678
FXUS61 KGYX 131818
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
218 PM EDT Sun Jul 13 2025

.SYNOPSIS...
There is a chance of a few showers or a thunderstorm during
peak heating this afternoon and early evening, mainly in the
mountains. A cold front will near the region on Monday with
widespread showers and thunderstorms, some of which could
produce locally heavy rainfall. Drier weather returns Tuesday,
with heat and humidity building in through late week. Chances
for afternoon showers and thunderstorms return late week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Skies have thinned through the morning with a mostly sunny day
away from the immediate coast and portions of the White
Mountains.

Low stratus and fog is clinging to the land/water interface,
indicating the likely resurgence of low clouds as the afternoon
wanes. Expect one more night of foggy and low cloud conditions
tonight before cold front brings drier air behind it Monday.

Some instability has built over western areas today, but kept
shower chances on the lower end with the outside chance of a
rumble of thunder overnight.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Monday, the main concern will be heavy showers and
thunderstorms, again bringing enhanced rainfall rates and the
threat of localized flash flooding.

Moist airmass has been no stranger of late with a string of 00z
soundings at or above the 75th PWAT percentile (around 1.36"),
and a few cases above the 90th (around 1.6"). A break is around
the corner, but lies on the other side of a slow moving cold
front approaching Monday.

Northern New England will be positioned along the trailing end
of the cold front, below the apex pushing through central
Quebec. This tail segment has been consistently modeled slow,
and its velocity will allow a final pool of PWAT (upwards of 2")
to build ahead of the primary forcing. Combined with warm cloud
layers of 12-13 kft, and high freezing levels, precip
production/efficiency will be well represented.

Concern for flash flooding will be where these moisture
dynamics overlap supportive instability. Believe WPC`s Slight
and Marginal ERO outlines this corridor well. This is draped
across the western half of the CWA, including much of NH and
southwestern ME. With another night of stratus and fog tonight,
the periphery from the foothills west should see a more rapid
increase in daytime instability w/ less low cloud in the AM.
Another factor will be ample MUCAPE expanding eastward as the
day goes on. This should provide fuel for storms ahead of later
forcing to carry into otherwise stable surface layers through
late morning and the afternoon.

Resultant rainfall rates in stronger cells will likely fall
between 1-2" per hour. Should areas of training or backbuilding
take place in the absence of mismatched cloud layer vs. LLJ
velocities, would expect the outlined precip efficiency to
quickly manifest localized flash flooding.

While there is plenty going for this setup, there remain a few
barriers that limit coverage and greater confidence. First, is
the SBCAPE footprint and how quickly morning clouds thin. HREF
ceiling probabilities keep the Midcoast and Kennebec Valley
overcast through mid afternoon, and thinning will just be
occuring around noontime for the southern half of NH through the
ME foothills. There will be heavy reliance on lift from the
incoming front to initiate showers/storms NW of the mountains
where instability builds first. Second, will be the progressive
lift provided by the front. While slow, this should be enough to
keep deeper showers/storms moving vs. anchoring to terrain like
we saw the past few days. Current coverage is not enough to
warrant a Flood Watch for Flash Flooding at this time, but
scattered cases of flash flooding will be possible.

Shower and thunderstorm coverage wanes in the evening as daytime
heating is lost. This will keep Monday night mostly dry with
thinning skies west to east.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Pattern Overview: Tuesday and Wednesday look mostly dry as the
500mb pattern is zonal over the region with surface high
pressure in control. Thursday and Friday are more unsettled as a
pair of shortwaves look to cross the region. We may return to
dry weather for the weekend as global models suggest a flip back
to zonal flow aloft with surface high pressure nosing back into
the region.

Impacts and Key Messages:
* Hot and humid temperatures will make a return Tuesday,
  becoming cooler towards the weekend.

