Portsmouth, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

103
FXUS61 KGYX 221756
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
1256 PM EST Mon Dec 22 2025

.SYNOPSIS...
A white Christmas is looking more likely for much of the area
as a system moves through Tuesday into Wednesday. Accumulating
snowfall and travel impacts are likely for Tuesday afternoon
into Wednesday morning. The pattern remains active with some
snow showers possible on Christmas, another snowfall possible
Friday night and Saturday, and mixed wintry possible for
Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Fair weather continues this afternoon across the area, with
gusty winds expected to taper off over the next few hours.
Clouds will then encroach from the southwest tonight as our
snowy system approaches. This likely keeps low temperatures in
the southern half of New Hampshire and far southern Maine in the
upper teens and low 20s. Elsewhere, it stays clearer most of
the night allowing temperatures to drop into the low to mid
teens, with some single digits possible in northwestern Maine.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
Impacts and Key Messages:
* Accumulating snow, generally 2-5 inches, will bring impacts
  to the Tuesday evening commute with locally higher amounts,
  6-8 inches, on the Maine coastal plain.
* A Norlun trough setup may bring isolated amounts up to a foot
  somewhere on the central Maine coast.

Snow begins to enter southwestern New Hampshire in the 8-9 am
window Tuesday morning as surface low pressure approaches the
region from the northwest, dragging a warm front up from the
southwest. Snow will then gradually overspread the area from
southwest to northeast entering southern Maine, closer to the 1
pm hour. Rates are expected to be generally light as forecast
soundings now suggest minimal negative Omega values within the
DGZ. However, with profiles also well below freezing the snow
character is expected to be on the fluffier side so it likely
accumulates efficiently. This may lead to some travel impacts,
particularly in New Hampshire, as early as late morning and
early afternoon. Timing for impacts in Maine start later, but
everyone should expect a less then ideal evening commute. We are
generally looking at 2-5 inches across the area, with locally
higher amounts, 6-8 inches, on the central Maine coastal plain.
The lower end amounts look to be in southern and western New
Hampshire as these locations end up on the outer fringes of the
deepening low.

On the note of the locally higher amounts, guidance has had a
consistently strong signal for the low deepening and closing off
as it moves off the coast setting up an inverted trough back
across Maine. This has the look of a Norlun trough setup as
onshore winds will funnel moisture off the ocean into the trough
creating a locally higher band of QPF somewhere along the Maine
coast. Models have been trending up with this locally higher
QPF footprint in the range of 0.5-0.75 inches, and with snow
ratio on the order of 12- 15:1 this could easily produce warning
level snowfall. Norlun troughs are notoriously finicky with
their footprint, sometimes being as much as 40 miles wide, but
on the other extreme they have been as small as just impacting a
few towns. They are also notorious for really putting down the
snow where they do form, so it is not out of the question for
someone to end up with snowfall nearing a foot or more, but
again this would likely be isolated.

Due to the uncertainty, I`m not eager to upgrade the watch this
forecast cycle, but the footprint is good. Hi-res models are
locking on to the formation of a heavier snowband moving up the
coast with soundings showing much more negative Omega through
the DGZ, that could push rates 1-2 inches per hour. The
fortunate thing is this looks to occur mostly late Tuesday night
which should help keep travel impacts to a minimum and allow
snow clearing operations to be unimpeded. The take away should
be 6-8 inches with isolated higher amounts near a foot possible
within the current Watch area. I did go ahead with the
Advisories as this is higher confidence and didn`t want to
ignore the rest of the area due to the uncertainty along the
coast.

The last thing I will address is the more marginal temperatures
along the coast that the models want to say will be rain or a
mix. Looking at forecast soundings show that the reality is that
the warm layer is extremely shallow, so I`m not convinced. I
think the more likely outcome is that temperatures will wetbulb
to freezing, this would make the snow character a little
stickier, but it would be snow nonetheless.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Overview...

