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515
FXUS61 KBOX 182307
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
707 PM EDT Tue Jun 18 2024

.SYNOPSIS...
Dangerous heat and humidity continues through Wednesday and
Thursday, away from the south coast where the sea breeze keeps
temperatures cooler. Near to record breaking high temperatures
are possible Thursday. Heat peaks on Thursday before more
seasonable temperatures return for the weekend. Showers and
thunderstorms possible each afternoon and evening Thursday thru
Monday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Hot, hazy, and humid conditions for this afternoon and into early
this evening across the region, as the mid-level ridge is centered
overhead. Highs today, away from the influence of the ocean, have
climbed well into the upper 80s and lower 90s. While near the ocean
those temperatures have provided a bit of relief, the south coast of
both Rhode Island and Massachusetts report highs in the upper 70s to
the low 80s. Will continue to monitor temperatures for the rest of
this afternoon as we challenge a daily record highs. For a full
list of records, see the climate section at the bottom of the
AFD.

Seen storms pop-up across Pennsylvania and portions of New York,
think the cap remains firm to avoid and shower development. If there
were a widely isolated shower/thunderstorm, would develop off of the
terrain of western Massachusetts. Otherwise, a dry evening ahead
with temperatures slowly falling through the 80s this evening, but
do not expect much relief overnight as lows only fall back to the
upper 60s and low 70s. These overnight temperatures will
challenge the daily warmest low temperature records. For a full
list of records, see the climate section at the bottom of the
AFD.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Highlights:

* Heat Advisory for most of southern New England, with the exception
  of coastal Rhode Island, south coast of Massachusetts, Cape Cod,
  and the Islands.

An anomalous  ridge of high pressure expanding across the
northeast on Wednesday, with forecast 500mb heights around 597
dam! For reference the upper air soundings at CHH show a daily
max of 590 dam and all time max of 603 dam. Temperatures
continue to warm aloft, +18c to +20c at 850mb, and +23c to +25c
at 925mb. These abnormally warm temperatures aloft and higher
starting temperatures leads to highs into the lower and middle
90s (away from the coast). Southwest winds over the relatively
cooler ocean waters (middle 60s) keep coastal Rhode Island and
the south coast of Massachusetts in the upper 70s to middle 80s.
Southwest flow does maintain if not slightly increases dew
points, mid 60s by the coast while the interior has dewpoints
between 68F-72F. Combination of ambient air temperature and
high dew points leads to dangerously hot conditions, heat index
of 97F to 102F, potentially as high as 104F in the northern
Merrimack Valley.

Converted `Excessive Heat Watch` to a `Heat Advisory` for Wednesday,
but continued the watch for potential higher values Thursday.
Elsewhere, have continued the `Heat Advisory` into Wednesday, this
includes the expanded zones of the Providence metro, along with
northern Plymouth and Bristol Counties in Massachusetts, which
includes coastal Plymouth County.

Those who work or need to be outdoors, be sure to keep hydrated and
take frequent breaks in the shade. If you can stay indoors in an air-
conditioned location, do so, and check up on relatives and
neighbors.

Overall a dry day, similar to Tuesday, cannot rule out a widely
isolated shower/thunderstorm, but given our location under the ridge
it will be difficult. While there is sufficient CAPE, the atmosphere
is capped with the warmer air aloft. The better chance for a shower
to develop would be off the terrain across northern ans western
Massachusetts.

Wednesday night is quite warm, no relief as temperatures only fall
back to the upper 60s to 70 degrees. Urban locations likely hold on
to the heat of the day, lows likely are around 70F-73F. These
overnight temperatures will challenge the daily warmest low
temperature records. For a full list of records, see the climate
section at the bottom of the AFD.

&&

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

* Dangerous Heat & Humidity continues Thursday, cooling off for
  Friday

* Near Record Highs with Heat Indices from 98 to 106 degrees on Thu

* Scattered showers/t-storms possible Thursday into the weekend.

* Excessive Heat breaks this weekend...but it still will be humid

Details...

Thursday our heat and humidity peaks beneath the broad ridge of high
pressure which has been over New England for several days. The
guidance and forecast has not changed appreciably for Thursday, and
500 mb heights continue to be highly anomalous leading to a much
warmer than average forecast of upper 90s to around 100F.
Exacerbating this will be high humidity with dewpoints continuing to
hover around the low 70s. Given the heat and humidity, instability
will be present on the order of 1000-1500 J/kg of CAPE maximized
over the interior. However, lack of good forcing apart from diurnal
heating will limit shower/t-storm coverage and minimal bulk shear
(<25 kts) will limit prolonged updrafts. Thus, any severe potential
is quite limited. Better forcing and marginally better shear to our
north mean a better chance for a severe storm there which could make
its way into northwest MA where the SPC has issued a Marginal Risk
for severe storms.

Friday a backdoor cold front courtesy of a surface high north of the
Great Lakes will limit high temperatures quite a bit, especially for
those further east. It`s a tough forecast as the timing of the front
will directly impact high temperatures and storm potential...some
locations may briefly touch upper 80s mid morning before
dropping into the 70s for the afternoon as cooler NE flow kicks
in. Either way, not expecting a repeat of the heat on Thursday.
This will also limit instability, keeping thunderstorm chances
confined to western SNE or potentially even further west. Again,
confidence on these details remains low subject to the
placement and timing of the front.

