South Portland, Maine 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

220
FXUS61 KGYX 121846
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
246 PM EDT Tue Aug 12 2025

.SYNOPSIS...
Hot weather continues through Wednesday before a cold front
approaches into Thursday. The slow approach will allow for
another warm day Thursday, but not as hot. There will be
scattered thunderstorms with the front, some of which may be
strong. However widespread rains are unlikely and most locations
will see little aid to growing deficits. The weekend looks to
be dry at this time with a warming trend possible by Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Cumulus field will continue through the afternoon as temps climb
into the 90s.

Little change in this evening`s forecast as high pressure gives
us many of the same talking points for yet another nighttime
period: heat during the day, good radiational cooling at night,
mostly clear skies.

Departing high pressure`s influence will be lesser tonight, and
that should allow for a bit more onshore flow starting after
midnight. Have again brought in guidance for overnight lows that
drops temps into the lower 60s for much of southern ME and all
but the southern third of NH.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
Key Messages:
* Another day of heat Wednesday, warmest for locations east of
  the foothills.
* Showers and storms develop in the early afternoon for the
  western half of the forecast area. Stronger cells may produce
  downbursts with gusty winds.

Wednesday morning begins very similar to the last few days, a
quick warmup under sunny skies. No big changes through noontime,
but will likely see a cumulus field develop earlier in the day
given additional moisture.

This moisture will permit deeper clouds as well. Combined with
warm surface temperatures, showers likely develop early to mid
afternoon with additional CAPE to bring a scattered
thunderstorms into the late afternoon and early evening. Mid
level lapse rates and shear are limited, thus there is a ceiling
to storm strength and severity. Regardless, forecast conditions
could yield isolated downbursts with locally gusty to strong
winds...mainly in the mountains and foothills.

Chance for precipitation brings question to temp trends through
the day. Expect the early sunny skies to permit a climb into
the upper 80s and lower 90s quickly. Longevity of heat will be
most limited in the western half of the forecast area as clouds
develop and showers slowly move east. With light onshore flow
increasing in the afternoon, the immediate coast will see some
reprieve into mid afternoon as well. Focus for the warmest
temperatures of the day will then be interior areas between the
coast and foothills. Have extended the Heat Advisory another day
here. While heat index values have been marginal, its enough
over this stretch to cause some heat stress.

Arriving cold front will provide forcing through the night for
showers and rumbles of thunder to continue. Storm motion will
likely be slow, and this should lead to localized wetting rain.
Efficiency leaves some improvement, but greatest amounts of
rain on the day will be where showers or storms can balance
available instability with enough movement to keep from raining
themselves out.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Thursday morning, a cold front moves through the region. The
front will allow for the development of pulse thunderstorms
Thursday afternoon. The environment looks to be unstable, but
lacking the necessary shear needed for severe storms to develop.
The flooding risk is also low due to dry antecedent conditions,
PWATs are only near 1.5 inches and notable unidirectional winds
are expected in the mid-levels and above, preventing storms
from becoming stationary.

Guidance is indicating upto about a half inch of rainfall is
possible with the frontal passage. This rain will be much needed
as previously dry conditions are starting to trigger a drought
over the area. Otherwise, Thursday and Friday will be warmer,
but not as hot as it has been feeling. Temperatures are expected
to be in the upper 80s for Thursday and Friday.

Dry and warmer weather is expected to continue through the
extended weekend, through troughing will allow for more cooler
temperatures to arrive for early next week. An upper-level low
over Canada may bring a weak cold front southward, with some
very light rainfall accumulations possible Sunday.

Next week`s forecast remains very dry, but troughing should
bring some cooler weather into the forecast. Highs look to be in
the upper 70s and lower 80s.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Short Term...VFR with winds subsiding this evening. Some BR
possible again in valleys and near Midcoast terminals overnight
tonight. VFR Wed morning, but cumulus field should develop late
morning with more population. These deepen in the afternoon with
SHRA and some TS developing towards HIE and western ME mtn
terminals. These will slowly move east through the afternoon,
continuing overnight (TS coverage will be less).

Long Term...
Reduced restrictions are expected Thursday, with showers and storms
likely through the day. Restrictions should lift by Friday morning,
with mostly VFR expected on Friday and Saturday. Restrictions may
lower again on Sunday due to an isolated shower or thunderstorm. VFR
is expected to remain through most of next week.

&&

.MARINE...
Short Term...Conditions remain free of SCA mention, but
departing high will aid in some building wave heights to 3 to 4
ft come Wednesday afternoon. Cold front arriving from the west
has slowed, likely not nearing the coast until Thursday
afternoon. However, showers will be near the waters Wednesday
evening and through the night.

Long Term...
Southwesterly winds upto 12kts are expected on Thursday. A passing
cold front will shift winds to northerly overnight. Northerly winds
pick up briefly on Friday morning, with 10-16kt winds expected.
Winds slacken and become light and variable by the end of the day on
Friday and stay light through daybreak Saturday. Saturday afternoon,
winds pickup from the south, with 7-12kt winds expected. Winds shift
to southwesterlies by Sunday morning, with wind speeds remaining in
the 7-12kt range. Seas will remain at 2-4ft through the entire
forecast period.

&&

.CLIMATE...
Daily record highs and year(s) for Portland, Augusta, and
Concord.

          Portland          Augusta       Concord
Aug 12    99F (2016, 1944)  93F (2002)    99F (2016, 1944)
Aug 13    99F (1947)        94F (2004)    99F (1944)

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Heat Advisory until 8 PM EDT Wednesday for MEZ012>014-018>022-
     033.
     Air Quality Alert until 11 PM EDT this evening for MEZ023>025.
NH...Heat Advisory until 8 PM EDT Wednesday for NHZ010-012-013.
     Air Quality Alert until 10 PM EDT this evening for NHZ013-014.
MARINE...None.

&&

$$


NEAR TERM...Cornwell
SHORT TERM...Cornwell
LONG TERM...Palmer
AVIATION...Cornwell/Palmer
MARINE...Cornwell/Palmer