Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 180455
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1155 PM CDT Fri Mar 17 2017

Updated aviation portion for 06Z TAF issuance

.SYNOPSIS...
Issued at 239 PM CDT Fri Mar 17 2017

Fairly quiet mid-March weather until the end of next week.

The large scale pattern over eastern North America will reamplify
the next couple days, then flatten again. Next week it will
gradually evolve to more of a split flow regime. Temperatures
will vary with the passage of each weather system, with no extreme
warm or cold expected. Overall, readings will probably end up
averaging a little above normal for the next 7 days. Precipitation
totals for the period will depend primarily on what falls late
next week as a southern stream storm system in the evolving split
affects the area.
&&

.SHORT TERM...Tonight and Saturday
Issued at 239 PM CDT Fri Mar 17 2017

The main short-term forecast issue is aligning weather elements
with the passage of a frontal system through the region this
evening. A small area of clearing immediately behind the front may
brush the southwest corner of the area early, allowing a brief
period of warm temperatures in that area. Otherwise, low clouds,
some fog, and drizzle will persist in advance of the front. Clouds
are widespread behind the front as well (except as mentioned
above), though a shift to west winds was resulting diminishing
fog over western Wisconsin. The fog may be a bit tougher to
dislodge from eastern Wisconsin since an inch or two of snow is
now on the ground and dewpoints have edged above freezing. Will
keep some fog into the evening, especially over the far east. But
do not expect visibilities to continue to drop once winds shift
west. Some mid-level moisture will shift back southeast into the
area this evening. Forecast soundings off the NAM, RAP and HRRR
suggest this will eventually result in a moist layer deep enough
to result in ice crystals. So gradually transitioned
precipitation from drizzle to snow showers and flurries overnight.

Quiet weather and a slow decrease in clouds is expected Saturday.
Trajectories will be favorable for lake-effect off Lake Superior
to work into north-central Wisconsin. But large-scale subsidence
and drying suggest just scattered snow showers and flurries are
likely, with only minor accumulations possible.

.LONG TERM...Saturday Night Through Friday
Issued at 239 PM CDT Fri Mar 17 2017

Main forecast concerns in the long term are timing/strength and
precip types with a weak system Sunday night into Monday then with
a much larger/stronger system toward the end of the week.

Dry weather is expected Saturday night as surface high pressure
and upper level ridging spread across the western Great Lakes. The
surface high quickly slides east of the area Sunday with the upper
flow becoming more zonal as an upper jet rides along the southern
part of a trough over Canada. Within the zonal flow, a cold front
will sag across the area Sunday night into Monday, along with
decent warm air advection (WAA) as 850mb temps climb 5-7C from
Sunday AM to Monday AM. The best forcing and moisture stays well
north of the area, but with the approaching cold front, WAA, and
some moisture being advected in on south winds. Think slight
chance / chance POPs are reasonable as there should be some
isolated/scattered shower activity, especially overnight Sunday
into Monday morning as model soundings continue to show some
saturation below 750mb. Temp profiles look warm enough for rain
for most of the period, but some snow could mix in over northern
WI, mainly with any post-frontal precip Monday morning.

Dry weather returns to the area behind the front as a sprawling
area of surface high pressure moves from northern Saskatchewan
Monday night to WI on Wednesday. The only exception could be far
north-central WI where some light lake effect activity is possible
from Monday night through Tuesday night as the colder air flows
over the relatively open waters of Lake Superior. However, the
high will bring some pretty dry air with it, so not expecting
much accumulation, if any, over northern WI.

As the high pressure shifts east of the Great Lakes later in the
week, attention turns to a developing low pressure system in the
Plains on Friday. A split flow aloft will make for a complicated
forecast as phasing/timing is always difficult. First, we will
have to deal with WAA and a warm front which will kick off an area
of precip Wednesday night. GFS is the most aggressive and
farthest east with the precip associated with these, with the
ECMWF and Canadian not as bullish as they hang on to some drier
air on the western side of the departing high pressure. Will put
some low POPs across north-central Wisconsin to cover for now, but
if there is more moisture available, those features could bring a
shot of wintry weather to the area before the main system
arrives. Although long range models are not drastically different
with the main system at the end of the week, there are still many
details to worked out. It is safe to say precip is looking likely
Thursday night into Friday, but who gets rain, snow, storms?, and
how much of each will have to play out the next few model runs.

Temperatures will be above normal Sunday into Monday, then a
return to near or slightly below normal behind the front on
Tuesday/Wednesday. Temps look to climb back to above normal ahead
of the next system next Friday.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1155 PM CDT Fri Mar 17 2017

Radar loop showed some showers moving across Wisconsin as
surfaces and 500mb lows were passing through far northern
Wisconsin/Upper Michigan. Ceilings were mainly IFR in the north
and MVFR (and scattered VFR) in central and east central
Wisconsin. Visibilities were VFR across central Wisconsin, except
in precipitation, and MVFR/IFR farther east and north. As a cold
front moves through the state and winds increase, visibilities
should increase as well. Expect plenty of MVFR and IFR ceilings
throughout the night before moisture becomes more shallow during
the day on Saturday and clouds start to break up. Lake effect snow
showers in the far north will result in MVFR conditions at times.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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



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