Area Forecast Discussion
Issued by NWS Portland, ME

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351
FXUS61 KGYX 222100
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
400 PM EST Sun Jan 22 2017

.SYNOPSIS...
A cold front will stall to our south through tonight as high
pressure builds by to our north over eastern Canada. A storm
system tracking up the coast will bring wintry precipitation to
the area late Monday and Tuesday. A cold upper trough will remain
over the area through the latter part of the week with a return to
colder temperatures. Scattered snow showers in the mountains and
foothills can be expected through the latter part of the week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
At 19z...the backdoor cold front was situated to our south and
west and will remain stalled there through tomorrow. A 1029
millibar high was centered just east of Hudson Bay. GOES imagery
showed extensive low clouds across the region. NWS Doppler radar
mosaic was showing spotty return over western and southern
sections of the forecast area on the cool side of the stalled
boundary. For tonight...clearing noted over Quebec province
vicinity of the Gaspe Peninsula will try to work south on a
cooler and drier north to Northeast flow. Expect we`ll see some
gradual clearing overnight over our northern and eastern Maine
zones. Elsewhere...we should remain mostly cloudy with onshore
flow and the stalled boundary to our south and west contributing
to some spotty light precipitation at times. This should be
drizzle and eventually flurries as the column cools overnight with
some isolated freezing drizzle not completely out of the question.
Lows will range from around 20 in the mountains to mid and upper
20s elsewhere.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
On Monday...colder and drier air from the eastern Canadian high
will continue to nose southward into the forecast area with clouds
possibly breaking up for a time as far south as Casco Bay into
northeastern New Hampshire. The onshore flow should keep low
clouds in place further south and west with some spotty light rain
or snow depending on boundary layer temperatures. Cloud cover will
advance back north and east during the afternoon as moisture surges
back north ahead of approaching coastal system. The leading edge
of the steadier precipitation shield should be approaching southern
New Hampshire towards early evening. Highs tomorrow will be in
the lower and mid 30s...except for upper 20s in the mountains.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
***Significant winter storm to affect the area Mon night/Tue***

A strong trof crossing the Southeast will roll up the East Coast
tonight through Tue. Ahead of the lifting trof...an anomalous Ely
flow will develop...in excess of -5 standard deviations. This will
feed sub-tropical moisture into the region Mon night and Tue. At
the same time ridging will increase ahead of the system 00z
Tue...most likely due to latent heat release in convection...and
allow surface high pressure to build into the Maritimes. This
action combined with Ely flow in the lower levels...will set up
cold air damming along the Ern slopes of the mtns. Again I have
taken the under on model 2 m temps...and feel that much of the
event occurring with temps around 32 degrees. Now that does depend
on how far S cold air can work behind the cold front today. At
12z...the CAR raob was -11C...colder than any model. Colder
dewpoints are also feeding SWwd thru Nrn ME...and having that
initial dry air at the surface will enhance any cold air damming.

National radar mosaic shows very N/S oriented convection across
the Southeast at this time. This is a favorable set up to
transport that sub-tropical moisture Nwd...rather than shunting it
Ewd. So at this time I am not worried too much about QPF. I feel a
good chunk of the area will see at least 1 inch...with near the
coastal front up to 2 plus inches. The strong Ely flow and cold
dome will likely lead to strong upslope signature to QPF
distribution. I enhanced QPF on the SE facing slopes and near the
forecast coastal front. This will point towards the Whites and
Monadnocks seeing some enhanced precip...and upslope cooling
which should help in the wintry ptype.

The strong Ely flow will also make for gusty winds. Initially the
deeper mixed layer will make it gusty across a lot of the forecast
area...but gradually the inversion developing aloft will keep the
wind from being too big a deal inland. Very near the coast some
gusts to 50 mph are possible...but there was not enough confidence
for any high wind watch at this time. Forecast soundings have been
showing less mixing and more inversion with time...and the wind
signal has slowly backed off with time.

