726
FXUS61 KBOX 230812
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
412 AM EDT Mon Jun 23 2025

.SYNOPSIS...
Dangerous heat and humidity through early next week peaks on
Tuesday. The heat begins to ease on Wednesday then turning
cooler for the end of the week into next weekend with daily
chances of showers and possibly a few thunderstorms.

&&

.NEAR TERM /THROUGH TONIGHT/...
400 AM Update:

Key Messages:

* Hot and oppressively humid conditions for most of Southern New
  England today, with light to calm winds. Highs in the mid 90s to
  around 100F away from the coast, with dangerous heat indices 100-
  110F. Extreme Heat Warnings/Heat Advisories remain vaild.

* Seabreeze this morning will keep the North Shore and immediate
  Boston/South Shore coasts "less-hot".

* Muggy and very warm night tonight, offering no relief.

Details:

Its been a pretty warm and muggy overnight, with dewpoint temps
upper 60s to low 70s. With light winds, air temps are a little more
varied but are generally in the upper 60s to the mid to even upper
70s (current 06z ob at Boston Logan was 78 degrees). Patchy
radiation fog has developed in some locations, but under expected
strong insolation, any mist or fog should disperse shortly after
sunrise. The main feature of interest is an anomalously strong upper
level ridge located near the Allegheny Mtns, a feature which is
expected to build northeast today and tonight. Meanwhile a sfc ridge
was nosing southward from ME into the Canadian Maritimes, which will
help bring a period of onshore flow to the immediate eastern coast
today.

While the immediate east coast of MA ends up being "less-hot" today
with an onshore flow/seabreeze developing early today, we still
expect today and tomorrow to have a combo of hot temperatures and
oppressive levels of humidity leading to dangerously high heat
indices for the majority of Southern New England. There have been no
changes to the existing heat headlines and remain valid. We again
encourage everyone to take protective measures to mitigate against
developing heat-related illnesses, including taking frequent breaks
in shaded or cooled/air conditioned areas and staying hydrated.

Full sun and 925 mb temps warming to as much as +27C will help push
high temperatures away from the RI/MA coasts into the mid 90s to low
100s, with heat indices in the 105-110 degree range. Compared to
Tuesday, today might arguably feel the most oppressive when you
factor in that winds will also be very light. Along the immediate
coast, we expect high temps in the mid to upper 80s, though Boston
Logan probably sees a late-day high once winds from the seabreeze
flip to an offshore/SSW direction.

For tonight, the upper ridge axis crests over SNE. At the same time,
we start to get into more of a westerly sfc gradient and modest
westerly winds. We expect another very warm and muggy night,
offering no appreciable relief from the daytime heat and humidity.
Lows in the low to mid 70s (mid/upper 60s Cape and Islands), and
should be a few degrees warmer than tonight. Could see south-coastal
fog re-develop again given the very muggy conditions and weaker west
winds.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
400 AM Update:

Key Messages:

* Tuesday is the hottest day of the stretch of heat and
  humidity.

* Away from the Cape and Islands, widespread upper 90s to low 100s
  high temperatures are expected which could threaten records.
  Heat indices 105-110F.

* Westerly winds around 10 mph with some modest gusts too.

* Warm and muggy night, and generally dry.

Details:

Tuesday ends up being the hottest day of the stretch across all of
SNE, as the very warm temps from overnight are expected to soar
under full sun. There will also be a boost from westerly downsloped
winds, which actually are a little on the breezy side (around 10 mph
with gusts up to 20 mph). With similar 925 mb temps to today,
forecast high temps should reach well into the upper 90s to low
100s! The west winds mitigating any seabreezes will mean that even
the immediate coast will see high temperatures to these values,
which includes sites such as Logan Airport and the Boston
waterfront. Daily record highs seem likely at some of our climate
sites on Tuesday, and in some instances could possibly threaten all-
time June high temps. It wouldn`t surprise even if some locations on
the Cape see highs reach 90 degrees, although the forecast calls for
mid to upper 80s. Dewpoints probably mix a few degrees lower during
the afternoon thru westerly downsloping flow and good mixing, which
means that heat indices should be generally similar to today
(though quite a bit hotter near the immediate coast), in the
105-110F range for most, and around 95-104 degree range for the
Berkshires.

