Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 201539
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1039 AM EST Mon Nov 20 2017

.SYNOPSIS...
High pressure building into the region today and tonight will
deliver cold temperatures across the region. Expect a brief warm
up on Tuesday before another cold front moves through the area
on Wednesday bringing a return to colder conditions that should
last through Friday. A brief warmup expected Saturday with
scattered showers ahead of another approaching cold front that
arrives Saturday night. High pressure delivers colder and drier
air for Sunday.

&&

.NEAR TERM /TODAY/...
1030AM UPDATE...
Light snow observed across the area this morning is in
association with a multi-pronged trough moving through the
region with only minor enhancements from upslope flow. The first
prong of this trough has moved east, while the second should be
arriving in a couple of hours. Thus although most of the light
snow has ended now, expect another chance of snow with the next
trough axis before the day is over. Like the last round, this
one will not be limited to upslope areas only, though total
snowfall will be quite light as there is not a lot of moisture
to work with. Have adjusted wind gust forecasts today as well
since a few areas have had some gusts above 40 MPH. Think that
these gusts will be lower as the day goes on, but it will be
another windy and cold day. Only minor tweaks to temperature
forecast was made.

730AM UPDATE...
Morning light is allowing the use of some webcams across NH and
a better gauge of where accumulating snow is taking place. I
have upped PoP to high chance and likely in most of the high
terrain now. This includes some light accumulations into the
foothills...especially in Oxford and Franklin Counties.

ORIGINAL DISCUSSION...
Secondary s/wv trof will cross the area early today. This will
renew CAA and allow winds to be quite gusty again during the
afternoon. I am not expecting it to be as windy as
yesterday...with generally 25 to 30 kt gusts. With favorable
dendritic snow growth temps in the low levels and abundant low
level moisture...upslope snow showers will continue thru most of
the day. Flow also becomes more Wly with time...and that may
bring more lake enhanced moisture into Wrn zones. I have
expanded slight chance and chance PoP...as well as brought PoP
into SWrn NH where lake enhanced bands of snow are drifting a
little more Nly than earlier in the night. Froude numbers remain
greater than 1 in the CAA regime...so snow showers should
consistently be able to top the Green Mtns and drift into Wrn
NH...as well as top the White Mtns and sneak into the foothills.
Some light accumulations are possible in Wrn NH Nwd thru the
White Mtns.

&&

.SHORT TERM /TONIGHT AND TUESDAY/...
Weak s/wv ridging aloft and surface high to the S trying to
nose into the area will allow winds to diminish around sunset.
There is a window for some radiational cooling tonight as warm
front lifts thru the area aloft and before return flow really
picks up in the boundary layer. I have generally stayed with the
cooler guidance sources...and also show a small non-diurnal
trend late tonight as return flow increases towards dawn.

Behind the warm front we also see a much drier low level air
mass...which should allow any remaining clouds and snow showers
in the mtns to scatter out/dry up. Return flow aloft will also
bring in some warmer temps...and allow even shallow mixing to
send the Srn and coastal zones on a run to the 50s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
A warm southwest flow Tue night into early Wed ahead of an
approaching cold front. The cold front will move rapidly through
the region Wed with scattered showers expected. In the mountains
some of the showers will likely change to snow showers as the
CAA occurs during the day. Not much QPF is expected with the
passage of the front as per models suggest. Models all indicate
the heavier band of rain will stay well offshore ahead of the
front. Behind the front, a large arctic ridge of surface high
pressure will build into the region Wed night through Friday with
dry conditions and much colder temps.

All models in general agreement about carving out a general broad long
wave trof position across the eastern US. This will mean
generally colder temps and mainly dry conditions and storm free.
The only exception being Sat as a brief warm southwest flow
develops scattered showers ahead of the next shot of cold air as
the upper trof gets reinforced bringing another shot of cold
arctic air across the region by Sunday.

&&

.AVIATION /16Z MONDAY THROUGH FRIDAY/...
Short Term...VFR conditions expected to prevail thru Tue. Local
MVFR is possible near HIE as upslope SHSN continue for much of
the day. Surface wind gusts at or above 25 kts expected this
afternoon at all terminals. Winds gradually late in the day and
overnight...and shift more SWly. Upslope clouds and SHSN come to
an end early Tue as much drier air moves into the area.

Long Term...MVFR conditions expected Wednesday as a strong cold
front moves through the region. VFR conditions will return by late
Wednesday and continue into early Saturday.

&&

.MARINE...
Short Term...Currently in a bit of a lull in wind speeds across
the waters. That will be short lived however...as a secondary
s/wv trof crosses the area today and renews stronger NW wind
gusts. Wind gusts will reach marginal gales outside the bays
around mid morning...so I have just extended the current gale
warning thru this evening. SCA will continue in the bays for the
same time. Tue winds becomes more SWly and may allow winds to
drop below SCA thresholds...though seas will likely remain near
or above 5 ft.

Long Term...Southwest flow may approach SCA criteria Tue night
ahead of an approaching cold front. The front moves across the
waters Wednesday. By Wednesday night a north to northwest flow may
briefly reach SCA conditions over the outer waters. High pressure settles
over the waters Thursday and Friday with light winds.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 10 PM EST this evening for ANZ151-
     153.
     Gale Warning until 10 PM EST this evening for ANZ150-152-154.

&&

$$

NEAR TERM UPDATE...Kimble
SHORT TERM...Legro
LONG TERM...Marine



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