Area Forecast Discussion
Issued by NWS Green Bay, WI

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722
FXUS63 KGRB 070913
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
313 AM CST Wed Dec 7 2016

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Thursday
Issued at 312 AM CST Wed Dec 7 2016

Discussion for this portion of the forecast will follow a little
later.

.LONG TERM...Thursday Night Through Tuesday
Issued at 312 AM CST Wed Dec 7 2016

Since the mean flow is expected to run nearly zonal to broadly
cyclonic across the CONUS through the extended period, this would
translate into fast-moving systems which will be difficult to time
such a progressive, low-amplitude flow. Initially, onset of colder
weather will be more of a lake effect issue for north-central WI.
However, potential for accumulating snow remains on the table
later this weekend with the first Pacific system. Main story for
next week will be the depth of the arctic air and exactly how cold
we can get.

Lake effect snow showers will continue over north-central WI
Thursday night with delta-T values in the lower 20s, favorable
trajectories and lake-induced pops around 500 J/KG. The only real
negative is hints on forecast soundings that inversion heights
will lower through the night which would limit (lessen)
accumulation potential overnight. The snowbelt region of Vilas
county could pick up an additional 1-3" of snow, which would bring
a 2-day total into the 6 to 10" range if current trends persist.
The rest of northeast WI will see cloudy skies and cool conditions
with a prevailing west-northwest wind at 5 to 15 mph. Min
temperatures to be in the lower to middle teens central, upper
teens to around 20 degrees eastern WI.

The lake effect snow showers will persist into Friday morning, but
remain somewhat limited by low-level inversion heights around 5K
ft. By Friday afternoon, a ridge of high pressure is forecast to
build into the Upper MS Valley/Midwest and start to back the winds
which would make trajectories become less favorable. The Vilas
county snowbelt could see another inch of accumulation before
tapering off later in the day. Central/east-central WI may be able
to see some mixed sunshine at times, but this will not help
temperatures as readings are only expected to be in the 15-20
degree range north, 20-25 degree range south.

While a few lingering light snow showers or flurries may still
reach Vilas county into Friday evening, the surface ridge axis is
progged to move into WI during the overnight hours and keep dry
conditions over the vast majority of the area. Even with this
ridge nearby, clouds may be hard to get rid of as WAA already
underway to our west. Keeping clouds around will not help
temperatures as colder air has already settled over the region.
Min temperatures to be in the single digits above zero central,
10-15 above eastern WI. The thickening clouds are expected to give
way to the onset of light snow, especially by Saturday afternoon
as mid-level forcing/WAA overspreads WI in advance of a mid-level
trough/surface cyclogenesis located over the central Plains. It is
conceivable that parts of central WI could pick up around an inch
of snow by 00z Sunday. Otherwise, any snow would be on the light
side with only minor accumulations expected. Max temperatures on
Saturday will remain 5 to 10 degrees below normal with readings
similar to Friday.

There continues to be some timing issues with this system as the
GFS is a good 12 hours faster than the ECMWF. This will ultimately
determine whether the better snow chances arrive Saturday night
(GFS) or on Sunday (ECMWF). Due to the fast-moving low-amplitude
flow, tend to lean toward the GFS which would bring potential
advisory-level snow accumulations to northeast WI. The snow
chances would carry over into Sunday, but in a diminishing mode
especially by Sunday afternoon. The WAA preceding the system will
help boost temperatures closer to normal on Sunday with readings
able to reach the lower 20s north-central, upper 20s to around 30
degrees east-central WI.

Only modest cold air is forecast by the models to get pulled into
WI behind the system and with trajectories maintaining more of a
westerly component, lake effect impacts for north-central WI
Sunday night/Monday appear minimal. Max temperatures on Monday
will be cooler with most locations in the teens, except lower 20s
near Lake MI. The passage of a strong cold front late Monday
night/Tuesday morning may bring a chance of light snow to
northeast WI, but the bigger story will be the first true taste of
arctic air this season with max temperatures Tuesday only in the
single digits north-central, to middle teens east-central WI.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1043 PM CST Tue Dec 6 2016

MVFR CIGS will prevail across the region through Wednesday
afternoon. CIGS across eastern Wisconsin could reach the low end
VFR category on Wednesday afternoon. Also, occasional flurries
will continue through much of the period across north- central
Wisconsin through Wednesday afternoon, with scattered flurries
across northeast and east-central Wisconsin. A more substantial
lake effect snow event will impact far northern Wisconsin later
Wednesday night into Friday that is expected to bring poor flying
conditions to this region. Gusty west to southwest winds may gust
to around 30 knots at times into Wednesday evening.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 3 AM Thursday to noon CST Friday for
WIZ005.
&&

$$

SHORT TERM.....Skowronski
LONG TERM......Kallas
AVIATION.......Eckberg



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