Finally the biggest question mark remains warm air aloft. The
22.12z ECMWF remains very cold...and nearly all snow for the
forecast area. The 22.12z GFS also stayed on the colder side of
guidance...with significant amounts of snow and sleet. The NAM on
the other hand...and to a lesser extent CMC...were warm and would
lead to more sleet and freezing rain. Given that models typically
hold the warm air aloft too long...I blended the 22.12z GFS and
ECWMF with the NAM to speed up the warmer air moving in. This
gives me more of a snow to sleet for much of the area. Before the
mid levels saturate fully...precip could start as sleet most
areas...before changing to snow or rain depending on surface
temps. With the warm layer on all model guidance between H8 and
closer to H7...I have leaned the forecast away from significant
amounts of freezing rain and kept it to around a tenth of an inch
total. Snow amounts were generated with less than a 10 to 1
ratio...and do carry a large amount of bust potential. More sleet
and those ratios could be closer to 3 to 1 or less...and more cold
air aloft and we will easily be 10 to 1. With so much uncertainty
still...I opted for winter storm watches for a large portion of
the forecast area for the potential of 6 inches of snow...along
with possibly significant amounts of sleet and some freezing rain.
I do envision the areas not in the watch possibly needing an
advisory down the road as well. Again the most likely areas to see
higher snow totals will be deeper inland where the surface and mid
level cold hangs on the longest...and areas where upslope
enhanced precip and cooling can help keep ptype snow.
Monadnocks...Whites and into the Wrn ME foothills. Warmer air
aloft sneaking up thru the CT River Valley and around into areas
N of the notches may cut down on snow totals there too.

Beyond the storm system the multi-model consensus was used.
Generally broad cyclonic flow and NW upslope snow showers will be
the dominant precip maker. Temps should average near to above
normal.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
Short Term /Through Monday/...Areas of MVFR with lcl IFR vcnity of
KPSM/KCON/KMHT terminal sites. Spotty drizzle and -SHSN psb mainly
south of a KLEB to KSFM line along with isold light freezing
drizzle.

Long Term...Onshore flow Mon evening will keep BKN to OVC CIGs in
all likelihood...with areas of MVFR and local IFR conditions.
Precip moves in quickly from the S and a prolonged period of IFR
or lower conditions will result in SN/PL/FZRA/RA. Right now warm
layer aloft looks rather high...and so PL should dominate mixed
ptype...with FZRA being brief in nature. SN is most likely over
the far interior...with CON...AUG...and HIE holding onto it the
longest. PL will move in from the S and W...with HIE and LEB
changing over faster than CON and AUG. MHT and coastal terminals
will likely see PL/SN early than change over to RA eventually.
PSM/PWM/RKD may also see NE surface wind gusts to 30 or 35 kt at
times. Low level moisture lingers much of Tue...and at least MVFR
conditions will linger behind the main area of precip.

&&

.MARINE...
Short Term /through Monday/...Northeast flow will strengthen
through tomorrow with small craft conditions deteriorating to
gales by late Monday.

Long Term...No change with marine headlines. Storm warnings for
the outer waters and gales in the bays. Strongest winds will be
during the overnight Mon...gradually diminishing as low pressure
passes E of the waters. We will need transitional gales and SCAs
on the backside of the system into Wed.

&&

.TIDES/COASTAL FLOODING...
Despite being in the low portion of our astronomical tide cycle,
large building waves may produce some erosion and splash-over near
the times of high tide Monday night and Tuesday. Preliminary storm
surge values appear to be around 1.5 to 2 feet with a persistent, strong
easterly wind developing. A coastal flood advisory may be needed from
the impact of the wave action.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Watch from Monday evening through Tuesday
     afternoon for MEZ018.
     Winter Storm Watch from late Monday night through Tuesday
     evening for MEZ007>009-012>014-019>021.
NH...Winter Storm Watch from Monday evening through Tuesday
     afternoon for NHZ005>011-015.
     Winter Storm Watch from late Monday night through Tuesday
     evening for NHZ004.
MARINE...Gale Warning from 3 PM Monday to 11 AM EST Tuesday for ANZ151-
     153.
     Storm Warning from 6 PM Monday to 11 AM EST Tuesday for ANZ150-
     152-154.

&&

$$

Schwibs/Legro



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