968
FXUS61 KBOX 222325
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
725 PM EDT Sun Jun 22 2025

.SYNOPSIS...
Dangerous heat and humidity through early next week peaks on
Tuesday. The heat begins to ease on Wednesday then turning cooler
for the end of the week into next weekend with daily chances of
showers and possibly a few thunderstorms.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Tonight:

Key Point

* Warm and humid with lows around 70F

Substantial height rises should cap the atmosphere off for the
remainder of the afternoon and evening, even with 3000-4000 J/kg of
SBCAPE.  There could be a few weak showers and a rumble or two of
thunder over the eastern waters this evening, where strong westerly
winds inland converge with strong southerly winds over the waters.
Instability is much lower over the water, so its unlikely that
anything that develops will become severe.

Temperatures this afternoon have quickly jumped into the upper 80s
to low 90s behind the showers from this morning. Temperatures could
climb further into the mid-90s this afternoon before peak diurnal
heating ends.  There is little relief from the heat tonight, as low
temperatures only drop into the upper 60s to low 70s.  There could
be some patchy fog overnight as dewpoints stay near 70F and winds
become light.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Key Points

* Dangerous Heat and humidity with heat index values as high as
  115F

* Not much heat relief overnight with lows still near 70F

Tomorrow:

Dangerous heat and humidity continues tomorrow as the upper-
level ridge and heat dome continue to build in southern New
England. 850mb temperatures will warm to around 20C, which
will translate to surface temperatures in the upper 90s to even
near 100F in the CT River Valley. With dewpoints still near
70F, the heat index, or feels-like temperature, will be between
105F and 115F across western Massachusetts and all of
Connecticut. Further east, the light pressure gradient and hot
temperatures will lead to strong sea breezes pushing inland
across eastern Massachusetts and Rhode Island, resulting in high
temperatures in the low to mid-90s and heat index values
between 95F and 105F. The only place to escape the heat
tomorrow will be Cape Cod and the Islands, where high
temperatures will range from the mid-70s to the low 80s. Skies
remain mostly sunny with dry conditions as the ridge continues
to suppress any precip chances.

Tomorrow night:

A significant part of why a heat wave is so dangerous is that
overnight temperatures offer little relief from the heat and
humidity.  Temperatures at midnight on Tuesday will still be in the
upper 70s to low 80s, and overnight lows will only drop to the low
to mid-70s.  Dewpoints remain in the 70s overnight, which will keep
that tropical feel to the airmass overnight.  With southerly flow,
there could be more widespread low status and dense fog across the
Cape and Islands and possibly into southeastern Massachusetts and
Rhode Island.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Key Messages:

* Peak of the heat will be on Tuesday with dangerously high heat
  indices 100 to 110 degrees

* Heat diminishes Wed but still hot away from the coast, then
  cooler for late in the week and weekend

* A few showers and t-storms possible Wed with locally heavy
  downpours

* Daily chances of showers and perhaps a few t-storms Thu through Sun

The dangerous heat peaks on Tue as anomalous mid level ridge builds
over the mid Atlc region. 850 mb temps around 22C and 925 mb
temps up to 28C are about as high as you will see in SNE. This
coupled with full sunshine and westerly flow will result in
widespread high temps in the upper 90s and low 100s, with temps
around 90 on Cape Cod and south coast beaches. Dewpoints will be
in the lower 70s in the morning, but well mixed boundary layer
may allow dewpoints to fall into the upper 60s in some locations
during peak heating. Still expect heat indices peaking at
100-110F. It will be a rather warm night Tue night with temps
above 80 through midnight away from the south coast before
dropping to mid 70s by daybreak.

The mid level ridge begins to break down Wednesday as polar jet
shifts southward. Slight cooling aloft and wind shift to E-NE will
take the edge off the heat somewhat, especially along the coast as
sea-breezes develop. But still a hot day with highs low-mid
90s inland and mid-upper 80s along the coast, cooler Cape/Islands.
Dewpoints will be dropping through the 60s which will keep heat
indices in check somewhat. Peak heat indices will be 95-100F across
CT and possibly into Springfield where heat advisories may be
needed. Weak boundary will be hanging around SNE and we have
instability with CAPES 500-1500 J/Kg along with elevated PWAT plume
so can`t rule out a few showers and t-storms. PWATs near 2 inches so
any showers or storms could contain locally heavy downpours.

Then true relief from the heat arrives Thursday through Sunday as
weak surface boundary settles south of New Eng with easterly flow
developing along with much cooler 925 mb temps. Temps will average
below normal with highs mostly in the 70s but it is not out of the
question a few days could be even cooler in some locations. There
will be daily chances of showers through the period as deep moisture
plume persists over the region with elevated PWATs 1.5 to 2 inches.
There is minimal to no surface instability during this time so
severe weather is not expected but can`t rule out a few t-storms
given some elevated instability in place.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

00z TAF Update:

Tonight: High confidence.

Mainly VFR, though possible fog near the south coast, cape and
Islands airports and interior valleys. Winds become light NW,
with N to NE winds developing along the eastern coast.

Monday: High confidence.

VFR. Light north winds become S and increase to around 5-10 kt
for most

Monday Night: Moderate Confidence

Light southerly winds may lead to more widespread low status and
fog overnight for the south coast including the Cape and
Islands.

KBOS Terminal...High confidence in TAF.

VFR. Gusty W winds to 25-30 kt this afternoon. Low chance for a
isolated shower this afternoon. Light north winds tonight

KBDL Terminal...High confidence in TAF.

VFR. Gusty W winds this afternoon. Light and variable winds
tonight.

Outlook /Tuesday through Friday/...

Tuesday through Tuesday Night: VFR.

Wednesday: VFR. Slight chance SHRA.

Wednesday Night: VFR. Slight chance SHRA, isolated TSRA.

Thursday: Mainly VFR, with areas MVFR possible. Chance SHRA,
isolated TSRA.

Thursday Night: Mainly VFR, with areas IFR possible. Chance
SHRA.

Friday: Mainly VFR, with local IFR possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Through Tomorrow night: High confidence.

Gusty winds this afternoon quickly diminish this evening turning
from west to north. Winds gradually turn south tomorrow and
remain light under 10 knots. Marine fog possible tonight, but
more likely tomorrow night with southerly flow.

Outlook /Tuesday through Friday/...

Tuesday through Wednesday: Winds less than 25 kt.

Wednesday Night: Winds less than 25 kt. Slight chance of rain
showers.

Thursday: Winds less than 25 kt. Slight chance of rain showers,
isolated thunderstorms.

Thursday Night through Friday: Winds less than 25 kt. Chance of
rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Extreme Heat Warning until 8 PM EDT Tuesday for CTZ002>004.
MA...Extreme Heat Warning until 8 PM EDT Tuesday for MAZ003>007-
     010>021-026.
     Heat Advisory until 8 PM EDT Tuesday for MAZ002-008-009.
RI...Extreme Heat Warning until 8 PM EDT Tuesday for RIZ001>007.
     Air Quality Alert until 11 PM EDT this evening for RIZ006>008.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ232>235-237-254.
     Small Craft Advisory until 2 AM EDT Monday for ANZ255-256.

&&

$$

SYNOPSIS...KJC/KP
NEAR TERM...KP
SHORT TERM...KP
LONG TERM...KJC
AVIATION...Frank/KP
MARINE...KJC/KP