157
FXUS61 KBOX 071807
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
207 PM EDT Mon Jul 7 2025

.SYNOPSIS...
Higher than normal heat and humidity expected through Tuesday.
Unsettled weather for the Cape and Islands tonight. Tuesday
some isolated severe storms are possible as well as heavy
downpours and localized flash flooding. Highest risk for
flooding for urban and poor drainage areas. Cooler weather
expected mid to late week. Possible break from unsettled weather
for the upcoming weekend.

&&

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

* Scattered downpours and thunderstorms continue through the
  first half of the evening

* Mild night ahead

* Another round of rain arrives for the Cape and Islands late
  tonight

Main story for the rest of the afternoon and evening is the heat and
humidity. Dewpoint values have crept up into the lower and even
middle 70s regionwide. The highest value I`ve seen so far has been
75 degrees at Quonset point. These soupy readings even extend
further inland with just about every site seeing readings above 70!
Temperatures in the upper 80s and lower 90s have paired with this
tropical airmass to increase heat index values to 95-100 degrees.

The other thing we`re watching today is the potential for downpours
and isolated thunderstorms. This morning`s 12z sounding at OKX
recorded a PWAT value of 2.15 inches, which quite high, but not the
daily climo max of 2.7 inches. Areas of showers and heavier
downpours associated with the broad circulation and almost PRE-esque
feature around the remnants of TS Chantal have developed across
coastal areas. Overall, activity will tend to weaken as it
moves northeast and away from better forcing closer to the
circulation. More scattered downpours are expected to develop
throughout the day, mainly across the interior where
differential heating may help to trigger some isolated storms.
Not every town will see rainfall, but localities that do could
see it fall at a rate of 1-2 inches per hour.

A warm and muggy night is expected as low temperatures only fall
into the 70s. Even warmer conditions will exist in urban areas where
lows may struggle to get lower than the 70s. Guidance shows the
remnants of Chantal finally moving offshore. The remnant 700mb low
may help to trigger some elevated showers and perhaps a thunderstorm
or two across the Cape and Islands overnight into very early Tuesday
morning.


&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
Key Messages...

* Isolated strong to severe storms possible with heavy downpours
  and potential for localized flash flooding.

* Heat advisory in effect for most of the region with heat index
 values climbing to between 95 and 100

Higher confidence in more widespread unsettled weather Tuesday as
forcing increases. It`s a somewhat complex setup for tomorrow as a
vort max approaches the region. Closer to the surface, a cold front
will slowly move south and east throughout the day. Diabatic heating
may slow the southward progress of this feature and push the timing
of widespread shower and thunderstorm coverage back by a few hours.
The third feature we`re watching is a strong seabreeze boundary that
CAMs have progged to develop across portions of Rhode Island and
Southeastern Massachusetts. These boundaries may serve as a focus
for convection and heavy rainfall later Tuesday afternoon and
evening.

Models still indicate favorable ingredients for heavy rainfall.
Broad anticylonic flow will advect high PWATs into the region. In
some instances values will approach 2.5 inches. Values this high are
around +2.5 STD above climatology and are certainly a significant
signal for heavy rain. Unsurprisingly model soundings have also
hinted at favorable conditions for localized flash flooding. The
most notable signals include weak winds through the column, deep
warm cloud depths, and tall skinny CAPE profiles. HREF ensembles
have started highlighting areas in our CWA with 5-15% probabilites
for 6 hour precipitation totals to locally exceeding the 100 year
annual return interval. Not every area will see heavy rainfall
tomorrow, but any storm that forms in this environment will be
capable of producing rainfall rates of 1-2 inches per hour.
Communities most at risk include poor drainage and urban areas with
little in the way of permeable surfaces.

The other hazard we`re watching is a more limited risk for some
severe thunderstorms. Temperatures in the upper 80s/low 90s with
dewpoints in the 70s will contribute to instability on the order of
1500-2000 J/kg of CAPE. However, other parameters are less favorable
for severe weather, namely mid level lapse rates near 5-5.5 C/km and
0-6km bulk shear <25kts. Even so, can`t rule out an isolated strong
to severe storm producing damaging wind gusts.

Finally, the Heat Advisory has been extended to go through the day
on Tuesday. The slow moving front isn`t expected to pass through the
CWA until after 00z which has bumped up short-term temperature
forecasts. We added the Cape and southeast Massachusetts to the
advisory as we expect dewpoints to climb into the middle and upper
70s.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
* Periodic chances for showers and thunderstorms each day through at
  least Friday.

