Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 182123
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
323 PM CST Sun Feb 18 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Monday
Issued at 318 PM CST Sun Feb 18 2018

Skies were mostly cloudy this afternoon with temperatures in the
upper 20s across the far north, and 30s over the remainder of the
region. The band of light snow across the far north this morning
shifted northward into Upper Michigan.

For this evening and overnight, followed the trends of the RAP13
which showed little or no precipitation across our area. Did
continue small chances of light snow across the far north as the
f-gen bands pulls out.

The forecast becomes very complicated due to boundary layers
temperatures and where the cold air will be during the day. MAV
guidance suggesting temperatures in the middle 30s south of highway
10 through much of the day. This has led to complication in the
weather headlines. Per coordination with the long term forecaster
and NWS La Crosse, will headline the first round of precipitation
with a winter weather advisory for a mix of snow, sleet and
freezing rain. Mid level lapse rates are fairly steep, thus
precipitation could fall as snow at a heavy rate for a brief
period of time. Based on the 850mb temperature profile, the
secondary system for Monday night and Tuesday appears to be more
of a freezing rain potential, thus continued the winter storm
watch for Monday night and Tuesday for some locations north and
west of the Fox Valley. For locations from Wautoma to the Fox
Valley east to the lake, boundary layer temperatures will be
critical as some guidance still showing temperatures in the
middle to upper 30s. Latest road temperature guidance also
suggested pavement temperatures in the upper 30s and 40s during
the day. To complicate matters, gusty northeast winds will usher
in colder air down the ice covered bay. Do think some sort of
headline will be needed by late afternoon across much of this
region. The midnight shift can take a look at the latest
precipitation trends for the second system to decide what headline
will be needed.

.LONG TERM...Monday Night Through Sunday
Issued at 318 PM CST Sun Feb 18 2018

Complicated weather system through Tuesday evening will be the
primary issue.

A surface cold front is progged to drop south of the area by
Monday evening while an 850 mb frontal boundary remains
positioned north from southeast Minnesota to near Marinette.
This scenario is leading to a temperature profile which supports
mostly freezing precipitation. However model guidance suggests
temperatures may start out above freezing over east central
Wisconsin starting Monday afternoon before falling late in the day
and especially Monday night. Progs track a surface wave along
this front over southeast Wisconsin later Monday into Monday
night as the front slides southward. Up to a quarter inch of water
equivalent or ice mix may approach Calumet and Manitowoc
counties. Considered a warning of some variety but still some
issues remain with temperature and precipitation trends. As a
result, will delay the start of the winter storm watch more into
Monday night for a start time.

Guidance temperature trends continue to be an issue into Tuesday
with several model guidance forecast temperatures rising above
freezing over much of east central Wisconsin.

High pressure then builds into the area Wednesday into Thursday
for a quieter stretch of weather. Another system is progged to
approach the area late in the week with the potential of more
mixed precipitation.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1139 AM CST Sun Feb 18 2018

Complex situation developing later tonight into Monday with
respect to mixed precipitation types. For the far north, it
should be a mix of snow and sleet, for locations just north and
west of the Fox Valley, the precipitation will start as a mix of
freezing rain, sleet and snow and then transitions over mainly
freezing rain later Monday afternoon into Tuesday. The situation
is even more complex across the Fox Valley east to the lake due to
questions with respect to boundary layer temperatures. Frontal
boundary is expected to drop southward across the area later
tonight. Increasing northeast winds expected later tomorrow
morning. In these types of situations, colder air funnels down the
bay quicker than expected. This could cause temperatures at or
slightly above freezing tomorrow morning at KGRB could fall below
freezing during the afternoon. Farther to the south at
KATW/KMTW/KOSH, temperatures could be several degrees above
freezing by late morning, then fall later in the afternoon. Better
icing potential in this area will be Monday night into Tuesday.
Otherwise, IFR cigs arrive across the north later tonight and push
southward into central and northeast Wisconsin on Monday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday afternoon through Tuesday
afternoon for WIZ038>040-045-048>050.

Winter Weather Advisory from 9 AM to 6 PM CST Monday for
WIZ011>013-018>022-030-031-035>037-073-074.

Winter Storm Watch from Monday evening through Tuesday afternoon
for WIZ020>022-030-031-035>037-073-074.
&&

$$

SHORT TERM.....Eckberg
LONG TERM......TDH
AVIATION.......Eckberg


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