533
FXUS61 KBOX 172301
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
701 PM EDT Sun Aug 17 2025

.SYNOPSIS...
Widely scattered thunderstorms mainly south of the Mass Pike are
expected through sunset. More widespread but brief, passing
showers are expected tonight as a cold front clears the area,
along with increased onshore breezes. Cooler/below normal
temperatures follow for much of the work week with a return to
seasonable temperatures by Friday and Saturday. Dry weather
dominates too outside a few brief showers possible at mid-week.
Major Hurricane Erin will bring dangerous rip currents and high
surf to ocean exposed beaches in the Wednesday through Friday
time frame.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

7 PM update...

Cloudcover early in the day and poor mid level lapse rates have
acted to significantly diminish the severe threat this evening,
with any cells that have formed remaining shallow. Expect this
to continue into the evening with sub severe thunderstorms as
convection moves into a less favorable instability environment
and we lose daytime heating.

Key Messages:

* Scattered showers / isolated thunderstorms mainly south of the
  Mass Pike thru sundown. Although severe weather isn`t
  expected, some of the stronger storms could produce CG
  lightning and brief downpours.

* Cold front brings more widespread, but brief passing showers
  thru midnight, with NE onshore breezes and overcast.

* Cooler and much less humid by daybreak, lows in the mid
  50s-low 60s.

Details:

After being briefly delayed due to low clouds taking longer to
disperse, strong heating is now underway with temps in the mid 80s
to lower 90s. However only modest destabilization has taken
place amid poor 700-500 mb lapse rates, with about 500-1000 J/kg
of CAPE following a mixed parcel, highest values in CT but even
greater towards the PA/NJ area. Sfc mesoanalysis shows that
just ahead of a more pronounced cold front, is a prefrontal
trough which has shifted winds to west and dewpoints falling
into the low 60s across northern and western MA; a deepening Cu
just east of this trough axis across central MA and eastern CT
has developed which has popped some low- topped showers.
Additional convective-type showers and a couple thunderstorms
could still pop up through sundown, a little greater in net
coverage over CT-RI-SE MA, however the risk for severe weather
is viewed as very low to nil, with activity sliding off towards
the southeast.

Otherwise, we will then be awaiting a strong cold front, which
currently trails from the Adirondacks in NY ENE through central
portions of VT/NH and into interior ME. This front heralds the
arrival of a substantial change in airmass more typical of late
summer to early Fall. This cold frontal feature probably offers the
best chance at seeing rain showers across a wider area, but being
undercut by a shallow cooler and less-humid airmass, probably won`t
be a risk with thunderstorms with its passage. Expect increasing
overcast with a gusty N to NE windshift (gusts 20-30 mph) along with
a brief period of light rain showers ending by midnight. Overcast
should then prevail for most of the overnight, but dewpoints will be
crashing into the upper 40s to mid 50s by daybreak. Lows tonight in
the mid 50s to lower 60s, higher values along the south coast, Cape
and Islands.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
330 PM Update:

Key Messages:

* Breezy to start but less gusty by afternoon. Full sun, much
  lower humidity and cooler with highs in the 70s (low 70s
  coasts).

* Clear, cool and light winds Monday night, lows in the 40s to
  low 50s.

Details:

A sprawling 1027 mb high pressure area will be building
southeastward from Quebec into Southern New England through Monday
night.

Overcast from the overnight should disperse early in the morning
with full sunshine and deep dry air. Dewpoint temps will be crashing
through advective and mixing effects into the low to mid 40s by the
afternoon, so a refreshing airmass compared to the last day or two.
Will be a little breezy to start the day, and while onshore flow
persists all day, the breeziness should be subsiding as we move into
the afternoon. A much cooler airmass and onshore winds should keep
highs in the 70s, with low 70s along the immediate east coast.

As high pressure builds in Mon night and a very dry airmass, expect
strong radiational cooling which will help temps really plummet once
the sun goes down. Used MOS-based approaches for lows, in the mid
40s outlying valleys/locales which typically radiate well in
clear/light wind conditions to the lower 50s. Nice evening to pop
open the windows.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Key Messages...

* Cooler next week with highs in the 70s through Thu, warming up
  into the 80s Friday into the weekend.

* Mostly dry with a low probability window for rain showers between
  late Tue and Thu.

* Hurricane Erin brings dangerous surf and rip currents mid/late
  week.

