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Area forecast discussion
National Weather Service Green Bay WI
350 am CST Wed Dec 11 2019

Forecast discussion for routine morning forecast issuance

Short term...today...tonight...and Thursday
issued at 349 am CST Wed Dec 11 2019

Bitter cold today and early tonight, then snowy conditions
expected late tonight into Thursday.

The Wind Chill Advisory appears to be working out just fine early
this morning, with many observations showing wind chills in the 20
below to 30 below zero range. No changes to the wind chill headlines,
which will continue through noon. Most of the forecast area had
clear skies, through lake effect clouds off the Bay and Lake
Winnebago were affecting our far eastern and southern counties.
Additional clouds associated with a weak low pressure system were
also brushing our southern counties. Highs today will range from
around zero in the cold spots of north central WI to around 10
above near Lake Michigan.

Temperatures are expected to quickly drop into the single digits
below zero across north central and far northeast WI early this
evening, due to mostly clear skies and light winds. However,
clouds will quickly overspread the region later this evening and
overnight, and warm air advection will result in rising temperatures overnight.
The rrq of an upper level jet and strong warm air advection/isentropic lift will
cause light snow to develop over mainly northern WI after
midnight, with 1 to 2 inches of powder possible in north central
WI by daybreak.

On Thursday, snow will overspread the forecast area as a low
pressure system and associated warm front arrive. The most
significant accumulations are expected over northern WI. Mid-
level moisture is expected to shallow out during the mid to late
afternoon, leading to the possibility of light freezing rain or
freezing drizzle.

In coordination with offices to our west, we have issued a Winter
Weather Advisory for snow along and north of a line from Wausau
to Sturgeon Bay from 3 am to 6 PM Thursday. Most of this region
should see 3 to 5 inches of snow, with local amounts near 6 inches
far northeast. This is very similar to snowfall amounts from wpc,
and close to the 50th percentile of all model forecasts. However,
confidence is only medium at this time. One concern is a dry
wedge in the low-levels, which lingers through early Thursday,
and could delay the start of snow or waste some of the best
forcing to achieve saturation. Another concern is that cips
analogs only support advisory criteria snow over far northern WI.

Long term...Thursday night through Tuesday
issued at 349 am CST Wed Dec 11 2019

The main highlights from this forecast period are the chances for
accumulating snow to start the weekend and below normal
temperatures arriving after the potential snow.

By Thursday night, the winter storm will be winding down as the
surface low pressure system shifts to the east. Locations along
the eastern half of the forecast area could see some lingering
flakes with little to no additional accumulations Thursday night.
High pressure will then move into the forecast area from the
northwest leaving dry conditions through Friday morning. At the
same time, an upper-level shortwave trough will dig across the
northern plains. Model guidance indicates a weak clipper system
riding along this trough could bring light snow accumulations to
the area Friday and Saturday. However, models are not in
agreement with the track of this system, timing, or the amount of
moisture associated with it. Therefore, did not veer from model
blend chance pops and low quantitative precipitation forecast amounts for Friday and Saturday for
now.

By Saturday night, a surface high pressure system will be pushing
into the northern plains funneling colder Canadian air into the
region. This could lead to steady temperatures on Saturday with
the high temperatures occurring in the morning. The cold air will
then continue bringing below normal temperatures through the
remainder of the weekend and into the beginning of next week.
&&

Aviation...for 06z taf issuance
issued at 1039 PM CST Tue Dec 10 2019

Other than some patches of isolated MVFR clouds, VFR conditions
are expected through Wednesday afternoon at all of the taf sites.
Mid and high clouds will then increase from west to east late
Wednesday afternoon and Wednesday evening ahead of an approaching
low pressure system. Winds tonight have not increased over land,
therefore will reduce speeds at the taf sites until later
Wednesday morning when daytime heating should bring down higher
wind speeds to the surface with gusts of 15 to 20 knots. Winds
should then ease Wednesday afternoon as high pressure builds in
across the western Great Lakes region.
&&

Grb watches/warnings/advisories...
Wind Chill Advisory until noon CST today for wiz005-010>013-
018>021-030-031-035-036-073-074.

Winter Weather Advisory from 3 am to 6 PM CST Thursday for
wiz005-010>013-018>022-030-031-073-074.
&&

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