202
FXUS61 KBOX 061520
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1120 AM EDT Sat Jul 6 2024

.SYNOPSIS...
Warm and very humid weather is expected over the next few days.
Showers and thunderstorms are expected today mainly over
interior MA and CT, with better chances for showers and
thunderstorms in southeast New England tonight. Mainly dry
Sunday afternoon through early Tuesday, but more unsettled
weather is on the horizon for middle of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
First batch of showers and isolated thunderstorms moved across
southern New England this morning. Expecting this band to move
off the coast before noon for most, but should be as late as 2
PM for the Cape and islands. Trend was for coverage of
thunderstorms to diminish as they move east into a more stable
layer.

Attention then turns to a possible second round of showers and
thunderstorms this afternoon. There remains considerable
uncertainty in the timing and location of these showers and
thunderstorms this afternoon and evening. There simply is no
strong focus to base a timing on. Latest SPC mesoanalysis showed
effective shear of 35-50 kt along with most-unstable CAPE values
around 1,000 J/kg. Taken at face value, these numbers would be
rather concerning regarding severe weather, especially with
visible satellite showing abundant sunshine to our west. The
ingredient which will be the limiting factor is poor mid level
lapse rates. While convective updrafts get going rather easily
later this afternoon, their longevity and intensity will not be
optimized.

Latest visible satellite data also showed cumulus clouds
blossoming across NY state into western MA. Best timing, at this
moment, is for showers and thunderstorm to become more of a
possibility between 3-5 PM. Much like last night, intensity of
any thunderstorms should diminish as they move east across
southern New England, especially toward and after sunset.

Minor tweaks to temperatures and sky cover, but will likely need
to make further adjustments through this afternoon.

Update: 7:25 AM

Widespread rain with embedded thunder along and west of I-91
with the most active/heaviest rain mainly from Hartford County
and areas south. Radar estimates rainfall rates between 2 and 4
inches per hour, as of now, no hydro issues as the storms are
moving along. Overall a tough forecast ahead, tried to highlight
areas where heaviest rain is falling now with increased POPs. As
mentioned, today will be best handled with frequent updates and
amendments.

345 AM Update:

It`s an overcast, warm and MUGGY early morning over Southern
New England. Stratus continues to blanket much of the area, with
current temps in the low to mid 70s, closely matching dewpoint
temperatures. Residual showers from the overnight continue over
southern RI, but they have been steadily weakening and should
continue to do so. We continue in a weakly-forced synoptic
pattern with ill-defined, nebulous forcing and a very humid
airmass in place. Aloft, we`re embedded in a seasonably strong
SWly flow with upper low over the northern Great Lakes and
amplified upper level ridging over Atlantic Canada. Well to the
southwest in northeast PA, noted cooling cloud- top temperatures
and an increasing number of cloud-to-ground lightning strikes
were noted associated with a developing cluster of t-storms in
the SW flow aloft.

When looking at the forecast for today, again, there is little
to no model-run consistency in this weakly-forced and very
humid synoptic setting. It renders forecast confidence,
especially as it pertains to shower and thunderstorm timing and
location, as extremely poor. Opted for a pretty broad brush when
it came to PoPs today - it`s really one of those situations
where t-storm threats need to be nowcasted and couldn`t really
say no to showers and storms at virtually anytime. I put
somewhat more emphasis on interior MA and CT as having the best
chances. Lesser, but more limited chances for RI and eastern and
southeast MA where stratus is expected to linger for much of
the day and temper heating/destabilization. Simple extrapolation
brings the early-Saturday storms now evolving over northeast PA
toward Hartford County and adjacent western MA by 530-6 AM, and
could produce frequent lightning and torrential downpours. It`s
still an open question how things evolve after this early-day
activity exits; there is some signal for storms redeveloping in
western New England and some could become strong: the NAM in
particular has a pretty impressive profile of 3000 J/kg CAPE and
45 kt of effective shear in the CT Valley, the shear being
driven by the stronger mid/upper SWly winds. The more obvious
risk in any storms today is torrential downpours, and that could
lead to street flooding in more persistent storms, although
they should be moving along at a good clip toward the NE today.
Because the guidance is all over the place with possible
outcomes on timing and location of storms today, I couldn`t
include any enhanced wording to the grids, but there is a risk
for hydro concerns along with some strong-tstorm potential.

