Londonderry, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

989
FXUS61 KGYX 271456
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1056 AM EDT Fri Jun 27 2025

.SYNOPSIS...
A warm front will lift northeast towards New England today bringing
increasing chances for showers tonight. Low pressure crosses
Saturday, bringing periods of rain and some thunderstorms. Weak
high pressure builds in Sunday and Monday for mostly dry
weather with increasing temperatures. Temperatures and humidity
continue to rise Tuesday ahead of a cold front that will bring
thunderstorms Tuesday afternoon into Tuesday night. Humidity
will abate behind the front Wednesday as high pressure returns
to the Northeast.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1050am Update...Low level moisture advection can be seen on
satellite this morning with a region of flattened cu across the
southern tier of NH counties. This is likely aided by leftover
morning moisture, and is expected to mix out around noontime.
Otherwise, mostly sunny day continues with forecast invasion of
high clouds later this afternoon.

6:35am Update... No notable changes with this update as the
forecast remains on track at this time. Valley fog is beginning
dissipate, with mainly sunny skies in place through the morning
hours.

Previous...

High pressure moves through New England today and off to the
east, bringing a mostly sunny first half of the day and an
increasing onshore breeze. With the mainly sunny skies,
temperatures warm into the low to mid 70s across most of the
region. After an initial warmup to the low 70s, temps fall back
into the 60s along the coast in the afternoon as winds shift to
southeasterly with the passing high.

As the high moves through today, a warm front also makes
progress through the Northeast, but likely stalls southwest of
New England by late today. This brings increasing cloud cover
during the afternoon hours from the west. While the front stalls
at the surface, warm air continues to move in aloft, with a
shower possible across northwestern areas before sunset this
evening

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Moisture continues to move in aloft overnight, as a cooler low
level marine airmass moves in at the surface from the east. A
wave of low pressure approaches from the west during the
overnight hours, with POPs increasing through the overnight. The
best forcing for rain looks to be across northern areas as
moisture lifts over the cooler airmass. By morning, periods of
rain and some scattered thunderstorms are likely across northern
locations, while more showery activity is expected further
south.

This trend continues through much of the day tomorrow as
periods of rain and showers move through the region along the
stalled front. There remains some question as to whether or not
the warm front at the surface will reach into Southern New
Hampshire tomorrow afternoon. This would bring with it warmer
temps, and also the potential for a few stronger storms in the
late afternoon. Right now the cool air looks most likely to win
out, with highs ranging from the upper 60s across southern New
Hampshire, to the mid 50s across northern and central Maine.

Rainfall amounts are looking lighter south of the mountains
with generally less than half an inch looking more likely for
much of central and southern New Hampshire, as well as southwest
Maine. Northern areas stand the best chance to see more
substantial rainfall totals, with 1-3" possible across the
north from the repeated rounds of showers and thunderstorms. It
remains to be seen exactly how far north the convection will
initiate on the frontal boundary aloft, so this precip gradient
is likely to still shift a bit going into the event.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Long term update...01z NBM has been incorporated into the long
term forecast. Improvement continues to be foreseen Saturday
night and Sunday as low pressure moves away. Warmer weather is
then expected with chances for showers and thunderstorms
centered around Tuesday and Thursday.

Previously...

Chances for rain will diminish late Saturday into Sunday
morning as the wave of low pressure moves offshore. Mostly fair
weather is likely across much of the area by Sunday afternoon
with highs climbing into the 70s. High pressure slides overhead
Sunday night and offshore Monday. This will bring fair weather
with temperatures into the 80s for highs. Humidity will also
start to increase and will peak on Tuesday when dewpoints will
make a run into the upper 60s to low 70s. These high dewpoints
combined with surface heating will likely yield ample CAPE
across the forecast area for thunderstorms that will become
likely Tuesday afternoon as a cold front approaches. Latest
Machine Learning guidance out of CSU is showing a decent signal
for strong to severe storms with this cold front. This seems
reasonable with global models suggesting a frontal passage near
and just after peak heating and modest height falls aloft.
Temperatures look to remain seasonably warm into the middle of
next week while dewpoints drop in the wake of the front.
Cyclonic flow aloft will linger keeping some chances for showers
in the forecast Wednesday and Thursday.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
Short Term...VFR prevailing today (outside of a brief MVFR deck
towards MHT this AM) and most of tonight. Showers increase
through the overnight from northwest to southeast, with MVFR
conditions possible at LEB and HIE by Saturday morning. MVFR
ceilings likely spread eastward tomorrow morning, with IFR
possible at all terminals by the early afternoon as periods of
rain and showers move through into the evening.

Long Term...Low pressure crossing the area Saturday will likely
keep cigs near MVFR to IFR thresholds with periods of rain.
Restrictions may linger through Saturday night before drier air
moves in Sunday. VFR likely prevails Sunday into Tuesday. A cold
front will bring chances for thunderstorms Tuesday afternoon.

&&

.MARINE...
Short Term...High pressure slides east across the waters today,
with a warm front stalling south of the waters tonight. A weak
low pressure system approaches from the west tonight, and slowly
crosses northern New England through the weekend. Conditions
look to remain below SCA levels through Saturday.

Long Term...Low pressure approaches from the west Saturday and
moves through the waters Saturday night. This will bring
persistent onshore winds with gusts around 20 kts and seas
climbing to 5-6 feet Saturday night into Sunday. High pressure
slides over the waters Sunday night and Monday. South to
southwest flow increases Tuesday ahead of a cold front.

&&

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

&&

$$


NEAR TERM...Clair/Cornwell
SHORT TERM...Clair
LONG TERM...Ekster/Schroeter