Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 131143
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
543 AM CST Wed Dec 13 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 424 AM CST Wed Dec 13 2017

Two jet streaks are combining to produce a clipper like system
that will bring snow to the area. The stronger of the two was
racing southeast from South Dakota at 10z, while the other was
still north of the Canadian border east of Lake Winnipeg. The two
interact with each other more as the day goes on, resulting in the
strengthening of the surface low as it moves across southern
Wisconsin towards north Indiana today.

The models have been tracking this system further north with time,
which seems reasonable based on the latest radar returns and surface
pressure falls. We decided to add some counties in northern Wisconsin
to the winter weather advisory after discussion with Marquette.
Much of the snow with this system will fall during the morning
hours as a coupling of the two upper jets produce strong vertical
motion. As the surface low moves into southern WIsconsin later
today low level winds shift to the northeast and help produce lake
enhanced snow for eastern Wisconsin through early evening. Blowing
and drifting snow is possible near the lake and bay during the
afternoon and evening hours.

Model precipitation forecasts and snow ratios suggest that parts of
east central Wisconsin could get six inches or more of snow, but we
decided to leave the winter weather advisory in place versus a warning,
as this system is more complex than the typical clipper system making
it difficult to determine where this heavier snow might occur.

.LONG TERM...Thursday Night Through Tuesday
Issued at 424 AM CST Wed Dec 13 2017

500mb ridge across western North America with downstream troughing
across eastern Canada into the northern United States will dominate
the weather pattern through the end of the work week. The pattern
is expected to flatten some over the weekend with a 500mb trough
moving across the central United States early next week.

The next in a series of upper level disturbances will sweep across
the area Thursday into Thursday night. The chance of lake effect
snow showers will continue Thursday across the far north. Did
bring in a chance of flurries over central and the remainder of
north-central Wisconsin Thursday afternoon. Expanded the chances
of snow showers or flurries eastward across the entire area
Thursday night. There may be a light coating of snow that could
cause some slick spots on area roads, bridges and sidewalks.

The cold cyclonic flow will lead to more cloudiness, along with
the chance of lake effect snow showers across the far north with
the chances of flurries over the remainder of the region on Friday.
For Friday night, the models are split between a dry forecast and
the chances of more flurries or light snow. Continued the chances
of flurries for most areas outside the snowbelt region of northwest
Vilas county. Next clipper could bring an accumulating snow to the
region Saturday into Saturday night. Beyond Saturday night, there
is a chance of light snow Monday night into Tuesday across the
entire region. The chances of lake effect snow showers continues
at times Sunday through Tuesday across the far north. Temperatures
return closer to normal over the weekend with temperatures at or
slightly above normal early next week.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 542 AM CST Wed Dec 13 2017

IFR conditions and snow expected across the area today.
Snow accumulations will be sufficient for plows to be used. The
snow will end from west to east during the late afternoon or early
evening hours. Clearing is expected over all but far northcentral
Wisconsin overnight.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM CST this evening for
WIZ010>013-018>021-030-031-035>039-045-048-049-073-074.

Winter Weather Advisory until 9 PM CST this evening for WIZ022-
040-050.
&&

$$

SHORT TERM.....RDM
LONG TERM......Eckberg
AVIATION.......RDM



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