Office: BOX
FXUS61 KBOX 080506
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
106 AM EDT Tue Jul 8 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 TODAY/...
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 is
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 /TONIGHT THROUGH 6 PM WEDNESDAY/...
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 NIGHT THROUGH MONDAY/...
* 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 /05Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z update...
Through 12Z...Moderate confidence.
IFR cigs expand from the south coast into most terminals by
06-10z. Winds light. Scattered SHRA likely around the Cape and
islands.
Today...Moderate confidence.
VFR. W winds 5-10 kts. Scattered SHRA/TSRA with heavy downpours
likely in the afternoon and evening. Low confidence in storm
placement and timing.
Tonight...Moderate confidence.
IFR cigs expand from east coast to as far west as ORH by 06z,
into western MA/CT terminals by 12z. Scattered SHRA/TSRA
continue through at least 06z.
KBOS Terminal...Low confidence in TAF only with regard to
timing of possible convection.
KBDL Terminal...Low confidence in TAF only with regard to
timing of possible convection.
Outlook /Wednesday Night through Saturday/...
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.
Friday Night and Saturday: Mainly VFR, with local IFR possible.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight: High confidence.
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 Night through Saturday/...
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.
Friday Night: Winds less than 25 kt. Slight chance of rain
showers.
Saturday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 8 PM EDT this evening for MAZ003>007-
010>019-026.
Heat Advisory from 11 AM this morning to 8 PM EDT this evening
for MAZ020>022.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>004.
Heat Advisory from 11 AM this morning to 8 PM EDT this evening
for RIZ005>007.
MARINE...Small Craft Advisory from 8 AM this morning to 8 PM EDT this
evening for ANZ235-237.
Small Craft Advisory until 2 AM EDT Wednesday for ANZ254.
Small Craft Advisory until 2 AM EDT Wednesday for ANZ255-256.
&&
$$
SYNOPSIS...FT
NEAR TERM...Belk/FT
SHORT TERM...FT
LONG TERM...Belk
AVIATION...Belk/BW/McMinn
MARINE...Belk/FT
