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Area forecast discussion
National Weather Service Green Bay WI
531 PM CST Thu Dec 12 2019

Updated aviation portion for 00z taf issuance

Short term...tonight and Friday
issued at 241 PM CST Thu Dec 12 2019

Light to moderate snow will diminish by early evening
as low pressure moves across the Fox Valley before moving over the
lake. The precipitation may end as some freezing drizzle south of
Highway 29 as mid level moisture and ice crystals exit the area.
Another 2 to 3 inches of snow are possible across the northeast
part of the forecast area, with an inch or less elsewhere. Lows
tonight will be a few degrees above normal.

Friday should be cloudy and seasonable with a chance of light snow
late in the day as an upper trough approaches from the northern
plains. Little or no accumulation is expected during the daylight

Long term...Friday night through Thursday
issued at 241 PM CST Thu Dec 12 2019

An active, progressive pattern is expected with the mean flow
going from west-northwest this weekend, to southwest early next
week, before switching to northwest as an upper ridge moves into
The Rockies. One system to initially already be impacting
northeast WI Friday night into Saturday with light snow/freezing
drizzle. Next system to mainly stay to our south Monday/Monday
night, followed by another shot of Arctic air mid-week. There
continues to be a debate among the models with the handling of a
clipper system Wednesday/Wednesday night.

A broad, elongated area of low pressure and cold front are
forecast to track across WI Friday night and bring US our next
chance of light snow and/or freezing drizzle. Forecast soundings
actually hint more at freezing drizzle after midnight, thus roads
could become slippery with a glaze of ice. Any snow accumulations
would be light, on the order of less than an inch. Min
temperatures to range from the middle to upper teens north-central
WI, middle to upper 20s near Lake Michigan. Colder air will filter into
the region behind the cold front for Saturday and with a mid-level
shortwave moving through to combine with a cyclonic flow, will
need to leave a chance pop in the forecast. Highest pops placed
over north-central WI due to lake enhancement on northwest winds.
Precipitation type should mainly be light snow by this time with
wrap-around moisture adding ice to the column, although a little
freezing drizzle cannot be ruled out. Additional accumulations to
be very light with most locations only seeing a dusting to perhaps
around one-half inch. Max temperatures on Saturday to be in the
lower 20s central WI, upper 20s to around 30 degrees eastern WI.

Light snow to gradually diminish Saturday evening as the cyclonic
flow weakens and high pressure begins to build east from the upper
MS valley. The exception would be north-central WI where
persistent lake effect snow could add up to another inch over
parts of Vilas County. Some breaks in the clouds are possible
later Saturday night with min temperatures to range from the
single digits above zero central WI, to the middle teens near Lake
Michigan. This high pressure will build into the western Great Lakes
region on Sunday and allow skies to become mostly sunny to partly
cloudy. It is going to be a cold day with Max temperatures in the
upper single digits to lower teens central WI, upper teens to
around 20 degrees eastern WI.

The high pressure is forecast to stretch from the northern plains,
through WI and reach the eastern Great Lakes Saturday night.
Generally partly cloudy skies are anticipated through the night
with some sub-zero min temperatures over parts of northern and
central WI. We continue to watch a system that is progged to move
from the Southern Plains into the Ohio/Tennessee valleys on Monday. The GFS
still sends the northern periphery of light snow into east-central
WI, while the European model (ecmwf) does not take the snow north of Chicago. The
CMC splits the difference with the northern edge of light snow
reaching southeast WI. Have removed the small pops from east-
central WI for Monday with Max temperatures to range from the
middle teens north-central, to the lower 20s east-central WI.

After a quiet and cold Monday night, models send a shortwave
trough into the Great Lakes on Tuesday. Preceding this trough will
be a cold front that will usher in another shot of Arctic air into
WI. Gulf moisture is non-existent, therefore do not expect to see
much in the way of snow (perhaps flurries?). Max temperatures for
Tuesday to be from 10 to 15 degrees central WI, 15 to 20 degrees
eastern WI.

A ridge of high pressure is forecast to push into western WI by
late Tuesday night. If skies can clear and winds decouple,
temperatures could really tank. Unfortunately, it is too difficult
to determine cloud trends at this point, so have gone conservative
by keeping min temperatures in the single digits above or below
zero. The European model (ecmwf) has backed off on the warm air advection snow it had forecasted
from its previous run for Wednesday and now mirrors other models
by keeping the day dry. Max temperatures for Wednesday to be from
10 to 15 degrees north, 15 to 20 degrees south.

A quick moving clipper system is forecast to dive southeast toward
Lake Superior Wednesday night and reach Lake Huron on Thursday.
Models keep any precipitation along and north of this clipper
track, thus little if any snow is expected from this system.
Slightly warmer air to get pulled into WI ahead of the clipper, so
Max temperatures on Thursday to be in the middle to upper teens
north, lower 20s south.

Aviation...for 00z taf issuance
issued at 531 PM CST Thu Dec 12 2019

Light snow and freezing drizzle will continue for a few more hours
as a low pressure system exits the region to the east. In its wake
IFR/MVFR ceilings will continue through the overnight hours. Mostly
MVFR ceilings are expected Friday, with a chance of light snow in
the afternoon in northern and central Wisconsin. Confidence in
snow chances is not high enough to include in this set of tafs.

Grb watches/warnings/advisories...
Winter Weather Advisory until 6 PM CST this evening for wiz005-

Winter Storm Warning until 6 PM CST this evening for wiz011>013-


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