Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 191911

Area Forecast Discussion
National Weather Service Gray ME
311 PM EDT Mon Mar 19 2018

High pressure will continue to settle over northern New England
tonight and Tuesday bringing continued colder than normal
temperatures. A storm system will pass to our south Wednesday
and Thursday likely bringing accumulating snow to much of the
forecast area. High pressure then gradually builds in through
the weekend.


No significant weather to speak of tonight as cold high pressure
gradually builds in across the forecast area. Clear to mostly
clear skies are expected overnight with diminishing winds. This
should mean temperatures falling to below guidance levels at the
good radiators and took that approach with mins.


Mostly sunny skies Tuesday with high pressure ridging in place.
Colder than normal temperatures will continue but with lighter
winds than Monday. Increasing high clouds likely later Tuesday
night as low pressure gathers well to our south.


High Impact Weather Potential: Potential for plowable snowfall
Wednesday afternoon and Wednesday Night. Potential for coastal
flooding particularly south of Portland late Wednesday through

Pattern: Early afternoon water vapor imagery reveals blocked flow
downstream of North America over Greenland /-NAO/ with longwave
trough axis east of our longitude...allowing a significant amount of
arctic air to pour down into the northeastern United States as a
result.  Over the eastern Pacific...there is a cutoff low spinning
off the western North America coast.  Between these features...there
are a series of weaker disturbances moving across the country in the
west northwest flow aloft.  There are indications that the
downstream block will give way this week...allowing the upstream
flow across North America to become increasingly progressive.  As
the trough now east of us begins to push will re-
load as energy over the Midwest carves arrives. The evolution of
this energy is the primary focus of this forecast package.
As we reach the weekend...ridging over central North America
will begin to arrive from the west.

The Details:

Wednesday - Thursday: Complex evolution to the mid and upper level
pattern portends reduced confidence through what will likely be the
most impactful portion of the long term forecast.  Energy now moving
through the Mid Mississippi Valley will be joined by rapidly moving
shortwave energy now coming ashore along the coast of California.
This will help force a digging trough over the southeastern United
States Tuesday night into early Wednesday. At the same time...
another mid level wave representing the remnants of the
departing eastern trough will cutoff north of New England. The
relative magnitude and interplay of these two features will
largely determine the sensible weather impacts in our region. A
fairly strong consensus has developed over the past 12-24 hours
which favors an initial wave of low pressure passing south of
the region on Wednesday with a stronger low taking shape off the
Mid Atlantic coast...and slowly tracking northeast late
Wednesday and Wednesday night...with a consensus track just
south and east of the benchmark. There is also broad agreement
on the H7 low track moving south and east of Cape Cod late
Wednesday night. Pattern recognition with this setup would favor
accumulating snow for about the southeastern half of the
forecast area with a plowable snowfall possible...especially the
closer one moves to the coast. Wednesday evening through
Thursday morning would currently be the most favored time for
travel impacts with any snow tapering to snow showers on
Thursday. EC-EPS has a strong signal for 0.25" liquid...with a
modest signal for 0.5"...with both of these signals highest
along the coast. advisory event from the mountains
south and east...with some potential for warning level snows
along the coast would be a most likely solution at this time.
Winds are also a potential concern for the coastal plain given
impressive pressure gradient between ~1030mb high over the Great
Lakes and ~985 low southeast of New England. Given what becomes
a persistent northeasterly wind...coastal flooding will become
a potential hazard. See that section of the AFD below.

Friday:  Differences in the evolution of the Wednesday-Thursday
storm persist into Friday.  While there is agreement that Canadian
high pressure will begin to build in from the north and west...the
orientation of the low level flow and amount of residual moisture
are in question.  Expect that we/ll at least see residual snow
shower activity in the mountains...with some potential for snow
showers to the south and east given the position of the mid level
trough overhead.  Temperatures aloft look to be close to...or just
below seasonal norms...and thus...expect temperatures just below
normal for this time of year.

Saturday: Mid level trough pushes east of the region with backing
flow overhead as closed low south of James Bay interacts with energy
moving across the mid and upper Mississippi Valley.  Residual snow
showers are again possible...although with the loss of cyclonic flow
aloft and some decrease in deep moisture...expect that they will be
less widespread than on Friday.  Despite the backing flow
aloft...temperatures at H8 don/t move...remaining at about -1
sigma...with highs in the lower 30s north of the mountains to just
above 40 in the foothills and along the coast being about all we/ll
be able to muster...about 5F below seasonal norms.

Sunday-Monday: Run to run changes in the guidance have been pretty
substantial at this range...with previous model simulations
advertising another fast moving wave in the increasingly progressive
flow.  However...the multi-day trend is favoring a stronger area of
high pressure building north of New England...favoring a drier and
cooler scenario.  Best threat of precipitation /likely in the form
of snow if it falls/ would be on Sunday with temperatures continuing
to be below seasonal norms with the polar front most likely south of
the region.


Short Term /through Tuesday Night/...VFR conditions are expected
tonight through Tuesday night with high pressure in place. Wind
gusts diminish this evening.

Long Term...Increasing potential for VLIFR/LIFR particularly
MHT-PSM-PWM-RKD beginning late Wednesday and continuing through
Thursday morning. VFR by mid morning Thursday and continuing
through Friday.


Short Term /through Tuesday Night/...SCA conditions continue on
the ocean waters as well as outer Penobscot Bay through this
evening before diminishing. Small craft conditions will likely
redevelop late Tuesday night as a storm system develops to our

Long Term...Given the northward trend in surface low position
in the Wednesday-Thursday timeframe, gale force winds are a
strong possibility for Wednesday into Thursday...and have issued
a gale watch with this package for this likelihood. Given the
forecast low level jet strength...storm force winds are possible
in the outer waters and will continue to watch this potential.
Winds and waves will subside beyond this through the end of the


Northward trend in coastal cyclone Wednesday-Thursday portends
another round of potential coastal impacts.  Surge guidance suggests
that water levels will increase Wednesday evening and overnight
Wednesday night...with 2` total tide departures possible.  Given the
forecast tides this week /see below/ this will likely bring us near
flood stage for at least the early Thursday morning high tide.
Compared to recent events...a somewhat weaker low pressure system
well offshore suggests 10-15` waves with an increasingly long
period.  Certainly will be watching over the next 24 hours and
considering potential headlines.

Tides -

Wed 2:10 AM - 10.2`
Wed 2:38 PM - 9.6`
Thu 2:55AM - 10.2`
Thu 3:28PM - 9.3`

Fort Point
Wed 2:20 AM - 9.7`
Wed 2:49 PM - 9.1`
Thu 3:05AM - 9.7`
Thu 3:40PM - 8.9`


MARINE...Gale Watch from Wednesday morning through Thursday afternoon
     for ANZ150>154.
     Small Craft Advisory until midnight EDT tonight for ANZ150>152-



NEAR TERM...Ekster
LONG TERM...Arnott is the U.S. government's official web portal to all federal, state and local government web resources and services.