218
FXUS61 KBOX 250631
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
231 AM EDT Fri Jul 25 2025
.SYNOPSIS...
Peak of heat expected Friday with elevated humidity resulting in
impactful heat, potentially dangerous if precautions not taken.
Highs expected in low-mid 90s, but will feel more like upper 90s to
low 100s. Showers and thunderstorms possible later Friday with a
cold front. Cooler and mainly dry Saturday with showers and
thunderstorms returning for Sunday. Outlook for early next week
shows summerlike warmth and humidity, with generally dry weather for
the majority of the time.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Wonderful summer afternoon across southern New England under a bit
of fair weather clouds. Temperatures are seasonable in the mid to
upper 80s and increasing dew points in the mid 60s. Over all there
are no weather concerns this afternoon or tonight. Overnight surface
high will shift further off shore. Clear skies tonight with a steady
southwest wind keep the boundary layer well-mixed and should limit
the development of coastal fog/stratus, despite increasing low-level
moisture. Temperatures dip into the low 70s and upper 60s overnight
with dew points in the upper 60s.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Key Messages:
* Dangerous heat and humidity for communities away from coastal RI
and southern coast of MA.
* Isolated to scattered thunderstorms Friday afternoon which could
be strong to severe - with damaging wind gusts as the primary
threat. A secondary threat, locally heavy rainfall may lead to
isolated flash flooding.
Friday will be the warmest and most humid day of the stretch. 925mb
temperatures reach the mid 20s Celsius and with a well-mixed BL will
have maximum temperatures in the lower to middle 90s. It is less hot
near the south coast (due to SW flow off the water) with a maximum
temperature in the middle to upper 80s. Heat Advisory remains in
effect for southern New England, excluding Cape Cod, islands, south
coast of MA & RI, and the Berkshires. Dews increase to the low 70s
but not out of the question we near 75F, this is tropical-like feel
and leads to heat incites in the upper 90s to lower 100s.
Storms are possible during the afternoon ahead of a 500mb trough and
surface cold front. Timing has come into better agreement for storm
development between 2pm and 8pm, the NSSL would be the only
outlier with an earlier initialization around noon in far
northwest MA. And storms clear the Cape and Islands by
10pm/midnight. There are good ingredients for a few strong to
severe thunderstorms, HREF mean CAPE are ~1,800J/kg, steep low-
level lapse rates of ~9C/km, and modest effective shear of 30 to
35 knots. We are lacking mid-level lapse rates, as we move past
sunset and lose that daytime heating, storms will begin to
fade. A few of these storms may pack a punch, SPC has upgraded
parts of southern New England to a slight risk, so a level 2 out
of 5. Thinking the main concerns are damaging straight line
winds and locally heavy rainfall within any convective storm. A
friendly reminder if you can hear thunder, move indoors, because
you are close enough to be struck by lightning!
As mentioned above, heavy rainfall rates may pose a risk for
isolated flash flooding. PWATs are near the daily climatological
records with forecast values near 2.3", couple this with deep
warm cloud layer of 12,000 ft and potential for slow moving
storms. HREF probability of the 6-hour precipitation exceeding
the 10 year ARI across eastern CT and western RI at 15% to 25% -
will need to be mindful of those areas prone to flash flooding,
but do not feel this is a widespread flash flooding event. But
would not be surprised if someone were to pick up a quick 1-3
inches under one of these heavier downpours. Did collaborate
those concerns with WPC and have expanded the marginal risk into
southern New England for Friday.
Friday night the cold front moves off shore and high pressure moves
down from Canada. Will lead to clearing skies and lowering humidity.
Wind shifts from the SSW to WSW during the evening, but will become
more NNW after midnight. Temperatures settle into the low and middle
60s across the Berkshires and northern Worcester Hills, elsewhere
will have lows in the upper 60s to low 70s.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Messages:
* Dry and cooler on Saturday.
* Showers and thunderstorms around Sunday.
* High temps mainly in the 80s next week with a few shower/storm
chances but mostly dry.
Saturday and Sunday...
