough and associated PV anomaly across the
central Plains tonight, continuing northeast as a negatively
tilted trough tracking through the western Great Lakes on Sunday.
This mid level low will also get a boost from isentropic lift as
winds are almost perpendicular to the 285K isentropic surface.

Model soundings show the column has fairly deep moisture
associated with it, making the choice of precipitation fairly
straightforward with rain or snow based on daytime surface
temperatures. Given daytime highs are expected to top out in the
lower to middle 30s mainly snow is expected across the forecast
area, with the best chance for rain across the eastern cwa given
slightly higher temperatures. Given the dynamics and moisture in
place this system looks to grind out 1 to 3 inches of snow on
Sunday, with some locations across central Wisconsin possibly
hitting 4 inches given the better moisture and proximity to
system dynamics.

.LONG TERM...Sunday Night Through Friday
Issued at 316 AM CST Sat Dec 3 2016

There is a chance for snow Sunday evening as a 500mb trough and
surface trough exit to the east. There is little chance for
precipitation from late Sunday night through Tuesday morning with
a weak mid level ridge passing over Wisconsin and a surface high
across the Great Lakes Region. Precipitation chances arrive
Tuesday afternoon as a surface system approaches, a 500mb low
moves from Texas to the Ohio Valley, and another 500mb low
develops near the US/Canadian border and moves east. The 00Z GFS
and ECMWF had similar solutions, though they did exhibit
differences, but the Canadian model had a much weaker surface
system and its 500mb low develops over the northern Plains. Rain
or a wintry mix is expected for about the eastern half of the
forecast area, but it should change to all snow by evening. Snow
chances then decrease during the overnight hours and there is
only a slight chance for snow in north central Wisconsin on

Much colder air will move into the state for the latter half of
the upcoming work week. Only made minor adjustments to model bend
PoPs were made for this part of the forecast. Looks like lake-
effect snow for north central Wisconsin while the rest of the area
is mainly dry.

High temperatures are expected to be well above normal for Monday
and Tuesday, then colder than normal (highs in the 20s) for
Wednesday through Friday.

.AVIATION...for 18Z TAF Issuance
Issued at 1145 AM CST Sat Dec 3 2016

A strong winter inversion will lead to mvfr clouds hanging around
into the evening.  Some suggestions that cigs will improve to vfr
later in the evening or early overnight, but not entirely sold on
that idea.  Otherwise, the most significant impacts revolve around
light snow arriving Sunday morning.  Expectations are for the light
snow to spread across the region during the morning hours, dropping
ceilings and visibilities to ifr/lifr with amounts of 1 to 3 inches.
Snow will continue through the afternoon before ending in the



SHORT TERM.....Kurimski

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