Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 012054
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
254 PM CST Thu Dec 1 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 254 PM CST Thu Dec 1 2016

In the wake of the upper-level low pressure circulation currently
over Quebec Province, east-west orientated trough will linger over
the western Great Lakes through the short-term portion of the
forecast. In addition, very weak impulses embedded within the
flow will also work their way southward toward Upper Michigan and
northern Wisconsin before shearing out. Combination of these
features along with some lake enhancement off Lake Superior will
keep widely scattered and shallow showery activity in the forecast
mainly across the north. Any snowfall accumulations over Vilas
County will be minimal once again, perhaps a few tenths of an
inch. Elsewhere, may see some patchy drizzle or sprinkles from
time to time but opted not to include in the grids.

Once again do not expect too much diurnal temperature variation
overnight as cloud cover still quite expansive across much of the
northern conus. Only exception would be over the NE quarter of the
forecast area for a time this evening with weak downsloping
effects. Overall, raised min temps tonight a couple degrees over
the model blend given persistent cloud cover.

On Friday, expect more clouds within cyclonic flow regime and a
continued chance for a few lake enhanced snow showers over
northern Vilas County. Temperatures will be a few degrees cooler
than today, mainly low 30s north to the upper 30s along the
lakeshore.

.LONG TERM...Friday Night Through Thursday
Issued at 254 PM CST Thu Dec 1 2016

Mean flow will be split initially this weekend, but consolidate by
the middle of next week with upper ridges over both coasts and an
upper trough over central NOAM. Main weather features that will
affect northeast WI would be the passage of a mid-level trough on
Sunday and a potentially bigger system Tuesday into Wednesday
night. This bigger system to consist of an upper low ejecting
northeast from northern Mexico toward the Great Lakes and jet
energy digging into the base of the developing upper trough which
will help to kick the upper low northward. While the models are
zeroing in on the track of the upper low, there are still
differences as to the impact that a separate upper low either on
or just north of the international border will have on the upper
low/track of the surface low as it lifts northeast across the
central CONUS. These differences will eventually determine where
the heavier snows would fall and where precipitation may be all
rain.

High pressure is forecast to stretch from the Midwest to the Ohio
Valley Friday night and gradually build toward WI during the
overnight hours. Winds will have enough of a westerly component to
finally end any lingering snow shower activity over Vilas county.
Otherwise, forecast soundings show plenty of low-level moisture
trapped under an inversion, thus another cloudy night is expected.
Min temperatures to be in the lower to middle 20s central WI,
middle to upper 20s eastern WI. The area of high pressure will
shift east and reside from the southern sections of the Great
Lakes to the upper reaches of the Ohio Valley on Saturday. There
is still hope that at least southern parts of the forecast area
may be able to weaken the low-level inversion enough to allow for
partial sunshine Saturday afternoon. Northern WI unfortunately
looks entrenched with low clouds through the day. Max temperatures
will be more seasonal with readings around 30 degrees north-
central, lower to middle 30s elsewhere.

As the surface high heads into the Appalachians Saturday night,
attention turns to a shortwave trough pushing across the northern/
central Plains. A return to southwest winds and the onset of weak
WAA will send more clouds into northeast WI, so have sky
conditions at or becoming cloudy during the night. Bulk of any
precipitation should remain to our west, thus have removed any
pops for the nighttime hours. Min temperatures to generally be in
the lower to middle 20s, but middle to upper 20s closer to Lake
MI. This shortwave trough is progged to quickly sweep into the
Great Lakes region and bring either light snow or mixed rain/snow
to the forecast area on Sunday. Precipitation type will be
dependent on low-level thermal profiles and time of day. This
would have the precipitation start as all snow in the morning and
then become mixed with rain across parts of central and all of
eastern WI in the afternoon. Gulf moisture is cut-off from this
system, thus QPF amounts will be on the light side (mainly at or
below 0.05"). This would keep any snow accumulations at an inch or
less with the higher values over central WI. Max temperatures will
be in the lower 30s north, middle to upper 30s south.

Light snow will linger into Sunday evening as the shortwave trough
departs, with improving conditions for later Sunday night as a
ridge of high pressure builds toward the Western Great Lakes. Any
additional snow accumulations would only be minor, likely just a
dusting. Northeast WI to be protected by this surface ridge as it
quickly slides toward the eastern Great Lakes on Monday. A few
peeks of sunshine is possible, but as the surface ridge pulls
away, clouds will be gathering to our south and west ahead of a
more complex weather system. Max temperatures for Monday are
expected to be in the middle 30s north, upper 30s to around 40
degrees south.

After a quiet/clouds Monday night, the weather pattern looks to
become more active starting on Tuesday as a 140 knot upper jet
helps to carve out a longwave trough over the western CONUS, as
well as help kick a closed upper low from northern Mexico (Sunday
night) into the Great Lakes (Tuesday). Exactly how much digging
this upper trough can occur will initially impact precipitation
type over northeast WI on Tuesday. The GFS is more progressive
with the upper trough, thus has colder air over WI when the
precipitation begins (all snow). The CMC and ECMWF have more
digging with the trough, thus the air mass over WI is not that
cold and would lead more to a mixed precipitation event. Since the
GFS has varied the most and is in the minority, prefer the CMC/
ECMWF solution and will keep precipitation a mix of rain and snow
north, a mix or all rain south.

Due to the vast differences between the GFS and ECMWF, along with
individual model run-to-run inconsistencies, do not have a good
feel on how the weather will play out Wednesday into Thursday.
Consensus model blend would favor taking the longwave trough into
central NOAM on Wednesday and lift this trough into the Great
Lakes on Thursday while closing the trough into an upper low. This
would bring another mixed precipitation event across northeast WI
on Wednesday before transitioning to all snow Wednesday night and
Thursday. The heavier QPF would fall Wednesday into Wednesday
night with an accumulation potential over all of northeast WI.
Thursday would see strong CAA sweep into the Great Lakes with a
chance of snow showers. Temperatures on Thursday could very well
be falling through the day with readings dropping below normal.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1147 AM CST Thu Dec 1 2016

A weakening upper-level low pressure system will slowly loose its
grip on the forecast area this afternoon and into tonight.
However, cyclonic low-level flow and weak upper-level impulses
will continue to keep clouds over the area through the TAF
period. Although mainly MVFR cigs are expected, scattered IFR
cigs with isolated MVFR vsbys due to lake enhanced snow showers
will persist during the afternoon over far northern Wisconsin.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....ESB
LONG TERM......Kallas
AVIATION.......ESB



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