861
FXUS61 KBOX 300015
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
815 PM EDT Tue Jul 29 2025

.SYNOPSIS...
Elevated heat and humidity will continue through Wednesday. Cloudy
weather with much cooler temperatures are expected Thursday
into Friday, with the potential for steady soaking rainfall
somewhere in Southern New England or the northern mid-Atlantic
region. Flooding could be possible in some locations but the
location of heaviest rainfall is unclear. An extended stretch of
dry weather then develops for the weekend into early next week.
Temperatures are seasonable with low humidity levels this
weekend, but with a warming trend for early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
* Near record heat this afternoon gives way to a very warm and humid
  night ahead

Heat dome/ridge provides dry weather tonight along with very warm
conditions. Low temps only falling to 65-70, low 70s for the urban
areas of Boston, Providence and Hartford. This combined with dew pts
in the upper 60s and low 70s will make for a very uncomfortable
night. Fog/stratus bank east of Nantucket may expand westward with
cooling blyr after sunset. Thus, low clouds and fog possible later
tonight for the south coast, including Cape Cod and the Islands.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Key Messages:

* Near record heat again Wed with highs in the 90s and heat indices
  95-100+. Not as hot along the coast given seabreezes

* Low risk of late afternoon isolated/widely scattered
  thunderstorms

850 mb temps around +20C, 925 mb temps +25C to +26C will support
another day of near record heat with highs in the mid 90s, 85-90
along the coast, with mid 80s Cape and Islands in response to
seabreezes. Record highs for Wed/July 30th are as follows:

BOS - 98F set in 1933
BDL - 98F set in 1988
PVD - 97F set in 1949
ORH - 95F set in 1949

We may fall just shy of these values, but nonetheless, another very
hot and humid day, with heat indices 95-100+. Thus, heat headlines
remain in effect. As for thunderstorm potential tomorrow, mixed
signals in the model guidance. Some of the models indicates deep mid
level dry air that inhibits convection through about 18z-20z. This
also shows up in the model SB instability, with CAPES falling
through the day, possibly a reflection of drier air mixing to the
surface (lowering dew pts). Thereafter, dry air exits offshore and
models suggest convection firing after 19z/20z, with seabreeze
boundaries as a possible focus. However, with the lack of height
falls it`s a weakly forced environment. This may keep the areal
coverage of the convection isolated to widely scattered. SPC kept us
in a marginal risk, which seems reasonable given the mixed
signals/low forecast confidence. If storms do fire, sufficient deep
layer shear of 30-40 kt for strong winds to be the main threat.

Wednesday night..

Cold front slips through the region. Isolated/widely scattered
showers/thunderstorms possible. Otherwise, another very warm and
humid night, with lows 65-70.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Messages:

* Low pressure near or south of Southern New England could bring
  rounds of steady rainfall Thurs into part of Fri. Could
  result in flooding but the exact locations are still
  uncertain. Flood Watches could be needed in later updates.

* Much below normal temperatures for late in the week - highs in the
  upper 60s to mid 70s with an onshore breeze.

* Nice weekend in store with seasonable temps (cooler lows) and dry
  weather.

* Still dry into early next week but with a warming trend.

Details:

Thursday into Friday:

An anomalous weather pattern looks to be taking shape for late in
the week, driven by a seasonably strong high pressure over eastern
Canada/northern New England and a weak area of low pressure
somewhere near the mid-Atlantic states or the central Appalachians.
Cloud cover and pretty stout onshore flow looks to offer
temperatures which are significantly cooler than normal (upper 60s
to mid 70s!). NE winds could be strong enough to yield a need for
potential small craft advisories for mariners.

The bigger concern which we`re monitoring though is the potential
for rounds of steadier rainfall which could lead to areas of
flooding, particularly for late Thurs into Fri. There are several
factors on the synoptic-scale which could favor heavy rainfall
falling somewhere from the mid-Atlantic, portions of CT/RI and into
western MA; near/south of the low pressure area is a moisture-rich
environment with PWATs 1.6-1.8", with what may end up being a rather
sharp west to east thermal gradient which could focus rounds of
heavier rain which could be more reminiscent of a frontogenetic
regime. QPF box-and-whisker diagrams from the 00z LREF, which
utilize the coarser-res ensembles (EPS/GEPS/GEFS) and not the finer-
scale guidance which we`re not yet in the forecast horizon to see
their output as yet, shows QPF values around 1-1.5" in the 50th
percentile at sites like Hartford and at Providence, but show values
potentially reaching up to 3". Pretty good signal for steadier
soaking rains, supported by the ECMWF EFI/Shift-of-Tails guidance
which also offers potential for an anomalous rain event. The issue
is the placement of the heaviest rainfall, which as mentioned above
has still quite a range from central/eastern PA northwest to
interior Southern New England.

