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317
FXUS61 KGYX 151802
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
202 PM EDT Tue Jul 15 2025

.SYNOPSIS...
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Surface high pressure is providing quiet weather with the exception
of morning and marine fog for the next few days. Daytime
temperatures in the 80s and 90s will produce high heat indices in
the mid 90s for some areas. Unsettled weather returns Thursday with
scattered to numerous showers and thunderstorms. This will be
followed by cooler and drier conditions Friday into the weekend.
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.NEAR TERM /THROUGH TONIGHT/...
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Impacts and Key Messages:
* Warm overnight apparent temperatures in southeastern New
  Hampshire will add to any heat stress accumulated today.

Daytime heating has led to some cumulus development across the
area, but dry mid level air should preclude any chance of
showers. The exception may be later this evening in far southern
New Hampshire where seabreeze convergence along a stalled
frontal boundary may tip off some brief light showers. This is
suggested in most of the hi-res models, so introduced low chance
PoPs to the forecast. Otherwise, clear skies will prevail
overnight allowing temperatures to drop into the mid to upper
60s south of the mountains and into the low 60s to the north.
Humidity will remain high overnight in southeastern New
Hampshire which will add to any heat stress accumulated today,
therefore extended the heat advisory to run overnight.
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.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
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Impacts and Key Messages:
* Heat indices will climb in to the mid to upper 90s in
  southeastern New Hampshire and far southwestern Maine, and low
  90s in many inland locations south of the mountains.

Wednesday will feature mostly sunny, but hazy skies as ridging
peaks overhead. This ridge will keep smoke elevated and mostly
out of our area once again, but the haze will be evident.
Forecast soundings suggest deep mixing with ample dry air in the
mixed levels. This would act to bring dewpoints down a bit
during the day and therefore keep many locations short of Heat
Advisory criteria. Therefore, have only expanded the Heat
Advisory slightly as confidence remains high in southeastern New
Hampshire and far southwestern Maine seeing heat indices in the
mid to upper 90s. Other inland locations still stand to see
heat indices in the low 90s, so heat safety should still be
considered when outdoors advisory or not. Areas north of the
mountains should be a little better off with the lower
dewpoints, and the coast should see a seabreeze develop, so both
of these areas likely only see temperatures and heat indices in
the upper 80s.

The ridge begins to break down Wednesday night as a shortwave
trough approaches from the west. This will increase clouds
overnight and even introduce a low chance for some light
showers, and maybe even a rumble of thunder, western zones late
evening and then across the area heading toward sunrise
Thursday. The increased cloud cover and elevated dewpoints will
result in a warm night south of the mountains with temperatures
only falling into the upper 60s and low 70s. Northern zones will
fall into the low to mid 60s. This increased low level moisture
likely results in fog development overnight as well.
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&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
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Key Messages

 - Scattered storms with heavy rainfall Thursday

 - Cold front Friday followed by less humidity and dry conditions

 - Seasonal temperatures for the weekend with cool nights

The ridge that has brought hot conditions across much of the
area on Tue/Wed will begin to break down Thu as a shortwave
enters the area from the NW. As a result, a surface low and cold
front will move slowly through the region, aiding in the chance
of showers and thunderstorms during the afternoon and evening
hours. Moisture out ahead of the front will be plentiful with
high PWATs and 70+ dewpoints. This high moisture, coupled with
moderate instability and deep layer shear, could lead to an
isolated strong storm or two as well as a chance for heavy rain
and localized flooding. Storm coverage looks highest over
northern NH and ME, closer to the front. Also worth noting is
the continued chance for high temperatures, and especially heat
indices, on Thursday. Despite increased cloud coverage leading
to lower daytime highs when compared to Wednesday, the
previously mentioned dewpoints could contribute to heat indices
over 90, especially along the southern coastal plain region
where clouds will be fewer.

The front should finally clear the area on Friday, ushering in
drier nw flow. Gustier winds are possible on Friday as 30kt
boundary layer could mix down to the surface, leading to gusts
of 20-30mph. This would lead to rough seas and boating
conditions, particularly in the northern Lakes Region. This
drier airmass and period of offshore flow will also decrease the
likelihood of sea fog, which has been prevalent over the last
few days. High pressure coupled with zonal flow aloft will
continue to usher in drier and cooler conditions throughout the
rest of the weekend and into early next week. Some embedded
features within the flow could spark a few showers and
thunderstorms. However due to the subtleness of these features,
confidence is low in the timing.
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&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
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Short Term...Terminals that saw IFR ceilings and visibilities
last night will likely see them again tonight. Similarly,
improvement to VFR should happen shortly after 12Z Wednesday.
Fog and low ceilings are likely once again Wednesday night as
well. No significant wind gusts or low level wind shear
expected.

Long Term...Stratus/fog possible again on Thursday morning,
then showers and thunderstorms with heavy rain could bring IFR
conditions Thursday, then improving to VFR under sunny skies
Friday. Mainly VFR thereafter.
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&&

.MARINE...
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Short Term...Winds and seas will remain below SCA conditions
through Wedensday night. Southwesterly flow will allow areas of
fog to develop tonight and again Wednesday night.

Long Term...Finally looking at some erosion of the persistent
sea fog with the frontal passage on Friday. NW flow will make it
across the coastal waters allowing in drier air, which will
persist into Saturday. Return flow will slowly bring in more
humid conditions, which could bring fog back later in the
weekend. Seas will be generally 1-3`, with some choppier seas on
Friday post-frontal. Winds will be out of the S for much of the
forecast, with the NW flow expected behind the front Friday
where winds could gust to 20kt. No notable swells, though
starting to pick up on some SE 12+ sec (<0.5`) later in the
model guidance.
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&&

.GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Heat Advisory from 11 AM to 8 PM EDT Wednesday for MEZ018.
NH...Heat Advisory from 11 AM to 8 PM EDT Wednesday for NHZ010.
     Heat Advisory until 8 PM EDT Wednesday for NHZ012-013.
MARINE...None.
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&&

$$

NEAR/SHORT TERM...Baron
LONG TERM...Venarsky
MARINE...Jamison