Forecast Discussion for GRB NWS Office
FXUS63 KGRB 201711

Area Forecast Discussion
National Weather Service Green Bay WI
1111 AM CST Sat Jan 20 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 341 AM CST Sat Jan 20 2018

Nearly zonal flow and the lack of any strong systems will make
for quiet weather today through Sunday. A weak upper trough
passing by to our north will be followed by at least some clearing
of the middle and high clods today. Highs will be close to what
they were yesterday.

Middle and high clouds are expected tonight, which will help keep
temperatures well above normal. Light winds and some snow melt
could produce some fog if there are breaks in the clouds.

CLoudy skies will continue Sunday, and there is a small chance of
some light rain or snow late in the day across the southernmost
counties as the next winter storm approaches.

.LONG TERM...Sunday Night Through Friday
Issued at 341 AM CST Sat Jan 20 2018

Forecast concerns continue to revolve around the impacts from a
winter storm due to move across the region late Sunday night into
Tuesday.  Over the past 24 hours, models continue trend further
south and slower.  The ecmwf has continued to lead the way with
these trends, so will therefore put more stock into its solution.

Sunday night through Tuesday...Low pressure will be gradually
strengthening as it moves northeast from eastern Kansas on Sunday
night to the IL/WI border by 00z Tue.  As the low draws closer,
increasing low level moisture will lead to chances of precip rising
from south to north through Sunday night.  Precip may start out as a
wintry mix of freezing rain/drizzle, sleet, and snow across central
to northeast WI, and snow further north.  A light glaze remains
possible in this area.  By late Sunday night into Monday morning, a
large swath of precip is anticipated to lift northeast across the
area, as upper divergence increases within a coupled jet structure,
and mid-level fgen also increases.  With a further south track, its
looking like the dividing line between all snow, and a wintry mix is
setting up from about Wisconsin Rapids to Sturgeon Bay for Monday
into Monday evening within the period of heaviest precip.  An area
over east-central WI may see rain for most of the event during this
period. North of this line, a swath of heavy snow remains a distinct
possibility, though the arrival of the dry slot during Monday
afternoon and Monday evening will likely limit the high end of the
snowfall potential. As the low passes to the east and the thermal
profile cools, all areas should see accumulating snowfall late
Monday night into Tuesday morning, though most precip should be
exiting by around midday Tuesday.  Prelim snow amounts could reach 6
to 10 inches over parts of central to far northeast WI, while
amounts will be considerably less where precip consists of wintry
mix or rain, around 2 to 5 inches.  Will let the next shift iron out
a few more details (timing/snow/ice amounts) before issuing a watch.

Rest of the forecast...Behind the system, more quiet and seasonable
weather will resume Tuesday night into Friday thanks to high
pressure. Though temperatures are likely to start out around normal,
they should return above normal by Thursday and Friday.

.AVIATION...for 18Z TAF Issuance
Issued at 1044 AM CST Sat Jan 20 2018

VFR conditions will continue into tonight. Later tonight, areas
of fog are expected to form along with the potential for low
clouds (IFR or lower) towards sunrise to a few hours past sunrise.
Moderate to high confidence fog will develop, but lower confidence
that the IFR or lower CIGS will develop across the area. If low
clouds do develop, they will be slow to erode on Sunday.

Looking ahead, a significant storm system is expected to affect
the area Sunday night into Monday night. Low level wind shear
is expected to develop Sunday evening and continue overnight.
The storm is also expected to bring heavy snow north and west
of the Fox Valley with more mixed precipitation across the
Fox Valley and lakeshore region. The heaviest snowfall/snowfall
rates are expected to fall on Monday as the system moves across
the area. It is likely that 6 or more inches of snow will fall
north and west of the Fox Valley. Precipitation types and snowfall
amounts from KISW east to the Fox Valley and lakeshore are still
highly uncertain. Gusty north/northeast winds also expected on
Monday into Monday night.





NWS GRB Office Area Forecast Discussion