Portsmouth, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

301
FXUS61 KGYX 200305
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1105 PM EDT Thu Jun 19 2025

.SYNOPSIS...
Storms are expected this evening as an area of low pressure drives a
cold front across the region, some of which could be strong to
severe. Humidity will lower behind the front for Friday, with gusty
northwest winds expected. More comfortable conditions settle in for
Saturday under ample sunshine, before oppressive heat and humidity
builds in for early next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
1105 PM Update...There will continue to be chances for showers
and occasional thunder across northern zones for the next couple
of hours while the threat for severe storms has ended. Repeat
rounds of thunderstorms did prompt a Flood Advisory across
central Franklin and central Somerset Counties that remains in
effect until 1230 AM EDT as showers upstream are tracking
towards this area. Have mainly refined PoPs with this update in
addition to ending the enhanced wording with thunderstorms.

840 PM...Have canceled the Severe Thunderstorm Watch for much
of the area with the exception of northern Counties where
current sub-severe storms show some signs of brief
intensification. Expect the severe threat to gradually diminish
with the loss of heating while repeat rounds of convection
across central Somerset County are introducing a flood threat.
Will continue to monitor this area for potential short fused
flood products over the next hour.

632 PM Update...Going forecast is largely in good shape with
the main focus of this update to refine PoPs and thunderstorm
coverage through this evening. A slight capping inversion noted
on the 19Z KGYX sounding and the best forcing still back over
Upstate NY has helped to keep storms widely scattered across the
interior. The best ML CAPE and shear is located along a
corridor from the Lakes Region of NH through the western
mountains of Maine to the Canadian Border where there are
currently three Severe Warnings out. Satellite trends suggest a
stable marine layer has pushed into the coast and recent runs of
the HRRR suggest chances for storms here and even across
southern NH will be very low. No changes to the current Severe
Watch as enough instability and shear will remain in place over
the next couple of hours that could sustain any additional
storms that develop mainly north of the Lakes Region of NH and
the foothills of western Maine.

Previously...

Clouds have largely cleared out since this morning (with the
exception of the Midcoast), and this has set the stage for
sufficient instability this afternoon thanks to the resultant
warming and dewpoints in the mid 60s to low 70s across much of
the area. Lift is also increasing across the area as a cold
front continues to approach from the west, and 30-40 kt of 0-6km
shear combined with the unstable conditions has created an
environment for some storms to become strong to severe this
afternoon and evening. Convection is already starting to
develop, and coverage/intensity should steadily increase the
rest of this afternoon and evening. The greatest threat is
along and to the north and west of the I-95 corridor, and a Severe
Thunderstorm Watch has been issued until 11 PM for much of western
ME, mainly for damaging winds and large hail in excess of 1" in
diameter. There is also a veering wind profile and enough 0-1km SRH
to where the could be a brief tornado or two. The risk is lower
along the coast where the seabreeze has moved in. Torrential
downpours will accompany thunderstorms, and even though storms will
be moving quickly, there is a conditional threat of isolated flash
flooding if any location receives multiple storms.

Instability may be sufficient enough for the threat of strong to
severe storms to last an hour or two beyond sunset, but coverage and
intensity will steadily wane after 10 PM with remaining storms
expected to become more elevated in nature. Storms should then be
mostly done by midnight or so, but some showers stick around
through tonight, mostly in the mountains. South of the mountains,
expecting a gradual decrease in cloud cover overnight, although
cloudier skies may stay put across eastern areas along with
some fog. For the rest of the area, can`t rule out patchy fog,
but I think winds will be up enough to where it shouldn`t be too
much of an issue. Winds may start becoming breezy toward
daybreak across western areas behind the cold front.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Low pressure will be centered just to the north of the area to start
out Friday with the cold front nearing the Midcoast.  he front will
quickly exit to the east as the low moves across the St. Lawrence
Valley, and the increased westerly winds behind the front will clear
out any lingering stratus/fog around the Midcoast by mid-morning.

And speaking of winds, that will be the main story for Friday. Model
soundings continue to advertise wind gusts of 30 to 40 mph in the
morning and afternoon, and the top of the mixed layer supports the
potential for some to top out in the 45 to 50 mph range, which could
result in damage to tree branches and even power outages. Given the
threat of severe weather today, have opted to hold off on any
additional headlines, but a Wind Advisory for Friday could be issues
as early as later this evening once the threat of severe weather
winds down.

