Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 091803 AAA
AFDGRB

Area Forecast Discussion...UPDATED
National Weather Service Green Bay WI
1203 PM CST Fri Dec 9 2016

Updated aviation portion for 18Z TAF issuance and Winter Storm
Headlines.

.SYNOPSIS...
Issued at 328 AM CST Fri Dec 9 2016

Snow showers ending in the Lake Superior snowbelt today. Snow
across the area this weekend, with the highest amounts in the
south. Cold snap still on target for the middle to latter part of
next week.

High upper heights/blocky flow remains over the northeast Pacific,
with the blocking extending east across North America at high
latitudes. To the south, a seasonably strong band of westerlies
was across the CONUS, with a low-amplitude trough over the Great
Lakes region. The westerlies will flatten back to a nearly zonal
regime the next couple days as the trough shifts east, then low-
amplitude troughing will redevelop over the Plains. The result
will be broad, strong, cyclonic upper flow dominating much of the
eastern CONUS during the latter part of the forecast period.

As typical, the fast, low-amplitude flow regime is resulting in
considerable model variability from run to run, which makes
pinning down the specifics of daily temperature and precipitation
forecasts difficult. But the big picture remains unchanged. For
the next several days, temperatures will vary with the passage of
individual systems, ranging from near to modestly below normal.
That will be followed by a cold snap with well below normal
temperatures during the middle to latter part of next week. The
large scale pattern favors active weather, with several
opportunities for snow. The weekend snow potential looks more
robust again, especially across the southern part of the area.
&&

.SHORT TERM...Today...Tonight...and Saturday
Issued at 328 AM CST Fri Dec 9 2016

No changes to lake-effect headlines this morning. Snow showers
continue to shift across the observing sites in western Vilas
county. It`s hard to get a firm grasp on totals until our COOPs
come in later this morning, but portions of western Vilas county
have probably received over a foot, with the significant amounts
likely extending into northwest Oneida county. As cloud-layer
winds back this morning, expect the focus of the heaviest snow
showers to shift into eastern Vilas county, and eventually out of
the forecast area. Drying aloft will also lead to a gradual
weakening of the snow showers as well.

Generally quiet weather is expected for the rest of the area and
the remainder of the short term. The main issue is temperatures
tonight. Those will depend on cloud trends. Expect some passing
clouds tonight, with both clear and cloudy periods. Edged mins
down across the north where a fresh snow cover now exists. But it
could get considerably colder that what`s in the forecast if the
clear periods dominate and winds drop off. The day shift can make
further adjustments if needed once cloud trends become more
evident.

Models have slowed the arrival of the snow, with most now dry
through 00Z Saturday. Trimmed PoPs Saturday, but was not
comfortable removing them totally as confidence is lowered by the
poor run-to-run consistency of the models.

.LONG TERM...Saturday Night Through Thursday
Issued at 328 AM CST Fri Dec 9 2016

Main forecast concerns to center around snow potential for the
latter half of the weekend into early next week. There are still
plenty of unknowns regarding this snow event as models continue to
waffle on the smaller scale details. Once the snow diminishes,
attention will turn to the much-advertised arctic air intrusion
that will send temperatures a good 20 degrees below normal by
mid-week with sub-zero min temperatures and bitterly cold wind
chills.

Models continue to indicate increasing isentropic lift/mid-level
forcing into the Great Lakes Saturday night, along with a hint of
an inverted surface trough extended from the central Plains into
the Great Lakes. The pressing issue remains how far north will the
expected band of snow reach into northeast WI as better lift/
forcing to be roughly along/south of the I-94 corridor. If this
trend persists, snow accumulations Saturday night could range from
a few tenths of an inch in Vilas county, to 2-3" over our southern
tier of counties (Waushara to Manitowoc). Any subtle shift north
of the dynamics could place the southern counties into advisory
criteria, so this will need to be watched. Min temperatures to
range from 5 to 10 above north-central, to the upper teens near
Lake MI.

As the main mid-level trough enters the Plains on Sunday,
anticipate a surface low to begin gradually strengthening over the
mid-MS Valley. Models remain inconsistent on whether there will be
a break in the snow Sunday, or will there be enough lift from the
right entrance region of the upper jet to sustain light snow
through the day? Based on the latest model output, the latter
seems favored, thus have raised pops across central/east-central
WI with accumulations generally in the 1-2" range. Max
temperatures should be able to reach around 20 degrees north-
central, to near 30 degrees east-central WI.

The surface low is progged to lift northeast toward southern
sections of the Great Lakes Sunday night and quickly push into
eastern sections of the Great Lakes on Monday. Meanwhile, the
trailing mid-level trough moves from the Midwest/Mid-MS Valley
Sunday night toward the eastern Great Lakes Monday. The forecast
issues continue to be the exact track of the surface low, as well
as the strength of the low pressure. Right now, any track would be
far enough south such that the northern periphery of the main snow
band would affect the southern half of WI. Accumulations to range
from practically a dusting far north, to 1-2" south. The overall
fast departure of this system will see snow come to an end Monday
morning with perhaps an additional one-half inch of accumulation
in the east. Otherwise, mostly cloudy skies should prevail for the
rest of Monday with max temperatures in the lower 20s north-
central, upper 20s eastern WI.

The next chance for snow arrives later Monday night or Tuesday
morning in association with the passage of a strong cold front.
Behind this front, the doors open to a surge of arctic air that
will settle over the region through mid-week. Expect to see
temperatures fall through the day on Tuesday with readings by
sunset already down to around zero north-central, mid teens near
Lake MI. Add in a blustery west-northwest wind and we could see
wind chills ranging from the mid teens below zero north-central,
to around zero east-central WI by dark.

Mainly dry and much colder conditions to set-up over the region
through mid-week, although will have to watch Vilas county because
any slight shift to a northwest component could lead to lake
effect snow showers. Exactly how cold we get will come down to
cloud cover and wind speeds as strong Canadian high pressure
slides southeast from western Canada into the central CONUS by
Thursday. Model consensus solution places min temperatures in the
single digits below zero both Tuesday night and Wednesday night,
except near Lake MI where values should remain above zero.
However, any substantial clearing could see temperatures reach
double digits below zero over north-central WI. Max temperatures
for Wednesday and Thursday will mainly only reach the single
digits above zero with daytime wind chills as cold as 15 to 25
below zero Wednesday afternoon. Be prepared to bundle up!.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1140 AM CST Fri Dec 9 2016

VFR conditions will prevail for the start of the TAF
period over eastern Wisconsin and parts of central Wisconsin. An
area of MVFR cigs over north central and western Wisconsin will
spread east to west across the state as a weak disturbance slides
over the western Great Lakes region overnight. Expect this
disturbance to depart Saturday morning to again produce VFR conditions
across much of the area.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Saturday evening through Sunday evening
FOR WIZ037>040-048>050.

Winter Storm Watch from Saturday evening through Sunday evening
FOR WIZ035-036-045.

Winter Storm Watch from late Saturday night through late Sunday
night FOR WIZ022.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Kallas
AVIATION.......TDH


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