Merrimack, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

553
FXUS61 KGYX 200629
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
229 AM EDT Thu Aug 20 2026

.WHAT HAS CHANGED...
No significant changes made to the going forecast.

&&

.KEY MESSAGES...
1. After some early morning fog today, the day should be mostly
dry and cloudy. There is a chance of late day showers across
southern NH. Friday will likely be dry.

2. Rain chances both weekend days with a frontal system nearby.

3. Drier conditions to start next week, but clouds/showers remain
possible in the interior.

&&

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

Fog will lift by mid-morning today, and another seasonable day
is expected temperature-wise with highs in the mid 70s to lower
80s along with a good deal of clouds. Most of the forecast area
will likely remain dry today but there are still some guidance
members showing the northern fringes of a system moving to our
south to clip our southern zones later in the day. Therefore, we
will retain a chance of showers for southern zones, mainly for
southern NH into the evening hours.

High pressure settles in for Friday with fair and dry weather
and lower dewpoint values. Will disregard the outlier HRRR at
this time which bring showers to southern zones during the
afternoon and evening.

KEY MESSAGE 2 DESCRIPTION...

An initially stalled front well south of New England will start its
climb north towards the region as a warm front on Saturday. One or
more waves of low pressure will ride along this boundary, bringing
an unsettled weekend with periodic rain chances. One complexity to
this setup is two separate waves of moisture; one originating from
the Southeast U.S. on low-level southerly flow, while from the west
will be a 500 mb trough amplifying, and likely resulting in a
surface low developing. It is unclear exactly how these two features
interact, with a range of outcomes from a full phase with locally
heavy rainfall, to two separate rainfall maximums, which may or may
not be over the forecast area. What is known however is it will be a
rather moist environment with dew points surging to the upper 60s
and ensemble PWATs on the order of 1.5-1.8", which is a respectable
signal for this range. NBM mean for precip is generally only around
half an inch however, likely owing to uncertainty over the
extent/spatial coverage of precipitation both days this weekend. So,
hope is not yet lost for some dry hours (although rainfall is badly
needed).

CIPS/CSU machine learning guidance indicates a low risk for strong-
severe storms on Sunday, which is the best chance we have to get
into the "warm sector" with guidance indicating highs possibly
reaching the low 80s in spots. Right now shear looks quite poor
however, so not overly intrigued with things as they stand currently.

KEY MESSAGE 3 DESCRIPTION...

The upper-level low to our west takes over as the main driver of
local weather to start next week, with current indications that it
may fully close off and stall over Quebec. This would bring cyclonic
westerly flow to New England to start the week, with some mixed
signals whether it is more of a dry or moist wrap-around flow. Based
on QPF signals and local pattern recognition, there will likely be
some upslope-driven clouds and vertically-shallow precipitation in
the White Mountains and surrounding higher-terrain in the interior,
with conditions most likely to be dry closer to the coast. Despite
slightly cool temperature anomalies aloft, highs likely stay near
average with some downslope warming effects towards the coastal
plain.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
Through tonight...Mainly VFR, but an area of marine fog/stratus
brings IFR or LIFR to KRKD and probably KAUG through early this
morning. Valley fog likely brings IFR/LIFR to LEB and HIE
through this morning. Conditions should improve to VFR by
13-14Z. VFR conditions likely the rest of the Thursday. Tonight
-SHRA are possible across southern NH through around 06Z. Valley
fog could then bring IFR or lower restrictions for LEB and HIE.

Outlook:

Friday-Saturday night: Generally VFR during the day with fog
possible at night. Some brief MVFR restrictions are possible at
coastal terminals Saturday if showers materialize.

Sunday-Sunday night: Generally MVFR conditions with widespread
rain expected. Rain may taper off Sunday night giving way to
areas of fog that would likely bring about IFR conditions.

Monday: Conditions return to VFR, but there may still be some
MVFR and/or IFR conditions early.

&&

.MARINE...
Through Tonight...SCA conditions are not expected. Winds
briefly turn west, but remaining light, as weak boundary moves
into the waters. Winds return to more southerly during the day
as a weak front approaches, and these will switch to
north/northwest tonight behind the front. Fog will also remain
possible at times, especially from around Portland eastward.

Generally sub-SCA conditions are expected to prevail late week
into early next week, but there is potential for a coastal
system to bring some brief SCA conditions over the weekend.
Areas of fog are also likely through much of this period.

&&

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

&&

$$

DISCUSSION...Barker/Ekster