471
FXUS61 KBOX 141714
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
114 PM EDT Fri Jun 14 2024

.SYNOPSIS...
Warm and muggy today with scattered showers and thunderstorms
this afternoon and evening...some of which may be severe mainly
northwest of I-95. A few lingering spot showers are possible
early Saturday...otherwise high pressure brings dry and
beautiful weather for the weekend with low humidity. A warm- up
begins on Monday with an extended period of excessive heat and
humidity possible beginning Tuesday and continuing through
Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
930 AM Update...

Given the current satellite, the 00Z NAMNest seems to
performing well as one of the only pieces of guidance picking up
on the bubbling cu and patchy light shower activity draped from
approximately from Orange MA to central CT. A more robust line
of showers remains just to the west of our CWA, just now making
it`s way into Berkshire County.

CAMs continue to lack consensus on the exact timing of storms
today with the potential for several rounds of storms through
about 03Z tonight. While there is still significant spread in
the guidance, the general consensus is that a first line of
convection, with perhaps a few embedded stronger cells, will
develop and move across the state between 16-19Z with a
stronger line of convection developing across western MA around
20Z before moving eastward through ~00Z.

Current mesoanalysis shows CAPE building to greater than
2000J/kg this afternoon with bulk shear values increasing to
around 30-35kt. DCAPE will decrease from a max of 900J/kg this
morning to between 500-700J/kg this afternoon, but do still
anticipate some strong to damaging gusts associated with the
second line of convection. Freezing levels around 12,000ft and
with shear a bit to low, at least in our area as bulk shear
climbs in excess of 45kt across northern New England/NY/PA,
severe criteria hail will be hard to come by.

705 AM Update...

Key Points

* Warm and muggy start to the day
* Scattered severe thunderstorms mainly NW of I-95

Previous forecast remains on track. Main concern continues to
revolve around the threat for scattered severe thunderstorms
this afternoon and evening with the main risk northwest of I-95.
Timing of the convection remains tricky...but appears we may
have two rounds. The first in the noon to 5 pm range on a pre-
frontal trough and perhaps a second round as the shortwave
approaches early this evening. Prior forecast discusses this all
below.

Today will be a warm and humid day with temperatures quickly
rising into the mid to upper 80s and dew points reaching the mid
to upper 60s. This will help set the stage for scattered severe
thunderstorms as a potent shortwave trough and cold front drops
SE across the region in the afternoon. As the cold front moves
through, a very narrow corridor of instability will be set up
across western MA and CT. There continues to be some
disagreement among the hi-res HREF guidance on how much
instability will be available mainly due to timing differences
on convective development. HREF mean shows near 1000 J/kg of
SBCAPE with the 90th percentile showing around 2000 J/kg. With
deep layer shear approaching 30-40 knots, the environment will
be supportive of organized clusters of severe thunderstorms.
Initiation remains a bit uncertain with some members of the HREF
initiating storms shortly after 12pm, while others holding off
as late as 4pm. latest 06z guidance is trending towards a faster
solution with height falls from the shortwave arriving earlier
in afternoon. Storms likely initiate off the high terrain in
Western MA/CT and southern VT/NH then move ESE through the
afternoon. Storms should quickly weaken as the approach eastern
MA and RI as they run into a more stable environment with less
instability and shear. The severe threat at this time looks
highest north and west of the I-95 corridor as highlighted by
the SPC slight risk.

Severe threats:

The primary severe threat will be strong to damaging winds with
steep low level lapse rates, DCAPE values near 700 J/kg, and
linear storm mode promoting straight line winds. The hail threat
has increased since yesterday due to models steepening mid
level lapse rates to 6-7 C/km. The freezing level still remains
above 10kft which should help to melt most hail before reaching
the surface. The tornado threat remains very low at this time
with 0-3km SRH around 100 m/s and the Sig Tor parameter well
less then 1.0. Storm mode also appears to favor linear clusters
with upscale growth. Not completely out of the question that a
discreet supercell could form at initiation before merging with
other cells into line segments or clusters.

Heavy Rain Threat:

Although the storms will be progressive with little to no training
expected, PWATS will be increasing into the 1.5-1.6 inches. CAPE
profiles have become more fat and supportive of hail over the last
24 hours due to steepening mid level lapse rates. Warm cloud depths
have also decreased to 8000ft. Despite these less favorable changes
in the environmental parameters, the HREF 3hr PMM does still
highlights a small area in western MA and CT with 10% probs for
greater then 3 inches of rain in 3 hours. This could lead to areas
of street and poor drainage flooding along with isolated instances
of flash flooding.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Tonight

Thunderstorms quickly weaken into showers as they move east into
less favorable environment and lose support from daytime heating.
The shortwave axis crosses through the region overnight which
will prolong the rain for eastern MA before tapering off by
morning. Overnight lows stay on the warm side in the low 60s
with overcast skies and rain.

