458
FXUS61 KBOX 160615
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
215 AM EDT Wed Jul 16 2025

.SYNOPSIS...
Heat and humidity peak today but lasts into Thursday. A cold
front will bring showers and thunderstorms Thursday before
relief from the heat arrives this weekend. Drier and more
seasonable weather is ahead next week.

&&

.NEAR TERM /THROUGH TODAY/...
215 AM Update

Key Messages:

 * Peak of heat and humidity today.

Upper ridge builds into southern New England today which brings
rising heights and warming temperatures aloft, making this the
hottest day of the week. Heat indices this afternoon are
expected to top out around 100 degrees in many areas away from
immediate coast where onshore winds will keep it slightly cooler
(but still hot). Along E MA coast, gradient remains weak enough
to support sea breezes for a few hours from later this morning
into early afternoon, then we should see winds shift back to
S/SW which will boost temperatures there into 90s.

Speaking of S/SW flow, we remain in the usual summertime pattern
of nighttime and early morning low clouds/fog near South Coast,
Cape Cod, and Islands which should persist today and through the
end of the week.

Despite a lot of instability, ridge will also help suppress
convective development as forecast soundings show a strong cap,
but it`s possible we see a stray shower or even a thunderstorm
form toward sunset as boundary layer cools off just a little,
similar to what we saw yesterday across interior. However, we
don`t have a lifting mechanism strong enough to overcome mid
level cap so it will be difficult to see anything organized or
potentially severe.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/...
215 AM Update

Key Messages:

 * Showers/non-severe storms possible overnight into Thu AM.
 * Severe storms possible late Thu afternoon/evening.
 * One more day of dangerous heat and humidity Thu.

Lead short wave over Ohio Valley heads east tonight as upper
ridge becomes suppressed and retreats offshore. It will provide
larger scale lift upon an airmass that is already unstable with
increasing PWATs, which should result in showers and perhaps
embedded thunderstorms overnight into Thu morning, especially
across western/central MA and CT.

High-res models show a few potential outcomes, either an area
of weakening convection heading into southern New England
overnight, or what`s been called the "7-10 split" where
convection splits into two areas where one lifts to our north
and the other shifts south, leaving much of the area dry in
between. In either case, none of the convective parameters are
favorable for severe weather, but certainly the anomalous
moisture could bring brief downpours.

Once short wave heads offshore later in the morning, subsidence
in its wake should prevent any additional activity from
developing until the approach of the cold front later in the
afternoon and evening. This is the main time frame of concern
for severe weather, especially in western/central MA and
northern CT, as environment should feature plenty of instability
with surface-based CAPE over 2000 J/kg, sufficient 0-6km shear
of 25-30kt, decent mid level lapse rates, and strong 0-1 km
shear in excess of 150 m2s2. Most of the high-res models show
potential for discrete storms ahead of front with potential for
wind damage and even a few tornadoes, before eventually merging
into small lines or segments capable of producing wind damage.

That said, there are timing differences among hi-res models and
ensemble members with some showing an earlier start to afternoon
development. Should that verify, that would lessen the
potential for severe weather since most of the parameters noted
above occur later in day, closer to cold front itself, and are
less favorable during the early to mid afternoon hours.
Something to keep in mind which hopefully gets resolved in later
runs.

Aside from the convection, we will have one more day of
dangerous heat and humidity, although extent of cloud cover
could limit afternoon heating. For now, we are expecting heat
indices well into 90s once again, but probably not as high as
what we expect today.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Updated 215 AM

Key Messages:

 * Still hot but lower humidity Fri.
 * Relief from heat arrives this weekend

Once cold front moves offshore Fri, W/NW flow will bring drier
air into region but airmass really doesn`t cool off sufficiently
until this weekend, when we should see temperatures more typical
of mid July which will last into early next week.

Overall, dry weather is expected but the front may return north
by Sunday which would bring scattered showers/storms, before
another short wave kicks everything out to sea Monday and
Tuesday.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

High confidence.

Low clouds and fog will bring IFR/LIFR conditions to much of
South Coast, Cape Cod, and Islands through sunrise, possibly
advancing into NE CT and most of RI/SE MA. These lower ceilings
will retreat southward after sunrise leaving VFR conditions by
early afternoon, but will then return around sunset and persist
tonight once again with widespread IFR/LIFR into Thu morning.

Otherwise, VFR with S/SW winds through tonight. Gradient remains
weak enough to allow for sea breezes along E MA coast for a time
later this morning into early afternoon, before S winds return.

Later tonight, areas of MVFR ceilings develop with showers
possible in western New England overnight, perhaps spreading
into more of southern New England Thu morning. Conditions then
improve again to VFR but we may see a round of showers/storms
later in day, especially in western MA/western CT.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday through Saturday: VFR.

Saturday Night: VFR. Slight chance SHRA.

Sunday: Mainly VFR, with local MVFR possible. Chance SHRA,
slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

High confidence through end of the week.

Winds and seas are expected to remain below SCA for next several
days, though outer waters E and S of Cape Cod/Islands may come
close ahead of cold front Thu night.

Main concern through end of week is areas of fog during
nighttime and morning hours, in addition to scattered showers
and thunderstorms late tonight into Thu morning and possibly
again Thu night.

Outlook /Thursday Night through Sunday/...

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Slight
chance of rain showers.

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Saturday: Winds less than 25 kt.

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

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 7 PM EDT Thursday for CTZ002>004.
MA...Heat Advisory until 7 PM EDT Thursday for MAZ003>007-010>021-
     026.
     Air Quality Alert from 11 AM this morning to 11 PM EDT this
     evening for MAZ008>011.
RI...Heat Advisory until 7 PM EDT Thursday for RIZ001>007.
MARINE...None.

&&

$$

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