Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 172330
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
530 PM CST Wed Jan 17 2018

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Thursday
Issued at 252 PM CST Wed Jan 17 2018

Dry conditions prevailed across the area during the afternoon
hours. Main weather concern for the rest of the afternoon and
evening will be gusty SW/W winds that will create some blowing and
drifting snow. Visibilities down to around 1 mile have been
reported across parts of northern and far eastern WI. Expect
these conditions to continue through the early evening before
mixing diminishes and winds die down. Will let the winter weather
advisory continue for Door, Kewaunee, and Manitowoc, as many
county/rural roads could still be experiencing some drifting.
Advisory may be cancelled early if winds die off faster than
expected near/after sunset. The worst conditions are expected
across Door County, where the most snowfall fell Sunday night into
Monday night.

Elsewhere, just patchy drifting snow (maybe a little blowing snow
as well) is expected through sunset, with the worst conditions in
open, rural areas. Otherwise, a dry night is expected. Although
winds die off this evening, they will remain in the 5 to 15 mph
for much of the night as boundary layer winds stay up, but gusts
should be reduced as a strong inversion keeps the stronger winds
from making it to the surface. The winds won`t allow temps to
plummet, despite the mostly clear skies, with lows ranging from
the single digits to middle teens for most spots.

A small, compact and potent shortwave / clipper system will dive
from southern Manitoba this evening into Upper Michigan Thursday
morning. Models in general agreement on strength and track of this
feature. However, there is some disagreement on if any snow will
be associated with it. Despite the strong dynamics, the
NAM/GFS/ECMWF are all dry, with the GEM showing around 0.01" near
the MI/WI border. Meso-models are a little more aggressive with
coverage and tend to favor that idea. Will increase POPs and snow
amounts over northern WI, but think accumulations will mainly be
under a half inch. Also added some flurries south of the snow
shower activity. Any lingering snow flurry activity should end
early Thursday as the system quickly exits the area. High temps
look to be above normal for much of the area, with readings
climbing into the upper 20s to lower 30s.

.LONG TERM...Thursday Night Through Wednesday
Issued at 252 PM CST Wed Jan 17 2018

A system that is expected to impact the area this weekend into
early next week is the main forecast concern through mid week.

Upper level flow becomes more zonal late this week and then
southwest as a mid level trough moves into the western CONUS. A
cutoff 500 mb low is expected to develop as the trough reaches
the Plains before it then moves into the Great Lakes region by
early next week. There are differences among the 12Z models in the
forecast path, timing and strength of the surface and upper level
features, so exact precipitation amount and types remain in
question.

Warmer temperatures are in store for the area into the weekend as
flow aloft becomes southwest and a surface system approaches the
region. Much warmer than normal conditions should persist into
early next week before cold air wraps around the departing surface
low and closed mid level circulation. Colder, but near normal
temperatures are forecast for Tuesday through Wednesday.

Based on a blend of the models, there is only a slight chance for
snow across parts of the area late Saturday night and Sunday
morning. Chance PoPs enter the picture starting Sunday afternoon,
with snow expected in the north, rain in eastern and parts of
central Wisconsin, with rain and/or snow from northeast into parts
of central Wisconsin. Precipitation should change to snow Sunday
night as the boundary layer cools and snow PoPs are likely or
higher during the night and on Monday. A change to rain or a mix
is expected on Monday as the boundary layer warms. Precipitation
should all be in the form of snow by Monday evening and chances
for snow drop off on Tuesday as the surface and upper systems
depart. After that, there is only some lake effect potential
downwind from Lake Superior through Wednesday.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 519 PM CST Wed Jan 17 2018

LLWS will wane some tonight into early Thursday, then increase as
a compact upper system passes just northeast of the area. The main
aviation concern is the potential for low cloud development. Not
much on satellite other than in far SW Ontario and SE Manitoba.
Those clouds do not look to be on a trajectory to reach the area.
But it is possible that additional low clouds will form beneath
the strong inversion across the area. Opted to bring MVFR cigs
into RHI late tonight and keep them there tomorrow based on the
strong signal across several guidance products. But that is still
a low-confidence aspect of the forecast.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM CST this evening for WIZ022-
040-050.
&&

$$

SHORT TERM.....Bersch
LONG TERM......MG
AVIATION.......Skowronski



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