748
FXUS61 KBOX 081931
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
331 PM EDT Mon Jul 8 2024

.SYNOPSIS...

Oppressive heat and humidity are expected to continue this afternoon
and tomorrow, and could continue into Wednesday as well.There is a
chance for thunderstorms north and west of I-95 Tuesday afternoon.
Still fairly humid late week, though temperatures are slightly less
hot, along with periods of rain and thunderstorm activity as the
remnants of Beryl moves towards the northeast.

&&

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

A very broad and persistent Bermuda high continues to be parked over
the western Atlantic through the foreseeable future preventing us
from seeing any true relief from this heat and humidity more akin to
the southeast U.S. than New England. Moist southwest flow continues
around the high. Hence, warm and very humid conditions continue this
afternoon. Dewpoints are "only" in the mid 60s for northwest MA as
opposed to southern portions of SNE where 70s are more common. This
keeps apparent temps in these areas below Heat Advisory criteria.
Those along the immediate coasts will see some relief thanks to
onshore prevailing SW flow for the south coast and seabreezes along
the east coast. Subsidence should tamp down any showers that may try
to get going late this afternoon. Overnight we won`t see much relief
unfortunately as the high dewpoints limit low temps to the low 70s.
This will also bring the return of fog and low stratus surging
inland much like we saw last night. Thinking continues to be that
this should remain along/just south of the I-95 corridor so mostly
will impact Cape Cod, the islands, and coastal RI/southeast MA.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...

On Tuesday SSW flow continues around the high and looks to increase
a bit, bringing much more moisture overhead with PWATs surging
closer to 2 inches. This moisture out ahead of the influx of
moisture from Beryl will interact with a front overhead and provide
a focus for scattered showers and thunderstorms. Given the anomalous
moisture content (1-2 standard deviations above normal) one of the
main threats from any storms on Tuesday will be heavy downpours that
could lead to localized flash flooding. A Marginal Excessive
Rainfall Outlook is in effect for a good portion of western/central
MA and CT. Similarly, there is a Marginal threat for severe weather
tomorrow afternoon from the Storm Prediction Center focused on a
weak mid level impulse moving overhead during the afternoon which
will help to kick off scattered thunderstorms, some of which could
be severe. Mid level flow will increase to near 50 knots helping to
increase bulk shear from sustained updrafts in combination with 500-
2000 J/kg of CAPE. One limiting factor will be poor mid level lapse
rates which may help to keep storms shallower. The primary threat
from any storms that do form would be flash flooding and strong
winds, then hail to a lesser extent.

As for the heat, the Heat Advisory continues through Tuesday. While
dewpoints will be increasing, actual temperatures will be less
thanks to an increase in cloudcover associated with the weak
shortwave and unsettled weather. This gives us lower confidence that
all locations within the Heat Advisory will hit the criteria, but
odds are favorable at this point. Tuesday night convection comes to
an end as sunset removes diurnal heating from the mix and we have
another warm and muggy night in store. We rinse and repeat with
regard to the return of fog and low stratus, especially for
southeast MA and coastal RI.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Highlights:

* Warm and humid conditions Wednesday through the upcoming weekend
  with no relief from the tropical-like humidity.

* Periods of rain and storms midweek into this upcoming weekend with
  the potential for heavy rains and stronger storms on Wednesday and
  Thursday.

Little change to the forecast with the synoptic pattern featuring a
mid-level ridge of high pressure centered over Bermuda. Persistent
southwest flow continues to funnel abnormally high moisture into
southern New England with no breaks from the high humidity for the
foreseeable future. Additionally, 850mb temperatures remain at or
above climatological normal through this coming weekend, which boils
down to a warmer than normal daytime and night time temperatures.

Getting caught up in the deep southwest flow are bursts of shortwave
energy riding the outer periphery of the subtropical ridge, plus the
moisture associated with Beryl may lead to periods of heavy rainfall
and potential for flash flooding mid to late week, highlighted by
WPC`s ERO.

Temperatures:

By midweek, there is a slight `cool off` in temperatures, there is
good agreement amongst the 08/00z guidance the 925mb have lowered
to 20C to 22C for much of the forecast period. What may cause a few
headaches this week is the amount of cloud cover and how that will
influence high temperatures. In general, afternoon highs are in the
80s, with Wednesday being the warmer of the days, highs in the upper
80s across much of the region. Southwest winds do keep the south
coast of Rhode Island and southeast Massachusetts cooler in the
lower 80s. As for dew points, still down right tropical in the lower
70s. During this update did not have the confidence to extend the
`Heat Advisory` into Wednesday, but if there were an area it would
most likely be Hartford County.

The summer warmth and humidity continues Thursday, albeit a few
degrees less than Wednesday, right through this upcoming weekend.
Afternoon highs are in the low and middle 80 and overnight lows in
the lower 70s. Still fairly humid, dew points hold steady in the
lower to middle 70s.

