-- Discussion containing changed information from previous version are highlighted. --
043
FXUS61 KBOX 172304
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
704 PM EDT Mon Jun 17 2024

.SYNOPSIS...
Dangerous heat and humidity arrives on Tuesday away from the south
coast and peaks in the Wednesday through Friday time frame. Near to
record breaking high temperatures are possible. The main threat for
scattered showers and thunderstorms will be Friday into the weekend,
but specific timing remains uncertain. We do expect the excessive
heat to break this weekend, but it will remain very warm and
humid.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

Marginal instability exits across western MA with SBCAPES around
500 J/kg but lack of forcing will prevent any convection through the
afternoon. Dry conditions tonight with mainly clear skies as upper
level ridge builds north into SNE. Surface high pres moves further
offshore with modest SW flow limiting radiational cooling with lows
mainly in the 60s.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
Tuesday...

* Dangerous heat and humidity ramps up away from the south coast
* Low risk for an isolated t-storm in the interior

Very anomalous upper level ridge builds over New Eng. In fact, 500
mb heights are maxed out for this time of year relative to CFSR
climatology. 925 mb temps increase to 24-26C in the interior which
will translate to highs low-mid 90s away from the south coast with
hottest temps in the CT and Merrimack valleys. SW flow will keep it
cooler across RI and SE MA with highs mainly mid-upper 80s while the
immediate south coast and Cape/Islands will be upper 70s to lower
80s. Dewpoints will be climbing into the mid-upper 60s with some 70
degree dewpoints in the CT and Merrimack valleys where heat indices
are expected to reach the low 100s. Elsewhere, away from the south
coast heat indices will reach mid-upper 90s. We converted the
Excessive Heat Watches for Tue to heat advisories and we trimmed the
heat advisory across much of RI and SE MA where heat advisories will
fall short of criteria.

The heat and humidity will result in moderate instability developing
with SBCAPES 1000-2000 J/kg. However, forcing is rather weak with
ridging in place and there may be a cap in place. HREF max updraft
forecast is suggesting isolated to widely scattered convection
developing in the afternoon/evening across interior MA so can`t rule
out a few showers or a t-storm but areal coverage will be limited
and any storms will be short lived as deep layer shear is quite low.
Continued slight chc PoPs across interior MA.

Tuesday night...

Any convection will dissipate in the evening, otherwise looking at
mainly clear to partly cloudy skies. Lows will be mostly in the mid-
upper 60s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
Key Points...

* Dangerous Heat & Humidity continues through Fri

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

* Main threat for scattered showers/t-storms is Fri into the weekend

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

Details...

We continue to beat the drum regarding an extended stretch of
dangerous heat and humidity which will stretch through the end of
the week. Guidance continues to be in excellent agreement that the
peak of the heat occurs Wednesday and Thursday. Relief won`t come
quickly, though, as it will be a more gradual easing of high
temperatures from Friday to the weekend. The culprit is a very
anomalous ridge of high pressure (sinking air which heats the
airmass) overhead. In fact, as the previous forecaster mentioned,
the magnitude of this ridging (600 dm) is rarely seen in southern
New England which signals the potential for record breaking heat.
The forecast hasn`t changed much in the last 24 hours, with highs
projected to peak on Thursday at or just over 100F in the warmest
locations like the CT Valley and Merrimack Valley. Making the
situation more dangerous is the moist airmass in place with
dewpoints in the upper 60s and low 70s making it feel over 105F in
spots. Thus, an Excessive Heat Watch continues for these locations,
with a Heat Advisory elsewhere. Don`t focus on the headline,
however, as it will be dangerously hot regardless. Something that
will exacerbate the hazard is that we`ll get little relief at night,
only cooling off to the upper 60s/low 70s. Expect mostly dry weather
for Wed and Thu but a few scattered t-storms are possible.

Friday into the weekend we get a little relief, but the real airmass
change won`t come until a cold front arrives around Monday
night/early Tuesday. That`s when dewpoints will finally drop back
toward the 50s. In the meantime, ahead of this cold front and its
associated shortwave the airmass will remain largely unchanged Sat-
Mon with highs in the 80s each day. The approaching shortwave will
also increase the chance of showers and thunderstorms each day
starting on Friday. Too soon to nail down timing details but
unsettled weather looks more likely through Monday.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
-- 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. SW wind 5-10 mph.

Tuesday...High confidence.

VFR. Low risk for an isolated afternoon shower or t-storm
across NW MA. SW wind 10-20 kt.

Tuesday night...High confidence.

VFR. S-SW wind 5-10 kt.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Tuesday Night through Saturday/...

Tuesday Night through Thursday Night: VFR. Breezy.

Friday through Friday Night: VFR. Chance SHRA, isolated TSRA.

Saturday: VFR. Slight 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.

Today:

Continued clear conditions with increasing southerly winds at
10-15 knots, gusting up to 25 knots across the near shore waters
along the south coast. Opted to hoist a short-fused small craft
advisory for these waters and seas may be choppy. Seas 2-4 ft

Tonight:

Clear conditions with slowly decreasing southwest
winds 10-15 kts. Seas 2-4 ft.

Tomorrow:

Clear conditions with increasing southerly winds gusting 20-25
knots once again. Seas 2-4 ft

Outlook /Tuesday Night through Saturday/...

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

Juneteenth: Winds less than 25 kt.

Wednesday Night through Thursday: Winds less than 25 kt. Seas
locally approaching 5 ft.

Thursday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Friday through Saturday: Winds less than 25 kt. Slight 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 from 11 AM to 11 PM EDT Tuesday for CTZ002.
     Excessive Heat Watch from Tuesday afternoon through Friday
     evening for CTZ002-003.
     Heat Advisory from noon to 7 PM EDT Tuesday for CTZ002-003.
     Heat Advisory from noon Tuesday to 7 PM EDT Friday for CTZ004.
MA...Air Quality Alert from 11 AM to 11 PM EDT Tuesday for
     MAZ005>007-010>012.
     Excessive Heat Watch from Tuesday afternoon through Friday
     evening for MAZ003-005-006-010-011-013-014.
     Heat Advisory from noon to 7 PM EDT Tuesday for MAZ003-005-006-
     010-011-013-014.
     Heat Advisory from noon Tuesday to 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 from noon Tuesday to 7 PM EDT Friday for RIZ001.
     Heat Advisory from noon Wednesday to 7 PM EDT Friday for
     RIZ002>005.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ231>236-250-251-254-255.
-- End Changed Discussion --

&&

$$

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