Tomorrow

Shortwave moves offshore with rising heights and high pressure
beginning to build in for the weekend. There may be some
lingering light showers in the morning in eastern MA, otherwise
mainly dry conditions with clearing skies in the afternoon.
Winds turn northerly advecting in cooler air for Saturday with
highs only in the mid to upper 70s. Humidity will also be
noticeably lower with dewpoints dropping into the 50s and even
the 40s across the western interior.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points...

* Dry/cool Sat night followed by a beautiful Sunday with low humidity
* Warmup begins on Mon with excessive heat & humidity Tue through Fri
* Heat & Humidity Peak in the Wed through Fri time frame
* Near Record Highs possible...Heat Indices between 95 & 104 at times

Details...

Saturday night and Sunday..

Large high pressure will build over southern New England Sat night
into Sun. A relatively dry airmass in place for mid June
standards...coupled with mainly clear skies/light winds will yield a
good night of radiational cooling. Overnight lows should bottom out
in the 40s across the outlying locations with 50s in the urban
centers. Plenty of sunshine on Sunday will allow for a beautiful day
along with low humidity. Highs will be well up into the 70s to
perhaps near 80 in a few spots.

Next Week...

Confidence continues to grow in excessive heat and humidity next
week. An anomalous upper level ridge will build northward into
southern New England next week. A warming trend begins on Monday,
but the significant heat/humidity potential looks to begin Tuesday
and peak in the Wed through Fri time frame.

There has been a strong signal amongst all the model guidance for
the last several days. The EPS/NAEFS situational awareness table
indicates parameters outside the models climatology which is signal
for the potential of a highly anomalous event...in this case heat &
humidity. Near record high temperatures will be possible. There are
fairly high probs of temps reaching well into the 90s for a couple
days and perhaps flirting with 100 degrees in some spots. Afternoon
heat indices in the 95 to 104 degree range are possible at times. It
will remain quite muggy at night so that will be another concern.

Strong upper level ridging in place will promote mainly dry weather
for much of next week. That being said...near record heat may
trigger the risk of a few t-storms at times but given lack of
synoptic scale forcing dry weather will dominate.

&&

.AVIATION /17Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

18z TAF Update: Moderate confidence (60%)

Main uncertainty is with timing of TS. First line moving
through eastern MA at 17z will move offshore by 19-20z, then we
are watching for a second line of TS to cross area between
20-24z ahead of cold front. Expect brief MVFR/IFR in any TS.

Otherwise VFR ceilings should prevail through tonight as SW
winds veer to W-NW and N overnight, except ceilings to lower to
IFR around Cape Cod and Islands. Slow improvement Sat morning
with VFR-MVFR ceilings gradually scattering out Sat afternoon as
N winds increase to 10-20kt with gusts to 25kt near coast.

KBOS TAF...Moderate confidence in TAF (60%). Best call on TS
timing is now through 19z, then another possible round 22z-00z.

KBDL TAF...Moderate confidence in TAF (60%). Best call on TS
timing is 21-23z.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday Night: VFR.

Monday through Tuesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today:

Increasing SW winds gusting up to 25 knots. A cold front will
sweep across the waters this evening. Thunderstorms will form
along this cold front inland this afternoon and weaken as they
approach the waters. A couple storms could still reach the
waters and bring strong wind gusts and lightning near the
coastal waters this evening. Seas 2-4 feet.

Tonight:

Steady light to moderate rain with embedded thunder possible.
Winds shift WNW and decrease to 5-10 knots overnight. Seas 2-3
feet.

Tomorrow:

Rain tapers off in the morning with clearing conditions in the
afternoon. Winds turn north and gust 15 to 20mph. Seas 2-4 feet.

Outlook /Saturday Night through Tuesday/...

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

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

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

Sunday Night through Tuesday: Winds less than 25 kt.

&&

.CLIMATE...
Daily Record High Temperatures...

Tuesday, June 18th

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

Wednesday, June 19th

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

Thursday, June 20th

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

Last Day of 100F (or greater)

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ230>237-251.
     Small Craft Advisory until 11 PM EDT this evening for ANZ250-
     254.

&&

$$

SYNOPSIS...Frank/KP
NEAR TERM...Frank/KP/KS
SHORT TERM...KP
LONG TERM...Frank
AVIATION...JWD
MARINE...Frank/KP
CLIMATE...Dooley