Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 091755
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1155 AM CST Mon Jan 9 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 328 AM CST Mon Jan 9 2017

Snow will continue to diminish across the area from west to east
early this morning as a mid level shortwave and cold front exit
the western Great Lakes. Mainly flurries are expected across the
area through daybreak before finally tapering off.

Another low pressure system will take aim for the region later
this afternoon and into tonight as warm air advection allows
temperatures to warm across the western Great Lakes. Abundant
isentropic lift this evening will provide some bursts of snow as a
mid level shortwave gets in on the action after midnight. The
abundant lift will take advantage of increasing moisture tonight,
as mixing ratios climb from 2 to 4 g/kg during the overnight
hours. This should allow for a good 2 to 4 inches of snow during a
short period tonight, which will be right around Winter Weather
Advisory criteria for our area.

Later on Tuesday the low itself will track through Wisconsin,
bringing the warm sector across the cwa and introducing enough
warm air for a changeover to a wintry mix or even rain at times
across east central Wisconsin during the afternoon. Some dry air
in the mid levels may be enough to take ice crystals out of the
equation with freezing rain a real possibility given the model
soundings. The exact amount of additional snow Tuesday is in
question given the mixed nature of the expected precipitation,
however even if snowfall amounts are muted on Tuesday, icy
precipitation should be enough to keep a Winter Weather Advisory
in place on Tuesday. Additional snowfall amounts on Tuesday could
total 1 to 2 inches, pushing totals to 3 to 6 inches tonight and
Tuesday. Therefore will issue a Winter Weather Advisory for the
entire cwa tonight and most of Tuesday given the expected snowfall
totals and the potential for icy precipitation on Tuesday.

.LONG TERM...Tuesday Night Through Sunday
Issued at 328 AM CST Mon Jan 9 2017

A much more active weather pattern setting up across the Great
Lakes this week with several systems to bring mainly snow to
northeast WI. Mean flow has now trended to becoming split by mid-
week with the southern stream diving southeast through southern
CA/northwest Mexico, then lifting northeast through the Ohio
Valley/TN Valleys. Meanwhile, the northern stream will dive
southeast from the Yukon, then rotate eastward across the northern
tier of states. The initial system will already be leaving
northeast WI Tuesday night, however additional northern stream
systems may bring snow chances back Wednesday, Wednesday night/
Thursday and possibly later next weekend. Temperatures will
continue to bounce around this week with readings going above
normal ahead of each system, then falling below normal behind each
system.

A very weak ridge of high pressure is forecast to move across WI
Tuesday evening, bringing some decrease in cloud cover. However, a
quick return to south-southwest winds after midnight will usher
the next surge of WAA into WI after midnight and may bring a
little light snow back to northeast WI. Do not anticipate much of
any accumulation at this point as the air mass aloft will need to
re-saturate. Min temperatures appear to settle into the 5 to 10
above range north-central, to the middle to upper teens east-
central WI. Models are in general agreement with the passage of a
cold front through WI on Wednesday (although the NAM is a good 6
hours slower). Once again, a small chance of light snow will be in
the forecast over northeast WI, but any accumulation would be very
minor and should not cause any issues. There may even be a bit of
sleet mixed in with the snow from OSH-MTW where temperatures
approach 30 degrees. Otherwise, look for max temperatures to reach
from 15 to 20 degrees north-central and 20 to 25 degrees central
and far northeast WI.

A better chance of seeing snow returns for Wednesday night as an
area of low pressure rides northeast along the old cold front from
the central Plains to southern sections of the Great Lakes by 12z
Thursday. The CMC and GFS indicate decent frontogenetical forcing,
especially over the southeast half of the state, therefore will
place highest pops across east-central WI. Pops could even be
higher (with more confidence) if the ECWMF joined the party.
However, this model focuses almost all of the precipitation to our
south. For now, kept pops in the low-end likely range for east-
central WI, tapering down to medium chance pops for north-central
WI. If the CMC/GFS do verify, we could see an inch or two of snow
southeast of a line from Marshfield to Wausaukee with perhaps a
little more sleet mixed in from OSH-MTW. Min temperatures to range
from around zero north-central, to the upper teens near MTW. The
chance of snow would linger through at least Thursday morning as
the surface low tracks northeast across the eastern Great Lakes
into southeast Canada. Additional accumulations should be at an
inch or less as the stronger mid-level forcing shifts to the east.
Colder air is also forecast to be pulled into the region behind
the departed system as 8H temperatures drop into the -10 to -18C
range by 00z Friday. Max temperatures on Thursday to range from
the middle teens north-central, to the middle 20s near Lake MI.

There is a small concern for lake effect snows over north-central
WI Thursday night as the next surge of very cold air overspreads
the region on northwest winds. The time window for lake effect
looks to be small however as a large area of Canadian high
pressure builds across the Upper MS Valley. For now, have kept
chance pops in the forecast for Vilas county, otherwise partly
cloudy skies for everyone else through the night. Thursday night
also looks to be frigid with min temperatures pushing the mid-
teens below zero north-central (even colder if skies can clear),
zero to 5 above lakeside. Mostly likely would need a wind chill
advisory for at least central WI Thursday night. This very strong
surface high will then shift into the Great Lakes on Friday,
bringing mostly sunny to partly cloudy skies to northeast WI. Max
temperatures will be well-below normal with readings struggling to
get above zero north-central, only around 10 above for eastern WI.

The main forecast issue concerning next weekend`s forecast will be
the movement of a southern stream shortwave trough as it digs
across the 4 corners region Saturday and crosses the southern
Rockies on Sunday. Low pressure will eventually spin up ahead of
this mid-level trough over the southern Plains and lift northeast
toward the mid-MS Valley by late Sunday. The big question is
whether there will be enough residual dry air over WI from the
retreating surface high to keep any precipitation from advancing
northward as the gulf opens up. The ECMWF says yes, while the GFS
says no. Consensus solution brings a small pop into our southern
counties Sunday afternoon which is plausible, so will not make any
changes. After another very cold night over the area Friday night,
look for temperatures to moderate closer to normal by Sunday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1155 AM CST Mon Jan 9 2017

A complex storm system approaching from the Plains
states will bring snow and IFR conditions to the area tonight and
Tuesday. The snow may mix with or change to sleet and rain at
OSH/GRB/ATW/MTW/SUE Tuesday. Winds should be rather light, so
significant blowing and drifting snow is not expected. Snow
plows and deicing equipment will be needed with snow of 3 to 6
inches in most places.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 PM this evening to 3 PM CST
Tuesday for WIZ005-010>013-018>022-030-031-035>040-045-048>050-
073-074.
&&

$$

SHORT TERM.....Kurimski
LONG TERM......Kallas
AVIATION.......MG



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