Area Forecast Discussion
Issued by NWS Green Bay, WI

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594
FXUS63 KGRB 072005
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
205 PM CST Wed Dec 7 2016

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Thursday
Issued at 155 PM CST Wed Dec 7 2016

Colder air continues to pour into the area on blustery west winds
today into tonight in the wake of an upper low system parked just
north of Lake Superior. This system was producing plenty of
clouds along with scattered to numerous snow showers, especially
over central and north central Wisconsin. Isolated flurries were
noted over eastern Wisconsin. 850 temps suggest the coldest air is
wrapping around on the base of the low today to likely explain the
robust snow showers early today.

Anticipate little change in conditions tonight as mid level
heights continue to fall with the passage of a trough axis. Snow
showers may diminish in intensity later today into this evening
as slightly warmer air aloft works across the area ahead of a
short wave axis. Winds turn more northwest overnight as the
trough axis shifts east and lake effect snow potential increases
across the far north with another surge of colder air.

Lake effects snows have plenty of support for Vilas County with a
long term favorable wind direction along with healthy numbers for
lake induced cape, delta T/s and snow growth region. Forecast
soundings suggests an inversion may begin to suppress the lake
effect snow toward Thursday night. Currently have a winter storm
warning for Vilas county with the focus of warning snow over the
northwest portion. Expanded a border Winter Weather Advisory for
Oneida but held off for Forest county at this time. Decent Lake
effect snow dynamics along with a moist boundary may support
larger lake plume development. In addition to the snowfall,
blustery northwest winds will be blowing around the fluff type
snow.

.LONG TERM...Thursday Night Through Wednesday
Issued at 155 PM CST Wed Dec 7 2016

A couple periods of active weather to focus on in the long term as
numerous waves zip through the mean cyclonic flow sitting over
the Great Lakes Region through next week. Main time periods to
monitor for higher impacts will be Thursday night and Friday as
the lake effect snow in northern Wisconsin tapers off, and then
the potential for a more robust system sometime this weekend.
Arctic air and bitterly cold wind chills are also possible
sometime next week.

Lake effect snow Thursday night into Friday...

Lake effect snow off of Lake Superior will be ongoing at 00Z
Friday. As we go through Thursday night, conditions eventually
become less favorable for lake effect in northern Wisconsin. After
06Z Friday, the CAA will begin to wane and 850mb flow will start
veering. So, the best chance for PoPs and heavier snow will be
before midnight on Thursday. Winds will continue to slowly veer
until becoming too westerly Friday afternoon to support snow
showers in northern Wisconsin. Any snow showers that makes it into
northern Wisconsin after Friday morning should be light.

Potential system this weekend...

Attention then turns to the possible system for the weekend.
Current long term models show a range of possible solutions.
Solution 1, supported by the southerly track on 12Z GFS and a
northerly track on tail the end of the 12Z NAM, shows a closed
low with a sharp 500mb shortwave swinging through Saturday night
and Sunday. With strong forcing and deep structure, this solution
would bring a swath of snow through Wisconsin Saturday evening
into Sunday night, with the heaviest precip Saturday night.
Solution 2, supported by the 12Z Canadian and the previous ECWMF
run, has more zonal flow at 500mb and therefore a weaker sfc
low/inverted trough swinging through the state Saturday night.
This would still bring snow to the area, but with lower totals.
Then there is the new 12Z ECWMF...which does have the closed low
and dynamic upper level system moving through with snow...but 12
hrs later than the GFS/NAM. At this time, favored the closed low
moving through Saturday night into Sunday, mainly because the 12Z
ECWMF run was completely different from not only the 12Z GFS, but
also the 00Z ECWMF run. Upped to slight chc PoPs for Sunday and
Sunday night and can monitor later model trends from there.

Given the differing tracks and intensities of this system across
the long term models, along with a complicated upper level jet
structure, there is obviously a lot of uncertainty with the
weekend snow forecast. A few points that are worth noting with
some confidence:

-Increasing confidence that it will snow at some point between
Saturday night and through Monday (will not be a rain or mix)

-Best chance for accumulating snow looks to be over central and
east central Wisconsin and south

-Potential for over 3 inches of accumulating snow in central and
eastern Wisconsin

Another feature to watch with this system is the potential for a
lake induced/inverted low to develop as the main system exits the
state. Some of the models hint at some higher QPF over far NE and
E Wisconsin with a weak low developing on Lake Michigan. This
could enhance PoPs and snow totals, especially if there is an
onshore 850mb flow, which would lead to further lake effect
enhancement. This system has the potential for boom or bust, and
anyone who will be traveling Saturday night through Monday should
monitor the forecast for potential impacts.


Next week...

Long term models disagree on the timing of a few systems mid week
next week as the flow become more zonal. There could be another
shot for some snow at some point next week, but when and where is
unknown. No major snow storms advertised at this point though.

The feature to watch for next week will be the cold shot of air
surging into the region. Models disagree on the timing of the
arrival of the arctic airmass, however its on each model, so it
will likely get colder next week. CPC shows a good chance of
below normal temperatures over the next week or 2, which is
reasonable given the 850mb temperature being advertised in longer
term guidance. It would not take much wind to get bitterly cold
wind chills values with the coldest air.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1008 AM CST Wed Dec 7 2016

Wrap around clouds and colder air spilling into the
state will continue to produce mainly MVFR cigs today into
tonight. MVFR vsbys due to snow showers will also continue over
parts of central and north central Wisconsin today, then shift
northward to north central Wisconsin later tonight with lake
effect snow development. IFR cigs and vsbys due to snow showers
will be on the increase across far North Central Wisconsin. A few
of these snow showers may reach the RHI taf site at times.
&&

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

Winter Weather Advisory from 3 AM Thursday to 6 AM CST Friday
FOR WIZ010.
&&

$$

SHORT TERM.....TDH
LONG TERM......Allen
AVIATION.......TDH



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