Office: BOX
FXUS61 KBOX 081218
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
818 AM EDT Tue Jul 8 2025
.SYNOPSIS...
Higher than normal heat and humidity expected through today. This
afternoon and evening brings scattered thunderstorms capable of
producing damaging winds and flash flooding. Cooler weather expected
Wednesday and beyond. Possible break from unsettled weather for the
upcoming weekend.
&&
.NEAR TERM /THROUGH TONIGHT/...
Key Messages...
* Strong to severe storms possible with heavy downpours and
potential for flash flooding.
* Heat advisory in effect for most of the region with heat index
values climbing to between 95 and 100
Warm and extremely muggy conditions continue early this morning with
patchy fog and widespread low clouds accompanying to start the day.
These will retreat with mixing in the hours after sunrise allowing
for plenty of diurnal heating leading up to today's expected
thunderstorms. A trough of low pressure is moving east from the
Great Lakes today as the remnants of post tropical cyclone Chantal
exit east of the Cape. As these features slide east a plume of
extremely moist air will be overhead with dewpoints in the upper 70s
making it feel positively tropical over much of SNE this afternoon.
PWATs over 2 inches are 2+ standard deviations above normal for us
this time of year, and this anomolous moisture combined with ample
instability and several forcing mechanisms are adding up to a decent
flash flood risk, especially for the southern half of the region. As
for instability, we'll have 1500-2500 J/kg of MUCAPE maximized south
of the MA Pike where the highest dewpoints lie. A shortwave within
the broader trough will pass overhead providing some synoptic lift
while at the surface a slow moving cold front behind the shortwave
and a surface trough will critically provide strong surface
convergence to initialize convection this afternoon and evening.
Thinking that the area of greatest concern is generally along/south
of the MA Pike where a nearly stationary convergent boundary is
showing up in high resolution guidance. Orientation looks to
generally be SW to NE, in line with nearly unidirectional SW flow in
the low/mid levels suggesting potential for slow moving and training
storms. With warm cloud depths near 14,000 ft suggesting efficient
warm rain processes, any storms that do form will have the potential
to drop an 1-2 inches of rain in an hour and cause localized flash
flooding issues, especially in urban areas. A Flood Watch has been
issued for the area thought to stand the greatest risk from mid
afternoon through the first half of the overnight hours.
The severe weather potential remains, with isolated damaging winds
possible, but factors like poor bulk shear and marginal mid level
lapse rates will limit the coverage of severe storms.
Finally, owing to the previously mentioned heat and choking
humidity, we'll have a Heat Advisory for one more day before relief
arrives.
&&
.SHORT TERM /WEDNESDAY/...
Key Messages...
* Isolated showers and thunderstorms possible but not a washout.
* Much cooler with highs in the 70s (east) and 80s (west).
The biggest change of note will be the cooler temperatures thanks
both to cold advection in the mid levels as well as surface winds
turning NE/onshore pulling in cooler air off the water. As such, the
eastern half of SNE should top out in the 70s while the hottest spot
will be western/central MA, especially the CT valley where highs
reach the mid 80s. Plenty of moisture sticking around with PWATs
still 1.5+ inches, but a weakly forced environment so any showers
will be scattered and difficult to nail down where exactly they'll
materialize.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Key Messages...
* Periodic chances for showers through Friday before a break in the
unsettled weather for the weekend.
* Near to below average temperatures.
Similar to what we'll see on Wednesday, the latter half of the week
features ample moisture (PWATS 1.5+ inches) and a weakly forced
environment under quasi-zonal flow. This brings a typical summer
time setup with rain and thunderstorm chances each day, favoring the
afternoon. The better synoptic forcing looks to come Thursday with a
weak shortwave overhead, so expect more widespread convection
Thursday than Friday as we approach a period of mid level ridging
for the weekend which may keep rain away.
Temperatures in the 70s on Thursday will slowly climb each day into
the weekend, but only back into the mid to upper 80s.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12Z update...
Today...Moderate confidence.
Ceilings scatter this morning becoming VFR. Slower trend for
improvement across the Cape and Islands scattering out by the
afternoon. 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: Mainly VFR, with areas IFR possible. Chance
SHRA, slight chance TSRA.
Thursday: MVFR/IFR conditions possible. Chance SHRA, slight
chance TSRA.
Thursday Night: Mainly VFR, with areas IFR possible. Chance
SHRA, slight chance TSRA.
Friday: Mainly VFR, with local IFR possible. Slight chance
SHRA, slight chance TSRA.
Friday Night: Mainly VFR, with local MVFR possible.
Saturday: VFR.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today and tonight: High confidence.
SW winds 15-20 kts with seas 2-4 ft on the eastern waters, 3-6 ft on
the southern waters. Showers and thunderstorms expected late evening
through the overnight hours.
Wednesday: High confidence.
Winds 5-10 kts out of the SW on the southern waters and out of the
NE on the eastern waters. Seas 2-4 ft.
Outlook /Wednesday Night through Saturday/...
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, slight chance of thunderstorms,
patchy fog.
Wednesday Night: Winds less than 25 kt. Chance of rain showers,
slight chance of thunderstorms.
Thursday through Thursday Night: Winds less than 25 kt. Seas
locally 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 through Saturday: Winds less than 25 kt. Seas
locally approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004.
Flood Watch from 2 PM EDT this afternoon through late tonight
for CTZ002>004.
MA...Heat Advisory until 8 PM EDT this evening for MAZ003>007-
010>019-026.
Flood Watch from 2 PM EDT this afternoon through late tonight
for MAZ011>013-015>022.
Heat Advisory until 8 PM EDT this evening for MAZ020>022.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>004.
Flood Watch from 2 PM EDT this afternoon through late tonight
for RIZ001>004-006-007.
Heat Advisory until 8 PM EDT this evening for RIZ005>007.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ235-
237.
Small Craft Advisory until 8 AM EDT Wednesday for ANZ254>256.
&&
$$
SYNOPSIS...BW
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...BW
AVIATION...BW/Mensch
MARINE...BW
