Area Forecast Discussion
Issued by NWS Green Bay, WI

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961
FXUS63 KGRB 202055
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
255 PM CST Sat Jan 20 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 254 PM CST Sat Jan 20 2018

Mostly cloudy skies prevailed across the region this afternoon. It
was another mild day with temperatures in the middle 30s to middle
40s.

For tonight, mostly cloudy skies are expected. A weak fgen band is
expected to set up across northern Wisconsin tonight, bringing a
slight chance of light snow across the north. Areas of fog are
expected overnight into early Sunday morning. If there are breaks
in the clouds for several hours, the fog could become locally
dense in a few spots.

Another mild day in expected on Sunday with highs in the 30s to
around 40. Thicker cloud cover should keep temperatures a few
degrees cooler than today. Some drizzle is possible late south of
Highway 10.

.LONG TERM...Sunday Night Through Saturday
Issued at 254 PM CST Sat Jan 20 2018

Focus is on the upcoming winter storm Sunday night through Monday
night, precipitation timing and type, snow and ice accumulations,
and headlines.

Models are in good agreement with a Colorado low lifting
northeast into the western Great Lakes and passing near the
Wisconsin/Illinois border Monday afternoon and evening. The
general trend has been to slow down the arrival of precipitation
with this system on Sunday night and early Monday, so sided with
the slower ECMWF/NAM models and backed off on pops and QPF a bit
from previous forecasts. The combination of best lift and
saturation occurs from about mid-morning through early evening on
Monday, so have focused the highest pops and QPF during this time
frame. A crosshairs signature (core of strongest lift coincident
with dendritic growth zone) is evident over north central and far
northeast WI Monday afternoon and evening, so moderate to heavy
snow is expected during this time frame. Consequently, our
greatest accumulations, roughly 6-10 inches, are anticipated north
of a line from Wausau to Mountain to Crivitz. A Winter Storm Watch
will be posted for this region.

Farther south, a combination of a weak warm layer aloft and
surface temperatures warming into the middle to upper 30s on
Monday, will result in significantly lower snowfall totals
in parts of central and east central WI. The biggest gradient in
the snowfall currently exists north of a line from ISW-CLI-SUE,
and these areas could easily need to be added to the watch if
the system shifts a little farther south or temperatures are
slightly cooler.

There will be several periods with potential for light freezing
rain or freezing drizzle, mainly due to mid-level drying and a
loss of ice crystals. Right now, the most likely time frames
would be late Sunday night into Monday morning, and again Monday
evening. Ice accumulations should be less than a tenth of an inch
in most locations. A combination of snow/ice accumulations will
likely result in a need for Winter Weather Advisories southeast
of the current watch area.

Northeast winds will crank up on Monday and Monday evening,
especially for the Fox Valley and lakeshore areas, where gusts to
30 to 40 mph are possible. A Gale watch has been issued for
The Bay and northern Lake Michigan marine zones Monday into Monday
evening.

The heaviest snow should end Monday evening, but light snow will
continue overnight into Tuesday morning. Models are suggesting a
band of snow developing just south of the forecast area late
Monday night, so will need to keep an eye on that with subsequent
forecasts.

High pressure and quiet weather is expected for the mid to late
part of the work week, with a nice warmup anticipated on Friday.
A cold front will bring a chance of rain or snow showers early
in the weekend.
&&

.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.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Monday morning through Monday evening
for WIZ005-010>013-018-019-021-030-073.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......Eckberg
AVIATION.......Eckberg



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