BOX issues Area Forecast Discussion (AFD) at Jun 22, 3:09 AM EDT690
FXUS61 KBOX 220709
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
309 AM EDT Sun Jun 22 2025
.SYNOPSIS...
Increasing clouds with scattered showers and embedded
thunderstorms through late this morning, although severe weather
is not expected. After morning cloud cover dissipates, hot and
humid weather begins and is expected to lead to high heat
indices, with extreme heat and humidity expected on Monday and
Tuesday. The heat and humidity then ease into the latter half
of the workweek, with daily chances at showers and thunderstorms
returning.
&&
.NEAR TERM /THROUGH TONIGHT/...
245 AM Update:
Key Messages:
* Showers with embedded rumbles of thunder/lightning flashes
between 4 AM to 10 AM, best chances for thunderstorms in
western New England. Severe weather is not expected.
* Mostly cloudy morning but turns mostly sunny by afternoon.
* High temps mid 80s to lower 90s, with heat indices around
95-100 degrees.
Details:
First, a note that the forecast package was completed early,
given the thunderstorm complex moving into northern NY early
this morning, and a need to monitor radar shortly.
The main feature of at least short-term interest is the severe
MCS in the Tug Hill and Adirondacks of NY. This MCS has formed
on the northeast periphery of steep midlevel lapse rates
associated with an elevated mixed layer (e.g. BUF 00z RAOB shows
700-500 mb lapse rates around 8 C/km), with most- unstable
CAPEs on the order of 1500-2500 J/kg. This MCS is tracking along
the upstream propagation component vectors, which are oriented
south- southeasterly per SPC's mesoanalysis. The most intense
portion of the MCS complex coming into far northwest NY is also
backbuilding into the more unstable air to its south and west.
The threat of severe weather in Southern New England from this
complex is decreasing, instead being more favored in central NY.
But that being said, it's important to note that there has been
active cloud- to- cloud and even some cloud-to- ground strikes
per lightning network data and GLM minimum flash area products
well east of the most intense portion of it into Quebec. As this
feature moves south- southeast and makes its closest approach
from about 3 to 10 AM, expect there to be mainly showers with
possible flashes of lightning and rumbles of thunder even into
eastern MA and RI. The best chance at seeing a stronger
thunderstorm would be in the Berkshires and parts of northern
CT. Rain amts from this early showers and thunderstorms wouldn't
amount to much; if anything, it would make it feel even more
balmy once the sun comes out and evaporates it. Most areas
should trend dry by late this morning.
Otherwise, the main story for today is that it's the first day
of high heat and humidity, but the morning thunderstorm complex
near and to our west is going to throw a monkey-wrench into
prior heat and humidity expectations for today. Because of a
residual canopy of cloud cover from the storm complex thru at
least the early afternoon, that will at least keep temperatures
from really soaring until after morning cloudiness starts to
scatter out. Current dewpoints are in the low to mid 60s, and
they will probably stay that way until the afternoon when they
should surge into the upper 60s to lower/mid 70s. Ended up
lowering high temperatures today to the mid 80s to lower 90s,
which cuts into today's highest heat indices to around 95-100.
Although it's fair to say this isn't truly dangerously high heat
indices, it's a marathon and not a sprint, with the expectation
that Monday and Tuesday end up being the hottest days of the
stretch. So we opted to not make changes to heat headlines to
keep the messaging simple. It'll also turn somewhat breezy this
afternoon too, with westerly winds gusting to 25-30 mph.
Finally, the risk for isolated thunderstorms this afternoon now
looks minimal, lacking much forcing and with model soundings
showing sufficiently strong capping.
For tonight, midlevel ridge associated with the building heat
dome over the Ohio Valley and northern mid-Atlantic settles into
the Northeast. Tonight should be very warm and quite muggy.
High pressure building into the Gulf of Maine tonight should
allow for a light NE to E wind to develop along the eastern
coast. Lows tonight in the upper 60s to low 70s for the eastern
coast, and into the mid to upper 70s inland. Rising dewpoints
could also favor fog development along the immediate south
coast.
&&
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Key Messages:
* Dangerously high heat indices expected Monday and Tuesday,
which may feel as high as 110 degrees in interior Southern New
England.
* Temperatures could approach or break daily record highs.
* Seabreeze near the eastern coast Monday could keep eastern MA
less hot, but still quite humid.
* Dry weather expected.
Monday and Tuesday still stand to be the most oppressive in
terms of heat and humidity, with dangerously high heat indices
expected. Extreme Heat Warnings, and Heat Advisories for the
Berkshires, remain valid for this period.
For Monday...ridging aloft will maintain full sunshine as 850 mb
temps rise to around +21C to +23C. Full sun will allow most
areas see their air temps soar to the mid 90s to low 100s! Because
of a period of onshore flow along the immediate eastern coast,
it may be less hot but still humid for as long as the onshore
flow prevails. Tough call if coastal MA actually gets to a 90
degree air temperature, and it probably won't do so until after
onshore flow flips to a SWly wind later in the day. Daytime heat
indices range from 95 degrees near the coast, to 105-110
inland. Monday night is very warm and muggy with lows in the mid
70s, with upper 60s over the Cape and Islands. This won't
provide much in the way of relief.
