-- Discussion containing changed information from previous version are highlighted. --
898
FXUS61 KBOX 181106
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
706 AM EDT Tue Jun 18 2024

.SYNOPSIS...
Dangerous heat and humidity arrive Tuesday away from the south
coast and then peaks in the Wednesday through Friday time
frame. Near to record breaking high temperatures are possible.
Heat peaks on Thursday before more seasonable temperatures return
for the weekend. Showers and thunderstorms possible each afternoon
and evening Friday thru Sunday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

-- Changed Discussion --
7 AM Update...

Hazy, humid, and hot are the key words for today`s forecast with
most ASOS locations making a run at 70F at the 7 AM observation.
As mentioned by the previous forecaster, isolated showers are
possible this afternoon but will likely be constrained to the
high terrain given lack of forcing and rising heights.



345 AM update...

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

Subtropical ridge continues to build across the region today with
500 mb heights rising to 594+ dam. This will be accompanied by a
warm sector airmass with lots of sunshine across the area, along
with dew pts rising to 65-70 and a anomalous warm airmass, with 925
mb temps of +23C to +25C and +18C at 850 mb. This supports highs of
90-95 across much of northern MA, including the city of Boston and
into northern CT and northern RI. These air temps combined with high
dew pts will yield heat indices in the mid to upper 90s this
afternoon. Hence, day 1 of our expected heat wave this week. Heat
advisories remain posted.

Not as hot along the south coast with highs in in the 80s, except
mid to upper 70s across the Cape and Islands, with S-SW winds 10-15
mph, gusting up to 20 mph at times, streaming across SSTs only in
the 60s. Hence, some relief along the south coast. The east coast of
MA may have a brief seabreeze develop from approximately 15z-19z,
when winds briefly turn to the SE, but should veer back to the SW
after 19z, yielding highs in the upper 80s and lower 90s.

Weak short wave currently across northern NY state is triggering
some isolated to scattered showers in that region. Given height
rises across SNE today, forcing for ascent will be weak and the
atmosphere will likely be capped. Thus, only than an isolated
shower/t-storm across western-central MA this afternoon, dry weather
prevails elsewhere.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
345 AM update...

* Not much relief tonight with lows 65-70
* Dangerous heat and humidity continue Wed away from the south coast
* Other than a spot shower/T-storm northwest MA, dry weather prevails

Tuesday night...

Mainly clear to partly cloudy conditions along with dry weather
prevail beneath building ridge across New England. Lows will be
mostly in the mid-upper 60s.

Wednesday...

595 dam ridge remains over SNE, providing mainly dry and hot
weather. Airmass warms slightly and combined with mostly sunny
conditions, this will support highs in the low to mid 90s from
northern portions of CT/RI and into northern MA. These air temps
will combine with dew pts of 65-70 to yield heat indices from 95-
100. Some relief south coast and islands, as SSW winds 10-15 mph
with gusts up to 20 mph at times, will provide somewhat of
refreezing breeze off the cooler ocean with SSTs in the low to mid
60s. As for precip, high amplitude anticyclone over SNE should
provide a mid level cap and keep our region mainly dry. Only area
for a low risk of an isolated shower/t-storm is across northwest MA

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
345 AM update...

* Heat peaks on Thursday with high temperatures in the upper 90s
  likely for the interior

* Temperatures on Friday remain uncertain with cold front nearby

* Cooler, but still muggy, conditions Saturday and Sunday with
  chances for afternoon showers and thunderstorms

Very persistent and anomolously strong ridge peaks in intensity
on Thursday with 500mb heights making a run at 600mb associated
with 850mb temperatures around 20C by afternoon. Given a more
NW/W wind component as ridge axis crests, will have some
downslope enhancement driving temperatures a few degrees warmer
compared to Wednesday. Will note that the overnight guidance
trended a bit cooler compared to previous model runs, with highs
now projected to remain just below 100F, though still cant rule
out a run at the triple digits in the southern CT and Merrimack
River Valleys. A Excessive Heat Watch remains in place for
Thursday with a determination on an advisory vs warning to be
made during later shifts. Shower activity "riding the ridge"
looks to remain to our north Thursday afternoon/evening, though
it is possible a stray shower develops along the MA/NH border.

Ridge begins to collapse south on Friday as a cold front drops south
from NH/ME into our region, increasing shower and t-storm chances
during the afternoon. There remains uncertainty in how fast the
front will drop south from northern New England, which leads to a
wide range in guidance regarding high temps, with an earlier frontal
passage yielding cooler daytime highs especially across the eastern
half of the CWA. For now, elected to follow the NBM for highs on
Friday, noting that future updates may need to blend in cooler
guidance.

More seasonable airmass remains in place through the weekend though
humidity remains high, which will introduce the chance for afternoon
and early evening t-storms each day through Sunday. While surface
instability wanes with sunset each evening, some storms could
continue into the early overnight hours. Cold frontal passage
sometime late Sunday-late Monday brings our next chance for more
widespread, stratiform precip before another prolonged period of dry
conditions.

&&

.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
Forecast Confidence Levels:

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

12z TAF Update...

High confidence for VFR, SSW winds 10-15 kt, gusts up to 20 kt
at times along the south coast and Islands. Low risk for an
isolated shower or T-storm this afternoon across western-central
MA. Low to moderate risk of brief seabreeze 15z-19z along
eastern MA coast, including KBOS, with winds become SE.

Tuesday night...High confidence for VFR, S-SW winds 5-10 kt
along with dry weather.

Wednesday...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.

KBOS TAF...High confidence in TAF. Only wrinkle is duration of
seabreeze today. Winds remain below 10 kt thru the column until
about 18z, then increase steadily after 18z. Hence, a southeast
seabreeze likely 15z-19z approximately, then shifting back to
SSW thereafter.

KBDL TAF...High confidence in TAF.

Outlook /Wednesday Night through Saturday/...

Juneteenth through Wednesday Night: VFR. Breezy.

Thursday through Thursday Night: Breezy. Slight chance SHRA.

Friday through Friday Night: Chance SHRA, isolated TSRA.

Saturday: Slight chance SHRA.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Forecaster Confidence Levels:

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

345 AM update...

* Fairly tranquil boating weather

Tuesday...

Clear conditions with increasing southerly winds gusting up to 20
knots at times. Seas 2-4 ft

Tonight and Wed...SSW winds and dry weather.

Outlook /Wednesday Night through Saturday/...

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

Saturday: Winds less than 25 kt. Slight chance of rain showers.
-- End Changed Discussion --

&&

.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...Air Quality Alert from 11 AM this morning to 11 PM EDT this
     evening for CTZ002.
     Heat Advisory from noon today to 7 PM EDT this evening for
     CTZ002-003.
     Excessive Heat Watch from Wednesday afternoon through Friday
     evening for CTZ002-003.
     Heat Advisory from noon today to 7 PM EDT Friday for CTZ004.
MA...Air Quality Alert from 11 AM this morning to 11 PM EDT this
     evening for MAZ005>007-010>012.
     Heat Advisory from noon today to 7 PM EDT this evening for
     MAZ003-005-006-010-011-013-014.
     Excessive Heat Watch from Wednesday afternoon through Friday
     evening for MAZ003-005-006-010-011-013-014.
     Heat Advisory from noon today 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 today to 7 PM EDT Friday for RIZ001.
     Heat Advisory from noon Wednesday to 7 PM EDT Friday for
     RIZ002>005.
MARINE...None.

&&

$$

SYNOPSIS...Nocera/KS
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...KS
AVIATION...Nocera/KS
MARINE...Nocera/KP
CLIMATE...BL