Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 132342
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
642 PM CDT Fri Apr 13 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 436 PM CDT Fri Apr 13 2018

Very complex weather setup tonight into Saturday, making for a
difficult forecast. Main concerns are precip type, amounts, and
timing...and the winds.

Synoptic and meso-models still not on the same page regarding the
first part of this powerful low pressure system. Thermal profiles
right on the cusp of snow/sleet/freezing rain across much of
central and east central WI through the night. A warm layer of 2C-
3C between 7000-10000 ft will melt the hydrometeor, with a long
skinny cold layer below, which should be sufficient to produce
sleet. The cold layer will slowly deepen through the night as the
northeast winds usher in cold air at the lowest levels. This will
allow for the precip to slowly transition from mixed precip to
snow from north to south. That transition won`t occur until
Saturday morning for locations in the far southeast (Manitowoc
Co.). Like was the case this afternoon, any convection can quickly
cool the column and change the rain or mixed precip to all snow
very quickly. If this occurs, or the warm layer aloft is a degree
or two colder, the snow totals will need to be increased. On the
other hand, of the column is a little warmer and doesn`t allow the
hydrometeor to refreeze, more freezing rain could occur. And with
the gusty winds, that could create significant issues with trees
and power lines. Temps look just cold enough for mainly all snow
over the north, but the northeast winds will cut into the
northward extent of the snow. In fact, parts of far north central
WI won`t see much snow tonight into Saturday morning.

In the end, decided to go with a winter weather advisory for the
wintry precip tonight into Saturday from Lincoln Co. to southern
Marinette Co. southward, as totals says below warning threshold.
That said, if precip stays all one type (snow or freezing rain)
the snow/sleet combined with the gusty winds will make poor
travel conditions.

Winds will continue to crank up this evening and overnight as the
pressure gradient tightens between the Hudson Bay high and the
developing low pressure. Winds around 4000 ft increase to 40-55
knots. Widespread wind gusts between 30 and 45 mph are expected.
Winds will be strongest across the Fox Valley and lakeshore.
Funneling down the bay could create locally higher gusts in/around
Green Bay where gusts between 45 and 55 mph will be possible.

.LONG TERM...Saturday Night Through Friday
Issued at 436 PM CDT Fri Apr 13 2018

Main concern for this period will be the ongoing winter storm
Saturday night into Sunday night. There will be a lull in
the precipitation Saturday afternoon which may linger into
early Saturday evening across far north-central and far
northeast Wisconsin. The next round of snow is expected to
move across the area Saturday night into Sunday evening,
making travel very difficult. The heaviest snowfall rates
are expected Saturday night into Sunday morning which
could be from 1 to 2 inches per hour. Snow will continue
through much of the day Sunday and continue into Sunday night.
Northeast winds will gradually decrease on Sunday into the
15 to 30 mph range. Ice shoves are still likely at times
Saturday night and Sunday. Will continue the winter storm
watch for now, but midnight shift will more than likely
upgrade to a winter storm warning.

Light snow will linger into much of Sunday night with a
chance of light snow into Monday as well. Below normal
temperatures will continue through the upcoming week.
The next chance of rain or snow will arrive Tuesday night
into Wednesday. Some timing differences noted on the models
which could affect precipitation types. It appears some
accumulating snow is possible across the north. No real
changes made to the Thursday/Friday time frame.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 640 PM CDT Fri Apr 13 2018

A winter storm moving slowly across the Midwest will
produce gusty northeast winds and MVFR or IFR conditions across
all but far northern Wisconsin tonight through early Saturday.
Precipitation will fall as a mixture of snow, sleet and rain in
most areas. The precipitation should diminish by midday Saturday,
with MVFR or VFR conditions in the afternoon.

The storm system will get close enough to the region Saturday
night and Sunday to bring significant snow to most of Wisconsin.
It could be mixed with sleet or freezing rain across the east
central portion of the state. Plows will be need in many areas
Saturday night and Sunday. Gusty northeast winds could produce
blowing and drifting snow Saturday night and Sunday.
&&

.HYDROLOGY...
Issued at 436 PM CDT Fri Apr 13 2018

Streams and rivers are likely to rise this weekend, especially
over the southern portion of the forecast area where a
significant rainfall and some melting of the remaining snowpack
is expected. The potential for ice shoves and flooding near the
mouth of the Fox River have been addressed with the Lakeshore
Flood Warning and Advisory.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 10 PM this evening to 4 PM CDT
Saturday for WIZ018>022-030-031-035>040-045-048>050-073-074.

Winter Storm Watch from Saturday afternoon through Sunday
evening for WIZ005-010>013-018>022-030-031-035>040-045-048>050-
073-074.

Lakeshore Flood Warning until 1 PM CDT Sunday for WIZ022-039-040-
074.

Lakeshore Flood Advisory until 1 PM CDT Sunday for WIZ050.
&&

$$

SHORT TERM.....Bersch
LONG TERM......Eckberg
AVIATION.......RDM
HYDROLOGY......Bersch



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