Drier air behind the front will keep locations south of the
mountains mostly dry, although there will still be enough moisture
for partly sunny skies with maybe a few periods of mostly cloudy. In
the mountains, more cloud cover is expected with a chance of showers
thanks to upslope flow. High will be mostly in the mid 70s to low
80s, except a tad cooler in the mountains.

Winds will ease Friday evening with the loss of mixing and will
continue to do so through the overnight hours. The last of the
upslope showers should also come to an end in the evening. Lows will
be mostly in the 50s with a few low 60s mixed in.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
1105 PM Update...No significant changes in the latest NBM with
strong signal for dangerous levels of heat and humidity Monday
into Tuesday. It does look like this will be a short duration
heat event with temperatures abating Wednesday into Thursday.


...Dangerous Heat Monday Through Tuesday...

By Saturday the region will remain under the influence of upper-
level NW flow aloft, as ridging begins to take shape to our south.
The lower dewpoints will rebound slightly, but generally allowing
for low humidity with temps 75-85 from N to S under ample sunshine.
As the ridge builds to our south Saturday Night, attention will turn
to upstream convection that models have shown traversing on the
periphery of the ridge into New England by Saturday Night. There is
low confidence on the placement of this feature, but have upped pops
due to the run to run consistency. The residual cloud cover will
linger through at least midday Sunday as a warm-front lifts north.
Humidity values will surge with dewpoints in the upper 60s.

Attention then turns to the much advertised heat dome with 500mb up
to 600 dm across the eastern U.S. by Monday through Tuesday.
Temperatures will reach 90 for many areas from the foothills
southward, warming another 5 degrees or so further by Tuesday.
Forecast temperatures are at/near record highs for some locations,
particularly for Tuesday which looks to be the hottest day of
the forecast. The humidity will be elevated as well, leading to
heat index values into the mid 90s and towards 100 degrees in a
few locations. The heat will linger until a cold front from
Canada drifts south. There is low confidence in the timing of
this feature, with a few model guidance suggesting heat could
linger into Wednesday, at least for S NH. The front will bring
some showers and thunderstorms, which is currently forecast for
Tuesday night. How far south the boundary sags south will
greatly impact how much relief from the heat the region will
experience.

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Short Term...Expecting generally VFR outside of showers and storms into
early this evening with the exception of low ceilings or even fog in
the PWM-AUG-RKD corridor. Showers and storms expected to move into
the region around 21Z this afternoon and could provide TEMPO IFR
conditions through around 02Z/20 this evening and may also include
strong wind gusts and hail. Storms will then mostly end by 03-04Z
with lingering showers possible overnight, mostly in the mountains.
A cold front will approach overnight and begin crossing through
around daybreak Friday, and until it crosses, it`s possible to see
more fog or low stratus, again more likely in the PWM-AUG-RKD region.

HIE and possibly LEB will see a chance of showers through at least
the first part of Friday and may also hold onto MVFR ceilings. The
rest of the terminals are expected to to remain VFR on Friday, but
the main story will be the gusty W/WNW winds. It looks like most
gusts will fall into the 25 to 35 kt range, but it`s possible some
could top out 40-45 kt. Winds will then follow a downward trend
Friday evening through Friday night while VFR is expected to
continue.


Long Term...Mainly VFR Saturday with increasing chances for
showers and storms Saturday night into early Sunday with
restrictions possible. VFR then expected Monday and Tuesday.

&&

.MARINE...
Short Term...A cold front approaches continues to approach the waters,
and then eventually starts to cross through around daybreak and
through Friday morning. Increasing southerly winds will bring SCA
conditions starting this evening, and these will continue through
Friday behind the cold front as winds turn west to southwesterly.
Winds stay westerly Friday evening/night and will diminish, allow
conditions to fall below SCA levels.

Long Term...An extended period of great boating conditions are expected this
weekend through early next week with a ridge over the region. Winds
will be variable to SE/SW at times between 5-15 kts. Seas will be 1-
3 ft for much of the period.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until midnight EDT Friday night for
     ANZ150.
     Small Craft Advisory from 4 AM to 8 PM EDT Friday for ANZ151-
     153.
     Small Craft Advisory until 8 PM EDT Friday for ANZ152-154.

&&

$$


NEAR TERM...Combs/Schroeter
SHORT TERM...Combs
LONG TERM...Jamison/Schroeter