Derry, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

642
FXUS61 KGYX 252311
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
711 PM EDT Sat Jul 25 2026

.WHAT HAS CHANGED...
Ni significant changes to the going forecast for this evening
and overnight.

&&

.KEY MESSAGES...
1. Pleasant weather continues through Sunday night under high
pressure.

2. Quiet weather comes to an end with unsettled weather
returning for the first half of next week with the potential for
areas of heavy rain.

&&

.DISCUSSION...
KEY MESSAGE 1 DESCRIPTION...
It will continue to be a pleasant afternoon and evening across
the region with temperatures into the lower 80s and low humidity
prevailing. Diurnally driven cu will dissipate with the loss of
heating this evening and this combined with light winds and low
dew points will allow for another night of radiational cooling.
There are some suggestions that a bit of high level cirrus may
arrive late tonight but this tends to not have a significant
impact on cooling. As a result, used mostly MOS guidance for
forecast lows with most places falling into the upper 40s to
lower 50s. Valley fog is likely once again overnight and there
could also be some fog towards the Mid Coast and adjacent
islands.

Surface high pressure will persist on Sunday into Sunday night,
allowing for continued dry conditions with near average
temperatures. High temperatures will be into the 70s to lower
80s (coolest along the coast), with low temperatures mostly
into the lower 50s.

KEY MESSAGE 2 DESCRIPTION...
Global models are in good agreement that an unsettled pattern
develops next week as several shortwaves look to traverse to the
broader 500 mb trough that has been sitting over the region for
quite some time now. However, this is about all that the models
agree on at the moment as the extent of precipitation we may
see as a result is very much up in the air. The Euro ensemble
has maintained its position of having a seasonably strong
vertically stacked low pressure move through the area in the
Tuesday-Wednesday timeframe. This is combined with stronger
moisture transport bringing PWATs up to 1.5 to 1.75 inches south
of the mountains, and as a result the ECMWF Ensemble is the
most bullish on QPF with high probabilities (50-60%) of
widespread amounts greater than an inch, and some moderate
probabilities (30-40%) starting to show up for amounts greater
than 2 inches. The GEFS and Canadian Ensemble are currently not
favoring the development of an upper low, and even keep the
surface low more to our south. The GEFS also has much weaker
moisture transport with PWATs in the 1.25 to 1.5 range. As a
result the current probabilities for more than an inch of QPF is
very low (~10%). Unsurprisingly this is making the current NBM
spread very large with the 25th percentile around a tenth of an
inch and the 75th percentile upwards of 2.5 inches. To say there
is currently uncertainty in the rainfall amounts is an
understatement, but the hope is that over the next couple days
the RAOB network will begin sampling this developing pattern,
and can better inform the models.

Thunderstorms are possible each afternoon as instability
gathers, even with daytime temperatures bordering on the
seasonably cool side. At this point there isn`t anything that
screams severe weather, but the uncertainty in low pressure
tracks isn`t helping that case either. I think the best way to
summarize the long term at this point is that there is a high
confidence in seeing periods of showers (and some thunderstorms)
which may be heavy at times, but exact amounts, the track of
low pressure, and the duration low pressure lingers are very low
confidence and trends are going to have to be monitored closely
over the coming days.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Through 18Z Sunday... VFR conditions will prevail through Sunday
night. The exceptions are at KLEB and KHIE where valley fog is
once again likely, especially between 09Z-12Z Sunday. Marine fog
is also possible at KRKD between roughly 08Z-13Z Sunday. SSE
winds will persist through 00Z Sunday at 5-15 kts before
becoming light and variable tonight and then becoming SSE again
on Sunday. No LLWS is anticipated through the period.

Outlook...
Monday: Generally VFR. Isolated afternoon showers and storms
are possible which may bring about TEMPO MVFR restrictions.

Tuesday-Thursday: This period is quite uncertain, but MVFR
conditions are likely to be the most common as low pressure
lingers overhead or somewhere close by. This is expected to
bring widespread rain showers. Fog would likely develop
overnight in the wake of rain showers bringing possible IFR
restrictions.

&&

.MARINE...
Winds and seas will remain below SCA criteria through Sunday
night as high pressure remains near or over the Gulf of Maine.

Generally sub-SCA conditions should start the week, but as low
pressure moves into the region toward midweek chances of 25kt+
winds gusts are going to increase. Wave heights are more likely
to reach or exceed 5 feet late week as the aforementioned low
pressure moves over the waters.

&&

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

&&

$$

DISCUSSION...Baron/Ekster/Tubbs
AVIATION...
MARINE...