832
FXUS61 KBOX 141924
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
324 PM EDT Sun Jul 14 2024

.SYNOPSIS...
Dangerous heat and humidity is on tap for our region Monday
through Wednesday, with the chance for mainly afternoon and
evening thunderstorms each day, and especially later Wednesday
into Wednesday night. A cold frontal passage late Wednesday into
Thursday will give way to a much more comfortable airmass to
end this work week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Relatively tranquil weather continues tonight. Slowly increasing
humidity, with a return of low clouds and areas of fog towards
the Cape and islands. Sea breezes breakdown this evening, with
light SSW to calm winds overnight. Higher dew points will keep
low temperatures around 70 degrees across most of southern New
England. Thinking mid 60s possible towards the higher terrain of

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
Increasing heat and humidity into Monday. Expecting maximum heat
index values between 95-100F. Heat Advisories continue.

Looking like it could be a more active weather-wise during the
afternoon and evening. An approaching mid level shortwave may
tap into this environment and generate some showers and
thunderstorms. We should be looking at most-unstable CAPE values
of 1,500-2,500 J/kg. That said, mixed signals in the guidance
about how robust mid level lapse rates will be. There remain
some guidance sources which show more of an elevated mixed
layer, the NAM being one of those, while others showed what has
been more typical of recent days where mid level lapse rates are
poor. At this time, leaning toward the weaker mid level lapse
rates and a later arriving shortwave. Thus, thinking the overall
risk for severe weather is low, and likely isolated at most.
That said, subtle changes could have a larger impact. Will need
to monitor this aspect of the forecast closely.

Any thunderstorms should weaken substantially near and after
sunset. It will remain muggy and warm Monday night.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Key Points...

* Very hot and humid conditions Tuesday into Wednesday

* Isolated to Scattered Thunderstorms possible Tuesday
  afternoon; cold frontal passage late Wednesday/Thursday
  brings potential for more widespread convection

* Refreshing airmass behind the cold front leads to a seasonable
  weekend

Generally zonal flow aloft Tuesday into the first half of
Wednesday as shortwave drops south from Ontario into the Great
Lakes Region. Very weak shortwave looks to develop Tuesday
afternoon across southern Ontario/Upstate NY before crossing
northern New England late Tuesday evening. Aforementioned more
robust shortwave across the Great Lakes deepens as it moves
eastward towards southern New England on Wednesday as cold
frontal passage generates more robust thunderstorm chances
during the late afternoon and early evening hours. Trough axis
will take some time to move seaward of the region, struggling to
pivot to our east until late Friday, with a broad trough
lingering over the region into the weekend.

Heat...

Heat will peak on Tuesday but will linger into Wednesday,
especially across Connecticut and Southeast MA, ahead of
approaching shortwave. As mentioned by the previous shift, 850mb
temps in excess of 20C will support widespread high
temperatures in the 90s away from the coast, particularly on
Tuesday. Dewpoints remain in question, which will be the primary
driver accounting for how high heat indicies are able to climb,
but confidence has grown over the last few model runs that a
more southwesterly surface flow component, coupled with westerly
flow aloft, will keep dewpoints subdued in the low 70s, with
perhaps a few mid 70s across interior RI and CT. Given forecast
trends in dewpoints, confidence has grown that heat index values
will remain BELOW Excessive Heat Criteria (ranging generally
between 98-103F on Tuesday, and 103F on Wednesday). Thus, the
Excessive Heat Watch for Tuesday has been converted to a Heat
Advisory for the entire region, except for the Cape and Islands
where there are no headlines in place. The Heat Advisory has
been extended into Wednesday for our Connecticut zones, as well
as northern RI and SE MA where confidence is greatest in 100F+
apparent temperatures Wednesday afternoon ahead of the front.


 Precipitation...

Westerly flow aloft and the aforementioned weak shortwave
Tuesday afternoon may provide enough forcing for some scattered
thunderstorms to develop, particularly across interior MA and CT
given the oppressive heat and humidity leading to high
instability. Cold frontal passage late Wednesday will bring the
best chance for widespread precipitation to the region. Timing
currently looks to be during the pre-sunset hours of Wednesday
to about the midnight hour. As previously mentioned, CSU Machine
Learning probs have highlighted a risk of damaging winds.
Additionally, given high PWATs, near 2", heavy rain is expected,
which is highlighted in the WPC ERO from 12Z Wednesday to 12Z
Thursday. Behind the front, much drier airmass moves into place.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Tonight...High Confidence

Mainly VFR with calm/light southwest winds. The exception will
be mainly near the south coast, and especially the Cape/Islands,
where areas of IFR-LIFR cigs/vsbys will likely develop, especially
across Nantucket.

Tomorrow...High Confidence

VFR. Steady southwest winds 10 to 15 knots with some afternoon
20+ knot gusts possible. This should fend off any sea breeze.
Some later afternoon/evening thunderstorms are possible,
especially across the interior. Brief MVFR possible in stronger
showers/storms.

Tomorrow Night...High Confidence

VFR. Convection diminishes near and after sunset.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday: VFR. Breezy. Slight chance SHRA, isolated TSRA.

Tuesday Night: VFR. Breezy. Slight chance SHRA.

Wednesday through Wednesday Night: Mainly VFR, with local MVFR
possible. Breezy. Chance SHRA, isolated TSRA.

Thursday: VFR. Chance SHRA, isolated TSRA.

Thursday Night: VFR. Slight chance SHRA.

Friday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Relatively tranquil boating conditions across the waters through
Monday night. The only issue will be areas of poor visibility
in fog overnight into Monday morning, mainly across the waters
south of the Cape, and especially around Nantucket. More fog
possible Monday night as well.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers, isolated thunderstorms.

Wednesday Night: Winds less than 25 kt. Local rough seas. Rain
showers likely, isolated thunderstorms.

Thursday: Winds less than 25 kt. Local rough seas. Chance of
rain showers, isolated thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from 8 AM Monday to 8 PM EDT Wednesday for
     CTZ002>004.
MA...Heat Advisory from 8 AM Monday to 8 PM EDT Wednesday for
     MAZ013-016>019.
     Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for MAZ003-
     005>007-010>012-014-015-020-021-026.
RI...Heat Advisory from 8 AM Monday to 8 PM EDT Wednesday for
     RIZ001>005.
     Heat Advisory from 8 AM Monday to 8 PM EDT Tuesday for RIZ006-
     007.
MARINE...None.

&&

$$

SYNOPSIS...Belk/KS
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...KS
AVIATION...Belk/KS
MARINE...Belk/KS