Area Forecast Discussion
Issued by NWS Green Bay, WI

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684
FXUS63 KGRB 110957
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
357 AM CST Sun Dec 11 2016

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 351 AM CST Sun Dec 11 2016

Snow today, lingering over the northeast into tonight, then a
cold snap for the middle to latter part of the week. More snow
possible late in the week and next weekend.

High latitude blocking will remain in place throughout the
forecast period, while a seasonably strong band of westerlies
persists to the south. The westerlies, currently zonal, will take
on a broadly cyclonic structure as deep upper vortex digs through
the Hudson Bay area mid-week, then back to a southwest flow regime
by next weekend as energy rounding upper ridge over the Gulf of
Alaska digs down the West Coast.

Temperatures will start out near normal, drop to well below normal
for much of the upcoming week, then rebound late. Given the two
significant snow chances (today and early next weekend), the snow
chance with the arctic front, and some lake-effect, precipitation
amounts are likely to end up above normal for the period.
&&

.SHORT TERM...Today...Tonight...and Monday
Issued at 351 AM CST Sun Dec 11 2016

Just a minor change to forecast headlines this morning. Will end
the advisory for areas along and south of Highway 29 a few hours
earlier. As expected, initial band of light-moderate snow has
streaked eastward across the region, with the heaviest snows
staying south of the area. The northward advance of the snow band
has halted the past few hours, but is set to resume again as flow
begins to back with the approach of the mid-level short-wave
trough. Adjustments to storm totals snows were modest. Trimmed
amounts a bit across the northwest part of the area, and edged
them up some near the lake and in the far south. Some areas near
the lake and over the far south could flirt with/hit warning
criteria. But given light winds and the low water content of the
snow, prefer to stick with the advisory through will continue to
monitor. The biggest potential issue with the forecast would be
if an organized lake band swings back into eastern Wisconsin and
drives snow totals several inches above current forecast. Will
upgrade if it becomes apparent that will happen.

Otherwise, added a mention of FZDZ for the afternoon and evening
in areas where mid-level dry slot punches eastward south of the
incoming shortwave. FZDZ certainly not a give as temperatures at
low-levels are almost cold enough to result in ice crystals even
with loss of seeding from above. But thought it was worth a
mention.

Generally quiet weather is expected late tonight into Monday in
advance of approaching arctic front.

.LONG TERM...Monday Night Through Saturday
Issued at 351 AM CST Sun Dec 11 2016

The main story for the bulk of this week will be the arrival of
arctic air that is expected to reach its max intensity over
northeast WI from Tuesday through Thursday. Temperatures are still
on track to be 15 to 25 degrees below normal with bitterly cold
wind chills that may need headlines mid-week. By late week, models
are showing a positive-tilted longwave trough will develop from
Nunavut to CA. As the mean flow turns southwest over the central
CONUS, this may allow for a system to develop over the southern
Plains and spread snows northeast into WI Friday into Saturday.
Will have to see how this system evolves and whether gulf moisture
can get pulled northward into the Great Lakes. If weather
conditions can come together, we will need to break out the snow
blowers and shovels again.

A strong cold front, accompanied by a mid-level shortwave, will
sweep through WI Monday evening and bring at least a chance of
snow showers across the forecast area. Would not be surprised to
see a couple of tenths of snow accompany the frontal passage, but
with increasing west winds, the snow may simply blow around and
everyone would end up with a dusting. Min temperatures will drop
into the zero to 5 below range north-central, single digits above
zero elsewhere except around 10 above near Lake MI. A strong area
of Canadian high pressure is forecast to move from the northern/
central Plains into the Midwest on Tuesday as arctic air continues
to overspread the Great Lakes. By 00z Wednesday, 8h temperatures
are expected to be in the -20 to -25C range with blustery west
winds. Even with sunshine, temperatures will be hard-pressed to
make any move up, with eastern WI likely seeing readings simply
fall through the day.

The surface high will slowly shift east and reside over southern
sections of the Great Lakes, Mid-MS Valley and Ohio Valley Tuesday
night. 8H temperatures to remain in the frigid -18 to -26C range
and with partly cloudy skies anticipated, we are looking at min
temperatures to plummet into the -5 to -10 range north-central,
zero to 5 above elsewhere except around zero at the lakeshore.
These cold temperatures, combined with a steady west wind at 10 to
15 mph, will send wind chills into the teens below zero east, 20
to 25 below zero central WI. Readings this cold would warrant wind
chill advisories for parts of the forecast area later Tuesday
night. Another area of high pressure is forecast to move southeast
into the northern/central Plains on Wednesday and continue to
provide/reinforce the arctic air mass into WI. Will continue the
need to watch Vilas county as any subtle shift in the wind
direction could send lake effect snow showers into northern parts
of the county. Otherwise, it will simply be a very cold day over
northeast WI with max temperatures struggling to get above zero
north-central, and only 5 to 10 above over eastern WI. Wind chills
to remain in the double digits below zero.

The sprawling area of high pressure is progged to stretch from the
northern Plains to the southeast CONUS Wednesday night into
Thursday keeping the arctic air in place. Another night with min
temperatures from 5 below to 10 below zero central, zero to 5
below east and around zero near Lake MI. Wind chills could drop
into the -20 to -30 degree range at times which would eventually
prompt the need for a wind chill advisory. The surface ridge axis
nudges closer to WI on Thursday with the models showing the crux
of the coldest air beginning to shift east. This may tack a degree
or two to max temperatures on Thursday, but hardly noticeable with
wind chills holding in the teens below zero.

One more very cold night expected over the region Thursday night
as the surface moves over the Great Lakes. Less wind may actually
allow min temperatures to be a bit colder than previous nights
with a double digit below zero reading possible over parts of
north-central WI. Less wind would however prevent the need for
anymore wind chill headlines. Models continue to show a surge of
WAA snows that will break out across the central CONUS and race
northeast into the Great Lakes on Friday. Increasing southerly
winds will aid in pulling gulf moisture north, so it now appears
that accumulating snow is possible over northeast WI, especially
by Friday afternoon. The WAA surge will also provide a boost to
temperatures with maxes ranging from 10 to 15 above central, 15 to
20 across eastern WI.

The positive-tilted longwave trough will be in place from northern
Canada to the southwest CONUS by next weekend with an area of low
pressure forecast to lift northeast across the Plains. The exact
track of this low pressure will be key as to how much snow may
fall over the forecast area Friday night into Saturday. Expect to
see the models waffle on this track for the next several days, but
if a track becomes favorable (passes just to our south and east),
we will see accumulating snow persist through Friday night before
ending later on Saturday with a definite need for snow removal
equipment. Stay tuned!.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 351 AM CST Sun Dec 11 2016

Low-end VFR and MVFR conditions prevailed across most of the area,
with better conditions currently across the north. Expect
conditions to worsen significantly this morning as the main snow
band shifts north into the area. Once in place, lower ceilings
will probably linger into tonight, though there are some
indications clouds could begin to break in east-central Wisconsin
after midnight.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM CST this evening FOR WIZ030-
031-035>040-045-048>050.

Winter Weather Advisory until midnight CST tonight FOR WIZ005-
010>013-018>021-073-074.

Winter Weather Advisory until 6 AM CST Monday FOR WIZ022.
&&

$$

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



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