129
FXUS61 KGYX 230245
AFDGYX
Area Forecast Discussion
National Weather Service Gray ME
1045 PM EDT Sun Jun 22 2025
.SYNOPSIS...
Dangerous heat and humidity build early this week before
temperatures cool back down towards seasonable levels mid to
late week. Unsettled weather expected at the end of the week and
through the weekend.
&&
.NEAR TERM /UNTIL 7 AM MONDAY MORNING/...
1045 PM Update...Minor update to reflect observational trends.
Impacts and Key Messages:
* No significant impacts expected
Hot, breezy, and dry conditions will continue into the evening
before we get some relief overnight. The Heat Advisory today has
been maintained as current apparent temperatures within it are
around 96F. Some weak returns are showing up on radar in the
foothills, but mid level dry air is likely keeping anything from
reaching the surface. The exception has been Mt. Washington
where they have been occasionally reporting showers.
Temperatures and dewpoints will take a diurnal dip which will
help give us one more comfortable night before oppressive heat
arrives. Lows north of the mountains look to end up in the mid
to upper 50s, with areas to the south in the mid to upper 60s.
&&
.SHORT TERM /7 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Impacts and Key Messages:
* Dangerous heat begins to build in as areas of southern New
Hampshire will see heat indices around 105F Monday, with of
the rest of the state and parts of interior western Maine
seeing heat indices of around 95F.
Surface high pressure moves overhead Monday with the 500mb high
continuing to build over the region. 850mb temperatures look to
warm upwards of +20C which, with the halfway decent mixing
forecast soundings depict, will continue to support surface
temperatures near or exceeding 90F for areas away from the
coast. The higher dewpoints near 70 degrees will be primarily in
southern New Hampshire which will push them toward apparent
temperatures exceeding the 105F threshold. There is some
suggestion in the guidance that maybe some slightly drier
dewpoints get mixed down with the continued northwesterly flow,
but with apparent temperatures exceeding 100F it is not worth
splitting hairs. For this reason went ahead and issued the
Extreme Heat Warning for southern New Hampshire where confidence
is highest that they will meet or exceed that threshold. The
rest of southern New Hampshire and even into southwestern Maine,
away from the coast, will still see some oppressive heat with
indices exceeding 95F, but an advisory will be sufficient there.
The New Hampshire and Maine coast will be spared by a seabreeze
that will keep apparent temperatures comfortable. The rest of
Maine will be spared by the comparatively cooler surface
temperatures, in the upper 80s, but heat indices will still be
around 90 degrees which is still potentially dangerous. I want
to stress that weather or not you are in a warning/advisory or
not, caution should be taken when outdoors during this period of
oppressive heat.
Temperatures won`t cool down much Monday night, before heating
up again the next day so the current warning area will run
through the night due to warm overnight temperatures being a
contributing factor to heat stress. Low temperatures will
generally be in the low 70s in the southern half of New
Hampshire, with upper 60s in the northern half and throughout
western Maine. This heat has potential to break daily records
for max daytime temperatures (see climate section below) and
possibly warm low temperatures.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
1045 PM Update...A weak cold front sagging south through the
area Tuesday evening may provide enough forcing to trigger a few
thunderstorms. Latest CAMs suggest there will be sufficient CAPE
and modest shear that may allow for some storms to become
strong to severe with the threat for storms diminishing through
the first half of Tuesday night. High pressure building over
southeast Canada will gradually advect cooler and drier air into
the region Wednesday and Thursday, although Wednesday will
remain quite warm with highs in the 80s to low 90s. A stationary
front settles south of New England the second half of next week
that will bring chances for showers Thursday into the weekend.
Previously...
Impacts:
*Dangerous and extreme heat expected Tuesday. Heat Index values
may exceed 105F across locations south of the mountains. Heat
index values may approach 100F north of the mountains.
*Thunderstorms are possible Tuesday evening, a few may become
strong.
