Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 171204
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
704 AM EST Tue Jan 17 2017

.SYNOPSIS...
Low pressure moves out of the Great Lakes today then redevelops
off the mid Atlantic coast by early Wednesday. This system will
bring widespread snow, with highest amounts in the south and some
mixed precipitation along the coast. Another weak front will pass
by to the north on Thursday. This will be mainly dry with just
clouds across the region and a few upslope snow showers along the
Canadian border. High pressure will build in for the remainder of
the week, with above normal temperatures expected through the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
TEmps quite variable early this morning, with clouds along the NE
zones, this turns out to be the warmest area. Have made some
adjustments for the next few hours based on this, but overall
forecast remains unchanged for today. PRecip should hold off in
all but SW zones until around 6 pm or later.

Previously...Our cold air mass that is moving out of the area,
will get one more chance to impact our weather, as it gets pulled
back west around the poleward side of a low that will be south of
the area, bringing snow to the region late today through at least
part of Wednesday. However, for the most part the daylight hours
will stay dry with increasing clouds, especially this afternoon,
and highs climbing to around 30 in the mountains and the mid-upper
30s along the coast and in srn NH. There is a chance that snow /or
rain could develop in Cheshire county and along the NH/MA border
around the time of the evening commute, but for the most part,
precip will hold off until around 00Z or later.

&&

.SHORT TERM /WEDNESDAY/...
For tonight, may see precip begin initially as rain especially in
Rockingham and eastern Hillsborough as warm boundary layer
lingers into early evening. Colder air aloft will push into this
areas quickly this evening, so it will change to snow fairly
quickly. The only areas it may stay more rain than snow would be
in the Hampton/Seabrook/Plaistow area. Otherwise, precip will
begin as snow everywhere else, and stay snow through most of the
night. Forecast is a little tricky given forecast amounts right
around that 6 inch warning criteria. Think that the heaviest will
be from south central NH NE thru the ALes region and into
interior SW ME, as this will be fueled by ESE upslope and
potentially good deformation as wedge of 850 mb cold air pushes
into warmer air working up from the south. Also this would
include inland side of coastal front as well. This is where some
banding may be possible overnight and could see some briefly
higher snowfall rates. Since system is passing south, amounts will
lower as you head nwd and into central ME, with bulk of precip
passing offshore E of Casco Bay. Coastal areas were kept a little
lower, as warmer air may work in on strong E flow over the waters,
and this could lower snow ratios or mix some rain in. But the dam
may be strong enough to keep the marine air offshore and may need
to push up to warning in coastal Cumberland and York counties.

On Wed, the heaviest precip will be moving east during the
morning and the afternoon could see some SHSN inland, and maybe
some SHRA or DZ near the coast, as weak inverted trough linger
thru the afternoon. The departing low should weaken the dam and
allow temps to rise, at least a little, above freezing on the
coast and in srn NH.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Overview: Blocked and split flow will continue through the
weekend. The forecast period starts with a strong ridge built over
the eastern Atlantic, blocking the flow. Behind this ridge a
trough is dug over Labrador with a series of weak short waves
passing through. Over the CONUS the flow remains split. While the
northern stream continues to drop south out of Canada across
Hudson Bay to our region a 500mb closed low remains over New
Mexico with additional waves moving up towards Northern New
England. The combination of blocking and split flow yields a very
low confidence forecast as blocking is generally slow to move and
poorly resolved and the split flow results in difficult timing. By
the start of the weekend the deterministic guidance has such a
large spread that inferring much beyond climatology and
persistence isn`t recommended.

/Thursday/ Thursday a wave will pass to our north from the
northern stream. This air mass is dropping out of northern Canada
and is very dry and will mostly result in clouds for the region.
In the mountains upslope flow will be enough to squeeze what
little moisture there is out. Increased PoPs and accumulations for
the far north giving 1-2" of accumulation for Pittsburg, NH
through Jackman, ME where upslope is most favored.

Friday high pressure will build into the region. The surface high
will be accompanied by upper level ridging as the closed low over
the southwest tries to break down and is reabsorbed into the main
flow. This strong ridge means some above average temperatures for
us with highs above freezing across the entire area to start the
weekend. Saturday there is a chance for a system to pass to our
south bringing a few showers with it.

Deterministic models show a major pattern shift for the start of
next week. The end of the blocking and split flow allows for
another system to move through on Monday into Tuesday bringing
the potential for widespread precipitation. However given the
uncertainty in the pattern this is a low confidence forecast and
have stuck close to what passes for a consensus of models.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Short Term /through Wednesday/...VFR thru most of today. Conds
deteriorate this evening as Sn pushes into the area from the
west, with IFR expected to linger into Wed, as low clouds are
expected with DZ possible near the coast.

Long Term...Thursday will start out as MVFR across the region as
clouds move in. The clouds will dissipate to VFR for all but HIE
where MVFR conditions will remain through the start of the weekend.
Some MVFR may reappear on Saturday in light snow and rain.

&&

.MARINE...
Short Term /through Wednesday/...
Low pres passing south of the waters will allow increasing E-NE
flow tonight into early WED, with SCA winds/seas expected.

Long Term... Friday a weak front will pass north of the waters
brining and end to the easterly flow from earlier in the week.
Conditions will subside Thursday as high pressure builds into the
region and remain calm and below SCA criteria right through the
weekend.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Warning from 7 PM this evening to 5 PM EST
     Wednesday for MEZ012-018>020.
     Winter Weather Advisory from 7 PM this evening to 5 PM EST
     Wednesday for MEZ013-021-023>026.
NH...Winter Storm Warning from 5 PM this afternoon to 5 PM EST
     Wednesday for NHZ004-006-008>010-015.
     Winter Weather Advisory from 5 PM this afternoon to 5 PM EST
     Wednesday for NHZ002-003-005-007-011>014.
MARINE...Small Craft Advisory from 1 AM to 6 PM EST Wednesday for
     ANZ150>154.

&&

$$
SYNOPSIS...Cempa
NEAR TERM...Cempa
SHORT TERM...Cempa
LONG TERM...Curtis
AVIATION...Cempa/Curtis
MARINE...Cempa/Curtis


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