* Near to below average temperatures by late this week.

A steady stream of moisture is directed towards southern New
England, with precipitable water values of at least 1.5 inches into
at least Thursday evening. For quite a few areas, these values are
expected to be over 2.0 inches at times. This means our region will
be at risk for downpours for a good portion of this week. That`s one
part of the puzzle.

The next part will be anything to generate lift. That looks to come
from a nearly stationary front nearby, but mainly to the south of
New England. This front appears to not be pushed far enough south to
not be a factor in our weather until sometime this weekend. Looking
higher up in the atmosphere, the core of a cold pool should remain
off to our northwest. Thus, no strong signals for pinning
down specific windows of time. Being between two synoptic features,
convection will play more of a role. This will favor the afternoon
and evening hours in general.

Temperatures still anticipated to trend near to below normal due to
a general easterly flow into this weekend.


&&

.AVIATION /18Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

18Z update...

Today...Moderate confidence.

MVFR to IFR along the south coast of RI and MA scattering out
12-14z. Cape/Islands struggle to improve today, gradually
improving into the early afternoon. SSW to SW winds 10-15 kts,
gusts 20-24 kts by early afternoon. Isolated showers and few
thunderstorms may develop after 16z, but low confidence on where
any storms will form.

Tonight...Moderate confidence.

IFR cigs expand from the south coast into most terminals by
06-10z. Winds light.

Tuesday...Moderate confidence.

VFR. W winds 5-10 kts. Scattered SHRA/TSRA with heavy downpours
likely in the afternoon and evening.

KBOS Terminal...Moderate confidence in TAF.

Low clouds develop to the south early this morning, but are
unlikely to reach the terminal. BKN mid-level ceilings Monday
with SW winds with gusts around 20 kts in the afternoon. Low
chance for an isolated shower/storm makes it east to to BOS
after 18z.

KBDL Terminal...Moderate confidence in TAF.

Forecast confidence is moderate beyond 10z with the potential
for lower ceilings. Isolated -SHRA/-TSRA possible after 16z.

Outlook /Wednesday through Friday/...

Tuesday Night: MVFR/IFR conditions possible. Chance SHRA,
chance TSRA.

Wednesday: Mainly VFR, with local IFR possible. Chance SHRA,
slight chance TSRA.

Wednesday Night through Thursday: Mainly VFR, with areas IFR
possible. Chance SHRA, slight chance TSRA.

Thursday Night: Mainly VFR, with local IFR possible. Chance
SHRA, slight chance TSRA.

Friday: Mainly VFR, with local IFR possible. Slight chance
SHRA, slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today and tonight: High confidence.

After a brief lull this morning, SW winds increase in the afternoon
to 10-15 kts with gusts 20-25 kts on southern waters, 25-30 kts on
the eastern waters. Will likely need a SCA for the north outer
waters zone. Seas 2-3 ft, increasing to 2-4 ft on the outer waters
late in the day. Seas increase to 5 ft for the southern outer waters
after overnight into Tuesday.

Tuesday: High confidence.

SW winds 15-20 kts with seas 2-4 ft on the eastern waters, 3-6 ft on
the southern waters.

Outlook /Wednesday through Friday/...

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, chance of thunderstorms. Local
visibility 1 to 3 nm.

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

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

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers, slight chance of
thunderstorms.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Tuesday for CTZ002>004.
MA...Heat Advisory until 8 PM EDT Tuesday for MAZ003>007-010>019-
     026.
     Heat Advisory from 11 AM to 8 PM EDT Tuesday for MAZ020>022.
RI...Heat Advisory until 8 PM EDT Tuesday for RIZ001>004.
     Heat Advisory from 11 AM to 8 PM EDT Tuesday for RIZ005>007.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Tuesday for ANZ235-
     237.
     Small Craft Advisory from 2 AM Tuesday to 2 AM EDT Wednesday
     for ANZ254.
     Small Craft Advisory from 8 PM this evening to 2 AM EDT
     Wednesday for ANZ255-256.

&&

$$

SYNOPSIS...FT
NEAR TERM...FT
SHORT TERM...FT
LONG TERM...Belk
AVIATION...McMinn
MARINE...Belk/FT