A drier post frontal airmass works its way into southern New England
on NW flow as surface high pressure drifts overhead beneath mid
level ridging. This will make for a nice, dry day for the first half
of the weekend featuring plenty of sun, light winds, and seasonable
temperatures. Inland locations will reach into the 80s while an
easterly onshore flow keeps the immediate east coast closer to the
upper 70s.
Sunday is more active as a subtle shortwave slides overhead through
the quasi-zonal flow and dewpoints increase with backing surface
winds. Thus, can expect increasing clouds and rain/thunderstorm
chances through the day on Sunday, though timing is uncertain; some
locations (especially east) may see more rain late Sunday into the
overnight hours.
Next week...
Beyond Sunday`s disturbance the region remains under generally NW
steering flow with a series of weak shortwaves moving through and
bringing periodic chances for unsettled weather. No strong signals
at this point for a large/organized system, and majority of the week
should be dry. As we get toward the latter half of the week guidance
suggests a building surface high which would keep things quiet into
the weekend.
&&
.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z update...
Through 12z Thursday: High Confidence.
VFR. SSW to SW winds 8-12 kts. Low chance of patchy fog/low
stratus to develop across the southern waters, impacting
terminals across southern Rhode Island and the southern coast of
Massachusetts. With lower confidence in this, opt`d to exclude
from TAF issuance.
Friday: Moderate in timing of storms, but high confidence in trends.
VFR. SSW/SW winds at 8-14 kts with occasional gusts up to 22
kts in the afternoon. Isolated to scattered TSRA possible. Best
timeframe between 18z through 02z as storms develop in northwest
MA and move southeast. Due to low coverage of storms, kept the PROB30
for TSRA at most terminals per latest CAMS. Within storms can
expect brief MVFR conditions, gusty winds, torrential rain, and
frequent lightning.
Friday Night: High Confidence.
Any lingering storms exit the coastal waters/islands by 06z.
Cold front drops from NW to SE early evening, shifting winds
from SW to NW speeds at 8-12 kts. Ceilings are generally VFR
with lingering MVFR possible for the outer Cape and Islands.
There is potential for a period of FG/BR for the Cape and
Islands after 00-02z after the cold front moves through.
Saturday: High Confidence.
VFR. Northeast winds 5-8 kts for the interior and 6-12 kts
closer to the coast.
KBOS terminal...High confidence trends, moderate confidence in
timing for KBOS TAF.
Exact timing of line of storms lower confidence. Storms are
expected to be scattered in coverage making it more difficult to
pin point exact timing. Kept as a PROB30 group.
KBDL terminal...High confidence trends, moderate confidence in
timing for KBDL TAF.
Outlook /Saturday Night through Tuesday/...
Saturday Night: VFR.
Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, chance TSRA.
Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA, slight chance TSRA.
Monday through Monday Night: VFR.
Tuesday: Breezy. 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.
Tonight...High Confidence.
Winds S to SW 10-20 kts. Gusts to 25 kts. Up to 30 kts possible over
the northern outer waters with sustained winds around 25 kts. Seas 3
to 5 ft possible in the northern waters, only to 3 ft everywhere
else. A Small Craft Advisory is in effect over the outer northern
waters from 20z Thursday through 12z Friday.
Friday and Friday Night...High Confidence.
SW winds 10-15 kts, closer to 20 kts for the southern waters.
Gusts 20-25 kts. Borderline criteria for SCAs for southern waters,
Cape Cod Bay, Nantucket Sound and Buzzards Bay. Storms develop late
afternoon into early evening as a cold front slides from the
northwest to southeast, then pushing south of the waters by early
Saturday morning. This does shift the wind to the NNW.
Outlook /Saturday Night through Tuesday/...
Saturday Night: Winds less than 25 kt.
Sunday: Winds less than 25 kt. Slight chance of rain showers.
Sunday Night: Winds less than 25 kt. Chance of rain showers,
chance of thunderstorms.
Monday through Tuesday: 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.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>004.
MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ250.
&&
$$
SYNOPSIS...BW/Dooley
NEAR TERM...Dooley
SHORT TERM...Dooley
LONG TERM...BW
AVIATION...Mensch
MARINE...BW/Dooley