Portsmouth, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

100
FXUS61 KGYX 150332
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1032 PM EST Thu Nov 14 2024

.SYNOPSIS...
Mostly clear skies overnight will give way to increasing
clouds Friday across central Maine with breezy conditions.
Widespread precipitation is not expected for the next week, so
drought and fire weather conditions remain at the forefront.
Gradually warming temperatures are expected into next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
1032 PM Update...
High clouds remain over southern and central New Hampshire as
well as far southwestern most Maine. Much of it is high and
thin, therefore a large diurnal trend will be in progress.
Further to the north and east, plenty of clear, cold and very
dry air remains in place with low surface dew points. Have
lowered min temperatures slightly from the previous package,
otherwise the forecast remains in line.

To note, a coastal front is attempting to form with convergent
low level winds along the southwest coast of Maine and Seacoast
of New Hampshire. However, once again, the atmosphere remains
very dry throughout a very deep layer for even clouds to form.

Coastal flood advisories have been issued for Friday. See
coastal flood section below.

Update...
Latest satellite imagery continues to indicated plenty of high
cloud cover over the southern two thirds of New Hampshire with
mainly clear skies elsewhere. Latest HREF trends shows this
moisture only very slowly moving to the east with time
overnight. Therefore, expect clear skies, light winds and low
surface dew points to remain over much of the region. This will
lead to radiational cooling with a quick drop in temperatures
tonight. Will be making some adjustments downwards with the near
term portion of the forecast.

Prev Disc...
The region remains in between lows as one to the northeast
retrogrades west, and one to the southwest weakens on approach.
Ridging in between is very dry, and we`ve been adrift in this
airmass for the past few days. This continues tonight, with
light winds and mostly clear skies. The only hint of cloud cover
will be thin cirrus advancing NE from NY/PA. The dry airmass
containing sfc dewpoints in the single digits to around 0 will
be ripe for overnight radiational cooling. The only factor
slowing overnight temp falls will be the light wind preventing
most open areas from fully decoupling.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
For Friday, near full sun continues for points in
central/southern NH as well as far southern ME. North, a deck
of clouds will invade from the NE through the morning. This
remains in place for much of the day with some rain showers
possible towards the Midcoast and into the Kennebec Valley. Have
gone a little below NBM guidance for high temps Friday here
given the cloud cast.

Overall, rain chances have lessened and pulled east for Friday
and Friday night. The invading moisture will run up against the
dry air mass in place, and think this will struggle to produce
more than a few showers if forcing allows. Models never fully
saturate to the surface towards central ME, thus confidence is
on QPF remaining very light if at all.

Expansive low level wind field from the backing low to the
northeast will prompt a stronger surface wind response Friday.
Lowlands will see gusts 20 to 30 mph, with higher elevations
peaking higher due to proximity to the 35-45kt 850mb winds. Not
only will that bring a stark difference in wind chills from
summits to trailheads, but also deep mixing tapping into
remaining dry air for the southern half of the CWA. Thus fire
weather concerns continue for Friday, see section below for
details.

Showers will tend to linger in the mountains and upwind into
Friday night. N to NW winds will lock cooler sfc temps near
freezing here, and there will be the chance for some light
freezing rain given model profiles and wet bulbing that may
occur in more stout showers. Confidence and areal coverage continues
to be low, and will forego headlines at this time.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
The extended forecast remains mostly dry and quiet. A low over Nova
Scotia brings the chance of a few showers into central Maine as it
retrogrades back towards New England. The retrograding low will
allow a northerly wind to develop, bringing colder air into the
region. Mostly clear skies in addition to CAA should make for colder
lows Sunday morning compared to Saturday morning. Higher seas and
high astrotides may bring some minor coastal flooding at high tide
on Saturday.

A quick shot of moisture arrives from Canada on Monday,
allowing chances for rain and snow showers. Precipitation will
be more isolated south of the mountains as downsloping dries out
the atmosphere in these areas.

A ridge moves in from the southwest on Monday, maintaining itself
through much of next week; temperatures are likely to run above
average. Gradually, the jet stream amplifies into a blocking pattern
as an upper-level low over the Great Lakes moves northward. This
upper-level low is stacked onto a surface low, allowing the surface
low to dissipate and occlude.

The upper-level low makes a shift into New England by the end of
next week, causing a low to develop somewhere along the dying cold
front associated with the previous surface low.  This low will bring
unsettled weather for the end of next week, along with the
possibility of some measurable and much-needed precipitation.
However, uncertainty is very high at this time due to the blocking
pattern, and details will rely on where exactly the new surface low
develops.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Short Term...VFR. NW winds increase with gusts to 25 kt Friday.
A VFR/MVFR deck invades from the NE through Friday, with MVFR
settling in the mountains Friday night.

Long Term...VFR is expected through the weekend. Unsettled weather
arrives on Monday, with some MVFR CIGs possible in showers. VFR and
clearer skies likely return to locations south of the mountains on
Tuesday, with low overcast skies reinforcing MVFR CIGs north of the
mountains.

&&

.MARINE...
Short Term...SCA continues tonight through Friday, and may need
extension into early Saturday morning. Waves are set to remain
steady through Fri night, with N winds becoming gusty and NW
Friday.

Long Term...Winds and seas will exceed SCA Thresholds Saturday and
Sunday. Seas of 2-3 feet are expected in Casco/Penobscot Bays with 4-
6 foot seas in the open waters. Winds this weekend will be out of
the northwest at 15-20 kts, potentially gusting to 25kts over open
waters. Seas and winds improve for the start of next week.

&&

.FIRE WEATHER...
Low level dry air remains in place for Friday, especially for
points south of a Portland to Fryeburg to Whitefield, NH line.
Here, another day of min RH values in the teens to 25 percent
range is expected Friday. Wind will be a larger factor Friday,
gusting 25 to 30 mph late morning through the afternoon. This
northwesterly wind will aid in some RH recovery into the late
afternoon, but cumulative drying over the past week may dampen
this effect. While light precipitation is in the forecast for
central ME and the mountains, it is not expected to be wetting.
Not as low RH values are forecast for the weekend.

&&

.TIDES/COASTAL FLOODING...
Water levels continue to overachieve at low tide before
diminishing to about a half foot or so at low tide over the last
few tidal cycles. Have opted to issue a Coastal Flood Advisory
for the mid morning high tide on Friday. This is using a blend
of ESTOFS and ETSS for the minor storm surge factor. Water
levels are progged to climb to near Portland`s 12 foot flood
stage and Hampton`s 11 foot flood stage in the Back Bay area.
Wave action should not be much of a factor with a north,
northwesterly flow continuing.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Coastal Flood Advisory from 9 AM to 11 AM EST Friday for
     MEZ023-024.
NH...Coastal Flood Advisory from 9 AM to 11 AM EST Friday for
     NHZ014.
     Red Flag Warning from 7 AM to 6 PM EST Friday for NHZ023>025.
MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ150>152-
     154.

&&

$$

NEAR/SHORT TERM...Cannon