*Unsettled and cooler weather towards the end of the week,
continuing through the weekend.
Details...Tuesday:
There are many moving parts to the forecast that will lead to
extreme heat on Tuesday.
Typically, extreme heat days in New Hampshire and Maine require
clear skies, offshore/N/NW/Westerly flow, anomalously high
500mb heights and anomalously high temperatures at the top of
the mixed layer, and high mixed layers as well. There is high
confidence that most, if not all of the following will come
together on Tuesday.
Some light westerly winds over the mountains will allow for the
mixed layer to lift over western Maine. The higher mixed layer
should allow for temperatures across interior western Maine to warm
substantially through the day Tuesday. An area of high dewpoints
will shift eastward as well, allowing for a very unusually hot and
humid day across much of Maine. Locations south of the mountains
should see temperatures in the upper 90s. A possible exception here
would be places in the coastal Midcoast, such as Rockland and
Boothbay. Still these locations too look to be anomalously hot,
looking at mid-80s there. Opted to expand the active Extreme
Heat Watch to the coast, as guidance suggests heat index values
should meet criteria even in most of the coastal zones.
A few clouds associated with a cold front
to the north and light upslope flow should keep temperatures a hair
cooler north of the mountains, though relief will be minimal and
Heat Advisories will still likely need to be issued. Temperatures
north of the mountains look to be in the low 90s in the valleys and
80s at higher elevations.
A weak cold front moves through the area Tuesday afternoon. Timing
is uncertain, some model guidance has the front moving through
earlier in the afternoon. If this is the case, The front could help
cool off temperatures a little. However, the consensus appears
to favor a later passage of the front, allowing for the
aforementioned heat to build through the day. If storms develop,
there is potential that they could be strong, with heavy rain,
hail and winds being the primary threats Tuesday evening. The
SPC has issued a marginal risk over most of northern NH and NW
Maine.
Wednesday and onwards:
Afterwards, the ridge boosting out temperatures shifts west as
an upper-level low over the Canadian Maritimes moves southward.
This shift should allow for temperatures to sharply drop off
through the remainder of the week, with upper-80s likely on
Wednesday, and low 70s on tap for the end of the week. The
cooler temperatures will arrive with unsettled weather on
Friday, continuing through the weekend.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Short Term...VFR will prevail at most terminals through
tonight, with the exception being valley fog that may bring
about visibility restrictions at LEB and HIE. Gusty winds will
taper off around 23Z as well. Fog will burn off quickly Monday
morning and then VFR will then be the prevailing condition
through Monday night.
Long Term...VFR expected through the day Tuesday, some
restrictions possible as a cold front moves through towards the
end of the day. VFR expected through Thursday as mostly clear
skies continue. Lower restrictions are possible on Thursday and
Friday as unsettled weather may move through the area.
&&
.MARINE...
Short Term...High pressure building over the waters will keep
wind gusts and seas below SCA thresholds trough Monday night. A
sea breeze is expected to develop Monday afternoon.
Long Term...Southwesterly winds at 7-15kts expected Tuesday
morning. Winds become variable at 7-12kts through the rest of
the week. Seas will be 2-4ft on Tuesday, and through the
remainder of the week.
&&
.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...
ME...Heat Advisory from 11 AM to 8 PM EDT Monday for MEZ012-033.
Extreme Heat Watch from Tuesday morning through Tuesday
evening for MEZ012>014-018>028-033.
NH...Heat Advisory from 11 AM to 8 PM EDT Monday for NHZ002>006-009-
010-013.
Extreme Heat Watch from Tuesday morning through Tuesday
evening for NHZ004>006-009-010-013-014.
Extreme Heat Warning from 11 AM Monday to 8 PM EDT Tuesday for
NHZ007-008-011-012-015.
MARINE...None.
&&
$$
NEAR TERM...Baron/Schroeter
SHORT TERM...Baron
LONG TERM...Palmer