Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 140514
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1214 AM CDT Sat Apr 14 2018

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 1153 PM CDT Fri Apr 13 2018

Going to upgrade most of C-EC and portions of NE to a warning for
the ongoing heavy snow, sleet, and freezing rain. Runs to 15Z when
there will probably be a lull. Will decide how to handle the
second phase of the storm with the 4am issuance. Headline coding
is below.
&&

.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 06Z TAF Issuance
Issued at 1214 AM CDT Sat Apr 14 2018

A winter storm moving slowly across the Midwest will
produce gusty northeast winds and IFR conditions across all but
far northern Wisconsin tonight through early Saturday. Precipitation
will be mostly snow, but may be mixed with sleet and freezing rain
south of a Wisconsin Rapids to Green Bay line. Snow plows will be
needed in most areas, and blowing and drifting snow could be a
consideration. 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 Storm Warning until 10 AM CDT this morning for WIZ020>022-
030-031-035>040-045-048-049-073-074.

Winter Storm Watch from this 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.

Winter Weather Advisory until 10 AM CDT this morning for WIZ018-
019-050.

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

$$

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



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