For Tuesday...Tuesday ends up being the peak of the heat across
all of Southern New England. With light WSW flow, 850 temps up
to around +23 to +24C, many areas away from the Cape and Islands
see air temps in the mid 90s to low 100s, with air temps on the
Cape reaching the upper 80s. With the westerly wind, even
Boston will have a strong chance at reaching 100 degrees. Heat
indices should be as much as 105-110 degrees. For Tue night, the
midlevel ridge axis shifts southward into the mid-Atlantic
waters, with more zonal flow aloft taking hold. A cool frontal
boundary will be lurking in northern New England Tue night, so
it is possible we'll have to keep an eye out for possible
t-storms coming in from the west and north, but there aren't any
compelling signals that hint at nighttime storm chances Tue
night. Something to monitor but forecast will call for dry
weather Tue night. Still on the warm and muggy side for Tue
night with lows in the mid 60s to lower to mid 70s.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Key Messages:
* Gradual cooldown starting Wed, but turning more seasonable by
late in the week.
* Mainly dry on Wed, but daily shower/storm chances return on
Thu thru Sat.
The heat looks to break some Wednesday, before returning to more
normal summer temperatures late next week. As for
precipitation, the strong ridge beneath the heat dome should
maintain rain-free weather into Wednesday. Some afternoon
showers or thunderstorms are then possible Wednesday afternoon
and evening. A greater risk for showers and thunderstorms
Thursday into Saturday as a frontal boundary lingers nearby.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update:
Through 12z Sunday: High confidence.
Mainly VFR; a band of showers or thundershowers (mainly in-
cloud lightning strikes) associated with the far eastern extent
of an MCS over New York will progress southeast across the TAFs.
Best chance at seeing TSRA at BAF and BDL, with PROB30s at BED,
ORH, and BOS. The most intense portion of the MCS will pass to
our west, though. SW winds around 5-10 kt to start, though may
become S, or even SE for the western airports.
Today: High confidence.
Ongoing SHRA/possible TS shifts south and/or dissipates by
14-16z. Any brief sub-VFR restrictions become VFR thereafter.
Winds become W to WNW around 10-15 kt with gusts 25-30 kt during
the afternoon.
Tonight: High confidence.
Mainly VFR, though possible fog near the south coast, cape and
Islands airports. 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, though will have prevailing E/SE winds at BOS until
late afternoon.
KBOS Terminal...High confidence in TAF. PROB30 for possible TS
(mostly in-cloud flashes of lightning) from 10-14z. Otherwise,
VFR rest of the day. Gusty W winds to 25-30 kt this afternoon.
KBDL Terminal...High confidence in TAF. VCTS with TEMPO TSRA for
a better chance at TSRA 10-14z, with brief downpours possible
but storms not expected to become strong or severe. Otherwise
VFR rest of the day. Gusty W winds develop this afternoon.
Outlook /Wednesday through Thursday/...
Wednesday: VFR. Slight chance SHRA.
Wednesday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA, isolated TSRA.
Thursday: Mainly VFR, with local IFR possible. Chance SHRA,
isolated TSRA.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Through Tuesday Night: High confidence.
SCAs remain in effect for all waters today. Possible in-cloud
lightning flashes this morning with passing showers. After
showers end, W winds increase to 15-25 kt with gusts to 30 kt.
Winds quickly diminish Sun evening and become light NE late Sun
night. Light E to SE winds expected on Monday, with SW winds
10-15 kt on Tue. Possible fog on the waters Sunday thru Tuesday
evenings.
Outlook /Wednesday through Thursday/...
Wednesday: Winds less than 25 kt.
Wednesday Night: Winds less than 25 kt. Slight chance of rain
showers.
Thursday: Winds less than 25 kt. Chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Extreme Heat Warning from 11 AM this morning to 8 PM EDT
Tuesday for CTZ002>004.
MA...Extreme Heat Warning from 11 AM this morning to 8 PM EDT
Tuesday for MAZ003>007-010>021-026.
Heat Advisory from 11 AM this morning to 8 PM EDT Tuesday for
MAZ002-008-009.
RI...Extreme Heat Warning from 11 AM this morning to 8 PM EDT
Tuesday for RIZ001>007.
Air Quality Alert from 11 AM this morning to 11 PM EDT this
evening for RIZ006>008.
MARINE...Small Craft Advisory from 8 AM this morning to 6 PM EDT this
evening for ANZ230-231-236-250-251.
Small Craft Advisory from 8 AM this morning to 8 PM EDT this
evening for ANZ232>235-237-254.
Small Craft Advisory from 8 AM this morning to 2 AM EDT Monday
for ANZ255-256.
&&
$$
SYNOPSIS...Loconto
NEAR TERM...Loconto
SHORT TERM...Loconto
LONG TERM...Loconto
AVIATION...Loconto
MARINE...Loconto
Source:
BOX issues Area Forecast Discussion (AFD) at Jun 22, 3:09 AM EDT----------------
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