Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 151145

Area Forecast Discussion
National Weather Service Green Bay WI
545 AM CST Fri Dec 15 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 358 AM CST Fri Dec 15 2017

Northwest upper flow will continue to produce mostly cloudy and
seasonably cold weather across the region today and Saturday.
Light snow produced by a surface and upper level trough should
exit the area by midday, except for northcentral Wisconsin where
some lake effect snow showers will continue. Partial clearing is
possible in the east during the afternoon and evening.

Jet energy rotating around the top of the ridge to our west will
approach the region later tonight and early Saturday and should
provide the upper support to produce some light snow. There is
even a weak coupled jet structure and mid level frontogenesis
that will help drive precipitation. An inch or two of fluffy snow
is expected over all but the far north.

The snow should lift north Saturday but diminish as the upper
support exits the region. It could end as a little freezing drizzle
as the mid level moisture departs but left it out for now.

.LONG TERM...Saturday Night Through Thursday
Issued at 358 AM CST Fri Dec 15 2017

The pronounced northwest flow pattern over the past week will
flatten this weekend, allowing for temperatures to return to
near normal on Saturday and then above normal early next week.
Timing of upper level disturbances and associated precipitation
chances still problematic at the beginning of the period. It now
appears that a stronger storm will affect the area toward the end
of the forecast period.

For Saturday night, added or increased the chances of light snow
Saturday evening across northeast Wisconsin as low level winds
turn to the southeast. 925mb temperatues off the models would
support some light snow shower activity off of Lake Michigan.
What is interesting about the Saturday night period is that the
GFS/WRF model are now indicating a surface trough across northeast
Wisconsin which may increase low level convergence. If this scenario
plays out, snow chances and snowfall amounts would need to be
increased. After midnight, some of the models would suggest that
the mid level moisture would scour out, so freezing drizzle would
be possible after midnight. Did end any precipitation at 12z
Sunday, but confidence in the end time is low. It is possible that
the light snow or freezing drizzle could linger through much of
Sunday morning.

Yet another clipper system is expected  to move across the region
Monday night, bringing a chance of light snow to northern
Wisconsin. Lake effect snow showers are possible Tuesday into
Tuesday night. Attention then turns to a more significant storm
that could bring a significant snowfall to portions of the area.
The model runs tonight would suggest that the precipitation
could be mixed across portions of the Fox Valley and lakeshore
region. It is too far out to pinpoint the track of the storm
and how much warm air would work into the area which could
impact precipitation types and snowfall amounts. Stay tuned!.

.AVIATION...for 12Z TAF Issuance
Issued at 544 AM CST Fri Dec 15 2017

variable conditions expected across the region through
midday, with some snow showers and MVFR conditions in some places.
Mostly VFR weather is expected this afternoon and evening, but
lower clouds and light snow will arrive from south to north late
tonight and early Saturday as an upper level disturbance moves
across the area.



LONG TERM......Eckberg
AVIATION.......RDM is the U.S. government's official web portal to all federal, state and local government web resources and services.