Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 101952
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
152 PM CST Tue Jan 10 2017

New Information added to update section

.UPDATE...
Issued at 152 PM CST Tue Jan 10 2017

Had to expand the warning into Vilas, Wood, and Portage due to
recent reports and continued heavy snowfall.

UPDATE
Issued at 1102 AM CST Tue Jan 10 2017

Adjusted times for the current winter weather advisory and winter
storm warning and added wind headlines for the late afternoon and
evening.

Will let the winter weather advisory that was in effect for the
Fox Valley and Lakeshore areas expire at 18Z as scheduled but
added a wind advisory in that area 22Z-06Z. Have kept the advisory
going for Wauapca and Waushara and extended it, and the other
winter weather headlines through 03Z.
&&

.SYNOPSIS...
Issued at 456 AM CST Tue Jan 10 2017

Active weather with several rounds of snow this week followed by
a brief shot of arctic air at the end of the week. In contrast,
January-thaw like conditions expected next week.

A closed upper anticyclone persisted over Alaska, anchoring a
a block over the northeast Pacific. But increasing amounts of
Pacific jet energy were undercutting the block. The positive
anomaly with the block will pull back westward during the period,
allowing the low-amplitude flow off the Pacific to surge across
the entire CONUS and southern Canada.

The current split upper pattern to the west was resulting in a
strong baroclinic zone across the CONUS. Disturbances riding
along the baroclinic zone will bring several rounds of
precipitation, likely resulting in above normal amounts for the
period. Temperatures during the early to middle part of the
forecast period will respond to north and south shifts in the
baroclinic zone as individual weather systems cross the region.
But a prolonged period of above normal temperatures will likely
begin next week when the low-amplitude westerly flow off the
Pacific dominates NOAM.
&&

.SHORT TERM...Today...Tonight...and Wednesday
Issued at 456 AM CST Tue Jan 10 2017

Very complicated forecast, with rapidly intensifying cyclone
expected to drive across the region today. Warmer air pushing
north ahead of the incoming system is forecast by most models to
be sufficient to change precipitation to mainly rain for a time
from ISW-GRB southeastward. But the northward advance of the warm
air will be critical, and a few of the models suggest mainly snow
throughout the day. Even the models that warm the lower-levels
enough for rain have soundings very close to 0C from the surface
up to about 800 mb. That is concerning, especially with deepening
system heading right across the area, and the likely position of
east-central Wisconsin near upper dry slot this afternoon. Strong
lift or convective cells could easily cause the precipitation to
flop back over to snow when the heaviest precipitation occurs.
Adjusted the forecast to better account for this possibility.

Meanwhile where precipitation is all or mainly snow, the latest
guidance suggested slightly higher totals than previous forecast.
So adjusted snowfall amounts and pushed the warning another tier
of counties to the west.

The next concern is the potential for strong winds as the cyclone
departs the area tonight. Model forecast soundings suggest the
potential to mix into 40-50 knots winds above the surface. Raised
winds considerably, added some blowing snow to areas where the
surface of the snow is unlikely to get capped by melting during
the day, and added mention of the winds to the HWO. A Wind
Advisory may eventually be needed for east-central Wisconsin, and
the winter weather headlines may need to be extended into early
tonight to account for the blowing and drifting snow across the
portions of the rest of the area, but thought it best to wait and
see exactly how the snowfall and above freezing temperatues play
out today before committing to headlines for tonight.

.LONG TERM...Wednesday Night Through Monday
Issued at 346 AM CST Tue Jan 10 2017

Main story for this period will be the bitterly cold weather at
the beginning of the period, then a moderation in temperatures
later in the weekend into early next week.

For Wednesday night, a jet streak moving east of the area will
bring an end to any light snow across eastern Wisconsin as arctic
cold front moves away from the area. Another jet streak is
expected to move across the upper Midwest on Thursday. The area
will be in the left exit region of 140 knot jet (WRF). There is
some concern about low level moisture, as the models have trended
to dry out the 850mb layer. Think there is enough forcing to get
some minor accumulations south of highway 29.

For Thursday night, another round of bitter wind chill readings
expected. A wind chill advisory may be needed for locations north
and west of the Fox Valley for wind chill readings of 20 below to
30 below zero. Winds should remain up through most of the night
into Friday morning, but those typical cold spots could go calm.
Did lower minimum temperatures Thursday night and highs on Friday.
Low temperatures may need to be lowered Friday night with fresh
snow cover and light winds. A gradual moderation in temperatures
is expected Saturday with readings at or above normal Sunday into
early next week.

It appears there will be a more vigorous system for the first half
of next week. The latest ECMWF has trended slower with the main
system. Will need to watch this feature.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1148 AM CST Tue Jan 10 2017

IFR conditions will continue across the area through
the evening hours with several aviation hazards.

Moderate to heavy snow will continue west of a STE to IMT line
through the afternoon and snow plows and deicers will be needed.
Blowing and drifting snow will continue tonight. A mixture of
rain and sleet will change to snow before ending further east.

Strong west winds gusting to 40 knots are possible around dusk at
PCZ/CLI/ATW/GRB/OSH/MTW/OCQ/SUE/MNM/EZS with rapid refreezing of
wet surfaces as temperatures drop quickly below freezing.

Winds will diminish and skies clear later tonight but clouds will
increase and snow should return to the whole area by Wednesday
afternoon. The snow should continue Wednesday night.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until midnight CST tonight for WIZ022-038>040-
048>050.

Winter Weather Advisory until 10 PM CST this evening for WIZ037-
045.

Winter Storm Warning until 10 PM CST this evening for WIZ005-
010>013-018>021-030-031-035-036-073-074.
&&

$$

UPDATE.........MG
SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......MG



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