Barnstable Town, Massachusetts 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

145
FXUS61 KBOX 121847
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
247 PM EDT Tue Aug 12 2025

.SYNOPSIS...

Patchy fog overnight gives way to another hot and humid day on
Wednesday. An approaching cold front will bring a chance for showers
and thunderstorms later Wednesday afternoon and evening.
Additional showers and thunderstorms are possible into Thursday,
but considerable cloud cover will limit instability. Seasonable
temperatures and lower humidity levels are expected for Friday
and Saturday, although temperatures briefly warm up again for
Sunday. After midweek, our next chance for rain is with a cold
front which looks to move in on Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...

Key Messages:
* Hot and dry this afternoon

* Mostly clear except for some patchy fog across southern RI and
  MA

SLP analysis shows a 1020mb surface high over the region with the
center of the anticyclonic circulation over coastal Maine. Aloft, a
588dm ridge and 850 temps of 18-20C are allowing for rapid warming
at the surface. Looking at another hot day today with most locations
away from the Cape and Islands likely seeing high temperatures in
the lower 90s. The saving grace for today is a deeply mixed and dry
boundary layer that should keep dewpoints and heat index values
lower. Outside of the high temperatures the other feature to watch
is the seabreeze. Guidance shows a bit of a later start to the sea-
breeze, likely not pushing inland until around 18z.

Tonight

Another quiet and calm night on tap with mostly clear skies.
Developing southwest flow will advect slightly higher dewpoints into
the region throughout the night. Lighter winds and clear skies
should allow for low temps to fall into the low to mid 60s across
the region. Patchy radiation fog and stratus are possible across the
south coast and Cape/Islands as increasing moisture is trapped
beneath a large subsidence inversion. Fog will likely be quick to
mix out Wednesday morning. &&

.SHORT TERM /WEDNESDAY/...
Key Messages

* Increasing heat and humidity on Wednesday

* Isolated to scattered thunderstorms possible Wednesday
  afternoon and evening

Wednesday

Increasing heat and humidity on Wednesday with dewpoints in the
upper 60s to possibly low 70s in the CT and Merrimack River Valleys.
Another hot day in store with high temperatures in the mid 90s. With
the increased humidity we can expect heat indices in the mid to
perhaps upper 90s.

A weak cold front will be the trigger for scattered showers and
thunderstorms later Wednesday afternoon. Not expecting much in the
way of severe weather with rather weak mid-level flow, poor lapse
rates, and effective shear <25kts. CAMs show CAPE values approaching
2000 J/kg so there could be a few instances of isolated stronger
downbursts and marginally severe wind. Bigger story will be the
chance for some heavier rain. HREF PMM precipitation forecast shows
swatches of 1"+ rainfall across portions of western and central
Massachusetts. The timing of the front will be well after peak
heating so activity will wane in coverage and intensity as it makes
its way east.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Key Messages:


* Still on the humid side Thurs, but considerable cloudiness with
  showers and t-storms as cold front moves offshore.

* Cooler with lower humidity levels Fri/Sat with drier weather.

* Warming trend with rising humidity levels Sun precedes a cold
  front on Mon.

Details:

Still on the humid side for Thurs as cold front will be slowly
lurching eastward and eventually offshore. Considerable cloudiness
limiting diurnal heating will cut into how much we can destabilize,
but we should still be able to muster another period of scattered
showers and thunderstorms. Not expecting severe weather with this
activity but could be capable of heavier downpours given the humid
airmass. Highs mid to upper 80s, with falling dewpoints/humidity
levels into the evening and overnight hours as ridging builds in
from the north.

High pressure then allows for dry weather and a cooler and lower-
humidity airmass to filter in for Fri into Sat. We get a brief
warmup into Sunday with rising humidity levels, which precedes a
cold frontal passage around Mon which will offer our next best
chance for rain.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

18Z TAF Update:

Tuesday Afternoon: High confidence.

VFR. Light S/SW winds around 5-10 kt with sea breezes along
both coasts (starting at BOS around 15z and PVD around 16-18z).
Sea breezes kick out toward the S/SSW 23-00z at 5-10 kts.

Tuesday Night: High confidence.

Mainly VFR, though coastal fog/stratus could bring IFR-VLIFR for
the Cape and Islands and potentially as north as PVD. Most
likely timeframe for development after 08z. Can`t rule
out the low chance for patchy BR in the CT Valley overnight. Light
SW winds less than 8 kts.

Wednesday: High confidence.

VFR. Southwest winds around 8-10 knots. Chance for localized
sea breeze at BOS. Chance for a few isolated to scattered
thunderstorms mainly after 18Z. Chances will be greatest west of
ORH.


KBOS terminal...High confidence in TAF. Seabreezes again
anticipated today around ~15z.

KBDL terminal...High confidence in TAF.

Outlook /Wednesday Night through Sunday/...

Wednesday Night: VFR. Breezy. Chance SHRA, slight chance TSRA.

Thursday: VFR. Chance SHRA, chance TSRA.

Thursday Night: VFR. Slight chance SHRA.

Friday through Saturday Night: VFR.

Sunday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

High confidence through the period.

South/southwest winds remain modest, generally below 10 knots.
This will keep seas on the lower side with significant wave
heights in the 2 to 3 foot range. Some fog/stratus may develop
over the south coast on Wednesday morning.

Winds increase out of the southwest to 10 to 15 knots on
Wednesday afternoon with a slight chance for an
afternoon/evening thunderstorm. SCY headlines may be needed east
of Boston where some gusts to 25 knots could be possible, though
confidence is low at this time.

Outlook /Wednesday Night through Sunday/...

Wednesday Night: Winds less than 25 kt. Chance of rain showers.

Thursday through Thursday Night: Winds less than 25 kt. Chance
of rain showers, slight chance of thunderstorms.

Friday through Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Air Quality Alert until 11 PM EDT this evening for CTZ002>004.
MA...Air Quality Alert until 11 PM EDT this evening for MAZ004>021-
     026.
RI...Air Quality Alert until 11 PM EDT this evening for RIZ001>008.
MARINE...None.

&&

$$

SYNOPSIS...Loconto/FT
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...Loconto
AVIATION...KJC/FT
MARINE...Frank/Loconto/FT