Temperatures on the whole today should be similar to yesterday,
with the warmest readings in the CT and Merrimack Valleys
around the periphery of stratus, in the mid to upper 80s. Kept
highs for RI and southeast MA in the upper 70s to lower 80s,
with less heating likely as stratus looks likely to stay socked
in much of the day.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
345 AM Update:

Tonight:

Uncertainties on storm coverage and timing from the Saturday
daytime hrs linger into tonight. We do expect there to be
showers and storms ongoing somewhere in the CWA, but it`s still
unclear exactly where and what the areal coverage of those
storms might be. Most of the guidance does show what amounts to
a weak surface trough sagging slowly southeastward with somewhat
lower dewpoints (mid 60s vs low 70s) across it. As this
boundary sags southward, it should focus the risk for showers
and storms toward southeast New England, with lesser chances
north and west. Localized downpours could still be possible,
although the risk for strong/severe storms should be low. Lows
should again be on the muggy side in the lower 70s.

Sunday:

Frontal boundary from tonight slowly sags southeastward into
the southeastern waters on Sunday. Sunday is shaping up to be a
dry day overall, but it will still be very warm and humid with
more hours of full sunshine adding to the humidity. Other than
on the Cape where residual cloudiness could keep highs into the
mid to upper 70s. Inland, more sunshine should bring highs well
into the 80s to lower 90s, and while dewpoints will be about 5
degrees lower than today, heat indices should reach into the
lower to mid 90s. So a drier day overall with lots of sunshine,
but also very warm and humid.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
Highlights:

* Dry Monday and first-half of Tuesday, better shot for rain or
  thunder comes in late afternoon to early evening across western
  areas of southern New England. Still rather warm and muggy both
  days.

* The summer heat, humidity, and daily rain/storm chances Wednesday
  through potentially Friday.

Sunday Night:

Dry overnight, areas of patchy fog possible during the early hours
of Monday morning. Warm and muggy, lows in the middle and upper 60s
to 70 degrees in urban centers like Hartford and Boston.

Monday and Tuesday:

Fairly warm days ahead with 925mb temperatures are on track to rise
between +23C to +26C, and FWIW, GFS shows +27C over the Merrimack
Valley. Expect afternoon highs both days between the upper 80s and
the lower 90s, while slightly cooler in the lower and middle 80s at
the coast due to the southwest/on shore winds. Dew points remain
elevated in the upper 60s to 70 degrees on Monday, then lower an
middle 70s on Tuesday. The combination leads to a `Heat Index` of
90F-95F on Monday and Tuesday, but Tuesday there is the potential
for a few locations to have a `Heat Index` 96F to 99F. At this time
do not expect any heat related headlines, but never the less it will
be quite warm! There will be little relief at night, overnight lows
are in the upper 60s and lower 70s. Though areas in and around the
centers of Boston and Hartford could be warmer in the middle 70s.

Warm and drier days ahead with southern New England sitting along
the outer periphery of a mid-level ridge and surface high - out over
the island of Bermuda. Model guidance suggests weak shortwave energy
ridge the ridge, though have higher confidence with a dry Monday
afternoon under a mixture of mid and high clouds. Better chance for
showers Tuesday afternoon, although lower confidence in areal extent
of the showers, greatest confidence would be the northwestern part
of the CWA, kept the `Chance` POPs here while most of the I-95
corridor left as `Slight Chance`. More substantial forcing arrives
late Tuesday evening through the overnight hours, this should
promote more widespread rain/thunder chances.

Wednesday through Friday:

Seasonably warm temperatures continues Wednesday through Friday,
with highs on Wednesday in the middle to upper 80s, then lower to
middle 80s on Thursday and Friday. And no relief from the mugginess,
dew points remain elevated in the upper 60s and lower 70s. Overnight
lows remain above normal in the middle and upper 60s, near 70 in
urban centers.

Unsettled period of weather both Wednesday and Thursday with daily
shower and thunderstorm chances, though do not think either day is a
washout. Timing remains quite difficult, as there is no large scale
forcing, rather bursts of shortwave energy each day.

Looking ahead, Friday, there are signs mid-level high over Bermuda
strengthens and expands into southern New England. This should lead
to a drying trend for Friday, but given the warm and humid atmosphere
diurnal differential heating long the terrain could lead to a
rogue shower or thunderstorm.

&&

.AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
Forecast Confidence Levels:

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

Today: Moderate confidence overall, low on timing and coverage
of SHRA/TS.

