-- Discussion containing changed information from previous version are highlighted. --
271
FXUS61 KBOX 302324
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
724 PM EDT Mon Jun 30 2025

.SYNOPSIS...
Cloud cover increases tonight, with a risk for showers and
thunderstorms overnight to early Tuesday morning. Tuesday is
very warm and humid with heat indices in the mid 90s. Another
period of showers and storms redevelops Tuesday afternoon, some
with torrential downpours, before clearing out for Tuesday
night. Very warm Wednesday and Thursday then drying out with
more seasonable temperatures heading toward the 4th of July. An
upper level disturbance may bring scattered showers and
thunderstorms Thursday, otherwise dry through the end of the
week. Heat and humidity return later next weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
315 PM Update:

Key Messages:

* Increasing cloudiness tonight, with fog and low clouds over
  southeast New England. Turning more humid too.

* Overnight to early Tue showers and embedded storms, timing
  approximately 3-9 AM. Although severe weather isn`t expected,
  storms could be capable of downpours and lightning which could
  impact the Tue AM commute.

Details:

Overall not too bad a day as we close out the month of June with
weak high pressure in control. At least through the early part of
the overnight, the vast majority of Southern New England should end
up being dry albeit with increased cloud cover. RI and southeast MA
will start to see fog and low clouds/stratus return northward
starting by early evening.

Forecast then starts to change during the latter half of the
overnight into the early Tue morning period. A warm front associated
with a very humid and conditionally-unstable airmass to its south
will be moving ENE approx. during the 3-10 AM timeframe. In tandem
with this warm front, active convective activity currently taking
place over the mid-Atlantic to parts of the OH Valley should begin
to approach our western MA/CT areas closer to 3-4 AM, which then
generally moves ENE towards the eastern coast around early Tue AM.
In a weakly-forced setting like this one as is customary, high-res
model guidance still remains frankly scattershot as far as where and
when the best risk for thunderstorms could lie in the overnight.
Some risk for storms could exist virtually anywhere, but think the
better shot for storms is mostly south of the Mass Pike. Severe
weather is not expected from this activity with weak windfields and
still pretty stable low-levels, but could still produce lightning
and heavy downpours, which could coincide with Tuesday morning
commute periods. While this activity should be coming to an end
toward daybreak in western MA/CT, it may still be ongoing for
eastern MA, RI and the Cape and Islands. Turns quite muggy tonight
with lows upper 60s to lower 70s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
-- Changed Discussion --
315 PM Update:

Key Messages:

* Early-day showers/embedded storms end by mid-morning, with dry
  weather thru midafternoon.

* Thunderstorms likely re-develop Tue late afternoon to early
  evening, soonest interior (after 3 PM) which then conglomerate
  and move southeast by sundown and offshore early Tue night.
  Main risk is from torrential downpours capable of urban and
  street flooding, with possible flash flooding where storms re-
  develop. More limited localized wind damage threat possible
  but secondary to the heavy downpours threat.

* Very warm and humid, feeling like the mid 90s Tue aftn.

Details:

Quite a bit of moving parts for Tuesday, due in part to the early-
day shower/thunderstorm risk and the recovery/destabilization
potential in the wake of this activity. This leads to a still lower
than average forecast confidence as it pertains to the timing of re-
developing showers and thunderstorms during the afternoon and early
evening, as well as to how warm temperatures and heat indices may
get.

We think leftover cloud cover from morning activity begins to
scatter out closer to noontime. So after the early morning
shower/storm activity ends, we should see a period of relatively dry
weather. How long that dry period holds on for is still a question
mark, but we think there should be some subsidence and relatively
drier period thru at least 3 PM. The risk for showers and
thunderstorms then increases more substantially around/after then as
a cool front interacts with a heated and humid airmass. starting in
interior Southern New England, then lurching southeast towards the I-
95 corridor around sundown, and then move towards the southern
coastal waters early Tue evening. Regarding thunderstorm
parameters for Tue, lapse rates in mid-levels are barely moist-
adiabatic if that, and wind fields in the lowest few km of
atmosphere are quite weak. However precipitable water values are
sizable at over 2", warm cloud depths around 12,000 ft with
CAPEs around 1500-2000 J/kg but is of a tall-skinny type of
profile. But I think the greatest risk, given the above, in any
thunderstorms which develop is from instances of street and
flash flooding. This is especially the case where storms can re-
develop over the same areas with the synoptic pattern favors
storms backbuilding and re-developing. And it could potentially
be a problem for the Tuesday afternoon/evening commuters. A more
limited risk for severe weather in the form of water-loaded
outflows/wind damage could develop but think this is a more
secondary risk than to the lightning and heavy downpours threat.
Included enhanced wording for heavy downpours and gusty winds
in the forecast, but of the two, I think heavy
downpours/instances of street flooding would be the main risk.
Activity should begin to move offshore by late Tue evening
before most if not all areas trend dry by early Wed.

