Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 190954 AAA
AFDGYX

Area Forecast Discussion...UPDATED
National Weather Service Gray ME
554 AM EDT Mon Jun 19 2017

.SYNOPSIS...
A warm and very humid airmass will remain across the region
through Tuesday. A cold front will approach from the Great
Lakes Region today and bring widespread shower and thunderstorm
activity to the region. Some of the thunderstorms could produce
damaging winds and torrential downpours, especially across
inland areas. On Tuesday, the cold front will gradually
weaken as it slides offshore. The next weak trough will move
across the area on Wednesday producing a few showers mainly in
the mountains and foothills. The next more significant system
approaches late Thursday into Friday bringing a return to
unsettled weather.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Update...Adjusted PoP based on latest radar trends. Most showers
have struggled to hold it together into the forecast area...so I
will trim PoP back to the W and keep things under likely for the
next several hours.

Previous discussion...Focus of the near term is on the
potential for flash flooding and severe thunderstorms.

For starters the flash flood threat is a little more clear
across the NW half of the forecast area. A deep moist air mass
is in place across the region...with PWAT values approaching 2
inches. However you choose to view this...2 to 3 standard
deviations above normal...or in excess of 200 percent of
normal...there is a lot of moisture to work with. Deep warm
cloud depths...greater than 10000 feet...will support very heavy
rainfall in any convection this afternoon. In addition...storm
motions are projected to be parallel to the approaching cold
front. So not only will storms bring heavy rainfall...but they
will likely track over the same areas as the front slowly creeps
Ewd. The flash flood watch remains in effect as a result.

More uncertain is the threat for severe thunderstorms. The
uncertainty is mostly related to the amount of sunshine today.
That deep...moist air mass responsible for the flash flood
threat will also support moderate instability this afternoon
with any modest amount of heating. Despite weak lapse rates
aloft...dew points sit around 70...and CAPE could be as high as
1500 J/kg with a little break in the cloud cover. This is
important because wind fields in the low to mid levels are
forecast to increase thru the afternoon today. Some model
forecasts show close to 50 kts at H8 by mid afternoon. In
addition models keep surface winds mainly S to SSW today. That
turning with height and increasing speed will support effective
shear near 40 kts. This will favor supercellular
structure...despite linear forcing along the front. Convection
allowing models are also showing initiation of storms in the
higher terrain early in the afternoon...perhaps related to the
elevated heat source or terrain induced circulations. Any such
storm would form in an environment more conducive for robust
updrafts. The deep...moist air mass will mitigate a large hail
threat...but any storm will carry a threat for damaging winds
thanks to that near 50 kt SW LLJ. Severe wording and damaging
winds will remain in the grids thru the early evening.
Finally...we will have to watch for channeled flow areas...like
the CT River Valley where Sly wind can hang on the longest. The
enhanced helicity associated with those backed surface winds
and low LCLs will lead to a low probability tornado threat.
Though the threat is localized...strong winds in the low levels
and turning in the lowest 1 km could lead to a brief tornado
stronger than EF0.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Front will slowly push thru the forecast area overnight. The
loss of daytime heating should allow storm intensity to drop
markedly from earlier in the day. Given the very moist
environment...any convection will still be capable of heavy
rainfall. Ahead of the front will also be another mild
night...with lows struggling to get into the 60s.

On Tue a weak s/wv trof will cross the area during the
afternoon. Despite weak lapse rates remaining over the Srn parts
of the forecast area...farther N will see slightly steeper lapse
rates. Model forecasts show around 500 J/kg MUCAPE building by
afternoon...so scattered thunderstorms are possible again.
Though this time around instability and moisture will be less
than we see this afternoon.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
The deterministic models are in decent agreement on the longwave
pattern into the upcoming weekend. We begin the period with an
upper trough centered across the Great Lakes and Mississippi
Valley. This trough will weaken as it propagates eastward and
off the northeast coast by early Thursday. Weak ridging follows
briefly on Thursday before a warm front pushes into New England
by Thursday night ahead of the next impulse racing eastward
along the U.S. - Canadian border. The warm front presses
northward across the area on Friday as low pressure races east
across Quebec province with the trailing cold front to cross the
region late Friday and Friday night. We`re left with residual
troffiness to start the weekend with the prospect for some
clouds and scattered convection mainly across the higher
terrain. The models diverge for Sunday... with the preferred
ECMWF/GFS blend yielding a mostly dry day before digging
shortwave energy carves out a deep trough to our west...with a
more significant storm system arriving in New England from the
Great Lakes and mid Atlantic region for Sunday night and Monday.

&&

.AVIATION /10Z MONDAY THROUGH FRIDAY/...
Short Term...Coastal LIFR/IFR stratus remains in place over the
Midcoast area. RKD and AUG remain LIFR at this hour...but with
flow direction not expected to change much thru morning I do not
expect the stratus to move much farther W. Otherwise scattered
MVFR CIGs are possible ahead of the cold front. Early this
afternoon SHRA/TSRA will form along and ahead of the front.
Local IFR conditions are possible in any convection...in
addition to strong wind gusts. Most likely areas to see strong
TSRA would include HIE...LEB...MHT...and CON. Strong TSRA threat
is much more uncertain farther E. Cold front will cross the area
tonight...clearing out low level stratus and TSRA. Afternoon
SHRA are possible in the mtns again Tue.

Long Term...

Wed...Sct MVFR in -SHRA.

Thu night - Fri...Areas of MVFR in SHRA/TSRA with lcl IFR in fog
and drizzle.

&&

.MARINE...
Short Term...SCA conditions will continue today in persistent
Sly flow. There will be some gusts above 25 kts...but mainly
seas will be above 5 ft outside of the bays. SCA conditions
continue into Tue as the approaching cold front will be slow
moving.


Long Term...

Tue night - Wed AM...Small Craft Conditions are possible outside
the bays.

Fri...Small Craft Conditions are possible outside the bays.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Flash Flood Watch from 2 PM EDT this afternoon through Tuesday
     morning for MEZ007>009-012>014.
NH...Flash Flood Watch from 2 PM EDT this afternoon through Tuesday
     morning for NHZ001>009-011-015.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ150>154.

&&

$$

NEAR TERM...Legro
SHORT TERM...Legro
LONG TERM...Schwibs
AVIATION...Legro/Schwibs
MARINE...Legro/Schwibs



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