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224
FXUS61 KGYX 212346
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
746 PM EDT Sat Jun 21 2025

.SYNOPSIS...
A disturbance will approach from the west early Sunday morning,
bringing the chance for scattered showers and strong
thunderstorms capable of producing damaging winds. A few
lingering thunderstorms are then possible later Sunday
afternoon. Dangerous heat and humidity build early next week
before temperatures cool back down towards seasonable levels mid
to late week.

&&

.NEAR TERM /UNTIL 7 AM SUNDAY MORNING/...
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745 PM Update...The convectively induced short wave associated
with an MCS that rolled across the northern Great Lakes this
morning is tracking east across Ontario as of this writing.
There have been earlier rounds of convection ahead of this wave
with latest radar showing scattered storms northeast of Lake
Huron. Latest 18Z CAMs and recent runs of the HRRR offer mixed
solutions into the organization of this current area of
convection as it tracks ESE across the Northeast through Sunday
morning. The NAMNest and RRFS suggest convection will lack
organization leading to weaker storms while the HRRR suggests
there will be potential for an MCS to maintain itself as it
reaches northern VT and northwest NH around 4 am. This
convection is then forecast to spread south and east reaching
southern NH and coastal Maine around 6 am. Overall forecast
thinking has not changed much and SPC`s latest outlook remains
mostly unchanged except for extending the Slight Risk for severe
storms into far northwest NH. Another variable that has started
to emerge is the signal for period of gusty winds associated
with a possible wake low across southern NH. The last two runs
of the HRRR show gusts to around 45 mph between 8 am and 10 am.
Will continue to monitor trends while the key message will be
there remains the threat for strong to severe wind gusts with
convection across much of NH and western Maine starting from 4
am across the NW to around 7 am across southern NH and coastal
SW Maine.

Previously...

Quiet weather this evening with just a few high clouds
encroaching into the west and winds generally going light an
variable. Our focus is centered on a progressive shortwave and
resulting MCS will ride the northern periphery of the upper
level ridge overnight, following along a frontal boundary draped
over New England. It still isn`t locked in on exactly where the
feature will track, but SPC has placed much of the northeast
including GYX into a marginal risk. CAMs favor the system
reaching our CWA, but as a weakening system as it dives
southeast from Ontario. However, there remains low confidence in
these nocturnal MCS`, and if it maintains some strength then
storms could easily pull some strong damaging winds to the
surface. The 12 HRRR is the most bullish suggesting 30-40kts of
0-6km shear, and mid- level lapse rates above 7 degrees per km,
resulting in storms with the potential for 50kt winds or greater
between 5-8 AM, mainly in NH. Best case and most likely
scenario is this feature weakens into scattered showers and
thunderstorms with some pockets of heavy rain, but worst case
could result in warning level conditions. Moisture pooling with
this feature will also support some heavy rainfall, but due to
the progressive nature of the feature there shouldn`t be more
than 1" for any given area, but repeat activity could quickly
accumulate and become problematic. WPC has a marginal ERO for
for most of NH and far w ME. Have added gusty winds and heavy
rain for all but eastern zones given the lower confidence on the
track being that far east.
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&&

.SHORT TERM /7 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
The remnants of any early morning MCS should clear out fairly
quickly, leaving some breezy conditions but generally clearing.
Humidity makes its return with dewpoints shooting up into the
60s and lower 70s in S NH. This is when the focus transitions to
the much advertised heat that will linger through Tuesday.
Temperatures will climb into the upper 80s to mid 90s. Can`t
rule out a few showers popping up due to increasing instability,
but don`t see much of a trigger to overcome the building
subsidence overhead.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
Pattern Overview: The focus of the long term will be
anomalously high pressure allowing for dangerous heat and
humidity to build into the region through Tuesday. It looks like
the ridge begins to break down on Wednesday with a surface cold
front bringing relief from the oppressive heat and humidity.
This will make for a more unsettled pattern late week as 500mb
becomes more zonal with some hints at shortwave troughs as well.

Impacts and Key Messages:
* Dangerous heat and humidity is expected Monday and Tuesday.
  An Extreme Heat Watch has been issued for areas south of the
  mountains and away from the coast where heat indices have
  higher confidence to be around 105F.

