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Office: GYX

FXUS61 KGYX 111459 AAB

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
959 AM EST Mon Dec 11 2017

A cold front will cross the region today...continuing snow
showers in the higher terrain. The cold will settle across the
area by tonight...and set the stage for the a wintry storm
Tuesday. Precipitation will overspread the area from west to
east early Tuesday...mostly starting as snow. Slowly warmer air
will work inland from the coast and change precipitation from
snow to rain. A narrow band of mixed precipitation is possible
between the rain and snow. Across the foothills and mountains
precipitation is likely to remain snow for the majority of the
event...and up to 6 inches or more is possible. Precipitation
will quickly come to an end Tuesday evening from west to east.
Behind that much colder air will move into the region and linger
through the end of the week.


10 AM Update...
Minor changes to up PoPs and QPF for current upslope showers
ongoing in the mountains and foothills. No other major changes
at this time. Will be interrogating new model data as it comes
in for tomorrow's event.

7am update... minor adjustment for current obs.

A cold front will move through today, with surface high
pressure will building into the region behind it while the core
of the upper level trough brings cold air in overhead.
Temperatures will remain fairly cool with highs just above
freezing along the coast an in the mid 20s north.

The cold air mass an initially clear skies will allow
temperatures to drop quickly after sunset, however increasing
cloud cover through the overnight in advance of the approaching
storm will keep lows from dropping below zero in the north.


*** Widespread snowfall expected Tuesday ***

Low pressure currently diving south through North Dakota will
intensify as it moves into the Great Lakes and cross Northern
New England on Tuesday bringing snowfall to the region.

Confidence is high in the timing of precipitation but only
moderate for snowfall amounts due to the potential for a
changeover to rain/sleet/freezing rain along the coast and thus
the winter storm watch will remain in place.

Precipitation will initially begin around daybreak on Tuesday
and spread from west to east across the area during the morning.
During this time the low will remain to our west over Lake
Ontario. This position will allow the cold air which settled
into the region overnight Monday to remain in place. A coastal
front will form with the cold air dammed against the mountains
and the above freezing temperatures remaining off shore for all
but the outer islands of the Maine coast. With this expect the
entire region to see snow as the warm advection ahead of the low
center brings moisture into the region. Greatest snowfall in
this time will be through interior southern New Hampshire where
the greatest moisture exists, along with good frontogenesis

As we move into the afternoon the setup becomes a bit more
tricky. The low center begins to reform and is expected to be
right along the Maine coast by evening. This sets up two key
features of the forecast. For the early to mid afternoon we'll
see the area of greatest forcing and qpf move east into Maine.
In combination with the existing coastal front, this has the
potential to create a region of high snow totals just inland of
the front, with snowfall rates above 1"/hr possible. The issue
of course is exactly where that coastal front is going to be.
At the same time as the forcing for higher snowfall totals is
moving east the surface low is also reforming and trying to
bring the warm air further inland, likely changing a portion of
the midcoast over to rain with a mix of sleet and freezing rain
along the boundary. Meanwhile almost as soon as the low can
form and bring the warm air, the dry slot will also arrive
bringing an end to the precipitation in the evening.

The net result of all this is a region of higher snow totals,
around 6-10" extending from Sullivan county in New Hampshire up
through the Maine foothills towards Bangor. To the north, along
the Canadian border we may see lower amounts just due to the
main forcing being more towards the coast. From Manchester, NH
and up along I-95 in Maine through to Augusta is really the
linchpin in terms of the warm air. This area could see high
snow totals if they remain on the cold side or low amounts if
the warm air is able to penetrate. Finally along the coast,
mixing with rain and sleet is expected, and here snow totals
will likely result in just an advisory level. While there is a
portion of the area where confidence is high enough for a
warning, with so much still in question have opted to just keep
the entire region in the watch.

The low center will move off to the northeast overnight Tuesday
with just upslope snow remaining along the Canadian border by
Wednesday morning.


In the wake of surface low pressure...the main upper low will
barrel across the region Wed. In addition to bringing the real
colder will also provide the instability for widespread
snow showers. While the focus will be in the higher terrain
where orographic lift will enhance vertical motion...the Arctic
front dropping H8 temps from near 0C to -20C over the course of
the day Wed will also allow for snow showers to organize along
the boundary. Given the high low level frontal
boundary...and low static stability...some of this activity
along the front may be in the form of snow squalls.

In addition to the cold and snow...winds will be quite gusty
Wed. Deep mixing in CAA will support frequent gusts around 30
kts...and possibly higher as some forecast soundings try mixing
to a 40 kt Wly LLJ around H9. Forecast soundings also indicate
the boundary layer will remain mixed into Wed night. I favored
raw 2 m temps for overnight readings...along with winds/gusts
higher than the multi-model consensus blend. Temps falling into
the teens and single digits coupled with the wind will produce
wind chill values below as cold as the teens below
zero in the Nrn zones.

The deep...cyclonic flow lingers Thu but will begin to relax
into Fri as the next S/WV trof approaches. This wave will race
thru the Great Lakes and lead to development of an ocean low
pressure Fri night into Sat. With the main baroclinic zone well
off shore this low shows no threat to the forecast area on the
11.00z model suite. That being said...the S/WV in question will
move into the Gulf of AK this afternoon. A sample of this
feature with 12.00z raobs will likely impact model solutions in
the coming 24 hours. Additionally...ensemble sensitivity really
begin to grow in the 48 to 60 hour window...suggesting that they
may not stabilize anytime soon. I have hedged towards a chance
of snow for the SErn third of the forecast area...higher than
the multi-model consensus blend for that reason.

The active Nrn stream continues into the weekend...with another
potential wave arriving sometime Sun or Sun night.


Short Term... A weak front will move through the northern
portion of the area today with MVFR in occasional SHSN expected,
elsewhere VFR. Low pressure will move through the region on
Tuesday. Expect conditions to rapidly deteriorate to IFR on
Tuesday morning with periods of LIFR in heavy snow expected for
Southern New Hampshire between 12Z and 18Z and into southern
Maine from 18Z- 00Z.

Long Term...Deep cyclonic flow will persist over the forecast
area into Thu. Moist...Wly flow will keep MVFR CIGs mainly
upwind of the mtns...along with upslope SHSN. HIE will see
periods of MVFR and possibly local IFR in SHSN. The upper low
crosses the area Wed afternoon...and that may allow for SHSN to
maintain outside of the high terrain. Local IFR conditions will
be likely in any SHSN that move downstream of the mtns.
Otherwise VFR conditions expected thru Thu. An ocean low
pressure will develop Fri and move NEwd paralleling the coast.
That may spread -SN to areas near the coast...though this is low
confidence at this time.


Short Term...Have extended the small craft advisory as winds
continue to gust to 25-30kts. Expect a brief break in conditions
late Monday as high pressure moves in. By Tuesday the
intensifying low will bring Gale conditions to the waters and a
Gale watch has also been issued.

Long Term...As low pressure deepens over Quebec...a strong
pressure gradient will set up over the coastal waters. A strong
Wly gale will continue into Wed night. Winds and seas gradually
diminish Thu afternoon. Another low pressure developing near the
Gulf of ME may extend SCA conditions into Fri.


ME...Winter Storm Watch from late tonight through late Tuesday
     night for MEZ007>009-012>014-018>022.
NH...Winter Storm Watch from late tonight through late Tuesday
     night for NHZ001>013-015.
MARINE...Small Craft Advisory until 7 PM EST this evening for
     Gale Watch from Tuesday morning through late Tuesday night for