-- Discussion containing changed information from previous version are highlighted. --
370
FXUS61 KBOX 171724
AFDBOX

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

.SYNOPSIS...
Increasing temperatures and humidity today along with gusty
south winds. Dangerous heat and humidity arrives on Tuesday and
peaks in the Wednesday through Friday time frame. Near to
record breaking high temperatures are possible with afternoon
Heat Indices between 98 and 106 degrees away from the immediate
south coast. 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 humid.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
945 AM update...

No changes to previous forecast. Area of low clouds in the CT
valley will be lifting to strato-cu with sct-bkn diurnal clouds
developing across SNE through the afternoon. Soundings show
marginal instability developing across western MA but presence
of a cap and minimal to no large scale forcing will prevent any
convection this afternoon.

Previous discussion...

Upper level ridge continues to build over the region with high
pressure still overhead. 850mb temps will be on the rise to +15C
ahead of the dangerous heat and humidity expected starting
Tuesday. Winds at the surface will also continue to increase out
of the south at 10 to 15 mph, gusting 20-25 mph. This will
bring high temperatures back up into the low to mid 80s with
dewpoints in the low 60s. Winds should be strong enough to keep
sea breezes at bay except near the south coast where southerly
winds will enhance the sea breeze and bring cooler daytime temps
in the upper 70s to southern RI and SE MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Tonight:

Center of the 595 dm ridge arrives overnight. Dewpoints will
continue to rise overnight with southerly flow. Even with mainly
clear skies and decreasing winds, overnight lows will only drop into
the mid 60s region wide.

Tomorrow:

Dangerous heat and humidity arrives Tuesday as temperatures rise into
the low to mid 90s. With dewpoints rising near 70F, the heat index
will rise into the upper 90s to low 100s. Due to this, a heat
advisory or excessive heat watch have been issued for much of SNE.
The South coast along with the Cape and Islands were left out due to
southerly flow bringing cooler temperatures off the ocean. The WPC
experimental heat risk tool highlights much of SNE in a moderate
risk for heat related impacts. What this means is that those who are
sensitive to heat, or without effective cooling systems could be at
risk. If you do have to spend time outdoors starting Tuesday,
remember to stay hydrated and take breaks in shaded areas or indoors
with air conditioning.

With large amounts of heat, comes large amounts of instability. HREF
mean SBCAPE values are above 1000 J/kg on Tuesday, However, an 875mb
warm nose will make it difficult for convection to break the CAP.
With almost zero shear and very dry upper levels, any convection
that does fire will have a difficult time maintaining itself. Most
of the Hi-res guidance is in agreement with this showing weak
showers with the exception of the NSSL WRF which seems a bit bullish
on convective coverage and intensity. Did add slight chance POPs to
interior NW MA to match the HREF 4hr max updraft probs at 10%.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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 Fri into the Weekend
* Excessive Heat breaks this weekend...but it still will be humid

Details...

As has been the case for several days...the models continue to be in
excellent agreement that the heat and humidity will peak in the Wed
through Fri time frame. The guidance indicates 500 mb height fields
approaching 600 dm...which is rarely seen in our region and a strong
signal for the potential of record heat. This is also supported by
the NAEFS & EPS Situational Awareness tables...which indicates
several parameters outside the models climatology.

The guidance supports near record highs well into the 90s...perhaps
touching 100 degrees in spots. Record highs will be challenged and
we may approach all time record highs for the month of June.
Regardless...afternoon heat indices are likely to be in the ballpark
of between 98 and 106 degrees away from the immediate south coast,
Cape and Islands. We opted to continue the Excessive Heat Watch
through Fri for the lower elevations of western MA/CT as well as
interior east/northeast MA. This is where the greatest risk is for
Heat Indices to reach or just exceed 105 degrees. Across the rest of
the region...opted to issue a Heat Advisory away from the marine
modified airmass near the immediate south coast, Cape and Islands.
There will not be much relief overnight with heat indices only
dropping into the 70s.

The strong upper level ridge will tend to result in mainly dry
weather Wed & Thu...but can not rule out an isolated convective
threat given the anomalous airmass in place.

The main threat though for scattered showers/t-storms will be Fri
and into the weekend as the upper level ridge begins to get
suppressed south. This will allow shortwave energy to impact us at
times on west to northwest flow aloft. Timing is difficult at this
point...but scattered showers & t-storms will be possible Fri into
the weekend. As the upper level ridge is suppressed to our
south...we do expect the excessive heat to break but it still will
be humid.

&&

.AVIATION /17Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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

18z TAF Update...

Through 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 Friday/...

Juneteenth: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA, slight chance TSRA.

Wednesday Night: VFR. Breezy.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA, slight chance TSRA.

Thursday Night: Mainly VFR, with local MVFR possible. Breezy.

Friday: Mainly VFR, with areas MVFR possible. Chance SHRA,
chance 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 Friday/...

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, slight chance of
thunderstorms.

Friday: Winds less than 25 kt. Chance of rain showers, chance
of 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...
CT...Excessive Heat Watch from Tuesday afternoon through Friday
     evening for CTZ002-003.
     Heat Advisory from noon Tuesday to 7 PM EDT Friday for CTZ004.
MA...Excessive Heat Watch from Tuesday afternoon through Friday
     evening 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>019-026.
RI...Heat Advisory from noon Tuesday to 7 PM EDT Friday for
     RIZ001>005.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ231>236-250-251-254-255.

&&

$$

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