For the weekend the airmass doesn`t change much ahead of our next
shortwave early in the week so high temperatures will remain similar
each day through Monday, in the 80s. The exception will be Saturday
along the east coast where continued NE flow keeps temps in the 70s.
Instability and shear increase Sunday into Monday as moist SW flow
increases ahead of an approaching shortwave/front. This will bring
the chance for scattered showers and thunderstorms each day,
though details are yet unknown. A cold front moves through
sometime Monday or Monday night bringing some relief from the
high dewpoints.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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

00z TAF Update...

Tonight... High confidence.

VFR, S-SW winds 5-10 kt along with dry weather.

Wednesday... High confidence.

Almost a rinse and repeat forecast, VFR, mainly dry weather along
with SW winds 10-15 kt with gusts up to 20 kt at times.

Wednesday Night... High confidence.

VFR. SW winds 8-12 kts along with dry weather.

KBOS TAF... High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: VFR. Breezy. Slight chance
SHRA, isolated TSRA.

Friday: Mainly VFR, with local MVFR possible. Chance SHRA,
isolated TSRA.

Friday Night through Saturday: Mainly VFR, with local MVFR
possible. Chance SHRA.

Saturday Night: Mainly VFR, with local IFR possible. Chance
SHRA, isolated TSRA.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, isolated TSRA.
-- End Changed Discussion --

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Wednesday Night... High confidence.

Vast high pressure provides good boating conditions for the midweek,
with dry conditions, and good visibility`s. Steady southwest
winds tonight through Wednesday and Wednesday night, wind speeds
are between 10 and 20 knots, a few isolated gusts may approach
25 knots on the outer eastern waters. Seas are generally 1-3 ft,
approaching 4ft on the eastern outer waters Wednesday afternoon
into the evening.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms.

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

Friday Night through Saturday: Winds less than 25 kt. Slight
chance of rain showers.

Saturday Night: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers, isolated thunderstorms.

&&

.CLIMATE...
All Time June High Temperature Record (Daily)

BOS - 100 F (06/06/1925, 06/26/1952 and 06/30/2021)
BDL - 100 F (06/26/1952, 06/30/1964)
PVD - 98 F  (06/25/1943, 06/15/1945 and 06/30/1945)
ORH - 98 F  (06/26/1952)

Most recent day of 100 F (or greater)

BOS - 100 F (07/24/2022)
BDL - 100 F (07/21/2019)
PVD - 100 F (07/28/2020)
ORH - 102 F (07/04/1911)*

* For ORH this is the only 100+ degree day in its period of record.

Daily High Temperature Records...

June 18th

BOS - 94 F (1907 and 1929)
BDL - 95 F (1957 and 1994)
PVD - 94 F (1929)
ORH - 93 F (1907 and 1929)

June 19th

BOS - 96 F (1923)
BDL - 95 F (1995)
PVD - 94 F (1923)
ORH - 93 F (1923)

June 20th

BOS - 98 F (1953)
BDL - 97 F (2012)
PVD - 95 F (1941)
ORH - 93 F (1953)

June 21st

BOS - 96 F (2012)
BDL - 96 F (1953 and 2012)
PVD - 96 F (1941)
ORH - 91 F (Multi-Years)

Daily Warmest Low Temperatures Records...

June 18th

BOS - 72 F (1929)
BDL - 70 F (1905)
PVD - 72 F (1929)
ORH - 69 F (1905 and 1994)

June 19th

BOS - 73 F (1995)
BDL - 72 F (1929)
PVD - 70 F (1995)
ORH - 72 F (1929)

June 20th

BOS - 78 F (1931)
BDL - 74 F (1931)
PVD - 74 F (1931)
ORH - 72 F (1931)

June 21st

BOS - 80 F (2012)
BDL - 73 F (1923 and 2012)
PVD - 75 F (2012)
ORH - 74 F (1923 and 2012)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
CT...Air Quality Alert until 11 PM EDT this evening for CTZ002.
     Heat Advisory from 8 AM to 7 PM EDT Wednesday for CTZ002-003.
     Excessive Heat Watch from Thursday morning through Friday
     evening for CTZ002-003.
     Heat Advisory until 7 PM EDT Friday for CTZ004.
MA...Air Quality Alert until 11 PM EDT this evening for MAZ005>007-
     010>012.
     Heat Advisory from 8 AM to 7 PM EDT Wednesday for MAZ003-005-
     006-010-011-013-014.
     Excessive Heat Watch from Thursday morning through Friday
     evening for MAZ003-005-006-010-011-013-014.
     Heat Advisory until 7 PM EDT Friday for MAZ002-004-007>009-012-
     015-016-026.
     Heat Advisory from noon Wednesday to 7 PM EDT Friday for
     MAZ017>019.
RI...Heat Advisory until 7 PM EDT Friday for RIZ001.
     Heat Advisory from noon Wednesday to 7 PM EDT Friday for
     RIZ002>005.
MARINE...None.
-- End Changed Discussion --

&&

$$

SYNOPSIS...BW/Dooley
NEAR TERM...Dooley
SHORT TERM...Dooley
LONG TERM...BW
AVIATION...BW/Dooley
MARINE...BW/Dooley
CLIMATE...BL