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Area forecast discussion
National Weather Service Green Bay WI
1013 PM CST Thu Dec 5 2019

Updated aviation portion for 06z taf issuance

Short term...tonight and Friday
issued at 308 PM CST Thu Dec 5 2019

Main forecast highlights are the light snow accumulations this
afternoon into tonight and the potential for some freezing drizzle
to mix in with the snow.

Light snow began to fall across far north-central Wisconsin this
afternoon as a weak clipper system shifted into northwest
Wisconsin. As the system tracks along the Wisconsin/u.P. Border
into tonight, the bulk of the precipitation is expected to remain
north of a line from Rhinelander to Kewaunee. Total snowfall
accumulations around one inch are still likely near the u.P.
Border with lesser amounts farther south. Forecast soundings
indicate the potential for the loss of ice crystals aloft at
times and a fairly shallow saturated layer in the lower levels.
This would lead to the possibility for freezing drizzle to mix in
with the snow at times. However, confidence is not high enough to
mention in the forecast at this time.

The precipitation associated with the clipper system will come to
an end from west to east after midnight. However, winds will
switch around to the northwest bringing additional chances for light
lake effect snow showers over Vilas County through early Friday
morning. Little accumulations are expected from these snow
showers as they'll be brief. Clouds will then be on the decrease
beginning over east-central Wisconsin. While the region is
expected to have mostly sunny skies Friday morning, lingering
lake effect clouds will stick around over Vilas County through the
afternoon. High temperatures on Friday will be a bit colder,
mainly in the 20s, due to the passage of the clipper system.

Long term...Friday night through Thursday
issued at 308 PM CST Thu Dec 5 2019

Mean flow to transition from nearly zonal this weekend, into a
highly-amplified flow consisting of upper ridges over the eastern
Pacific/western Atlantic and a deep upper trough over east-central
noam by mid-week. The Main Point of contention remains with the
potential winter storm early next week as models continue to
struggle with a potential phasing between the upper trough and jet
energy moving across the southern Continental U.S.. models are in better
agreement with the blast of Arctic air that will overspread WI by
mid-week. Temperatures could be 15 to 25 degrees below normal both
Wednesday and Thursday.

High pressure shifts toward the eastern Great Lakes Friday night
with a return flow to develop across WI. Look for clouds to
increase through the night as warm air advection overspreads the region. If we
can saturate the lower levels of the atmosphere, there could be
some flurries over parts of the area after midnight. If there were
to be any light snow, it would be relegated to far northern WI
where there would be slightly better forcing from a shortwave
diving southeast over northern sections of the Great Lakes. Min
temperatures to dip to around 10 degrees north, 10 to 15 above
central WI and middle to upper teens east-central WI.

Any light snow or flurries should end by Saturday as the shortwave
exits the region and there are no other relevant features to kick
off any precipitation. A persistent warm air advection pattern remains over WI
thanks to an increasing southwest wind aloft. If there is a
problem on Saturday, it will be cloud trends as the warmer air
aloft interacts with the colder air near the ground. This would
allow a low stratocumulus deck to develop, but it is difficult to
determine where these clouds would form. For now, prefer to go
mostly cloudy over much of northeast WI with Max temperatures
around 30 degrees north, middle to upper 30s over southern
sections of the forecast area.

A cold front is forecast to move across the upper MS valley later
Saturday night. There may be enough lift to bring a small chance
of mixed precipitation to central WI, including a little freezing
drizzle. Fortunately, any precipitation looks really light (if it
happens at all), but a few slippery spots on area roadways will be
possible. This cold front gradually pushes across northeast WI on
Sunday and should have enough lift and moisture present to at
least keep a chance of light precipitation in the forecast.
Forecast soundings indicate there might not be enough moisture
aloft, such that any precipitation that does fall would be either
drizzle or freezing drizzle. Max temperatures on Sunday are
expected to reach the middle 30s north-central WI, lower 40s for
eastern WI.

Models show a piece of energy to have ejected out of the new upper
trough situated over The Rockies Sunday night. This energy,
coupled with a weak surface wave riding northeast along the cold
front, would bring an increasing chance for light snow through the
night. The upper trough sweeps across the plains on Monday with a
surface low starting to strengthen over the mid-MS valley. Light
snow still looks on track across the region Monday as
frontogenetical forcing spreads across WI. Colder air to begin
getting pulled into the region with Max temperatures on Monday
only in the lower 20s far north, lower to middle 30s east-central
WI.

The latest trend among the models is to not have a phased system
between the upper trough and southern stream jet energy until the
system is to our east. Therefore, while light snow will continue
to fall across northeast WI Monday night, a significant
accumulation does not look likely. That being said, models have
always had problems with phasing/non-phasing systems and the
forecast could still change. Anyone with travel plans early next
week should monitor later forecasts for updated information.
Strong cold air advection to then quickly spread across WI on Tuesday with
temperatures either steady or slowly falling through the day.

Bitterly cold air to be the dominant weather headlines Tuesday
night/Wednesday. Temperatures could be 15 to 25 degrees below
normal with some sub-zero min temperatures north/central WI and
wind chills in the teens to around 20 below zero by daybreak
Wednesday. Max temperatures for Wednesday will struggle to get
above zero over north-central WI, with single digits above zero
readings over most of the area. As for lake effect snow potential,
expect some accumulation as 800 mb temperatures over Western Lake
Superior reach around -25c between late Tuesday into Wednesday
morning. High pressure building into WI on Wednesday should
gradually end the snow showers by late morning or early afternoon.

This surface ridge quickly moves across WI Wednesday night and
depending on cloud cover, we could be in for a really cold night.
The Arctic air to already start pulling away from WI on Thursday
with warm air advection returning to the area. There are questions as to whether
we will be able to saturate sufficiently to allow for any light
snow to develop. Have gone with very low pops for now. There will
be a bump up to temperatures as readings on Thursday rise into the
teens.
&&

Aviation...for 06z taf issuance
issued at 1013 PM CST Thu Dec 5 2019

Low pressure moving across Central Lake Michigan will
produce MVFR ceilings in most places overnight. IFR ceilings and
snow showers or flurries are possible north of a Rhinelander to
Washington Island line.

Drier air will produce clearing skies late tonight or early Friday.
The clearing should happen first where a northwest wind is downsloping
across eastern Wisconsin. Clouds will clear last in the Northwoods
area. Good flying weather is likely Friday afternoon and Friday
night across the region.
&&

Grb watches/warnings/advisories...
none.
&&

$$

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