Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 131722
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1122 AM CST Wed Dec 13 2017

Updated aviation portion for 18Z TAF issuance

.UPDATE...
Issued at 1053 AM CST Wed Dec 13 2017

Upgraded the winter weather advisory to winter storm warning for
parts of northeast Wisconsin. Getting reports of 6 inches over
north-central WI, with focus shifting downstream into northeast WI
for the rest of the day. Winds will also pick up over northeast WI
by mid to late afternoon, causing blowing and drifting for the
start of the evening commute. For Brown County in particular, the
worst conditions should be felt over the northern part of the
county, where snow totals will be the highest, and the gustiest
winds (to around 30 mph) should occur coming down the Bay.
&&

.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 18Z TAF Issuance
Issued at 1114 AM CST Wed Dec 13 2017

Snow will continue for most area through mid-afternoon, then the
snow will end from northwest to southeast during the late
afternoon or early evening hours. The worst conditions should
occur over northeast WI where increasing northeast winds to 25 kts
will cause blowing and drifting of the snow. Clearing is expected
for a time over all but far north-central Wisconsin overnight.
More mvfr cigs arrive on Thu morning.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 6 PM CST this evening for WIZ005-
010>013-018>021-030-031-035>038-045-048-049.

Winter Storm Warning until 9 PM CST this evening for WIZ022-040.

Winter Storm Warning until 6 PM CST this evening for WIZ039-073-
074.

Winter Weather Advisory until 9 PM CST this evening for WIZ050.
&&

$$

UPDATE.........MPC
SHORT TERM.....RDM
LONG TERM......Eckberg
AVIATION.......MPC



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