BOX issues Area Forecast Discussion (AFD) at Jul 24, 7:16 AM EDT
098
FXUS61 KBOX 241116
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
716 AM EDT Thu Jul 24 2025
.SYNOPSIS...
Heat begins today with high temperatures in the upper 80s to low
90s. 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 PM THIS EVENING/...
Key Messages:
* Above normal temperatures with increasing humidity today.
* Heat Advisory in effect today through Friday.
Details...
The main axis of a 500mb ridge continues to shift east across
southern New England today. Ensemble and deterministic guidance show
anomalously warm temperatures aloft in place with 850mb temperatures
17-20C and around 20-26C at 925mb. Model soundings show sufficient
mixing in the boundary layer to bring down the warmer temperatures
aloft, supporting highs in the upper 80s and low 90s in many places.
Breezy SW flow should shut down sea breezes along the waters of the
north and south shore, and Boston. The South coast will likely be on
the cooler side from onshore flow with highs in the low to mid 80s.
Similar temperatures for the Cape/Islands. Southerly flow will try
to advect in higher dewpoint air; however, this will likely be
combated by efficient mixing. This will keep heat indices close to
highs in the low-mid 90s. The marginal humidity combined with heat
will make it borderline Heat Advisory today. Given the expected
heat Friday and mild overnight lows, we opted to start the
Advisory today, extending through Friday.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Key Messages:
* Peak of heat expected with elevated humidity making it feel like
upper 90s to low 100s.
* Heat Advisory in effect through evening.
* Scattered showers and thunderstorms possible mid afternoon-mid
evening. A few may be strong to severe.
Details...
Tonight:
Mild night expected with moisture continuing to advect in from the
south. Low temperatures stay in the upper 60s to low 70s.
Friday:
The heat and humidity are expected to peak Friday with with
850mb temperatures peaking around 20C and 925mb temperatures
ranging 24- 28C among most model guidance. Model soundings show
sufficient mixing helping bring down the warm 925mb temperatures
and breezy SW winds. It will be hotter than Thursday with
temperatures in the low to mid 90s in many places. The added
moisture will bring heat indices into the upper 90s to low 100s.
The south coast will lean a bit "cooler" than other locations
with the breezy onshore flow. A Heat Advisory will be in effect
on Friday for central and east MA, northern CT and northern RI.
An approaching shortwave/cold front in a hot, humid, and marginally
unstable airmass will increase chances for showers and thunderstorms
Friday. Marginal instability (MLCAPE< 1000 J/kg) builds ahead of the
front Friday afternoon. Mid-level lapse rates are poor and 0-6km
bulk shear is weak making widespread organized severe unlikely, but
a few strong to severe storms are possible. Damaging wind will
be the main hazard with any stronger storms. Model soundings
emulate more of a skinny Cape profile with PWATs 1-2" which will
support localized heavy downpours in storms. Can't rule out the
potential for localized street/urban flooding in a storm or
two. NSSL ML probs and CSU ML probs sit around 30 percent for
chance of severe right now. This seems to align with SPC's
"marginal risk" for our region with potential for a few strong
to severe storms in the mix. Still some spread among guidance
with the timing, but overall the best timeframe appears to be
mid afternoon to mid evening (~2-9PM) with scattered storms
developing in western MA, moving E/SE toward the evening.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Key Messages:
* Dry weather with a cooldown in temps Sat, but storminess returns
on Sunday.
* Summerlike warmth and humidity for early next week, and generally
dry most of the time.
Details:
Saturday and Sunday:
Behind Friday's front, a brief drier airmass works into the region
for Saturday resulting in a mainly dry day. Temperatures will be a
good amount cooler as well with highs in the 80s with upper 80s for
the CT Valley and low 80s along the coast.
An embedded shortwave in the flow aloft drops across the region
Sunday bringing back cloudiness and increased chances for showers
and perhaps a couple thunderstorms. Highs in the upper 70s to low
80s generally.
Early Next Week:
The northeast stays under northwest flow aloft next week which will
allow for the passage of a few embedded disturbances in the flow. No
signal for impactful weather, but this warm and sufficiently moist
pattern should support a round or two of scattered showers/storms
early next week. Timing will need to be ironed out as we get closer.
&&
.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
12z TAF Update:
Thursday: High confidence.
VFR. Breezy SW winds 10-15 kts, perhaps a bit stronger for the
Cape/Islands. Gusts to 20-25 kts.
Thursday Night: Moderate confidence.
VFR for most locations. Monitoring potential for patchy fog for
Cape and Islands, but still uncertain if it develops due to
steady SW winds around 10 kts overnight. Not enough confidence
to include in TAFs at this time.
Friday: High Confidence. Moderate on shower/storm timing.
VFR. SW winds 10-15 kts with gusts around 20 kts. BKN midlevel
clouds develop in the afternoon. Scattered showers and
thunderstorms possible in afternoon. Lower confidence in timing,
but best timeframe will be between 18-01z as showers/storms
move from west to east. Lightning, brief heavy downpours, and
brief gusty winds possible within storms.
KBOS terminal...High confidence in TAF.
KBDL terminal...High confidence in TAF.
Outlook /Friday Night through Monday/...
Friday Night: VFR. Breezy. Slight chance SHRA.
Saturday through Saturday Night: VFR.
Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, chance TSRA.
Sunday Night: VFR. Breezy. Chance SHRA, slight chance TSRA.
Monday: VFR.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Thursday through Thursday Night...High confidence.
Winds S to SW at 10-15 kts for the AM, increasing after 18z to
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...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.
Outlook /Friday Night through Monday/...
Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.
Saturday through Saturday Night: Winds less than 25 kt.
Sunday: Winds less than 25 kt. Slight chance of rain showers,
slight chance of thunderstorms.
Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, slight chance of thunderstorms.
Monday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Air Quality Alert from 11 AM this morning to 11 PM EDT this
evening for CTZ002.
Heat Advisory from 11 AM this morning to 8 PM EDT Friday for
CTZ002>004.
MA...Heat Advisory from 11 AM this morning to 8 PM EDT Friday for
MAZ003>007-010>019-026.
RI...Heat Advisory from 11 AM this morning to 8 PM EDT Friday for
RIZ001>004.
MARINE...Small Craft Advisory from 4 PM this afternoon to 8 AM EDT
Friday for ANZ250.
&&
$$
SYNOPSIS...Mensch
NEAR TERM...Mensch
SHORT TERM...Mensch
LONG TERM...Mensch
AVIATION...Hrencecin/Mensch
MARINE...Mensch
Source: BOX issues Area Forecast Discussion (AFD) at Jul 24, 7:16 AM EDT (https://mesonet.agron.iastate.edu/p.php?pid=202507241116-KBOX-FXUS61-AFDBOX)
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