Area Forecast Discussion
Issued by NWS Portland, ME

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163
FXUS61 KGYX 070340
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1040 PM EST Tue Dec 6 2016

.SYNOPSIS...
High pressure moves off to the east tonight while an elongated
trough of low pressure moves into New England from the west by
morning. This will spread some light snow into parts of the area
around the morning rush hour, but accumulations are expected to be
very light. A slow moving upper level low pressure system will
move through southern Canada Thursday and Friday, spreading some
snow showers into the mountains. This will also drive a cold front
through the area later on Friday bringing much colder weather for
the weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
1035 PM....Again, mainly dome temperature tweaks overnight, and
some tweaks to pops for the next few hours, but otherwise
forecast in good shape. Radar echoes are outpacing the actual
precip as you have to go S and W to KBDL and KPOU to find anything
reaching the ground. Previous timing of 09-11Z for steadier light
snow in NH still looks reasonable.

715 PM...Previous forecast look in good shape, and have only
adjusted temps a bit overnight, mainly to show mins a little bit
earlier, around or shortly before midnight across NH. Otherwise ,
could see a few flurries in Srn NH and the CT vly after midnight,
but a steadier light snow looks to hold off until shortly before
daybreak in these areas, 09-11Z, as precip works to moisten some
very dry mid layers.

Previously...Regional radar shows precipitation spreading through
northeast Pennsylvania and northern New Jersey as of around 3PM.
This is in association with a shortwave trough and developing
surface low pressure tracking through the Mid Atlantic states.
This feature is expected to move east to the south of New England
tonight into Wednesday, while another spoke of energy rotates
around the upper level low currently over Minnesota and moving
into the Great Lakes. Northern New England will be caught in
between these two diverging systems, with some of the moisture
associated with the southern one being pulled northward into the
upper low. As a result, we expect that as precipitation moves in
from the southwest during the early morning hours, it will
decrease in intensity and eventually dissipate as it moves east.

For tonight, high pressure moves east while high level cirrus
clouds begin moving in from the southwest. With high pressure over
eastern parts of the area for the first part of the evening,
expect pretty good radiational cooling conditions especially
considering the snow cover. Although clouds will be increasing
with time, as recent history has shown us these high level clouds
do not have near as much of an insulating effect as lower clouds
would. Temperature forecast tonight will be quite tricky, as
temperatures will likely level off around midnight or possibly
rise a bit over New Hampshire as clouds increase and light snow
moves in. Temperatures will range from the upper teens in the east
to the upper 20s in the southwest.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Light snow should have begun moving into New Hampshire by
Wednesday morning. Given the disconnect between the two diverging
systems, expect total precipitation amounts to be fairly light.
Precipitation type should be mostly snow, though temperatures will
warm as precipitation ends and there could be some sprinkles of
light rain as precipitation ends. Total snowfall amounts should be
around an inch or less, with even lesser amounts further to the
east.

Should see some breaks in the clouds Wednesday night to the south
of the mountains which will allow temperatures to fall back into
the mid to upper 20s for most of the area.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
The general pattern in the extended is a wintry look. The 06.12z
GEFS and ECMWF EPS agree on a few key features. Probably most
importantly being ridging thru AK and the Arctic...pushing the
cold air Swd into Canada. The proximity to the CONUS gives us a
better chance at seeing at least modified pieces of that air mass.
This is evident in the tendency for both ensemble suites to favor
trofing across the Northeast. For example...the 06.12z ECMWF EPS
keeps all of Nrn New England below 0C at 850 mb thru the end of
the run. At the same time there is a faint signal for Southeast
ridging...which should act to keep the storm track in our
neighborhood.

More specifically...Thu will begin the step down as a cold front
crosses the forecast area. Upslope snow showers should be most
prevalent...though a scattered flurry downwind of the mtns is
possible. The upper trof axis lags back until early Fri...and
another round of upslope snow showers and scattered flurries is
likely with this feature. Cool NW flow and upslope snow showers
continue thru the first half of the weekend. Sat night high
pressure builds in...and could set the potential for a very cold
night. With mid level temps in the negative teens to near minus 20
it has a shot at the coldest night of the season for
many...including some sub-zero readings in Nrn zones. For now
blended a little towards MEX guidance as the change in air mass
and slightly anomalous nature will make the multi-model blend
struggle to catch up. I say slightly anomalous because current
forecasts are around one standard deviation below normal...cold
but not really pushing records or anything.

Attention will then be on late Sun into Mon. A strong trof moving
thru the flow will be the next precip maker. Model guidance is
aggressively dropping the polar vortex thru the Canadian Prairies
and sending cold air Ewd...while this storm system is
consolidating over the central CONUS. I am leaning on the cooler
side of guidance for this system...especially in the Nrn zones.
There is a mixing risk for areas south of the mtns and near the
coast...but it is too early to get that detailed in the grids. For
now kept things at a rain/snow mix for areas where warmth surface
and aloft would be most likely to creep in.

&&

.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
Short Term...VFR conditions should prevail through most of the
night, but cloud heights will be decreasing from southwest to
northeast by morning. Some light snow is possible as well, mainly
at Lebanon and Whitefield, but minor accumulations are also
possible at Concord and Manchester. Should see MVFR ceilings
areawide on Wednesday as flurries or light snow track across the
area. Some improvement to VFR is expected to the south of the
mountains Wednesday night.

Long Term...In general cold and dry NW flow is expected for the
majority of terminals thru the weekend. The best chance for more
widespread precip will be with the passage of the main upper trof.
SHSN will be possible at all terminals...but most likely for HIE
where upslope flow will enhance coverage. The upslope flow will
keep MVFR or lower conditions lingering around HIE into Sat before
high pressure builds in overnight.

&&

.MARINE...
Short Term...Light winds expected over the waters as a very weak
trough moves across the Gulf of Maine late on Wednesday. Wave
heights should remain quite low as well.

Long Term...A series of cold fronts are forecast to cross the
waters late in the week. This will bring about a long duration NW
flow. This should allow seas to build above 5 ft on the outer
waters...and a period of 25 kt gusts for all waters late in the
week into Sat.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$
SYNOPSIS...
NEAR TERM...Cempa/Kimble
SHORT TERM...Kimble
LONG TERM...Legro
AVIATION...
MARINE...



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