Coordination with surrounding offices and WPC agreed to hold on
flood watches given the varied QPF maxima, but later shift(s) may
need to consider one for parts of Southern New England. WPC`s
Excessive Rain Outlook indicates Slight Risk for excessive rainfall
in CT and western/central RI - and that`s probably the area that is
most at-risk for a possible flood watch - with Marginal Risk of
excessive rain spanning the rest of Southern New England. PoPs were
increased into the Likely to low Categorical range for Thu night
into part of Fri before decreasing later into Fri.

The Weekend into Early Next Week:

Canadian high pressure ridges into Southern New England in this
period, offering an extended period period of dry weather.
Seasonable temperatures this weekend with seasonable to slightly
cooler than normal nighttime lows, so overall a really nice
weekend looks to be in store. Looks generally dry into the
early part of next week too, although with a warming trend to
temperatures and dewpoints back on the rise too.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

00z TAF Update:

Tonight: High confidence.

VFR for the majority of Southern New England. A fog bank off
Cape Cod could move into ACK and perhaps to HYA, although winds
turning westerly could reduce its westward extent. Better chance
at IFR visby at ACK. Winds become W/NW 5-10 kt thru midnight,
then shift to N/NE 5 kt or less toward the pre-dawn hrs.

Wednesday: Moderate confidence, some uncertainty if
thunderstorms develop and coverage.

IFR/LIFR possible across the Cape and Islands early. Otherwise, VFR
an dry thru 18z. After 18z, isolated to widely scattered
thunderstorms may develop. Low confidence on areal coverage. We
handled this uncertainty with a PROB30 after 18z. Low prob of a few
robust storms, with strong winds the main threat.

Wednesday night: low confidence on showers and thunderstorms.

VFR likely, except IFR/LIFR south coast, including Cape Cod and
islands in low clouds and fog. Isolated to widely scattered showers
possible along with isolated -TSRA.

KBOS terminal...High confidence in TAF through 18z Wed, with VFR and
west wind 10-15 kt. Winds become light NE toward morning. Wed,
ENE winds early become SE then SW late in the day. Dry weather
thru 18z, then isolated/widely scattered showers/thunderstorms
possible after 19z/20z.

KBDL terminal...High confidence in TAF thru 18z. Then some
uncertainty on development and coverage of showers and thunderstorms
after 18z Wed.

Outlook /Thursday through Sunday/...

Thursday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, slight chance TSRA.

Thursday Night: Mainly MVFR, with local IFR possible. Breezy.
SHRA likely, isolated TSRA.

Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA.

Friday Night: VFR. Breezy. Slight chance SHRA.

Saturday: VFR. Breezy.

Saturday Night: VFR.

Sunday:

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Wednesday night...High confidence on winds and seas, lower
confidence on timing and areal coverage of potential thunderstorms.

Patchy dense fog likely tonight and again Wed night. Typical summer
pattern with light winds through the period. Isolated to widely
scattered thunderstorms possible after 4/5pm Wed into early Wed
evening. A cold front will provide a wind shift to the NE toward Thu
morning.

Outlook /Thursday through Sunday/...

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

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft. Rain showers
likely, isolated thunderstorms.

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain
showers.

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

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

Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Wednesday for CTZ002>004.
MA...Heat Advisory until 8 PM EDT Wednesday for MAZ003>007-010>021-
     026.
     Air Quality Alert from 11 AM to 11 PM EDT Wednesday for
     MAZ020>024.
RI...Heat Advisory until 8 PM EDT Wednesday for RIZ001>007.
     Air Quality Alert from 11 AM to 11 PM EDT Wednesday for RIZ006-
     007.
     Air Quality Alert until 11 PM EDT this evening for RIZ006-007.
MARINE...None.

&&

$$

SYNOPSIS...Loconto/Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...Loconto
AVIATION...Loconto/RM/Nocera
MARINE...Loconto/Nocera