Derry, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

838
FXUS61 KGYX 112307
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
707 PM EDT Fri Apr 11 2025

.SYNOPSIS...
A cutoff low will slowly move north, east of New England
through the weekend. This will bring an extended period of cool
and unsettled weather conditions. The system then moves away by
Monday with a return to drier and warmer conditions early next
week as high pressure returns. A cold front approaches from the
west Tuesday, with an upper low influencing conditions into
midweek.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
707 PM Update...After reviewing 18Z guidance and recent runs of
the HRRR have decided to issue a Winter Weather Advisory for
portions of western NH where heavy snowfall rates during the
pre-dawn hours into late morning will likely lead to difficult
travel. This recent guidance resulted in an increase in QPF and
snowfall amounts while storm total snowfall amounts may be quite
variable over short distances do to elevation dependence. These
heavy snowfall rates will be associated with a band of Fgen
forcing at H8 lifting into into southern NH and far SW Maine
around 7 AM. As mentioned in the previous discussion below, the
transition from rain to snow will also be dependent on rates
with this latest update increasing snowfall amounts in areas to
the east of the Winter Weather Advisory. This band then looks to
pivot NW spreading burst of heavy snow across the NH Lakes
Region into the Whites and points westward.

Previously...

High pressure remains positioned across the Canadian Maritimes,
as low pressure continues to organize and move northward from
the Carolinas. Cool northeasterly flow and mainly cloudy skies
between the two features continues tonight, with lows mainly
settling into the mid 30s tonight. Across northern areas, a few
more breaks in the clouds likely allow temps to drop into the
upper 20s to low 30s.

The night remains mostly dry through midnight, but the next
round of precip will begin to push in from the south after
midnight into southern New Hampshire. Precip may start off as
light rain, but as the precip becomes heavier a transition to
snow is expected. The higher elevations across southwest New
Hampshire stand the best chance to pick up 2-4" of snowfall, but
it will be highly elevation dependent and won`t accumulate on
the roads nearly as well. Elsewhere, sufficient precip rates
should allow for a burst of snow for a few hours with minimal
accumulations.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
The burst of wet snow continues to pivot northwestward through
the morning tomorrow. Accumulation efficiency drops off during
the daytime tomorrow, but even-so rates may be enough to
briefly cause a slushy layer on the roads, even in the lower
elevations. Similar to southwest New Hampshire, accumulations of
a few inches will mainly be confined to the higher terrain
through the Lakes regions of Maine and New Hampshire and into
the mountains. As precip lightens up during into the late
morning and afternoon, a transition to a showery light rain is
likely.

Showers and some drizzle continues into the night tomorrow, but
a break in the steady rain and snow is expected most of the
night. However, the next round of precip will approach from the
southeast as the weak low pressure system drifts northward
through the night. The bulk of this round will hold off until
Sunday, but some steadier precip may reach the coast by daybreak
on Sunday. Similar to the previous few rounds, precip type will
be dependent on rates, and will be even more important as temps
will be slightly warmer going into the next round.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Overview:Low pressure continues up the East Coast Sunday,
passing over or just outside the Gulf of Maine. This keeps damp
conditions along at least the coast. Brief surface ridging
brings a dry and warm day Monday. The next weather system will
be broadening low pressure over northern Michigan pushing east.
This will swing an occluded/cold front through the forecast area
Tuesday before residing near New England through midweek.

Details: Broad low pressure will be morning northward up the
East Coast Sunday. Positioning takes the core of moisture well
offshore, but keeps precip chances likely along coastal areas of
the forecast area. Guidance has been very inconsistent with how
this system tracks and evolves through the late part of the
weekend. Because of this, current precip chances are rather
broad to account for a couple of possible solutions until
confidence improves.

There are two scenarios that stand out. The first is a more
prominent, stationary low deepening in the Gulf of Maine before
slowly moving northeast. This would increase QPF along the coast
and also into the Kennebec Valley region as potential banding
increases rates. This could also be a snowy outcome, albeit wet
and heavy with low ratios. The other, which leans most for the
going forecast, is a more progressive low that struggles to
pivot Atlantic moisture back towards interior portions. Because
the Sat system consolidates quicker and further out in the Gulf,
a lot of the forced moisture is instead advected north. Cyclonic
flow thus pulls in dry northerly air across the mountains,
downsloping into the interior. The coast remains dreary with
showers, but a bulk may avoid stratiform rain which will focus
around the Midcoast and Penobscot Bay region.

Deeper dry still looks to arrive Monday. This will be a nice
break between dreary systems, but clouds may still be around.
Temperatures push into the 50s, with a hint of lower 60s
possible in southern NH. At the same time, surface low pressure
will begin occluding over the northern Great Lakes, tracking
east towards New England.

Precip chances increase late Monday night through Tuesday.
Guidance has a quick moving cold front/triple point low passing the
area Tuesday morning which will bring rain or showers. Behind
the passage, winds may be gusty out of the west. Daytime mixing
could increase gust factor further, but will need to hone in on
timing for that. The low will become vertically stacked over
Quebec, but remain fairly progressive towards the Canadian
Maritimes. This looks to keep a tight pressure gradient over the
forecast area into mid to late week with potentially unsettled
and breezy conditions.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Short Term...MVFR to VFR conditions continue into tonight. IFR
conditions move into southern terminals late tonight with rain
and snow, and spread northward through the morning tomorrow.
Mainly IFR conditions linger through tomorrow night with
showers. The best chance for more MVFR ceilings will be at HIE
later Saturday night.

Long Term...A trend from IFR to MVFR should be underway Sunday
morning with mostly rain showers across interior terminals and
south coastal terminals. RA may be more continuous north of PWM,
but remains uncertainty on coverage and if SN mixes in. All
sites trend VFR Monday, with additional restrictions possible
late Monday night into Tuesday morning.

&&

.MARINE...
Short Term...SCA conditions develop in northeasterly flow by
Saturday, and continue through Saturday night as low pressure
moves northward toward the Gulf of Maine.

Long Term...SCA condition continue Sunday into Sunday night as
low pressure pulls north towards Nova Scotia. N winds become NW
and then W Monday as the low pushes further northeast. Wave
heights likely lower through Monday afternoon with below SCA
conditions through to Tuesday morning. Here, a cold front or
weak low could bring brief SCA conditions.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...Winter Weather Advisory from 5 AM to 5 PM EDT Saturday for
     NHZ005-007>009.
     Winter Weather Advisory from 2 AM to 2 PM EDT Saturday for
     NHZ011-015.
MARINE...Small Craft Advisory from noon Saturday to 8 PM EDT Sunday for
     ANZ150-152-154.

&&

$$


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