The Norlun trough departs the Maine coast Wednesday morning,
with clearing through the day. A weak disturbance passes though
on Christmas Day, with a few snow showers possible. The next
system then approaches on Friday, with more snow possible Friday
night and Saturday. The pattern remains active, with another
system possible for Sunday and Monday.

Details...

Snow comes to an end Wednesday morning as the Norlun trough
moves offshore and departs to the east. Seasonable temps are
expected as highs range from the mid 20s across the north, with
mid 30s along the coast. Breezy conditions are also expected,
with north wind gusts around 20-30 mph. Christmas Eve then looks
quiet and cool, with winds easing and temperatures falling
through the 20s. Lows bottom out in the teens overnight.

A weak shortwave swings through Christmas morning, bringing
some scattered snow showers, especially to northern areas. Up to
an inch of snow will be possible across the north, with
coatings possible elsewhere. More sunshine returns for the
afternoon hours, with highs ranging from the mid 20s to mid 30s
again.

Colder air returns for Thursday night and Friday, with lows in
the single digits, and highs in the teens and 20s. Friday starts
off dry, but clouds increase through the day as the next storm
system approaches from the northwest. There still remains a lot
of question as to how far into our area moisture will reach with
this system as high pressure across Atlantic Canada works to
keep the storm track south and west of New England. The best
chance for snow comes Friday night and Saturday, with the
highest chances across New Hampshire. We`ll continue to watch
this system, but right now it looks like it would either be snow
or a miss in most areas.

Should the Saturday storm be a miss, the next chance comes the
next day on Sunday. This system looks to track closer to New
England, with a greater chance for mixed precip. With it still
being 6 days away there aren`t too many details to discern at
this point, but given the active pattern confidence there is
relatively high confidence for impactful wintry precipitation on
Sunday, possibly into Monday.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Short Term...Fair weather and VFR conditions continue through
tonight with gusty winds tapering off early this evening. MVFR
ceilings and light snow don`t arrive until the end of the TAF
period for most terminals (18Z Tuesday). Tuesday afternoon into
early Wednesday morning expect widespread snow to bring
conditions down to IFR or lower. Heavy snow is possible for
coastal terminals from PWM up through RKD overnight Tuesday.

Long Term...Lingering LIFR to IFR conditions improve to VFR on
Wednesday as snow ends from west to east. Some MVFR conditions
are possible Christmas morning with scattered snow showers, then
VFR returns in the afternoon. MVFR ceilings are more likely to
linger at HIE with upslope flow developing. Restrictions are
then possible again late Friday through Saturday morning, with
the best chance for this across western terminals. Conditions
improve Saturday and Saturday night, then more restrictions are
likely Sunday with snow and mixed precip likely moving into the
region.

&&

.MARINE...
Short Term...Northwesterly gusts taper off below 25 kts and
seas fall below 5ft this evening. Winds then switch around to
southeasterly for Tuesday as a disturbance brings rain and snow
to the waters. As low pressure moves offshore and deepens winds
with back to northwesterly early Wednesday morning and wind
gusts and seas will build back above SCA criteria.

Long Term...Northerly gales ease Wednesday, with SCA conditions
lingering through at least Thursday from residual seas.
Northwesterly gales are then possible late Thursday through
early Friday. SCA conditions are possible Friday night and
Saturday in northeasterly flow as low pressure tracks southwest
of New England. A stronger low pressure system is then possible
for Sunday and Monday.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Winter Weather Advisory from noon Tuesday to 7 AM EST
     Wednesday for MEZ007>009-012>014-018-023-033.
     Winter Storm Watch from Tuesday afternoon through Wednesday
     afternoon for MEZ019>022-024>028.
NH...Winter Weather Advisory from noon Tuesday to 7 AM EST
     Wednesday for NHZ001-002-004-006-009-010.
MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ150-
     152-154.

&&

$$


NEAR/SHORT TERM...Baron
LONG TERM...Clair