386
FXUS61 KBOX 081730
AFDBOX

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

.SYNOPSIS...
Oppressive heat and humidity are expected today and tomorrow,
and could continue into Wednesday as well. Dry weather is
expected today, but there is a chance for thunderstorms north
and west of Interstate 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 PM THIS EVENING/...

Clear skies have given way to some widely scattered diurnal
cumulus this afternoon, but not much in the way of any real
significant shade. Heat indices of up to 99F are being observed
out there this afternoon with temps in the upper 80s/low 90s and
dewpoints in the upper 60s/low to mid 70s.

Previous discussion...

Our weather pattern continues to be little changed from the
last couple days. Weak sea-level pressure gradient in place
along with a continued stream of subtropical moisture
maintaining dewpoints in the mid 60s to lower to mid 70s,
highest over southeastern New England. Most areas in RI and
eastern/southeast MA near and southeast of I-95 are socked in
with low clouds and fog.

There`s been an increasing number of sites with visbys down to
one quarter mile in RI and southeast MA, with Providence
reporting a visibility of less than a quarter mile for several
hrs. Given that it`s the Monday after the Fourth of July holiday
weekend and there could be more traffic volume on the roads in
addition to the typical commute traffic, we opted for a Dense
Fog Advisory for RI and southeastern MA, Cape and Islands. Since
it looks like visbys will improve into the morning for RI and
adjacent southeast MA, this segment of the advisory runs until 8
AM Monday; with anticipated delayed improvement for the Cape
and Islands, this segment is slated to expire at noon. There
have been patches of fog elsewhere in portions of the CT Valley
and into Metrowest, but it is more patchy here. As we`ve seen
over the past couple days, low clouds and fog should gradually
retreat into the waters in all areas by late morning/noontime.

A very warm and humid day is expected with several hours of
sunshine for much of Southern New England. There also won`t be
any relief from breezes away from the coastlines, and large-
scale subsidence should suppress, literally, the risk for
thunderstorms today. Expanded the Heat Advisory to include the
Greater Springfield metro area (eastern Hampden County forecast
zone) as well as Kent County in RI. Although dewpoints should be
in the low 70s in eastern and southeast New England, further
inland in interior MA, models show mixing taking place and that
could reduce dewpoints into the low to mid 60s. That could keep
some areas in the Advisory from reaching Advisory criteria, but
we felt it was marginally close enough. Heat indices in the
Advisory area should reach into the mid 90s, with some upper 90s
popping up in the Merrimack and CT Valleys. Highs should reach
into the mid 80s to the lower to mid 90s, with upper 70s to mid
80s Cape and Islands with a shorter period of full sun.

&&

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

Tonight:

Persistence forecast again for tonight. Stratus and fog that
shifted into the waters again looks to return back
northward/landward tonight into the overnight. The exact
northward areal extent of this fog and stratus layer is still a
bit unclear but in general it should be roughly similar to this
morning (near/southeast of I-95). Lows in the upper 60s to the
mid 70s.

Tuesday:

SSW flow on Tuesday looks to be a little stronger than the last
couple days, and that will allow for a greater transport of
lower to middle atmospheric moisture. Dewpoints should return
back into the middle 70s for much of the area - resembling
bathwater out there tomorrow.

Heat Advisory was maintained for Tuesday as well, and the
higher dewpoints than today means that we won`t need as much
heating to reach Advisory levels. Some minor reservations in
that compared to today, there should be more cloud cover around
in the SW flow aloft, even as morning low clouds and fog
scatter/disperse into the waters again. There is also the
potential for thunderstorms on Tuesday afternoon as well as a
weak ripple in the 500 mb flow rotates ENE from the mid-
Atlantic, with areas north and west of I-95 being a little more
favored. SPC has designated a large portion of Southern New
England into portions of NH in a Marginal risk for severe
thunderstorms on Tuesday. If storms indeed develop, localized
straight line wind damage would be the primary risk, along with
torrential downpours. But specific to the heat, both of the
above factors cast a little uncertainty on how warm temperatures
may get. But humidity levels Tuesday still will be really
oppressive. Brought highs into the mid 80s to low 90s, producing
maximum heat indices in the mid to upper 90s in the Heat
Advisory area, with upper 80s to lower 90s surrounding it to
include remaining portions of northern MA and the Cape and
Islands.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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 /18Z MONDAY THROUGH FRIDAY/...
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 /Tuesday Night through Friday/...

Tuesday Night: Mainly VFR, with local IFR possible. Areas FG,
slight chance SHRA, isolated TSRA.

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

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

Thursday: Mainly MVFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA.

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

Friday: Mainly VFR, with local IFR possible. Breezy. 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 /Tuesday Night through Friday/...

Tuesday Night: Winds less than 25 kt. Areas fog, slight chance
of rain showers, isolated thunderstorms. Areas of visibility
1 nm or less.

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

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

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
rain showers, isolated thunderstorms.

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain
showers, isolated thunderstorms.

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Tuesday for CTZ002>004.
MA...Heat Advisory until 8 PM EDT Tuesday for MAZ005-011>013-017-
     018.
RI...Heat Advisory until 8 PM EDT Tuesday for RIZ001>004.
MARINE...None.

&&

$$

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