115
FXUS61 KGYX 161332
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
932 AM EDT Wed Jul 16 2025

.SYNOPSIS...
Hazy, hot, and humid conditions are expected again today.
Widespread high temperatures in the upper 80s to lower 90s will
occur along with high humidity. It will make many areas over
southern New Hampshire and parts of southwestern Maine feel more
like 95 to 100 degrees. Relief will be on the way in the form of
a cold front Thursday. However one more day of sticky weather is
expected ahead of that boundary. Showers and thunderstorms will
be possible Thursday, and depending on timing some of those
could be strong to severe. And while rainfall will not be
widespread, if it does rain it will likely be torrential. Cooler
and drier weather will arrive Friday and continue into the
weekend.

&&

.NEAR TERM /THROUGH TODAY/...
930 AM Update...Minor changes to temperatures as we are already
off to a warm start this morning as clear skies are aiding in
efficient mixing. This resulted in max temperatures a degree or
two warmer in spots, but in the grand scheme of things this
isn`t a big change as a hot and humid day is on pace.

550 AM Update...Minor changes to reflect latest observational
trends.

Previous discussion...While the bulk of the marine fog remains
across southern New England and the outer edges of the Gulf of
ME...some areas have developed along the coast mainly north of
Casco Bay. This while gradually expand thru sunrise. Inland some
patchy valley fog is possible after recent rains...but
otherwise clear conditions thru morning.

Today will be another hot and humid day. The primary concern was
heat index values. There are model differences...even with this
short lead time...with the amount of mixing today. However more
model guidance mixes out than not...so I opted to blend a little
of this guidance into the NBM to reduce the coverage of 70+
dewpoints. The result is some slight expansion of head index
values in the 95 to 100 degree range. I added the rest of
southern NH and included Merrimack and interior Cumberland
counties to the existing Heat Advisory.

The latest HRRR guidance some near surface smoke will linger
over the area this first half of the day. It will tend to clear
out/move northeast thru the day. Given the levels forecast I
included haze in the grids. It will be a largely dry day...and
if any convection were to occur it would likely be very isolated
and tied to heating of the higher terrain.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
Embedded short waves within a broad trough over eastern North
America will bring chances for showers and thunderstorms Thursday.
The majority of model solutions bring a leading short wave across
northern New England Thursday morning. Behind this wave, a trailing
short wave leads to a surface low tracking through the St Lawrence
Valley Thursday afternoon with the attendant cold front crossing
Thursday night. It will be warm and humid Thursday with highs into
the 80s and dewpoints in the low 70s. Depending on cloud cover, some
areas south of the mountains that see sunshine could warm into the
low 90s which would bring heat indices into the mid 90s.

The timing and evolution of the leading short wave will modulate the
convective parameter space ahead of the cold front and recent CAM
runs offer a variety of solutions. Some solutions suggest the
leading short wave will arrive late enough to act upon an unstable
and moisture rich airmass that would result in scattered storms that
could be strong around mid day into early afternoon. These solutions
suggest the atmosphere will not quite recover ahead of the cold
front along with the front crossing overnight with little fanfare.
Other solutions suggest less activity with the leading short wave
and the cold front crossing sooner and into an unstable environment
that could produce strong to severe storms Thursday evening. SPC has
placed much of the area in a Marginal Risk for severe storms which
seems reasonable given the amount of instability and deep layer
shear increasing with the arrival of the cold front. In additional
to the Marginal Risk for severe storms, PWATs will be high with
ensemble means ranging from 1.75 inches across the north to over 2
inches across the south. Storm motion looks to be swift, while CAMs
suggesting repeat rounds of storms would bring an isolated flash
flood risk.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Long Term Update...No significant changes with the latest NBM for
the extended period. Models continue to suggest the cold front will
be pushing offshore Friday morning with drier air arriving on steady
NW winds. High pressure builds in Friday and crests over the region
Saturday for fair weather, low humidity, and highs in the 80s.

Previous discussion:
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.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Short Term...Areas of IFR are developing again this
morning...mainly from Casco Bay northward along the coast. This
will primary affect RKD...but some IFR or lower conditions may
work into AUG. Additionally inland valley fog is possible at LEB
and HIE. Conditions return to VFR after sunrise. Areas of IFR or
lower will once again develop after sunset tonight and linger
thru Thu morning.

Long Term...Stratus/fog scatter out Thursday morning, then
showers and thunderstorms with heavy rain could bring local IFR
conditions Thursday. However coverage of showers and storms is
low confidence. Improving to VFR under sunny skies Friday and
mainly VFR thereafter.

&&

.MARINE...
Short Term...Areas of fog this morning along the coast from
Casco Bay northward. Winds and sea will remain below SCA
thresholds. Fog will tend to linger over the coastal waters thru
Thu until a cold front can bring some drier conditions and
offshore winds.

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.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Heat Advisory until 8 PM EDT this evening for MEZ018-019.
NH...Heat Advisory until 8 PM EDT this evening for NHZ008-010-011-
     015.
     Heat Advisory until 8 PM EDT this evening for NHZ012-013.
MARINE...None.

&&

$$

NEAR TERM...Baron/Legro
SHORT TERM...Schroeter
LONG TERM...Schroeter
AVIATION...Legro
MARINE...Legro