Area Forecast Discussion
Issued by NWS Portland, ME

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668
FXUS61 KGYX 152008 CCA
AFDGYX

Area Forecast Discussion...CORRECTED
National Weather Service Gray ME
408 PM EDT Sun Apr 15 2018

.SYNOPSIS...
A frontal boundary draped across the area will continue to
generate mixed precipitation through the overnight hours.
Precipitation is expected to change from a wintry mix to rain
from south to north tonight and tomorrow. As the system
currently in the Great Lakes region moves through New England
tonight and tomorrow, strong gusty winds are expected to develop
along with a period of heavy rainfall. A broad area of
weakening low pressure will persist over the region Tuesday and
will shift east on Wednesday. Another area of low pressure will
approach from the west Wednesday night and will move east
through the region on Thursday. Low pressure will slowly shift
east into the maritimes for the remainder of the period.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Mid level warm front continues to wash out along and N of the
LEB to PWM line. Dry air is still lurking just to the NE of the
forecast area over The County and Downeast ME...so whatever
precip is falling is very light. To the S of the front there is
a bit of a break in precip...with the except of far Srn NH where
some ocean effect precip continues to fall. With H9 temps
forecast to hold around -8 to -10 C...that light ocean effect
precip may continue thru the evening in the Ely flow.

The next batch of precip to worry about is taking shape across
the Chesapeake at this writing. It will continue to move N and
expand in area. Surface temps are not expected to move much this
evening...meaning the majority...if not all...of the forecast
area will be below freezing. Another round of mixed precip is
expected...and for that reason I have just extended all winter
wx advisories into Mon...and expanded Ewd into central and
Midcoast ME. Forecast soundings still show very deep low level
cold...so I do expect sleet to be the predominant ptype. That
being said...there is plenty of cold air in place and high
pressure is expected to remain in a very favorable position for
continued cold air damming. In the overnight period any freezing
rain that falls should have no problem accumulating.

In the mid levels behind the front ESE winds will ramp up
tonight. With the strong inversion lowering towards ridge top
level...a favorable set up will be in place for downslope wind
gusts. The Wrn slopes of the higher terrain will see gusts of 40
to 50 mph...with localized higher gusts in the steeper terrain.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Early Mon the area of precip from the Mid Atlantic will be
lifting thru the forecast area. Parts of the winter wx
advisories may be able to drop as precip moves out and temps
edge up above freezing. I have gone colder than the coldest
model guidance for temps...and even that may be too warm given
the propensity for guidance to rush the inversion mixing out.

Towards midday the core of the LLJ and strongest forcing for
ascent will arrive. PWAT values in excess of 2 standard
deviations above normal will support heavy precip...mainly in
the form of rain as strengthening SE winds slowly warm the
boundary layer. Widespread QPF of 1.5 to 2 inches is
expected...and for flooding concerns see the hydrology section
below.

Ahead of the cold front itself the core of the LLJ will lift
across the area. Near the coast...especially N of PWM...SE gusts
approaching 50 mph are possible. ECMWF EPS have very high
probabilities for 40 kt gusts...and given that added confidence
another wind advisory has been issued for this threat...in
addition to the downslope winds across Wrn NH tonight into Mon.
The coastal wind gusts will continue into late Mon evening before
the LLJ moves NEwd.

Precip will quickly end from W to E as the cold front sweeps
across the forecast area. Upslope showers...changing to snow
showers...will linger on the backside of low pressure into Tue
morning.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Long term begins with a surface low in place over the Great
Lakes with an occluded front moving out of northern New England,
and a closed upper level low over western New York state. As the
upper level low ever so slowly migrates to the east, the cold
pool aloft will likely destabilize things enough for scattered
afternoon showers through Wednesday night.

The possible bigger story begins Wednesday night though. The GFS
is indicating low pressure moving out of the midwest and driving
east and south across PA. This would place northern New England
in a strong baroclinic zone with precipitation being generated
during the day on Thursday. Right now it looks like it would be
all rain. The 00z ECMWF was taking this system and developing a
coastal low out of it, with temperatures cold enough to generate
snow. However, the 12z ECMWF now has a more southerly track and
takes the system far enough south that it ends up being a miss
for us. Will rely more on the GFS as it has at least been
stable, but will need to monitor things as they progress.

Zonal flow aloft then sets up for the remainder of the extended
period with little in the way of weather.&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Short Term...Precipitation has come to an end at most TAF sites,
with a few exceptions being noted. Sites are primarily IFR, but
will likely become IFR/LIFR during the overnight hours as more
precipitation moves in. By 06z, western TAF sites will be
experiencing LLWS and by 12-18z, most of them should be. In some
locations it will be close, but chose to include it as it could
have operational impact.

Long Term...VFR with areas of MVFR ceilings and vsby in
scattered showers Tuesday. VFR with areas of MVFR ceilings
Wednesday. IFR/LIFR ceilings developing late Wednesday night and
Thursday.

&&

.MARINE...
Short Term...NE flow will continue over the coastal waters and
slowly veer to Ely thru Mon. Winds will also gradually
increase...with gale force gusts expected after midnight. Winds
become more SEly late Mon...with some gusts approaching 45 kts
outside the bays. LLJ crosses the waters Mon night...with winds
becoming Wly behind the cold front and decreasing.

Long Term...
Will need to watch seas Wednesday night and Thursday as they may
approach SCA criteria.

&&

.HYDROLOGY...
A very moist air mass will continue to surge northward ahead of
a strong low pressure system in the Great Lakes. The heaviest
precip is expected Mon afternoon into the evening. A large area
of 1.5 to 2 inches QPF is expected...especially along and
southeast of the higher terrain. The question is mainly how much
snow melt we get in the headwaters...as temps are forecast to
remain near freezing for most of those areas. Ensemble river
guidance does forecast a couple locations in NH going above
flood...but not widespread enough threat for a flood watch at
this time. More likely there could be ponding of water in poor
drainage areas as well as river flows near flood.

&&

.TIDES/COASTAL FLOODING...
Beach erosion and splash over still possible for high tides Mon
and Mon night. Current storm surge forecasts keep tide gauges
below flood stage Mon...but given the possibility for
erosion/splash over a statement may be needed midday Mon. I
preferred the ESTOFS guidance thru Mon night...with E flow
likely creating a storm surge in excess of 1 ft. That could
yield some minor flooding across the Seacoast of NH...possibly
into York Co Mon night.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory until 8 AM EDT Monday for MEZ018-023.
     Winter Weather Advisory until noon EDT Monday for MEZ007>009-
     012>014-019>022-024>028.
     Wind Advisory from 2 PM Monday to 2 AM EDT Tuesday for
     MEZ025>028.
NH...Winter Weather Advisory until 8 AM EDT Monday for NHZ003-
     005>015.
     Winter Weather Advisory until noon EDT Monday for NHZ001-002-
     004.
     Wind Advisory from 2 AM to 8 PM EDT Monday for NHZ001>003-005-
     007-011.
MARINE...Gale Warning from 8 AM Monday to midnight EDT Monday night for
     ANZ151-153.
     Gale Warning from 2 AM Monday to midnight EDT Monday night for
     ANZ150-152-154.

&&

$$

SYNOPSIS...Pohl
NEAR TERM...Legro
SHORT TERM...Legro
LONG TERM...Pohl
AVIATION...Pohl
MARINE...Pohl/Legro
HYDROLOGY...Legro
TIDES/COASTAL FLOODING...Legro



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