Portsmouth, New Hampshire 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

396
FXUS61 KGYX 200652
AFDGYX

Area Forecast Discussion
National Weather Service Gray ME
252 AM EDT Fri Jun 20 2025

.SYNOPSIS...
Strong westerly winds will prevail today behind a sharp cold
front with lowering humidity. A disturbance will approach from
the west Saturday night into Sunday, bringing the chance for
scattered showers but otherwise mainly dry and comfortable
conditions are expected. Heat and humidity then looks to briefly
return early next week before temperatures cool towards
seasonable levels by mid to late week.

&&

.NEAR TERM /THROUGH TODAY/...
Latest RAP13 pressure analysis early on this Friday morning
shows closed low pressure located over southern Quebec with the
H5 trof axis trailing behind over central NY State. At the
surface, a sharp cold front is located near the CT River Valley
with a wind shift to the west behind this front. Nighttime
microphysics and water vapor imagery shows a plethora of clouds
across the region and radar data shows a narrow area of
convective showers moving east-northeastward over central NH in
association with the crossing front. Current temperatures are
into the 60s and 70s and little in the way of additional cooling
is likely through sunrise.

The aforementioned cold front will exit to our east later this
morning as closed low pressure tracks towards the Crown of ME.
This combined with sfc high pressure located near Hudson Bay
will cause a negative H5 height anomaly and unseasonably strong
pressure gradient over the region. Deep mixing combined with a
strengthening LLJ of around 50 kts at the top of the mixed layer
will result in a gusty day with westerly wind gusts between
35-45 mph and a few gusts nearing 50 mph. Given that trees are
fully leafed out, this could cause down tree limbs and a few
trees and power lines could be downed. This introduces an
elevated power outage threat and therefore a Wind Advisory has
been issued for all of NH as well as western ME with the
exception of the Mid-Coast region.

These winds will also create potentially dangerous conditions on
area lakes with waves up to around 5 ft forecast for Sebago Lake
and Lake Winnipesaukee. Stronger winds can also be expected
across the higher terrain.

High temperatures will be into the 60s across the north with
upper 70s/lower 80s south. Dew points will fall through the day
back into the comfortable 50s. Scattered showers will persist
across the far north and mountains but elsewhere it should be
mainly dry with partly sunny skies.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/...
Winds will quickly diminish this evening and overnight tonight
as sfc high pressure builds in from the west. This combined with
mainly clear skies and relatively low dew points will likely
allow for radiational cooling. Therefore used MOS guidance for
overnight lows, which brings readings down into the 40s in some
inland and northern valleys with 50s in most other locations.
Valley fog is likely to develop overnight.

Saturday will feature comfortable conditions as high pressure
crests over the area. High temperatures will be into the 70s and
80s under partly to mostly sunny skies. Westerly winds will be
weaker as well at around 10-15 mph.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
1105 PM Update...No significant changes in the latest NBM with
strong signal for dangerous levels of heat and humidity Monday
into Tuesday. It does look like this will be a short duration
heat event with temperatures abating Wednesday into Thursday.


...Dangerous Heat Monday Through Tuesday...

As the ridge builds to our south Saturday Night, attention will turn
to upstream convection that models have shown traversing on the
periphery of the ridge into New England by Saturday Night. There is
low confidence on the placement of this feature, but have upped pops
due to the run to run consistency. The residual cloud cover will
linger through at least midday Sunday as a warm-front lifts north.
Humidity values will surge with dewpoints in the upper 60s.

Attention then turns to the much advertised heat dome with 500mb up
to 600 dm across the eastern U.S. by Monday through Tuesday.
Temperatures will reach 90 for many areas from the foothills
southward, warming another 5 degrees or so further by Tuesday.
Forecast temperatures are at/near record highs for some locations,
particularly for Tuesday which looks to be the hottest day of
the forecast. The humidity will be elevated as well, leading to
heat index values into the mid 90s and towards 100 degrees in a
few locations. The heat will linger until a cold front from
Canada drifts south. There is low confidence in the timing of
this feature, with a few model guidance suggesting heat could
linger into Wednesday, at least for S NH. The front will bring
some showers and thunderstorms, which is currently forecast for
Tuesday night. How far south the boundary sags south will
greatly impact how much relief from the heat the region will
experience.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...
Short Term...Pockets of low ceilings/FG will persist until
around 12Z this morning and result in IFR to LIFR
restrictions... mainly at KRKD. VFR conditions with then prevail
today at most TAF sites except at KHIE where MVFR CIGs will
persist along with scattered -SHRA at times. Gusty westerly
winds are expected with gusts between 30-40 kts. Winds will
quickly diminish by 00Z this evening with VFR conditions until
after midnight when valley FG may develop and bring restrictions
at KLEB, KHIE, and KCON. VFR conditions will them dominate on
Saturday with westerly winds of 5-15 kts. No LLWS is anticipated
through the period.

Long Term...Increasing chances for showers and storms Saturday
night into early Sunday with restrictions possible. VFR then
expected Monday and Tuesday.

&&

.MARINE...
Short Term...Went ahead and upgraded the small craft advisory
over the outer waters to a gale warning as westerly wind gusts
up to 35 kts are now expected today along with seas of 3-7 ft.
Over the bays, westerly wind gusts up to 30 kts can be expected
with seas of 1-4 ft. Winds and seas diminish tonight and remain
low on Saturday as high pressure builds over the waters.

Long Term...An extended period of great boating conditions are
expected Sunday through early next week with a ridge over the
region. Winds will be variable to SE/SW at times between 5-15
kts. Seas will be 1- 3 ft for much of the period.

&&

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Wind Advisory from 10 AM this morning to 8 PM EDT this evening
     for MEZ007>009-012>014-018>021-023>025-033.
NH...Wind Advisory from 8 AM this morning to 6 PM EDT this evening
     for NHZ001>015.
MARINE...Gale Warning until 8 PM EDT this evening for ANZ150-152-154.
     Small Craft Advisory until 8 PM EDT this evening for ANZ151-
     153.

&&

$$

NEAR TERM...Tubbs
SHORT TERM...Tubbs
LONG TERM...Jamison/Schroeter