Details: Monday: Monday will be the first of our very hot days
as an anomalously high ridge allows 850mb temps to climb upwards
of +22C. Current forecast soundings don`t show mixing quite to
that level, but it looks close so this would equate to actual
temperatures in the upper 80s to mid 90s. Locally higher surface
temperatures in the upper 90s look likely along the Connecticut
River Valley. Of course with dewpoints in the upper 60s and low
70s, the bigger concern will be with apparent temperatures. It
is worth noting that the higher dewpoints in the low 70s are
more concentrated in New Hampshire Monday along with the higher
temperatures in the mid to upper 90s in the southern half of the
state. For this reason the Extreme Heat Watch remains over just
the southern half of New Hampshire where heat index values of
105F are most confident. The other thing to mention is that we
won`t be seeing much in the way of relief overnight as
temperatures remain in the 70s. Warm overnight temperatures can
also contribute to heat related illness so the the Watch runs
right through the night. It is recommended to make
preparations/plans now for this extended duration heat.

Tuesday and Wednesday: Heat continues Tuesday with higher
dewpoints shifting east as well as more efficient mixing up to
850mb which will bring Western Maine into the Extreme Heat
threat, the areas south of the mountains and away from the coast
anyway. Actual temperatures in the mid to upper 90s inland
could feel more like 100- 105F+. Far southern New Hampshire,
where actual temperatures may hit the triple digit mark, could
even see heat indices approach 110F. For this reason the Extreme
Heat Watch will remain extended into inland western Maine for
Tuesday afternoon with southern New Hampshire also remaining
unchanged through Tuesday. I want to emphasize that areas
outside of the watches are expected to see heat indices of 90+
which are still dangerous. Relief will come first to northern
zones as a cold front enters the area Tuesday evening. This will
bring about lower dewpoints and temperatures along with a
chance for some showers and thunderstorms. It is looking like
areas south of the mountains wont be as lucky as the front takes
its time sinking southward. Low temperatures in these locations
likely remain in the upper 60s to around 70. The front looks to
clear the area some time Wednesday morning bringing the relief
of lower dewpoints area wide. While Wednesday will still be
warm, in the 80s, it comparatively will feel like a pleasant
summer day. Low temperature dip back into the 50s and low 60s
Wednesday night, which will also be welcomed.

Thursday-Saturday: The pattern becomes more unsettled late week
as our ridge breaks down and global models advertise a more
troughy and relatively cooler trend. Based on NBM consensus we
are looking at chances of showers each day with high
temperatures in the 70s.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Short Term...VFR prevalent across the region under the
influence of high pressure. An area of showers and thunderstorms
will move into the region overnight and early Sunday, bringing
periods of MVFR ceilings, and IFR in any thunderstorms. The main
concern is LLWS with a decent low level jet around 40-50kt.
Only have TSRA mentioned for NH terminals given low confidence.
Weather will improve behind the shortwave, with VFR conditions.
LLWS will linger through late morning before mixing brings
breezy conditions to the deck.

Long Term...VFR will be the prevailing condition through
Thursday, with a slight chance for afternoon showers each day.

&&

.MARINE...
Short Term...Winds will increase overnight out of the south as
a wave of low pressure move by to our north. This will bring in
small craft conditions with gusts around 25kt. High pressure
building in behind this feature will quickly dampen winds and
seas for Sunday night. A beach hazard statement is issued for
paddle craft due to cold water temperatures.

Long Term...High pressure over the waters will keep wind gusts
and seas well below SCA criteria through Thursday. Afternoon
seabreezes are likely to develop each afternoon as well.

&&

.CLIMATE...
Anomalously high pressure will allow for dangerous heat and
humidity to build into the region. This heat could potentially
be record breaking for Monday (6/23) and Tuesday (6/24). Below
are the records for our climate sites

  Site             Record June 23rd    Record June 24th

Portland Jetport    91 (1983)              93 (1976)
Augusta             89 (1999)              93 (1963)
Concord             94 (2020)              95 (1980)

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Extreme Heat Watch from Tuesday morning through Tuesday
     evening for MEZ012>014-018>022-033.
     Heat Advisory from 11 AM to 8 PM EDT Sunday for MEZ018-023.
NH...Heat Advisory from 11 AM to 8 PM EDT Sunday for
NHZ007-008- 010>015. Extreme Heat Watch from Monday morning
through Tuesday evening for NHZ005>013-015. MARINE...Small Craft
Advisory from 7 AM to 8 PM EDT Sunday for ANZ150- 152-154.
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&&

$$


NEAR TERM...Jamison/Schroeter
SHORT TERM...Jamison
LONG TERM...Baron