Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 060203 AAC

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
903 PM EST Mon Dec 5 2016

High pressure moves in from the west tonight and crosses through
the area on Tuesday. A weakening trough of low pressure approaches
from the west Wednesday morning with more light snow possible. A
cold front arrives from the northwest on Friday ushering in some
of the coldest air of the season so far for this weekend.


9 PM Update...
Area of main ascent as well the precipitation shield has shifted
over eastern Maine and is headed towards the Canadian maritimes.
PoPs were decreased along the Mid Coast especially. Light upslope
snow showers will be ongoing overnight but will decrease towards
morning as upper level support moves away. Snowfall totals in NH
and ME were general got anywhere from 1-3".

Expecting some patchy black ice in areas where cloud cover is
absent or will be absent...allowing freezing fog to form. The
morning commute could be messy once more, and have issued an SPS
for this concern.

Temperatures will only drop a few more degrees across the region.
Winds should stay up around 3-5 mph with high pressure arriving
towards morning.

545 PM Update...
Bulk of the snow is now moving into eastern Maine with a cold rain
noted over Rockland as well as the capes and islands. Some
additional flurries are possible behind the system over the
coastal plain and inland as the vorticity lobe shifts away the
next few hours... but PoPs will be less than 10% and any
additional accumulations will be negligible. However the highest
peaks should see another couple inches in upslope showers

Roads, bridges, overpasses, and walkways will remain slick with
temperatures well below freezing tonight.

Previous discussion...
Weak low pressure in the Gulf of ME will continue E tonight.
Within the last couple of hours MWN has gone to W
winds...indicating that the upper trof is passing thru at least
some of the forecast area. This corroborates drying on the latest
WV satellite imagery. As this trof axis passes...snow will wind
down from W to E. It has ended across much of NH at this
hour...and will do so in ME zones over the next few hours. As the
snow ends...coastal front will slide back out to sea from areas
near the coast and capes where it worked inland. This temp drop
could result in some refreezing on slick conditions
will linger into the evening. The W flow and lingering low level
moisture will result in some upslope snow showers tonight too. And
I have left high PoP in the NW slopes to account for these...and
they may be persistent enough for another inch or two on top of
what has already fallen today.


S/wv ridging and high pressure move in for Tue. Much of the day
will be clear and comfortable temps for this time of year. The
main focus is on a Southeast s/wv trof that will be lifting
towards the Mid Atlantic during the day. The wave will be shearing
out with time however...and model guidance pretty rapidly weakens
forcing for ascent as precip enters the forecast area. Initially
isentropic lift is modest for parts of Wrn New England...but this
gradually wanes by early afternoon. Lift will mainly be tied to
the passage of the upper trof...and so snowfall looks likely but
amounts at this time look to be less than an inch. Timing is
probably the more important snow will be arriving
around or during the morning commute in NH.


Broad troughing in the center of the continent will shift east
into New England later this week as the core of the upper level
low moves east into eastern Canada. As this low moves northeast
the flow behind it will become more zonal in its wake. A broad
trough moving into the west coast on Friday will track east across
the country this weekend, possibly brewing up a storm for early
next week as it arrives into New England. The details:

By Wednesday morning northern New England will be caught in
between two disconnected waves, one moving out to sea south of New
England and the other associated with the upper low moving through
the Great Lakes and southern Canada. An area of lift along a weak
trough between the two will generate some light snow as it moves
into western New England Wednesday morning, but as it moves east
it will lose a lot of its support with the precipitation
dissipating as it arrives into our area. Expect the best chance of
snow and greatest accumulations to occur across western and
southwestern New Hampshire where 1 to 2 inches is possible.
Further east should see some flurries or up to an inch. This will
be arriving around the time of the morning commute, so even the
light accumulations could cause some slick roadways.

Models had been advertising another wave moving nearby on
Thursday, possibly generating offshore low pressure and snowfall
for our area. However, models are generally in good agreement now
that this will not happen at all. Instead, the primary upper
trough moves through the area on Thursday, eventually generating
low pressure well out to sea tracking into the Canadian Maritimes
on Thursday. The result is near normal temperatures on Thursday
with a cold front moving through Friday night turning temperatures
colder for this weekend. The cold northwest flow on Friday will
allow some downslope warming (into the mid 30s anyway) for the
coast, but the mountains will stay in the 20s. On Saturday it will
be even colder with the entire region staying in the 20s. Saturday
night is shaping up to be the coldest night of the year so far as
surface high pressure moves east into the area. Still a good
amount of uncertainty on how well the various pieces will align
for a great radiational cooling night, but for now expect
widespread teens with single digits in the typical cold spots.
This forecast could be too warm if the high moves into the area a
little earlier or clouds stay away more than currently forecast.

Models not in very good agreement on the timing and strength of
the wave moving across the country this weekend and arriving in
New England early next week. The GFS brings a sharp trough into
New England Sunday night and spins up a coastal low with some
snowfall on Monday, while the ECMWF holds the trough back and
doesn`t arrive until Monday night with a potentially warmer
scenario unfolding. For now it is only safe to say that there is
the potential for some precipitation early next week and that
precipitation type and amounts are still quite uncertain.


Short Term...Widespread IFR conditions continue across much of
SWrn ME. As upper trof passes...and coastal front shifts back out
to sea dragging colder air behind it...conditions will improve
to VFR. AUG will remain IFR the longest...while RKD may bounce
back to IFR as the coastal front slips back out to sea and they go
from RA back to SN. NW flow however will keep clouds stuck in
upstream of the I anticipate HIE to remain at least MVFR
with occasional SHSN thru the night. High pressure Tue brings VFR
conditions to all terminals. Very late Tue night SN will move back
into the area from the SW to NE. SW NH terminals like
LEB...MHT...and CON are most likely to see some IFR before 12z

Long Term...Conditions deteriorate from west to east Wednesday
morning with snow moving in. This will dissipate as it moves east,
so the most likely airport to be affected will be Lebanon with
lower chances east of there. Still could hang on to an MVFR or at
times IFR ceiling across most of the area on Wednesday before
clearing out Wednesday evening. A northwest flow Thursday into the
weekend will bring a chance for upslope snow showers in the
mountains and Whitefield could be MVFR most of that time period.


Short Term...As upper trof passes and weak low pressure moves into
the Gulf of ME...winds will become NWly and increase. Model
forecast soundings snow mixing enough to get a few gusts close to
25 kts...but more likely below that. Seas will increase as
well...but to around 4 ft on the outer waters. At this time I have
not issued a SCA...but a brief window of marginal SCA conditions
would not be surprising around 06z. High pressure moves over the
waters Tue...with winds and seas diminishing. NE flow returns Tue
night as the next warm front approaches from the SW.

Long Term...Offshore winds expected on Thursday, increasing
Thursday night into the weekend as a cold front brings in colder
air from Canada. This will likely lead to a period of advisory
level wind speeds.





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