400
FXUS61 KGYX 232322
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
722 PM EDT Mon Jun 23 2025

.SYNOPSIS...
Dangerous heat and humidity across parts of the area peaks on
Tuesday. Some of the highest temperatures of the last several
years will occur in many places. Readings will climb well into
the 90s and may even approach 100 degrees in some areas. It will
be 10 degrees cooler Wednesday but that will still be hot in
places. The relief finally arrives Thursday in the form of a
backdoor cold front. The cooler air will move in on northeast
winds and bring temperatures back down into the 70s. However
with the cooler weather will come higher chances for showers
into the weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

7:15pm Near/Short term Update... The most notable change with
this update was to add coastal Rockingham, York, and Cumberland
counties to the extreme heat warning for Tuesday. The immediate
shoreline and beaches may escape the worst of the heat part of
the day, but all the main population centers in these zones
should plan to see heat indices in the 105-107 degree range
tomorrow. Based on the performance of the HRRR and 3km NAM for
today, and a developing downslope wind direction tomorrow there
was reason to believe that temps would end up slightly warmer
for tomorrow. There hasn`t been a major change to the forecast
itself, mostly just a tweak of about 1-3 degrees in the forecast
heat indices, but it was enough to push these areas into the
Extreme Heat Warning criteria.

Otherwise, temperatures are on track to make for a very warm
night in most areas. Temperatures remain in the mid 90s across
parts of southwestern and south central New Hampshire at this
hour where the Extreme Heat Warning runs through the overnight,
with most of the night experiencing temperatures in the 80s
before lows touch the upper 70s around sunrise.

Previous...

Impacts and Key Messages:
* Warm overnight temperatures ranging from the mid-60s to low
  70s may add to heat stress built up after a hot day.

Today`s heat headlines are verifying well with many weather
stations in the warning area reporting a heat index of 105F with
abundant heat index readings of 95+ south of the mountains. A
weak seabreeze is keeping the coast a bit cooler, but dewpoints
jumped up there so locations are still reporting heat indices
85-90F. An extensive cumulus field has developed across the area
and hi-res guidance continues to want precipitation to fall out
of them, but I continue to believe that it`s way too dry for
that so I have maintained a dry rest of the day and night. The
only place where this may not be true is north-central Somerset
County where ongoing convection in Ontario and Quebec may sneak
in early on tonight. With the very dry air aloft lapse rates are
near 7 C/km so there is a non-zero chance that if a stronger
storm does move into the area it could produce strong winds. For
this reason SPC does have a Marginal severe risk for that area.
We really see any relief from the heat overnight as low
temperatures only end up in the upper 60s to low 70s. With
continued high dewpoints this will feel like the mid to upper
70s for much of the area. These kind of apparent temperatures
overnight can add to heat stress that has built up from the
previously hot day, so staying cool and hydrated when out and
about will remain the case through the night.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Impacts and Key Messages:
* The hottest temperatures of the season combined with high
  dewpoints will make for dangerous apparent temperatures around
  105F for inland areas south of the mountains. Even the coast
  may see apparent temperatures close to 100F.

With temperatures reaching 90F in central and southern New
Hampshire this past Sunday, this will be the final day of an
official heatwave. For everywhere else this will be the second
of two very hot days. Surface high pressure shifts eastward
tomorrow, but the 500mb ridge will continue to build overhead
sustaining our 20C+ 850mb temperatures and dewpoints around 70F.
Forecast soundings continue to suggest some mixing down of
drier air which may drop dewpoints a degree or two in some
locations, but with this efficient mixing also bringing about
higher surface temperatures, apparent temperatures are still
going to be very close to Extreme Heat Thresholds. With this
being the first heat event of the season I didn`t want to split
hairs between 103 and 105 for advisory versus a warning. I used
this same methodology yesterday and its working out well so
Extreme Heat Warnings are sufficient for most inland areas
tomorrow as confidence is high on them getting very close if not
meeting or exceeding 105F. For the coastline and areas south of
the mountains , confidence is high that they will see apparent
temperatures 95F to around 100F, so issued Heat Advisories for
those locations. For everyone the message remains the same, it`s
going to be HOT! It is important to be prepared, especially if
you plan on being outdoors. Stay cool, hydrated, and know the
signs of heat related illness.

