Londonderry, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

206
FXUS61 KGYX 261035
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
635 AM EDT Tue May 26 2026

.WHAT HAS CHANGED...
Cancelled a portion of the Small Craft Advisory that was set to
expire at 8am. Winds and seas here have since fallen below
criteria. Otherwise, no significant changes to the going
forecast.

&&

.KEY MESSAGES...
1. Expect mainly dry and warmer weather through Wednesday but a
cold front could lead to a few showers and a rumble of thunder
or two tonight or Wednesday.

2. A cooler and more unsettled pattern develops the second half of
this week, peaking next weekend.

&&

.DISCUSSION...
KEY MESSAGE 1 DESCRIPTION...

High pressure settles in across most of the northeast this
morning with light winds mainly out of west or southwest. We
should see some fog in the early morning given the light winds,
recent rainfall, and dewpoints in the low to mid 50s -
particularly in the valleys.

East coast high pressure will sag south this afternoon as a low
amplitude upper level ridge axis moves across the forecast
area. A shortwave will flatten the ridge a bit as a surface low
moves into central Quebec this afternoon/evening. A cold front
will extend south southwest from this low and start to approach
the northeast CONUS tonight. Most of the synoptic forcing will
just clip our area, mainly remaining north of the International
Border and over northern Maine, but a few isolated to scattered
showers will be possible along the higher terrain ahead of the
cold front in the afternoon or evening. A few rumbles of thunder
will also be possible but instability will be limited. Any
showers and storms should diminish fairly quickly with the loss
of daytime heating.

The cold front will cross the region tonight into Wednesday. A
few early day showers and storms will be possible on Wednesday if
they can form in time along the front before it moves out to
sea. The latest NAM Nest suggests we could see 500 to 1000 J/kg
of MUCAPE along the frontal boundary late morning/early in the
afternoon across far southern New Hampshire. With 30 to 40 knots
of deep layer shear in the forecast, there could be a brief
window for a stronger storm or two here. A few isolated showers
will remain possible across the mountains the rest of the day.

Regarding temperatures, it will be much warmer today as a warm
front lifts north across the area. Highs will mainly range from
the mid 70s north to the low to mid 80s south. It will be quite
mild tonight as well with lows only dipping into the lower 50s
to the lower 60s. With the cold front moving through, locations
across and north of the mountains will see some slightly cooler
temperatures on Wednesday, but the rest of the forecast area
will see another round of highs in the low to mid 80s. Wednesday
night lows will range from the mid 40s north to the mid 50s
south.

KEY MESSAGE 2 DESCRIPTION...

After a couple of warm days, longwave troughing develops over the
eastern CONUS, cooling temperatures down to near or below seasonal
normals for highs through at least this weekend. Ensembles are
suggesting a rather anomalous blocking pattern developing by this
weekend. Upstream ridging over Hudson Bay, combined with troughing
over the SW CONUS, will resemble an omega block pattern. This is
likely to result in persistent troughing over the Northeast U.S. for
the foreseeable future.

Daily diurnal shower chances are likely, fueled by a persistent cold
pool aloft. Both 850 mb and 500 mb temperatures will be anomalously
cold for this time of year, peaking this weekend. In fact, freezing
levels may be at or below 850 mb, which is rather impressive for the
end of May. This cold pool aloft will have arctic origins due to
northerly flow aloft. Deterministic guidance is hinting at a more
organized low pressure arriving from Canada that could bring more in
the way of widespread rainfall. While model agreement in a track
from north to south through New England is rather impressive, timing
and spatial differences remain notable at this time. Details will
become clear in the coming days, but unfortunately a cold and wet
trend has become apparent for at least part of next weekend. In
fact, cannot rule out graupel or mountain snow given such cold
temperatures expected aloft.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Through 12z Wednesday...Fog dissipates early, leading to
widespread VFR today through Wednesday morning. WSW breeze picks
up later this morning, with a weak sea breeze bringing an
onshore wind shift to PWM/PSM around 18z this afternoon. Drier
airmass should keep fog at bay tonight, with some lowered cigs,
perhaps MVFR, towards the mountains. A couple hours of LLWS
possible tonight as a 40kt lower jet passes through the region.

Outlook:

Wednesday: MVFR or localized IFR restrictions may return with
showers and thunderstorms. The best chances will be over LEB
and HIE. VFR expected Wednesday night.

Thursday-Friday: Scattered showers and a few storms could lead
to brief periods of MVFR to IFR restrictions, mainly during the
afternoon and early evening hours each day. Otherwise, mainly
VFR expected.

Friday night-Saturday: Potential for more widespread rainfall and
IFR restrictions, but uncertainty remains.

&&

.MARINE...
Light westerly winds are expected to continue through the
morning and afternoon. An SCA is in effect for elevated seas of
3-6ft through this same timeframe. Winds will become
southwesterly and strengthen to near SCA-levels this evening.
Elevated seas and winds start to subside by Wednesday morning.

Thursday-Monday...Winds will likely be primarily out of the
north Thursday into Friday with low pressure to the east or
southeast of the Gulf on Maine. Conditions will mostly remain
below SCA levels during this time but can`t rule out a brief
period of 25 kt gusts Thursday night. A more organized low
pressure dropping southward out of Canada may then bring a
higher chance of SCA level winds and seas over the weekend.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ150-
     152.

&&

$$

DISCUSSION...Barker/Hargrove
AVIATION...Cornwell