927
FXUS61 KBOX 162002
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
402 PM EDT Wed Jul 16 2025

.SYNOPSIS...
Increasing cloudiness tonight with risk for showers during the
pre-dawn hours. A cold front will bring showers and
thunderstorms tomorrow, with some becoming strong in interior
Southern New England. Relief from the heat then arrives late
this week and into the weekend. Other than a risk for showers
and storms late Saturday or early Sunday, drier and more
seasonable weather otherwise prevails for early next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
350 PM Update:

Key Messages:

* Dry weather thru the predawn hours, though fog and low clouds
  return from the southern waters early tonight.

* Showers with embedded rumbles of thunder possible early Thurs
  AM, but severe or hazardous weather is not anticipated.

Details:

Although a couple of buildups in the heat and humidity of the day
were briefly able to overcome background subsidence from ridging
aloft and pop a couple short-lived showers, these have fizzled
quickly and in turn has led to a largely dry day. Stratus which has
retreated to the southern waters and the Islands is expected to
return back northward tonight once the sun goes down. This has been
the case the last few nights.

However ridging aloft will weaken and shift eastward early in the
overnight, with modest 500 mb height falls associated with a lead
shortwave disturbance aloft over Lake Erie/southern Ontario
vicinity. Current satellite and composite radar mosaic shows
scattered to numerous storms across western NY into western PA and
eastern OH. While the vast majority of the overnight ends up being
dry, models indicate some of this activity working its way ENE into
Southern New England during the pre dawn to mid-morning Thursday
period. Did increase PoPs to Chance levels during the early morning
hours; there is some elevated instability around to support some
potential for rumbles of thunder. The bigger issue is that models
are still pretty much mixed in terms of outcomes regarding coverage,
including the "7-10 Split" idea mentioned by the previous forecaster
where activity passes to our north and also into the southern
waters. Later shift(s) will need to refine this once it becomes more
clear, but other than passing downpours, we`re not likely to see
hazarous weather from any of this activity. Very muggy and warm
night with lows in the mid 70s, close to dewpoint temps.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
350 PM Update:

Key Messages:

* Heat Advisory still in effect for Thurs for elevated heat indices,
  although areas in eastern MA and RI will be slow to shake free of
  cloud cover.

* Possible severe thunderstorms late in the day (soonest after 4 PM,
  more likely 6-10 PM) in interior Southern New England, but the
  coverage could be more limited.

Details:

Overcast conditions are likely to begin the day, along with some
areas of showers, perhaps accompanied by rumbles of thunder. Shower
activity should be pulling eastward and offshore of Southern New
England by around noontime. This occurs as a seasonably strong, 992
to 1000 mb low pressure treks through the St. Lawrence River Valley.
After early-day showers come to an end, it leaves Southern New
England in a narrow warm sector during the early to midafternoon,
with uncertainties on the extent to which we can turn mostly clear
or at least partly cloudy. Current thinking is that the area from
western and central MA into CT stands the best chance at trending
mostly clear to partly cloudy.

The coverage of cloudiness during the afternoon will greatly
influence both the heat and humidity forecast for Thursday but also
on the potency of potential strong thunderstorms tomorrow afternoon
to early evening. We opted to leave the Heat Advisory as is with no
changes to its status for Thursday. If cloud cover is slow to
dissipate, that could really cut into how warm we get tomorrow and
could reduce heat indices substantially, though even in cloud cover
it will still be quite humid. This looks to be the case for eastern
MA and into portions of RI, where stronger heating will at best be
delayed until late in the day. A better chance at warming
temperatures into the lower 90s is more likely in the interior, and
with that will be a large degree of surface based instability to
values around 2500-3000 J/kg of CAPE from the Berkshires/Litchfield
Hills east to central MA and northeast CT. Wind fields in the lowest
3-km or so of atmosphere are fairly strong with some curvature too,
although the strongest deeper-layer shear lies to our north and
west. Latest guidance indicates a pre-frontal trough developing
somewhere either into the Champlain/Hudson Valley or the MA/NY/CT
border area, with scattered t-storms developing along it later in
the day. We think the timing of widely scattered thunderstorms looks
to be later in the day, probably not sooner than 4 PM but more
likely after 6 PM into the Berkshires, then moving eastward into
western MA/CT and perhaps into central MA closer to 8-10 PM. It is
possible but unlikely that storms could make it further east from
there. If storms can develop into western and central MA and CT,
they could pose both gusty to damaging straight line winds, but also
a smaller risk for a tornado or two given the curving hodographs
with 0-1 km shear magnitudes as high as 25 kt. We also included
mention of gusty winds and heavy rain enhanced wording in the
forecast for the western roughly half of Southern New England.

