Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 250922
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
522 AM EDT Fri Jun 25 2021

.SYNOPSIS...
Weak low pressure will pass near the coast today. This will
bring scattered showers south of the mountains and relatively
cool temperatures will a lot of clouds around. Heat and
humidity builds over the weekend into next week with chances for
afternoon showers and thunderstorms, mainly in the mountains.
Heat indices will peak on Monday into the mid and upper 90s with
little signal for a cool down in the long term, especially
across southern New Hampshire.

&&

.NEAR TERM /TODAY/...
Impacts...Patchy dense fog possible for eastern portions of
western ME this morning.

520am Update...A quick update here to temperatures to account
for the latest observations and to update the areal extent of
the fog over eastern portions of western ME. No other changes at
this time.

Of immediate concern is developing areas of fog near Penobscot Bay
and inland portions of western Maine from Androscoggin County to
points north and east as seen on GOES imagery. Rockland recently
dropped to 1/4 mile for about an hour in one such area of
fog...so it stands to reason that 1/4 mile visibilities are
likely present in all of them. Current areal extent of the fog
precludes needing an advisory, but will continue to monitor
trends this morning.

Otherwise...cloud cover continues to slowly increase across the
region this morning as high clouds move in from the west and low and
mid-level clouds move in from the south. The low and mid-level
cloudiness is associated with an area of low pressure that is
currently centered just south of Long Island. The low will slowly
push north as the morning progresses, weakening as it does so.
Regional radar mosaic shows scattered showers over southern New
England, and these will push north into our region later this
morning. These showers should remain limited to coastal locations,
where a few hundredths of rainfall will be possible. Some of the
showers could briefly produce moderate rainfall rates. Precipitation
chances will diminish this afternoon as the low weakens and pushes
north out of the region.

The rest of the region will remain dry but under partly to mostly
cloudy skies. Highs will range from the lower 70s over much of
western ME to the upper 70s to lower 80s in interior locations of
NH.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Impacts...Patchy fog will be possible again tonight, primarily on
the coastal plain and the northern valleys.

Tonight should be rather quiet with the possible exception of a
stray shower on the Midcoast. Mostly cloudy skies are expected
across the region as lows drop into the upper 50s to lower 60s.
While I did not include any fog in the weather grids tonight, want
to highlight the possibility here. The best chances for fog will
likely be for those locations that see rainfall today, but think
that many locations on the coastal plain and the northern valleys
could see some patchy fog as well.

The well-advertised warming trend begins on Saturday as a warm front
moves through the region during the day. Highs will be noticeably
warmer, ranging from the upper 70s to the mid 80s. Afternoon showers
and thunderstorms will also be possible, primarily for northern and
western zones.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
A period of above-average summer heat starts at the beginning of
the long term period as deep layer ridging builds in from our
southwest.

A warm air regime Saturday night will be the leading edge of our
hot air mass. Enough forcing for ascent may be present to allow
for some shower and thunderstorm activity during the night,
especially in the mountains where the best ascent should occur.
Ridging continues to build aloft on Sunday and this will aid in
high temperatures reaching the 88-94 degree range depending on
location and if any lingering cloud cover occurs. Much of the
forecast area will remain dry on Sunday with the western ME
mountains possibly seeing a few afternoon thunderstorms
depending on the strength of the ridging by that point.

Dry and warm Sunday night with lows a few degrees either side of
70. Hot day on Monday with some potential for cooling on the
immediate coast. There is good agreement in the guidance for a
mid to upper 90s day with dewpoints in the upper 60s which
should be sufficient for a heat advisory for portions of the
forecast area. Not seeing much in the way of support for
thunderstorms even with some guidance suggesting that a subtle
trough will move though late in the day and during the evening
hours. We`ll have to keep an eye on that. In fact the 00z ECMWF
and GFS and several ensemble members move the trough through
Monday night which allows for dewpoint temperatures to be around
10F cooler on Tuesday than on Monday. If this occurs, it will
feel much better out there with much lower heat indices Tuesday
afternoon.

For Wednesday and Thursday there will be some question as to how
hot and humid it will be. A good portion of the guidance suite
at least temporarily moves the center of the mid and upper level
high farther south and east out over the Atlantic. This may
open the door for more pronounced short wave passages
potentially meaning better chances for precipitation and cooler
temperatures.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
Short Term...Low and mid-level cloudiness, along with some fog,
will allow for MVFR/IFR conditions at all terminals except for
LEB and HIE beginning this morning and continuing through the
day. Conditions will improve at MHT and CON by this evening, but
PSM/PWM/RKD/AUG will likely remain in MVFR/IFR into tonight.
Finally, stronger southwest winds on Saturday should bring all
terminals to VFR. HIE will have the best chance at brief
restrictions in showers and thunderstorms on Saturday.

Long Term...Mainly VFR conditions expected Saturday night
through Tuesday. However, with increasing moisture Saturday
night we may have to deal with low clouds and some fog,
especially on the coast.

&&

.MARINE...
Short Term...Showers and patchy fog will be possible over the
waters today, while areas of fog are expected over the waters
tonight. Winds and seas will remain below SCA criteria through
Saturday morning, but winds may begin to gust to 25 kt beginning
Saturday afternoon.

Long Term...A persistent south and southwest wind develops by
Saturday night which may bring winds and seas to SCA thresholds
for the Saturday night period. This likely continues into Monday
as the fetch will not change much. Areas of fog and haze are
possible as warm air moves over colder water.

&&

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

&&

$$

NEAR TERM...Watson
SHORT TERM...Watson
LONG TERM...Ekster


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