Area Forecast Discussion
Issued by NWS Portland, ME

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812
FXUS61 KGYX 140744
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
344 AM EDT Fri Jun 14 2024

.SYNOPSIS...
A strong cold front will push towards the region today with
scattered showers and thunderstorms...some of which have the
potential to become strong to severe. This front moves offshore
tonight with cooler and drier air arriving for the weekend.
After another seasonable day Monday...temperatures and humidity
will build through the middle of the week with an extended
period of hot and humid conditions expected.

&&

.NEAR TERM /TODAY/...

High Impact Weather Potential:  Strong to severe thunderstorms
possible today with damaging winds and large hail.

Pattern: Early morning water vapor imagery reveals a shortwave
trough pushing east across eastern Ontario into western Quebec.  The
associated surface cold front spawned convection across Ontario that
has pushed through New York and into Northern New England...decaying
as it does so as it runs out of instability to work with.
Tracking the cold front and associated convective activity will
be the primary forecast focus today...as well as severe
thunderstorm potential.

Through daybreak: Decaying convective line continues to push
east towards the region as of this hour with a substantial
variation in temperatures across the CWA between locations that
have remained coupled seeing temperatures still near 70...while
the cooler sheltered locations have falling into the upper 50s.
MUCAPE values are essentially nil as you cross the CT River so
while some shower activity will reach the area through
daybreak...do not expect much in the way of thunder with no
severe threat with temperatures largely holding steady before
rising after 6am.

Today: Challenging convective forecast today with pre-frontal trough
and remnant shower activity overhead to start the day before the
surface cold front arrives this afternoon.  Quite a bit of
cloudiness is advertised with questions on how much destabilization
occurs ahead of the surface cold front.  The 3km NAM is rather
robust...pushing 70F dewpoints into southern areas which supports
MLCAPES 1500-2000 J/kg with good deep layer shear.  The HRRR has
been somewhat less robust given about half the amount of SB/MLCAPE
as surface dewpoints only reach the lower-middle 60s...which appears
more reasonable given early morning regional surface observations
which show no 70F dewpoints across the northeastern quarter of the
country.  The GFS/RGEM are even less impressed with the setup having
the majority of the second round of convection develop south of our
region across southern New England.  Recent renditions of the HRRR
represent a good compromise solution which show a line of convection
after 3pm in the foothills...which pushes to the coast through
evening.  In this setup...MLCAPES look to be closer to 1000 J/kg
/lapse rates look good through H7...but are weak above this/ with 30-
40kts of deep shear which will support updraft organization.
Overall this favors primarily a wind threat with some hail
potential given storm organization. SPC has expanded the slight
risk across much of southern NH / southwestern ME which lines
up best with the juxtaposition of shear and afternoon
destabilization. Will continue to focus on this area in the
morning Hazardous Weather Outlook. Expect highs to push into the
lower 80s across southern NH and mid/upper 70s elsewhere...
though if more sun materializes...a few extra degrees will be
possible.

&&

.SHORT TERM /TONIGHT THROUGH SATURDAY/...

High Impact Weather Potential: Minimal.

Pattern: Shortwave and associated vort max within larger longwave
trough digs as it pushes into New England tonight slowing the
progression of the surface cold front with a weak wave potentially
developing along the front before both features move east of the
region during the day Saturday allowing drier/cooler air to
overspread the region from the northwest.

Tonight: Any remaining convection from Friday evening will weaken
and push offshore during the evening hours with clouds slower to
clear as the shortwave approaches the coast.  Could see a few
residual showers near the coast for the overnight though expect most
of the activity will remain offshore.  Given Friday/s
rainfall...areas to the north that clear will have the potential to
see some patchy fog development with cloud cover likely limiting
that potential closer to the coast.  Cold advection behind the
surface cold front will allow lows to fall into the 50s throughout
the region...with a few readings around 60 across southern NH.

Saturday: Offshore cold front will stall for a time over the Gulf of
Maine as low pressure well southeast of Cape Cod pushes north and
east...which may allow for a few lingering showers along the coast
to start the day but northwesterly flow and associated dry advection
strengthens during the day which should clear skies and moderate
northwesterly winds.  T8s slowly fall towards 5C by evening.  Expect
highs in the upper 60s in the mountains with mid/upper 70s to the
south as northwesterly flow will give some downslope assistance to
boost temps in the dry airmass.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

...Multi Day Heat Expected Next Week...

High Impact Weather Potential: Multiple days of heat indices in
excess of 95 to 100F beginning Tuesday likely continuing through the
end of the week.  The potential exists for heat indices in excess of
105F especially over southern NH and SW ME.

