Portsmouth, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

149
FXUS61 KGYX 070240
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1040 PM EDT Tue May 6 2025

.SYNOPSIS...
A cut-off low continues northward this evening, bringing
showers and thunderstorms. Fog is likely tomorrow morning, and
will stick around through the day tomorrow along the coast.
Relatively warmer and drier conditions return, but showers are
likely tomorrow and Thursday. Rain and cooler conditions return
with the next low pressure system for Friday into Saturday.
Warmer and drier conditions return with High pressure for Sunday
and early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
1040 PM...Minor update to PoPs and temperatures to reflect the
latest observed trends. Latest radar shows scattered showers
moving south to north across eastern New England with this
shower activity expected to diminish over the next few hours.

655 PM Update...Going forecast is in good shape and have mainly
refined PoPs based on latest observations. Two areas of showers
are moving NNE across the area with one moving over Maine
mountains and central Maine and the other moving through
southern NH. Recent runs of the HRRR have additional areas of
showers blossoming over the area through midnight with PoPs then
decreasing through the rest of tonight. Many areas south of the
mountains are experiencing fog at this hour and will have to
monitor for the development of dense fog later tonight along the
coastal plain.

Previously...

Currently, an occluding surface low is situated over the Great
Lakes. As this low nears New England, an attached occluded
front will move northward, overtaking a warm front. The front
will bring showers and thunderstorms through the remainder of
the evening. Guidance has generally continued to trend drier
with these showers and storms, with rain totals likely not
exceeding an inch of rainfall through tomorrow morning.
Southerly flow tonight will allow for the coast and much of
central ME to stay in the fog/low-stratus tonight. Lows tonight
should be in the lower 50s.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Fog will break up across the interior by the late morning hours
tomorrow, but light, onshore flow will help keep fog hanging on
along the coast.

The aforementioned low`s center arrives in New Hampshire tomorrow
afternoon. The clearer skies across the interior will help
destabilize the atmosphere, potentially allowing for some
convective initiation tomorrow afternoon. The environment is not
conducive to strong storm development, and forecast soundings
suggest these will be ordinary pulse thunderstorms that pose
little impact other than perhaps some isolated gusty winds.
These storms should be across NH in the afternoon, with storms
weakening and moving out of the area tomorrow evening. Fog may
back-build right back into central ME tomorrow night as light
southerly flow could allow for more marine fog to advect inland.
Most fog should mix out by the AM commute on Thursday.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
1040 PM Update...No significant changes noted in the latest NBM.
Another widespread soaking rain is likely Friday into Friday
night as slow moving low pressure crosses the region. The NBM
favors a warming and drying trend over the weekend into early
next week.

Overview...

The slow moving upper level low currently across the Northeast
moves into the Canadian Maritimes on Thursday. Another upper
level low deepens across the eastern Great Lakes by late
Thursday, and slowly moves through the Northeast on Friday and
Saturday. High pressure begins to build in on Sunday, and
persists into early next week with a warming trend.

Details...

Thursday features more sunshine south of the mountains with a
northwest flow, and more clouds and cooler temperatures through
the higher terrain. Highs warm into the 60s downwind of the
mountains, with low 70s into southeast New Hampshire. Cooler
conditions with some scattered afternoon showers are likely
across the north with highs mainly in the 50s.

By Friday, the next upper level low approaches from the west,
with a surface low likely developing and bringing another batch
of showers into the region for Friday. Cool, cloudy, and raw
conditions are expected Friday as highs remain in the 50s.
Depending on just how organized the surface low can become,
there is the potential for some heavier rainfall amounts.
Similar to this past system, this would likely be more localized
and convective in nature, so we`ll have to wait a little longer
to get into the high res model guidance window to try to pin
down these areas.

Saturday features slowly improving conditions as the low slowly
transits through New England. Scattered showers are still
likely, but more breaks of sun should allow temperatures to
reach into the 60s by Saturday afternoon.

Sunday marks the start of a warmer and drier pattern as high
pressure builds into the Northeast. Another cut off low likely
develops, but this time across the southern US, with ridging
building north of the low. This directs a warmer airmass north
of the low and into New England on a westerly flow. Temps warm
into the 60s to low 70s on Sunday, with more widespread 70s on
Monday.

At this point, Tuesday looks even warmer as highs warm into the
mid to upper 70s across much of the area. However, it`s wise to
be suspicious from this far out at this time of year as a back
door could easily keep temps cooler as high pressure moves
offshore. So we`ll continue to monitor the progression of this
warm up over the next few days.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
Short Term...
Fog, showers and thunderstorms should keep restrictions down
through the remainder of the evening. Once the storms move out,
fog and low stratus will build in, keeping restrictions down
through tomorrow morning. Rain and thunderstorms keep
restrictions down tomorrow afternoon. Tomorrow night, southern
NH goes to VFR as skies start to clear out. However, fog builds
back in everywhere else, keeping restrictions down across
coastal and Maine sites.

Long Term...Mainly VFR are expected on Thursday, with brief
showers and MVFR conditions possible at LEB and HIE. Conditions
then lower to MVFR and IFR Thursday night and Friday with
periods of a rain and fog. Conditions gradually improve on
Saturday, with VFR returning by Sunday and persisting into early
next week.

&&

.MARINE...
Short Term...Southerly flow at 9-18kts is expected through
tomorrow night. Winds shift to southwesterlies by Thursday
morning. Seas remain below SCA thresholds and stay steady at
2-4ft through Thursday morning.

Long Term...A broad area of low pressure slowly approaches the
waters on Thursday and Friday, and moves east of the waters
Saturday night and Sunday. Some marginal SCA conditions are
possible during the Friday and Saturday timeframe from this
system. High pressure builds in for late Sunday and early next
week.

&&

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

&&

$$


NEAR TERM...Palmer/Schroeter
SHORT TERM...Palmer
LONG TERM...Clair/Schroeter