Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 170312
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1012 PM CDT Thu Mar 16 2017

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 955 PM CDT Thu Mar 16 2017

Decided to issue an advisory for much Central WI for the
overnight hours. Observations to the west with the band of
precipitation approaching central Wisconsin were reporting mainly
rain, while surface temperatures at 9 pm were around the freezing
mark with surface dewpoints very dry. Still may turn to more snow
due to evap cooling overnight, but 850 mb temps rise to near or
just above zero over central wisconsin to support more of a mix.
Later shifts may need to expand the advisory overnight especially
across the north. HRRR and latest NAM keeps the precipitation west
of GRB through 12z.
&&

.SYNOPSIS...
Issued at 340 PM CDT Thu Mar 16 2017

A round of wintry precipitation tonight into tomorrow, otherwise
fairly quiet weather for the next week.

The large scale pattern will deamplify and then reamplify some
during the next few days. After that, the main change will be a
gradual evolution toward a more split flow regime next week.
Temperatures will warm to a little above normal for the weekend,
then drop back to near or a little below normal for much of next
week. Precipitation amounts will probably end up a little below
normal for the period.
&&

.SHORT TERM...Tonight and Friday
Issued at 340 PM CDT Thu Mar 16 2017

Clear and dry conditions this afternoon will give way to snow or
a wintry mix overnight into Friday morning before surface
temperatures warm above freezing, resulting in a change to rain.

Temperatures across the area reached the mid 30s to lower 40s this
afternoon. Dew points to the west of the Bay and Fox Valley were
mostly in the single digits, while teens dew points were common
farther to the east. Relative humidities were in the 15% to 30%
range in most locations. The dry air was evident on the 12Z GRB
sounding which showed some signs of moisture around 700mb but was
otherwise quite dry with a PWAT of 0.10".

Radar mosaic loop through early this afternoon showed an area of
precipitation across the Dakotas and far western Minnesota. This
was associated with an approaching mid level short and surface
system. 12Z models were slower in bringing precipitation into the
forecast area, which seemed reasonable based on the amount of dry
air in place. Based on forecast soundings from around the area,
precipitation should start out as snow late this evening with the
potential for some freeing or mixed precipitation toward morning
in central Wisconsin. Freezing/a mix is possible across northern
Wisconsin Friday morning while the rest of the area changes to all
rain as temperatures warm. A change to all rain should occur in
the north during the afternoon.

Highest QPF is forecast to be between 06Z and 12Z over the western
part of the forecast area, and 12Z to 18Z in the east. Snowfall
totals should be mostly in the 1.5" to 2" range across the north,
with 0.5" to 1" farther south and near Lake Michigan. Ice
accumulations in central and north central Wisconsin are expected
to range from 0.01" to 0.04".

.LONG TERM...Friday Night Through Thursday
Issued at 340 PM CDT Thu Mar 16 2017

Scattered snow showers and flurries are likely Friday night, and
possibly into Saturday, as a strong mid-level shortwave digs into
the central Great Lakes region and begins to close off.
Trajectories will become favorable for lake-effect snow showers
off Lake Superior to reach north-central Wisconsin on Saturday,
but by then drying and large-scale subsidence will serve as
limiting factors.

Quiet weather is expected Saturday night and Sunday as high
pressure shifts across the area. The return flow on the back side
of the high looks to be strong enough to ensure temperatures are
above freezing before precipitation chances increase ahead of the
next shortwave and frontal system that will approach from the
west. A return to cooler temperatures will follow the passage of
those systems.

Other than some adjustments to PoPs and weather in the first
couple periods of the long-term portion of the forecast, no
significant changes to the initialization grids were necessary.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1003 PM CDT Thu Mar 16 2017

Cigs will continue to lower overnight as mixed precipitation
moves into the area. A mix of mvfr and ifr cigs and vsbys
expected by Friday morning. Conditions expected to gradually
improve to a higher end MVFR or lower end VFR Friday mid afternoon
in the wake of the surface front. Scattered mvfr cigs due to snow
showers will return over northern Wisconsin with colder air
returning to the region.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM CDT Friday for WIZ030-035>037-
045-048.
&&

$$

UPDATE.........TDH
SYNOPSIS.......Skowronski
SHORT TERM.....MG
LONG TERM......Skowronski
AVIATION.......TDH



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