Tue should end up being very warm to hot and also quite humid, which
will bring elevated heat indices. Tempering that to an extent will
be some degree of cloud cover. High temps in the mid to upper 80s
and dewpoints in the mid 70s would favor it feeling closer to the
mid 90s. This doesn`t meet the threshold for heat advisory
criteria but it still will be quite warm and humid nonetheless.
-- End Changed Discussion --

&&

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

* Very warm Wed-Thu. Scattered showers and t-storms possible Thu

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

* Heat and humidity return Sun-Mon

Details...

Weak trough/cold front appears to get hung up in the coastal plain
Wed with elevated PWAT axis near 2 inches near the south coast,
before drier air pushes southward across the region during the
afternoon. Can`t rule out a few lingering showers near the south
coast Wed morning within the moisture plume, otherwise dry and very
warm conditions with highs well into the 80s. 70+ dewpoints linger
near the south coast but less humid airmass will begin to move south
across the region during the afternoon.

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 /23Z MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
Forecaster Confidence Levels...

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

00z TAF Update:

Tonight: High confidence in TAF/trends but moderate on timing.

IFR-LIFR stratus and fog advances northward from Cape Cod and
immediate south coast overspreading RI and SE MA to south of BOS by
06z, with MVFR further inland. SHRA/possible embedded TSRA
moves in from eastern/southern NY after 07z, TS possible
anywhere but somewhat better chance for the BDL/HFD-PVD/SE MA
area. These storms would not become strong were any to develop
but could still pose risk for lightning and brief IFR visby
downpours.

Tuesday: High confidence in TAF/trends but moderate on timing.

Early-day SHRA/possible TS thru 14z then trends to VFR. Another
period of TS more likely late in the day (after 20z), but could
start as soon as 18z in interior Southern New England. Storms
could produce torrential downpours and brief gusty winds. SW
winds around 5-10 kt with occasional gusts.

Tuesday Night: High confidence.

SHRA/TS moves southeast towards the southern waters thru 02z,
with gradual improvement to VFR thereafter. Possible BR/FG south
coast until SHRA/TS clears the southern waters.

KBOS Terminal...Moderate confidence in TAF. Stratus will
approach the airport from the south after 06z. Confidence is
not high in IFR so added a BKN010 in the TAF and will re-
evaluate at 06z. Early-morning SHRA from 09-14z Tue, outside
chance at TS but better chance south and west. VFR thereafter
approx 14-22z with SW breezes but risk for SHRA/TS returns by
22z (indicated with PROB30s).

KBDL Terminal...Moderate confidence in TAF. VFR thru 07z,
SHRA with embedded TS 09-12z Tue. VFR thereafter approx 13-19z
with S winds but risk for SHRA/TS returns by 19z (indicated with
PROB30s).

Outlook /Wednesday through Saturday/...

Wednesday through Wednesday Night: VFR.

Thursday through Thursday Night: VFR. Slight chance SHRA,
isolated TSRA.

Independence Day: VFR.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels...

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

Tonight: High confidence.

Dry weather with SE to S winds around 10-15 kt and seas 2-4 ft.
Main risk for mariners tonight is fog over the waters, and a
potential risk for thunderstorms early Tue AM.

Tuesday and Tuesday Night: Moderate confidence.

SCA remains valid for Tue as SW winds increase to around 25 kt,
with seas building to 4-6 ft. Early-morning showers and
thunderstorms possible, then dry weather for most of the
afternoon. The risk increases for showers and thunderstorms
again for late in the day into the mid Tuesday evening hours,
some could be capable of frequent lightning, heavy downpours and
locally rough seas.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.

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

Thursday: Winds less than 25 kt.

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

Independence Day: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 11 AM Tuesday to 6 AM EDT Wednesday
     for ANZ250-254>256.

&&

$$

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