A cold front moves in later Thursday evening and overnight, which as
it passes will act to bring an end to the spell of heat and
humidity. PWATs actually tumble below 1 inch by daybreak, with NW
winds 10-15 mph and gusts 20-25 mph.

&&

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

* Relief from the heat and tropical humidity arrives Fri.

* Showers and possible thunderstorms late Sat and into Sun.

* Trending more seasonable by early next week.

It now appears that a cold front will finally cross southern New
England some time Friday morning. This will finally break the heat
and tropical humidity across our region. In addition, there is very
little chance of rainfall as well. These conditions are expected to
persist through most of Saturday as well.

A warm front late Saturday into Sunday should feature our next
chance for some showers and thunderstorms. This will be accompanied
by a spike in humidity closer to feeling tropical again, but its
brief. High pressure over eastern Canada brings a return to more
average conditions for late July early next week. Not seeing much
risk for rainfall, at least until the middle of next week.

&&

.AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

18z TAF Update:

Through 00z Thursday: High confidence.

VFR, with IFR-LIFR stratus adjacent to the New England south-
coastal waters. A pop-up SHRA possible but largely dry weather
prevails. S to SW winds around 10 kt, although with SE
seabreezes flipping to SW by 20-21z.

Tonight: High confidence in TAF/trends but moderate on both the
timing and on SHRA coverage.

Mainly VFR, although should see IFR-LIFR stratus and fog
returning northward to areas near/south of I-95 and in the CT
Valley between 00-08z. Risk for warm frontal SHRA/rogue TS
between 08z to 13-15z Thu, but uncertainty on how widespread the
shower threat may be. PROB30s included in TAFs given this
uncertainty but may need to opt for TEMPOs or include as
prevailing FM groups in later issuances. S winds 5-10 kt.

Thursday: Moderate confidence.

Warm frontal SHRA/possible TS moving eastward and offshore thru
15z Thu. Sub-VFR cloudiness likely to continue until then as
well, and we should then see conditions improving to at least
SCT-BKN VFR ceilings. Risk for TSRA / possible +TSRA for western
New England TAFs (ORH, BAF, BDL) after 20z, but for now will
message with PROB30s give uncertainties on coverage. TSRA risk
further east is less likely, if any develop at all. S/SW winds
around 10-12 kt with gusts to 20 kt.

Thursday Night: High confidence.

Cold front moves through the TAFs; any TSRA should weaken to
showers after 02z, with conditions becoming all VFR at all
airports. Winds become W/NW around 10-15 kt with low 20s-kt
gusts post-frontal.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday through Monday/...

Friday through Saturday: VFR.

Saturday Night: VFR. Chance SHRA, slight chance TSRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, chance TSRA.

Sunday Night: VFR. Chance SHRA.

Monday:

&&

.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 levels through
Thursday with south winds around 10-15 kt. Main concern through
Thurs 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.

A cold front arrives on Friday, which could bring conditions to
near SCA levels as NW winds increase to around 20-25 kt and seas
nearing 5 ft.

Outlook /Friday through Monday/...

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

Friday Night through Saturday: Winds less than 25 kt.

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

Sunday: Winds less than 25 kt. Chance of rain showers, slight
chance of thunderstorms.

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

Monday: Winds less than 25 kt.

&&

.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 until 11 PM EDT this evening for MAZ008>011.
RI...Heat Advisory until 7 PM EDT Thursday for RIZ001>007.
MARINE...None.

&&

$$

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