While heat remains the focal point of tomorrow, the frontal
boundary that will be on its way to bring us relief could also
be the forcing for some convection Tuesday evening. Confidence
in coverage at this time is low due to the abundance of dry air
that will be a limiting factor, but looking at current modeled
timing of the front I would think any convective activity would
be north of the mountains so I limited PoPs and thunder to this
area. The reason this could be notable is that the dry air aloft
also works to improve lapse rates so anything that does develop
would have the potential to produce strong downburst winds. SPC
maintains a Marginal severe risk for our area to cover this
potential.

Tuesday night may still feel a bit sticky especially south of
the mountains as it takes some time for the frontal boundary to
work through, but dewpoints will be on the downward trend. Lows
look to end up in the low to mid 60s north of the mountains and
upper 60s to low 70s to the south.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Key Message: Heat breaks midweek as a backdoor cold front
provides some relief and return to more seasonable temps.

Impacts: After one more very warm day Wed...no significant
weather impacts are anticipated.

Forecast Details: Ridge axis will tend to retrograde west thru
the end of the work week. This will allow heights to lower
across the Canadian Maritimes and set up the potential for
backdoor cold front to provide some relief from the heat.

At least Wed we should still see very warm temps across the
local area. While much cooler than Tue...some low 90s and upper
80s readings appear likely...especially across southern areas
well ahead of any backdoor boundary. Dewpoints are not
expected to be as high...so apparent temps will remain in the
low to mid 90s.

The true relief will arrive Thu. With the front thru the area
temps will be back in the 70s. This will also come with a little
more in the way of cloud cover and threat of
showers...especially near the front itself.

For the rest of the period we remain on the northern edge of the
ridging. This will place us outside of the real heat but near
the so called ring of fire. Convective episodes will be expected
to develop over the Plains and roll eastward along the periphery
of high pressure. Some decaying remnants will threaten the area
at times...so much of the extended will feature some PoP. The
highest chance will come with a more coherent forcing
mechanism...so that will likely have to wait until the next
passing S/WV trof over the weekend.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
Short Term...Fog is less confident tonight, but did want to
hint at patchy development at the valley terminals tonight.
There is also a signature that some marine fog/low stratus may
develop and move into PWM and RKD, but again confidence is low.
If anything does develop it would mix out pretty quickly Tuesday
morning, with VFR prevailing the remainder of the day. A
thunderstorm near HIE is possible Tuesday evening.

Long Term...Largely VFR conditions expected in the extended. A
backdoor cold front will bring relief from the hot weather but
bring back a chance of showers. Local MVFR or lower is possible
in any showery weather...but chances are not particularly high
at this time.

&&

.MARINE...
Short Term...High pressure moving over the waters will keep
wind gusts and seas below SCA criteria through Tuesday night.
The seabreeze is expected to fail tomorrow, so expect southwest
flow over the waters.

Long Term...Winds and seas expected to remain below SCA
thresholds. Behind a backdoor front Wed into Thu a steady
northeast breeze may pick up...but at this time 25 kt gusts are
not anticipated.

&&

.CLIMATE...
Anomalously strong high pressure will continue dangerous heat
and humidity into Tuesday. Record breaking temperatures remain
possible Tuesday (6/24). Below are the records for our climate
sites:

  Site                 Record June 24th

Portland Jetport           93 (1976)
Augusta                    93 (1963)
Concord                    95 (1983)

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Heat Advisory until 8 PM EDT this evening for MEZ012-033.
     Extreme Heat Warning from 11 AM to 8 PM EDT Tuesday for
     MEZ012>014-018>024-033.
     Heat Advisory from 11 AM to 8 PM EDT Tuesday for MEZ025>028.
NH...Heat Advisory until 8 PM EDT this evening for NHZ002>006-009-
     010-013.
     Extreme Heat Warning from 11 AM to 8 PM EDT Tuesday for NHZ006-
     009-010-013-014.
     Heat Advisory from 11 AM to 8 PM EDT Tuesday for NHZ002>005.
     Extreme Heat Warning until 8 PM EDT Tuesday for NHZ007-008-011-
     012-015.
MARINE...None.

&&

$$


NEAR TERM...Clair
SHORT TERM UPDATE...Clair
SHORT TERM...Baron
LONG TERM...Legro