--Pattern and Summary--

The long term period opens with a mobile longwave trough overhead
which will move east of the region by Sunday.  Beyond this...a
significant pattern change is in the works...with longwave troughing
digging down the west coast of North America which will help push
western US ridging to the east.  The result will be a building ridge
across the eastern half of the United States on Tuesday with this
ridge locking in place over the northeast for the middle and latter
portions of the week.  This ridge looks to be rather impressive for
any time of the summer...not to mention mid June...with H5 return
intervals approaching or exceeding 30 years by Wednesday and
Thursday and nearing the top end of the GYX sounding climatology.
Thus...the primary forecast concern for the long term will center on
temperatures rather than precipitation as the proximity of the ridge
next week will likely preclude much in the way of rainfall while
temperatures will potentially near record highs centered around the
first day of astronomical summer.

--Daily Details--

Saturday - Sunday: One last stretch of dry and seasonable weather is
expected to open the period this weekend as offshore cold front
pushes east on Saturday with Canadian high pressure building
overhead for Sunday.  The ensemble guidance envelope includes some
members that have a few showers along the coast as the frontal
boundary slows over the Gulf of Maine...but expect the day to
feature morning clearing...seasonable temperatures /highs in the
upper 60s in the mountains to the upper 70s across southern NH/ and
dramatically lower dewpoints than on Friday.  This sets up a good
radiational cooling night Saturday night with 40s common across the
area.  Expect some of the northern valleys will dip again into the
upper /and perhaps middle/ 30s.  Sunny weather expected for Father`s
Day with T8s in the upper single digits suggesting highs in the 70s
to around 80 from north to south.

Monday: High pressure settles south of Maritime Canada with deep
layer ridging building towards the region from the west will allow
return flow to strengthen...with temperatures building to star the
week.  Monday looks seasonably mild with nearby high pressure /weak
gradient/ indicating a robust sea breeze with highs along the coast
in the 70s...and temperatures reaching the lower to middle 80s
inland.

Tuesday - Thursday: T8s push into the upper teens by Tuesday with
some potential to push above 20C by Thursday...which represents a 1
in 10 year to 1 in 30 year event for this time in June.  Fully
mixed...+20C suggests mid 90s which is well-captured by the NBM for
Wednesday/Thursday.  This is right in the vicinity of daily records
for this period /for example...CON for Tuesday, Wednesday, and
Thursday is 98F/.  A slightly more southerly trajectory to the
gradient should allow the immediate coast to stay cooler on Tuesday
/ 70s to lower 80s / with a seabreeze but by Wednesday and Thursday
the gradient turns more westerly with the heat pushing to the coast.
Dewpoints begin the period in the lower 60s on Tuesday...and then
into the mid/upper 60s by Wednesday-Thursday with some ensemble
members going higher than this. While a few ensemble members have a
convective complex trying to push into our area at some point in the
extended...this has little ensemble support and conceptually doesn/t
fit given our proximity to the center of the ridge.  Thus...will
maintain a dry forecast through the period.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
Short Term...Showers across NY will continue to weaken as they
reach the terminals towards daybreak with little in the way of
restrictions as they pass overhead through the morning.
This afternoon...expect another round of showers and
thunderstorms to develop with scattered MVFR/IFR restrictions.
Friday night...a few additional showers will be possible for the
coastal terminals with some potential isolated restrictions
with patchy fog developing inland depending on the extent of
rainfall Friday afternoon. This could yield local IFR
restrictions.

LLWS will continue through daybreak Friday with 1.5kft winds
30-40kts from the southwest.

Southwest winds around 10kts for the overnight will continue
through frontal passage and associated shower/thunderstorm
activity Friday afternoon with winds shifting to the northwest
<10kts Friday night.

The greatest chances for strong thunderstorms will be
CON/MHT/PSM though all sites have the potential for lightning in
the 17-00Z time window.

Long Term...Any lingering showers should depart the region
early Saturday...with VFR conditions and northwesterly winds
10kts before winds diminish Saturday night with light winds/VFR
conditions Sunday through Tuesday.

&&

.MARINE...
Short Term...Southwesterly winds bring marginal SCA gusts today
along with 3-5` waves. Waves subside tonight as a cold front
crosses the waters shifting winds to the northwest...with
northerly winds expected to continue for the day Saturday.

Long Term...High pressure builds over the waters this weekend
before settling south of the waters early next week. Given this
setup, winds/waves are expected to remain below SCA levels
through the long term period.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ150-
     152-154.

&&

$$

ARNOTT