Merrimack, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

774
FXUS61 KGYX 041941
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
341 PM EDT Wed Jun 4 2025

.SYNOPSIS...
Heat and humidity builds Thursday ahead of a slow moving cold
front that will bring scattered showers and storms Thursday
afternoon and evening, a few of which could be strong to severe.
The front will linger near New England Friday into the weekend
with waves of low pressure bringing daily chances for showers
and storms. High pressure briefly builds in early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
The rest of the day is a basically a what you see is what you
get forecast. Warm/hazy conditions will continue with filtered
sunshine from the elevated wildfire smoke. For tonight, the
increased dewpoints will keep temperatures mild and mostly in
the 50s and low 60s in some places.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
The outlook for Thursday continues to be a hot one. We`ll
continue to see mostly sunny into early afternoon with dry air
and the upper ridge more or less still in place. There could
still be lingering elevated wildfire smoke, but it`s modeled to
not be as pronounced as today. Good mixing and even warmer air
aloft will allow temperatures to climb higher than those of
today with 850mb temps of +16 to +19C, which supports highs
reaching the upper 80s to low 90s away from the coast. With
dewpoints climbing into the lower 60s over much of the area
ahead of a slow-moving cold front, it will feel more humid out
with heat index values forecast to reach the low-mid 90s.

As the front continues its approach, the ridge still start
losing its grip in the afternoon over the area, especially
toward the foothills and mountains. With increasing lift
from the front, we should start seeing showers and
thunderstorms develop during the afternoon and into the early
evening hours. Instability is favorable for a few strong to
severe storms with hail and damaging winds as the main hazards
with mean MUCAPE from the HREF coming in around 1000-1500 J/kg.
Wind shear is a little more marginal at 25 to 30 kt in the
0-6km layer, and there are a couple of other potential limiting
factors. Mid-level lapse rates don`t look particularly
favorable, and dry air aloft may also limiting coverage...which
is what a lot of the 12Z CAMs seem to hinting at. However, the
trade off with the dry air is that it increases DCAPE and the
potential for strong to damaging wind gusts in any robust
updrafts that get going.

Farther to the south and toward the coast, forecast soundings
are showing quite a bit of dry air aloft as well as a small
temperature inversion, which is expected to keep chances lower,
especially near the coast where the seabreeze will probably add
even more stability.

Showers/storms will then taper off through the evening, but
there will be a continued low chance of showers overnight (20%)
along with patchy fog. Overnight lows remain very mild and in
the 50s and 60s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Friday starts off unsettled and warm. Highs in the upper 70s and
lower 80s are likely as ridging remains overhead. Upper-level
divergence and a mid-level shortwave should allow for a surface low
to develop and move northeast Friday night and into Saturday. A few
thunderstorms are likely Friday afternoon, as warm temperatures help
build instability. A band of MUCAPE in the range of 700-1200 J/kg,
and a little bit of wind shear could help develop showers and
storms, though the severe threat remains limited. However, PWATs
exceeding 1.5 inches could allow for these storms to produce
efficient rain rates, plus the lack of directional wind shear may
allow for some storms to train, potentially bring prolonged heavy
rain, and localized minor flash flooding to a few. In addition, the
WPC has issued a day 3 marginal risk Excessive Rainfall Outlook for
much of western New Hampshire.

There is some uncertainty on a specific track, but the general model
consensus has a rain axis pivoting over central NH and Maine by
Saturday morning. Steadier rain may continue through the day
Saturday. It should be a little cooler, with Saturday`s highs
expected to be in the 60s and low 70s.

By Sunday, some lingering showers are possible earlier on as the
front progresses offshore. Any of these remaining showers should
clear the area in the afternoon. A dry Monday looks likely as
ridging quickly builds back into the region. Another shortwave
arrives towards the middle of next week, with more widespread rain
possible Tuesday and Wednesday. The end of next week looks drier,
though a low may try to move in over next weekend. Next week`s
temperatures look to be in the 70s through much of the week.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Short Term...Mainly VFR through Thursday, although there may be
a bit of fog or low stratus late tonight into Thursday morning
with potential looking too low for TAF inclusion. Otherwise, a
cold front brings increasing chances for showers and storms
Thursday afternoon and evening which could bring TEMPO IFR
restrictions should they pass over a terminal. These should
diminish through Thursday evening, but then there may be fog or
low stratus to contend with Thursday night.

Long Term...
MVFR expected Friday morning, with LIFR likely with patchy fog along
the coast. Restrictions lower Friday afternoon as thunderstorms
develop across the northeast. Restrictions are expected to stay down
through Saturday evening at least, as steady rain and thunderstorms
move through the area. Restrictions may improve for Sunday and
Monday, as showers and storms become increasingly more isolated.

&&

.MARINE...
Short Term...Southerly flow continues through Thursday with
conditions remain below SCA levels but may brief switch to more
westerly overnight and into early Thursday morning. A cold front
approaches from the north and west late in the afternoon and
evening on Thursday, and ahead of this front, fog may return
over the waters along with a chance of showers and a couple of
storms. Fog likely lingers into Thursday night.

Long Term...
Variable winds at near 10-15kts expected through the weekend
and into early next week. 1-3ft seas expected Friday and
Saturday. Seas gradually increase on Sunday, seas may reach SCA
levels over the open waters along the Midcoast Sunday afternoon.
Seas gradually diminish afterwards, through the first half of
next week.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Air Quality Alert until 11 PM EDT Thursday for MEZ023>028.
NH...Air Quality Alert until midnight EDT tonight for NHZ013-014.
MARINE...None.

&&

$$


NEAR TERM...Combs
SHORT TERM...Combs
LONG TERM...Palmer