Precipitation:

Mid-level energy from Beryl will be transported from Texas to the
northeast. While there is uncertainty with exact location and timing
of the shortwaves, it will be moving over a loaded atmosphere. As of
now, the better forcing does appear north and west of southern New
England, but any storms will have the potential to produce tropical
downpours and possibly flash flooding. Per the 08/00z guidance,
forecast PWATs are 2"+, with outsiders indicating 2.5" for Wednesday
and slightly higher PWATs on Thursday. These are significant PWATS,
2-3 standard deviations above what is normal for Wednesday, and 3.5
standard deviations above what is normal on Thursday. Another way of
looking at this, these forecast values may reach near the highest
record PWATs per the climatological soundings done at CHH, OKX, and
ALY. For reference, the MAX PWATs per the sounding climatology at
ALY, OKX, and CHH are 2.75", 2.62", and 2.73" respectively.

WPC has Slight (at least 15%) ERO for Wednesday and Thursday across
northwest Massachusetts and points north and west, while much of the
CWA has a Marginal (at least 5%) ERO. These two days will need to be
closely watched for flash flooding potential.

Stronger storms are possible Wednesday and Thursday as well. SPC has
generally thunder, with a small Marginal risk of severe weather just
west of southern New England. With the dynamic remnants of Beryl in
the vicinity of the region there is plenty of ingredients for storms
to develop, SREF indicates on Wednesday MUCAPE is 1000 to 1500 J/kg,
30 to 40 knots of 0-6km shear, and 100 units of 0-1km helicity. CSU
has most of southern New England highlighted for thunderstorm winds,
around 5% to 15%, and even low risk for an tornado, around 2% to 5%.

Unsettled conditions do continue late week and into this upcoming
weekend with shortwave energy continuing to ride the periphery of
the subtropical ridge. This will lead to periods of rain and storms
Thursday into the upcoming weekend.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

18z Update:

This afternoon: High confidence.

VFR for all except ACK where there is high confidence that it
remains IFR- LIFR all day. Light south winds, with seabreezes at
BOS and PVD.

Tonight: High confidence in trends, moderate confidence on the
timing and northward coverage of fog/low stratus.

ACK will continue to deal with LIFR in fog and low stratus.
Initial VFR then degrades as stratus and fog at IFR-LIFR levels
will again return inland. Exact timing and how far north the
IFR- LIFR layer makes it is still uncertain; generally should
follow a similar 00-09z timing as the last few nights, with
gradual improvement from NW to SE during the 09-12z Tue
timeframe. VFR outside of these areas, with higher confidence
near/north of the Mass Pike. Light winds.

Tuesday: Moderate confidence.

Any sub-VFR stratus/fog conditions improve to VFR for most,
though still some degraded conditions anticipated for the Cape
and Islands. Potential for SCT TSRA from an HFD-ORH-LWM line
north and west after 18z Tue. S-SW winds 8-12 kt, possible
seabreeze at BOS.

Tuesday night...Moderate confidence.

Expecting IFR/MVFR condition to return to the south/southeast
coastal termainls overnight but confidence on the north/westward
extent of these sub-vfr conditons is low to moderate.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Wednesday through Saturday/...

Wednesday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA.

Wednesday Night: MVFR/IFR conditions possible. Chance SHRA,
isolated TSRA.

Thursday: MVFR/IFR conditions possible. Breezy. Chance SHRA,
isolated TSRA.

Thursday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SHRA, isolated TSRA.

Friday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA.

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

Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA,
isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Tuesday night: High confidence.

Winds and seas to remain below SCA criteria in this forecast
period. Southerly winds will be on the light side tonight,
around 10 kt or so. Southwest winds pick up a little more on
Tuesday, into the 15-20 kt range on all waters. Seas 3 ft or
less on all waters. The main concern for boaters continues to be
reduced visibility from fog, which looks to continue even into
Tuesday night.

Outlook /Wednesday through Saturday/...

Wednesday: Winds less than 25 kt. Slight chance of rain
showers, isolated thunderstorms, patchy fog.

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

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, isolated thunderstorms.

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

Friday through Friday Night: Winds less than 25 kt. Seas up to
5 ft. Slight chance of rain showers, isolated thunderstorms.

Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Tuesday for CTZ002>004.
     Air Quality Alert from 11 AM to 11 PM EDT Tuesday for CTZ002.
MA...Heat Advisory until 8 PM EDT Tuesday for MAZ005-006-011>013-
     017-018.
RI...Heat Advisory until 8 PM EDT Tuesday for RIZ001>004.
MARINE...None.

&&

$$

SYNOPSIS...BW/Dooley
NEAR TERM...BW
SHORT TERM...BW
LONG TERM...Dooley
AVIATION...BW/Dooley
MARINE...BW/Dooley