* Next chance of rain not until around next weekend but details are
  uncertain.

High pressure continues to dominate southern New England`s weather
through late week, keeping things dry and temperatures on the cool
side over average for late August. By late next weekend an
approaching mid level shortwave and surface low pressure will
approach from the Midwest bringing a plume of warmer and more moist
air ahead of it. This will result in temperatures climbing back up
into the 80s Friday and Saturday while dewpoints creep back up into
the upper 50s/low 60s. So, it will be a bit more humid but not
anything excessive. Precipitation-wise there are two windows; first
a meager shortwave mid-week may bring some widely scattered showers
to the region on Wednesday but not everyone will see rain. Secondly,
that approaching shortwave brings the return of rain chances
sometime next weekend, but there is low confidence on how quickly it
arrives, be it Saturday or later. The biggest story this week will
likely be the marine/coastal impacts from Hurricane Erin. As it
veers well offshore of SNE it will nonetheless send plenty of energy
our way in the form of large waves, heavy surf, and dangerous rip
currents. Timing would be generally Wed-Fri, most affecting our
south facing, ocean exposed beaches.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

00z TAF Update:

Tonight: High confidence.

A cold front will be progressing southward from 00-04z from
north to south, accompanied by a gusty windshift to N/NE, a
brief period of rain showers in some areas, and ceilings
dropping to MVFR levels. N/NE gusts 20-25 kt (isolated 30 kt
gusts at times). Although showers should come to an end by 05z,
MVFR ceilings and NE breezes are likely to persist through most
of the overnight, scattering to VFR after 08z in NE MA.

Monday...High confidence.

Lingering MVFR ceilings improve to VFR by 15z in all areas. NE
winds around 10-12 kt with gusts 20-25 kt early but will be
slowly decreasing into the afternoon while shifting to E.

Monday night...High confidence.

VFR. Diminishing easterly winds.

KBOS terminal...High Confidence in TAF. Mainly VFR pre-frontal. Though
a limited risk for TS could exist between 23-01z, the overall
risk for TSRA seems to be on the downswing. A gusty N/NE
windshift likely by 02-03z with cold frontal passage (gusts
20-25 kt), with MVFR ceilings developing post-frontal.

KBDL terminal...High Confidence in TAF. Mainly VFR, although a
somewhat better chance for storms exists between 20-01z. A gusty
north windshift likely by 01-03z with cold frontal passage, with
MVFR ceilings developing post-frontal.

Outlook /Tuesday through Friday/...

Tuesday through Tuesday Night: VFR.

Wednesday: VFR. Slight chance SHRA.

Wednesday Night: VFR. Breezy. Slight chance SHRA.

Thursday through Thursday Night: VFR. Windy with local gusts up
to 30 kt.

Friday: Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today through Monday night...High confidence.

Good mixing over the land ahead of an approaching cold front will
result in near shore south coast wind gusts of 25 knots this
afternoon. We have hoisted small craft headlines for some of our
southern sounds and Bays. While these winds temporarily diminish
early this evening...winds will shift to the NE and gust between 20
and 30 knots late tonight into Monday across most waters with good
mixing in the cool air advection pattern. Therefore...small craft
advisories are in effect for most waters over this time. These small
craft conditions should diminish late Monday/Monday evening as
gradient weakens.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Local rough seas.

Tuesday Night: Winds less than 25 kt. Areas of rough seas.

Wednesday: Winds less than 25 kt. Areas of rough seas. Slight
chance of rain showers.

Wednesday Night: Winds less than 25 kt. Rough seas up to 16 ft.
Slight chance of rain showers.

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 17 ft. Slight chance of
rain showers.

Thursday Night: Strong winds with gusts up to 30 kt. Rough seas
up to 14 ft.

Friday: Moderate risk for Small Craft Advisory winds with areas
of gusts up to 30 kt. Rough seas up to 11 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 10 PM this evening to 8 PM EDT
     Monday for ANZ230-250-251.
     Small Craft Advisory until 4 PM EDT Monday for ANZ231>235-237.
     Small Craft Advisory until 7 PM EDT this evening for ANZ236.
     Small Craft Advisory from midnight tonight to 8 PM EDT Tuesday
     for ANZ254>256.

&&

$$

SYNOPSIS...Loconto/BW
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...BW
AVIATION...Loconto/BW
MARINE...Loconto/BW