Details: Tuesday: High pressure noses into the region Tuesday
with subtle 500 mb height rises allowing 850 mb temperatures to
climb to around 17C. With mostly sunny skies and good mixing
this will amount to surface temperatures in the upper 80s and
low 90s south of the mountains, and low to mid 80s to the north.
We will be fresh on the heels of a frontal passage so dewpoints
won`t be overly oppressive, but even with them in the mid to
upper 60s temperatures will feel a couple degrees warmer. Clear
skies prevail Tuesday night but the dewpoints will keep low
temperatures in the mid to upper 60s south of the mountains and
in the low 60s to the north.

Wednesday and Thursday: Wednesday looks like the hottest day in
regards to actual temperature as shortwave ridging peaks,
allowing temperatures to climb a few degrees higher. Much of the
area south of the mountains likely ends up in the low 90s, with
upper 80s to the north. Dewpoints remain similar to Tuesday,
but with the warmer surface temperatures some locations may
reach heat index values around the mid 90s. Flow turns
southwesterly Wednesday night which will begin to drive up the
dewpoints and make for a warmer night, with many locations south
of the mountains only bottoming out around 70, and upper 60s to
the north. An approaching shortwave trough may bring showers to
New Hampshire and the western Maine mountains overnight. This
will also increase cloud cover keeping surface temperatures a
few degrees cooler Thursday, but the southwesterly flow acts to
increase dewpoints further. Much of the area likely sees
dewpoints in the low 70s which will make it feel very similar to
Wednesday with heat indices approaching the mid 90s south of
the mountains. The region will be sandwiched between frontal
boundaries with a shortwave trough moving through, so heating of
this moist airmass should lead to afternoon showers and
thunderstorms. CSU machine learning is already showing low
probablilites that some stronger storms are possible, so this
will be a good period to keep an eye on. Elevated dewpoints once
again keep low temperatures around 70 south of the mountains
and in the mid to upper 60s to the north.

Friday-Sunday: Global models are in pretty good agreement that
Friday features a frontal passage which would bring relief from
the humidity and kick start a cooling trend. As usual in these
situations the front will take some time to clear resulting in
southern zones still holding on to some heat and humidity. A hot
and humid air mass plus lifting from a front usually results in
more widespread thunderstorm activity, again CSU machine
learning suggests some stronger ones, but timing will be key and
it`s too far out in time to speculate on coverage. Will stick
with the afternoon hours being the best chance for thunderstorms
to develop. Behind this front we should see much more
comfortable dewpoints and temperatures for the weekend with high
pressure taking control and keeping things mostly dry other
than chances for pop-up showers and thunderstorms in the
afternoons.

&&

.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
Short Term...Ceilings will again thicken and lower tonight with
IFR to LIFR conditions when compounded with rebuilding fog.
Monday morning will see clouds thin west to east, but Midcoast
terminals like RKD and AUG may well stay IFR/LIFR through Monday
morning and early afternoon. SHRA and TS develop in the
afternoon for NH and western ME terminals. TS may contain
erratic winds and heavy downpours, causing local MVFR/IFR. These
dissipate after 00z, with conditions slowly improving towards
VFR overnight.

Long Term...VFR likely prevails on Tuesday and during the day
Wednesday. Increasing moisture Wednesday will likely lead to fog
development overnight and again overnight Thursday. Showers and
thunderstorms are also possible Thursday afternoon, but outside
of these ceilings should remain mostly VFR.

&&

.MARINE...
Short Term...Conditions remain below SCA. Fog and marine stratus
will continue to hamper visibility for a good portion of the
coastal waters and harbors. A cold front will approach the
waters Monday afternoon, passing overnight into Tuesday.

Long Term...Favorable boating conditions continue as the waters
remain on the periphery of the Bermuda High. Some showers and
thunderstorms may move over the waters late week with a frontal
passage. Increasing southwesterly flow midweek may also lead to
areas of fog.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.

&&

$$

NEAR/SHORT TERM...Cornwell
LONG TERM...Baron