Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 200001
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
601 PM CST Sat Jan 19 2019

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Sunday
Issued at 300 PM CST Sat Jan 19 2019

A band of heavy lake-effect snow was making its way out of
Manitowoc County this afternoon. Lake-effect clouds and some snow
showers moved into north-central Wisconsin during the day.

Expect generally quiet weather conditions tonight and Sunday as
surface high pressure and a weak mid level ridge move into the
region. There is a chance for snow showers in far north-central
Wisconsin, mainly during the evening. Below normal low
temperatures are expected tonight. Winds should be strong enough
to keep temperatures from going into free-fall, but will also
cause wind chills to reach advisory criteria in north-central
Wisconsin overnight.

Below normal temperatures will persist on Sunday be there should
be plenty of sunshine across most of the area.

.LONG TERM...Sunday Night Through Saturday
Issued at 300 PM CST Sat Jan 19 2019

High pressure across the Great Lakes will clear out skies across
much of the area Sunday night, allowing for temperatures to fall
well below zero across central and north-central Wisconsin, with
lows around zero across east-central Wisconsin and the lakeshore.
Temperatures across north-central Wisconsin will approach -20 with
light winds. Given the light winds Wind Chill headlines are not
anticipated at this time for Sunday night.

The main exception to the cloud free night will be near the
lakeshore Sunday night where Lake Effect Snow will continue across
these counties through Monday with a northerly wind direction.
There could even be pre-conditioning from Lake Superior during
this time period. The winds seem to favor more diffuse bands
rather than one organized band, therefore snowfall totals should
be fairly light during this period.

Attention then turns to a fairly significant system slated to
impact the western Great Lakes region Monday night through Tuesday
night as a low pressure system emerges from the central Plains
Monday night, then heads northeast through northern Illinois
Tuesday night. The models are in better agreement this run as the
ECMWF has come more in line with the GFS and Canadian model in
bringing the system through as an open wave in the mid levels
rather than a closed off low that tracks through much slower.
Therefore confidence in timing is better this run than in previous
forecasts. Despite the model agreement there are still some
differences that exist with the models, especially how quickly
snow ends Tuesday night.

This system looks to occur in a few waves, with Warm Air Advection
snow falling across the northern 2/3rds of the area Monday night
with the highest amounts across the north being the first wave.
The second wave will occur Tuesday afternoon and Tuesday evening
when the main surface low tracks to the south and snow falling
from the deformation zone of the main low concentrating across the
southern half of the cwa. Snow looks to then taper off later
Tuesday night as the main low shifts off to the east with a
possible contribution from Lake Michigan boosting totals near the
lakeshore. There is a period on Tuesday where there could be some
freezing rain that occurs as the column is moistening across
portions of east-central and northeast Wisconsin, however this
looks to be short lived if it does occur and should not be a big
impact on the overall event itself.

Snowfall totals from this system, from Monday night through
Tuesday night, look to generally be in the 3 to 6 inch range, with
locally higher amounts possible. Despite these snowfall totals
this will be a relatively long-duration event so the headlines
that will need to be issued in subsequent forecasts is a bit murky
as Warning criteria may not be met in the timeline required.
Therefore this looks to be a borderline high end Advisory or low
end Warning depending on if heavy snow can occur in a small enough
window or during a high impact time to warrant a tip in the
scales.

A clipper system will bring another chance for snow Thursday and
Thursday night. Given this system will be of Canadian origin and
not tap into Gulf moisture, snowfall amounts from this system will
be rather light. Once this clipper system exits most of the area
will be dry to end the week and into early next weekend. The main
exception will be across far north-central Wisconsin where LES
will continue through the rest of the forecast period. Several
inches of snow could fall in the LES belt region of Vilas County
during this period.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 555 PM CST Sat Jan 19 2019

Generally VFR conditions will prevail across the forecast area
through the TAF period. The only exceptions will be across
northcentral Wisconsin where northerly boundary layer flow across
Lake Superior continues to bring bkn SC deck as far south as RHI
this evening. Cigs will generally hover around 3kft with perhaps
occasional MVFR cigs and vsbys in widely scattered snow showers
especially north of the RHI TAF site. Elsewhere bkn SC deck will
impact far NE Wisconsin around IMT to MNM with cigs AOA 3kft.
Finally some lake-induced SC off Lake Michigan will brush MTW TAF
site from time to time overnight but generally VFR conditions
should prevail there.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory from 1 AM to 10 AM CST Sunday for WIZ005-
010>012-018-019.
&&

$$

SHORT TERM.....MG
LONG TERM......Kurimski
AVIATION.......ESB


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