453
FXUS61 KBOX 011740
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
140 PM EDT Tue Jul 1 2025

.SYNOPSIS...
We`ll have another chance for showers and thunderstorms this
afternoon and evening. Warm but a bit less humid Wednesday and
Thursday, then drying out with more seasonable temperatures heading
toward Independence Day. An upper level disturbance may bring
scattered showers and thunderstorms Thursday, otherwise dry through
the end of this week. Heat and humidity return late this weekend
into early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Key Messages:

* Scattered showers/t-storms into this evening. Some of the stronger
  storms could produce damaging wind gusts and locally torrential
  rainfall capable of flash flooding

* Showers and t-storms diminish late this evening with shower threat
  shifting to south coast overnight

Scattered t-storm activity expected to develop through mid-late
afternoon and continue into the evening ahead of a cold front.
Moderate instability with CAPES 1000-2000 J/kg and marginal
effective shear up to 30 kt support loosely organized storms with
damaging wind the primary severe threat. HREF updraft helicity
swaths are more focused to the south across the mid Atlc where
greater threat for severe wx. Abundant moisture with 2+ inch
PWATs and moderate instability also favorable for wet
microbursts as well as localized torrential rainfall capable of
flash flooding. There remains uncertainty on how convection will
play out but CAMs are targeting interior locations with greater
storm coverage although can`t rule out a few storms closer to
the coast. Heavy rainfall probs from the HREF are focused across
interior MA and CT where best chance of storms are into this
evening.

Mid level trough axis moves slowly east from New York tonight with
deep moisture axis gradually shifting toward the south coast late
tonight. Expect convection to diminish by late evening, but
approaching mid level trough acting on deep moisture will keep risk
of showers all night. The best chance of showers and an isolated t-
storm will shift to the south coast late tonight within the moisture
axis, while some drier begins to filter into northern MA .

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
Key Messages:

* Continued chance of showers near the south coast Wed

* Isolated t-storms possible Wed afternoon

Wednesday...

Axis of 2 inch PWATs will be a bit south of the coast for much of
the day with right entrance region of weakening jet across the
region. As a result, can`t rule out a few showers near the south
coast within the moisture axis, otherwise drier air will continue to
advect southward across the region. This should lead to partial
sunshine developing away from the south coast while clouds dominate
near the south coast. Will have to monitor for isolated convection
developing in the afternoon along a weak boundary that stalls across
SNE. Instability is marginal with CAPES 500-1000 J/kg but this could
be enough for an isolated shower or t-storm developing, mainly south
of the MA Pike where deeper moisture is present. Further to the
north, moisture is more shallow so convection threat will be quite
low here. Highs will be in the 80s, with upper 70s along the south
coast. Somewhat less humid air will move into northern MA as
dewpoints drop through the 60s. However, dewpoints around 70 will
persist south of the Pike.

Wednesday night...

Some lingering showers possible over the Cape/Islands as shortwave
moves through, otherwise dry weather with clearing skies as
subsidence develops behind the departing shortwave. Stratus and
patchy fog expected to redevelop over the Cape/Islands. Lows will
settle into the 60s.

&&

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

* Very warm Thu with scattered showers and t-storms possible

* Drying out with more seasonable temperatures and less humidity for
  the 4th of July

* Heat and humidity return Sun-Mon

Details...

Upper trough amplifies over the NE Thu-Fri as upper low digs
southward through Quebec and into northern New Eng Fri. Increasing
forcing for ascent ahead of the trough will lead to chance of
showers/t-storms Thu afternoon, especially interior. Given
increasing mid level wind field and favorable mid level lapse rates
approaching 6.5 C/km, we think there will be a conditional severe wx
threat if there is enough moisture/instability. The magnitude of
instability is uncertain and SREF probs are rather meager with
CAPES. Instability will be the key for Thu, but CSU and NCAR ML
guidance is indicating some risk for severe. Very warm temps are
expected Thu but dewpoints may mix out and fall through the 50s
which would be a inhibiting factor. Stay tuned. Then cold front is
expected to move offshore by Fri with NW flow bringing less humid
airmass and more seasonable temps for the 4th of July.

Looking ahead to next weekend into early next week, upper trough
exits followed by rising heights and ridging building back into the
region. This will result in increasing heat and humidity, especially
by Sun and Mon.

&&

.AVIATION /18Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

18z TAF Update:

Through tonight: Moderate confidence.

A mix of VFR and MVFR this afternoon with scattered t-storms
developing through this evening. Coverage of storms will be
greatest in the interior with brief lower conditions, gusty wind
and heavy downpours in any t-storms.

IFR-LIFR stratus and fog developing over the Islands will expand
northward along the south coast this evening, but remain south
of Boston. VFR should persist in the interior.

Wednesday: High confidence.

VFR generally, though IFR cigs will linger over the Cape/Islands
in the morning. Then stratus and fog redevelop over ACK by late
afternoon. Risk for showers will continue near the south coast,
with low risk for an afternoon t-storm.

Wednesday night: High confidence.

Mainly VFR, but patchy stratus and fog will redevelop along the
south coast.

KBOS Terminal...Moderate confidence in TAF. Expect VFR to
persist, except brief lower conditions in any t-storms after
21z.

KBDL Terminal...Moderate confidence in TAF. VFR, but risk for
SHRA/TS returns by 20z.

Outlook /Thursday through Sunday/...

Thursday: VFR. Slight chance SHRA, isolated TSRA.

Thursday Night through Saturday: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Tonight through Wednesday night:

Persistent SW flow through the period. 25 kt nearshore gusts will
diminish this evening with 10-20 kt speeds thereafter. A few t-
storms possible this evening with areas of fog developing over
the waters tonight into Wed morning.

Outlook /Thursday through Sunday/...

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

Saturday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231-
     236-251.
     Small Craft Advisory until 10 PM EDT this evening for
     ANZ232>235.
     Small Craft Advisory until 9 AM EDT Wednesday for ANZ250-254.
     Small Craft Advisory until 8 PM EDT Wednesday for ANZ255-256.

&&

$$

SYNOPSIS...KJC/MHB
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...BW
AVIATION...KJC/BW
MARINE...KJC/BW