The upper level heat ridge builds further southward on Tuesday
evening, as a cold front drapes itself over northern New England. We
could have some showers or thunderstorms to monitor to our north,
but these appear more likely remain north of SNE and thus offered
dry weather. Coming out of the very hot Tuesday and with westerly
winds continuing, lows Tuesday night stay in the 70s across most of
Southern New England.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Key Messages:

* Very warm again on Wednesday, although cooler near the coast
  with onshore flow. Possible need for heat advisories for
  interior Southern New England.

* Cooling trend toward near to cooler than normal temps for Thu
  thru the weekend as onshore flow develops.

* Daily chances of showers and perhaps a few t-storms Thu
  through Sun as well.

We then get into a stronger westerly mid-level flow on Wednesday,
as upper level ridge continues to shift southward. Slightly
cooler temps aloft and a NE to E wind shift, leading to an
onshore flow for the eastern coast. But still a hot day with
highs low- mid 90s inland and mid- upper 80s along the coast,
cooler Cape/Islands. We could still see heat indices around Heat
Advisory criteria again on Wednesday in western and central MA
and CT. So we could need Heat Advisories for these areas after
the extreme heat warnings expire, though there will be more in
the way of cloud cover and even possibly some showers and
t-storms given PWAT values near 2" and MUCAPEs on the 1000-1500
J/kg range.

We finally cool off in all areas on Thursday right through the
weekend with a prolonged period of onshore flow. Anticipate
highs closer to the low to mid 70s, which are cooler than
normal for late June. However daily shower/thunderstorm chances
appear each day as a series of weak/hard to time waves move
through the west flow. It still looks like thunderstorm
parameters on the global models/ensembles are low enough such
that severe weather doesn`t look likely with these daily
storm chances.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

06z TAF Update:

Through 12z Monday: High confidence.

Mainly VFR, though patchy IFR-LIFR BR/FG to develop before
sunrise in some locations. Best chance at BAF and the Cape/ACK
airports. Light winds (calm at times), though will become a
light N to NNE toward 12z Mon at BOS.

Today: High confidence overall, though moderate on start time
of coastal seabreezes.

Any BR/FG from overnight disperses early (before 13z) with VFR.
Light and variable winds, with seabreezes at BOS, PVD and the
Cape airports. Thinking seabreeze develops early in the day, as
soon as 14z at BOS and 16z at PVD.

Tonight: High confidence.

Mainly VFR, though patchy BR/FG possible again with better
chance for the Cape airports. Light west winds, increasing in
speed toward morning to around 5-10 kt.

Tuesday: High confidence.

Any BR/FG from overnight disperses shortly after sunrise with
VFR thereafter. W winds increase to around 8-12 kt with gusts to
20 kt.

KBOS Terminal...High confidence in TAF. VFR. NW winds overnight
bcm NE toward 11-12z; seabreeze then develops as soon as 14z.

KBDL Terminal...High confidence in TAF. VFR. Light, valley-
driven S winds today. Hazy conditions possible given hot and
humid weather.

Outlook /Wednesday through Friday/...

Wednesday: VFR. Slight chance SHRA.

Wednesday Night: VFR. Chance SHRA, isolated TSRA.

Thursday: Mainly VFR, with local IFR possible. Chance SHRA,
isolated TSRA.

Thursday Night through Friday: Mainly VFR, with local IFR
possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Tuesday Night: High confidence.

Conditions remain sub-SCA through this period. Light winds,
easterly near the immediate coast, for today, with an increasing
west wind tonight through Tue night to around 10-15 kt with
gusts 20 kt by Tue night. Nightly risk for fog on most waters.

Outlook /Wednesday through Friday/...

Wednesday: Winds less than 25 kt.

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

Thursday: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms.

Thursday Night: Winds less than 25 kt. Slight chance of rain
showers.

Friday: Winds less than 25 kt. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Extreme Heat Warning until 8 PM EDT Tuesday for CTZ002>004.
MA...Extreme Heat Warning until 8 PM EDT Tuesday for MAZ003>007-
     010>021-026.
     Heat Advisory until 8 PM EDT Tuesday for MAZ002-008-009.
RI...Extreme Heat Warning until 8 PM EDT Tuesday for RIZ001>007.
MARINE...None.

&&

$$

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