Somewhat stronger confidence in ceiling trends, with MVFR-IFR
ceilings being more persistent/stubborn to improve in RI and
southeastern MA today. Elsewhere, MVFR-IFR to start but offering
one-category improvement to BKN VFR/MVFR north and west after
14z. SW winds around 10-15 kt today.

On SHRA/TS, given available guidance, confidence in timing and
coverage of showers and thunderstorms and their evolution today
is poor. Have moderate confidence for mainly dry weather through
18-19Z or so across interior southern New England.

Message is that SHRA/TS are expected today. In general, airports
to the north and west have a somewhat better chance at seeing
SHRA/TS and less so for PVD and the Cape airports, but they
can`t be ruled out anywhere and virtually at any time.

Tonight: Moderate confidence overall, low on timing of SHRA/TS.

Sub-VFR likely thru midnight for most airports, as weak frontal
boundary sags SE toward the coastal waters. SHRA/TS likely to
be ongoing somewhere in the airspace, with trend being for a
gradual SE shift towards the south coast. Should see gradual
improvement in flight categories from NW to SE, but sub-VFR
likely to continue into early Sun AM for the south coast. Winds
continue SW around 5-10 kt, though will turn WSW late.

Sunday: High confidence.

Improvement to VFR expected on Sunday for most, but can`t rule
out periodic SHRA and sub-VFR at ACK (more so in the morning)
as frontal boundary stalls. WSW winds 5-10 kt.

KBOS TAF...Moderate confidence overall, low confidence on
SHRA/TS timing and coverage. MVFR to begin, with some
scattering/lifting of cloud bases into VFR/MVFR range late this
morning. SHRA/TS possible virtually anytime today, and will
need TEMPOs to provide more specifics as current fcst confidence
on those aviation parameters are low. Better chance tonight as
boundary sags southward. SW winds around 10 kt.

KBDL TAF...Moderate confidence overall, low confidence on
SHRA/TS timing. IFR ceilings to start, but should see
improvement toward VFR-MVFR range. Better chances for SHRA/TS
here today, but the timing is uncertain and could occur
virtually anytime. Will need TEMPOs to provide more specific
timing. S winds around 10 kt, shifting to WSW late tonight.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly VFR, with areas IFR possible. Patchy BR.

Monday: VFR.

Monday Night: Mainly VFR, with local IFR possible. Patchy BR.

Tuesday: VFR. Slight chance SHRA, isolated TSRA.

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

Wednesday: VFR. Chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Update: 3:30 AM

* Rip Current Statement: For all beaches along the south coast
  of southern New England, which includes Cape Cod and the
  neighboring Islands between 8 AM to 8 PM, Saturday, July 6th.
  When you arrive at the beach, ask the lifeguard about rip
  currents and other potentially dangerous water conditions
  expected for the day.

Today through Sunday Night:

Persistent south to southwest flow and winds 10 to 15 knots with
near shore gusts between 20 to 25 knots lead to seas building to
5 feet along the outer southern waters. Have expanded the
advisory to include Buzzards Bay, Martha`s Vineyard Sound, and
Nantucket Sound as well as Block Island Sound and Rhode Islands
Sound. While this is a marginal advisory, recreation boating
season is in full swing and felt it was appropriate, as a way to
bring awareness. Greater risk for showers and thunderstorms
reducing visibility over the southern waters Saturday, but
widespread storms not expected.

Residual seas of around 5 feet Sunday afternoon, drier with less
in the way of wind. Advisories may continue solely for the
most southern outer waters for marginal seas.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Patchy fog. Visibility 1 to 3 nm.

Monday: Winds less than 25 kt. Patchy fog. Local visibility
1 to 3 nm.

Monday Night through Tuesday: Winds less than 25 kt.

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

Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents until 8 PM EDT this evening for
     MAZ020>024.
RI...High Risk for Rip Currents until 8 PM EDT this evening for
     RIZ006>008.
MARINE...Small Craft Advisory until 8 PM EDT this evening for
     ANZ232>235-237.
     Small Craft Advisory until 8 AM EDT Sunday for ANZ254.
     Small Craft Advisory until 11 AM EDT Sunday for ANZ255-256.

&&

$$

SYNOPSIS...Loconto/Dooley
NEAR TERM...Belk/Loconto/Dooley
SHORT TERM...Loconto
LONG TERM...Dooley
AVIATION...Belk/Loconto/Dooley
MARINE...Loconto/Dooley