Merrimack, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

823
FXUS61 KGYX 041602
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1202 PM EDT Sun May 4 2025

.SYNOPSIS...
A stationary front will reside along or just off the coast today
as moisture flow remains overhead. This will bring periods of
showers today and tonight. With cut off low pressure remaining
in the Ohio Valley, unsettled conditions continue into early
week with continued chances of rain and showers.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

11:55am Update... Mostly minor updates to POPs and temps
through the rest of the day. No notable changes as the forecast
remains on track. A steadier shield of showers and light rain
gradually presses further south through the afternoon.

640am Update...Just some slight changes to PoP this morning
based on current radar display. Forecast is on track, with
NAMnest run from last night verifying pretty well with precip
locations.

Previous Discussion...
Another damp spring day set today, but lacking fuel for
thunderstorms. A cut off low positioned over the Ohio Valley and
broad Bermuda High will keep the weather pattern over northern
New England nearly steady state through early week. The
unsettled conditions today will be helped by a mid level trough
dipping through central Quebec.

Moisture flow aided by southerly LLJ along the East Coast will
keep a plume of PWAT values around 1 inch overhead. With any
lift or forcing in this environment, it will be easy to produce
periods of rain or showers. Convergence between the incoming mid
level trough and stationary boundary off the coast will provide
this, and guidance continues to suggest a primary band of
rain/showers beginning across the mountains early this morning
and slowly pivoting south. Moving in unison south of this band,
scattered showers will be occuring through the day. The more
scattered coverage a result of a layer of dry air in the mid
levels.

Considering the moist environment, it will be difficult to get
peaks of sun today. Perhaps some clouds thin enough in central
Somerset later today. Temperature reflect this, only pushing
into the upper 50s to around 60.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
By this evening, focus of showers will have shifted south
across central/southern NH and southern/coastal ME. Dry air
arriving in the mid levels deepens across the north and this
will provide a sharp cutoff of precip. HREF members are in
pretty good agreement with timing/placement of this cutoff, and
have adopted these into the PoP forecast.

With the mid level trough pushing off the Canadian Maritimes
Monday and cut off low still over the Ohio Valley, southerly
suppression of moisture is relieved. PWATs again climb north
into the afternoon, with showers continuing across NH and into
western ME.

Thinner clouds towards central ME will promote slightly warmer
temperatures on Monday. Highs climb towards the lower 60s, while
much of points south see another day of mid to upper 50s.

Through Monday, QPF will be beneficial for ongoing
abnormal/moderate drought locations in the forecast area. Rain
rates will be slow enough to prevent rapid runoff or flash
flooding, but paced well to soak in across southern NH.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
1020 PM Update...

A shift in the seasons is evident in the mid to upper level pattern
over North America through the upcoming week. A pair of cut off lows
will meander over the CONUS with the jet stream shifting north into
Canada. The easternmost low will influence the weather over New
England Tuesday through at least Wednesday. As this upper low
attempts to exit Thursday a trough will drop SE out of Canada with
ensembles favoring troughing along the East Coast through the end of
the week. There will be chances for showers every day Tuesday
through Friday while there will also likely be some extended periods
of dry conditions. Ensembles are in good agreement that a widespread
soaking rain is likely Tuesday into Wednesday with mean QPF around
1.0 to 1.5 inches. Thereafter, PoPs will run in the 20 to 40 percent
range Thursday into the weekend. Wednesday looks like the warmest
day with highs in the upper 60s to low 70s with some partly cloudy
skies in the afternoon. Most other days in the period will have
highs in 50s to 60s.

Previously...

Impacts / Trends:

-Generally a cool, damp and showery week ahead.

-Foggy, with soaking rain likely Tuesday into Wednesday AM

-Showery weather continues through Thursday AM

---------------------------------------------------------------------

Temperatures Tuesday are also likely to be tampered, as onshore
flow could advect low-level stratus into most of northern New
England. There could be a sharp temperature gradient depending
on how far northerly the dense clouds go, with warmer
temperatures likely in clearer areas in the north. However, the
most recent GFS and NAM runs both take the temperature gradient
all the way to the Canadian border, so almost everyone should
see a gloomier and rainy Tuesday, with highs in the 50s most
places.

An upper-level low stalled out over the Ohio River Valley will
arrive in the northeast Tuesday night, bringing a slow-moving
surface low and steady rain to New England Tuesday evening. Rain
could continue through the day Wednesday, with the heaviest rainfall
amounts most likely arriving Tuesday night into Wednesday morning.
Impacts are not likely at this time, with rainfall totals between 1-
1.5" of rain possible through Wednesday night.

The upper-level low finally moves through the area Wednesday night,
though conditions do not really look to get drier. The
aforementioned upper-level low integrates into an upper-level low
over Canada, which moves southward, bringing more showery weather
through Thursday.

Ensemble members in both ECMWF and GFS camps become very bimodal
towards the end of this week. Some members show high pressure moving
in, allowing for a potentially dry next weekend. Other members show
a low developing over the Carolinas, moving up the coast and
potentially bringing unsettled weather Friday and Saturday.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
Short Term...MVFR/IFR continues today, with more of a trend to
MVFR for most terminals later this afternoon. SHRA will trend
south through the afternoon. These continue overnight,
particularly in southern NH. With a steady pattern, ceiling and
vis restrictions remain steady today and into tonight.

Long Term...Low-stratus, patchy fog and showers will likely lower
restrictions through most of the first half of the week. A few
rumbles of thunder are possible Tuesday night as well. Restrictions
may stay down through the remainder of the week as unsettled weather
continues.

&&

.MARINE...
Short Term...Winds and seas are expected to remain below SCA
thresholds thru the period. Stationary front will remain over
the waters, providing calm flow but with fog and showers.

Long Term..Northeasterly winds at 10-15kt and 2-4ft seas are likely
Monday morning. Winds and seas stay below SCA thresholds through the
first half of the week, though seas gradually increase Tuesday night
as a low moves through the area. Winds and seas should stay below
SCA thresholds. Winds will also shift to southerlies through the
same timeframe.

&&

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

&&

$$


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