145
FXUS61 KBOX 092017
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
417 PM EDT Tue Jul 9 2024

.SYNOPSIS...
Oppressive heat and humidity are expected to continue today and
tomorrow with isolated shower/thunderstorm chances in the
afternoon/evening hours, mainly across western and northern
Massachusetts. Quite warm and very humid weather will continue
through the end of the work week. While at least isolated
showers and thunderstorms are possible at anytime, it appears
the main risk for more widespread activity with torrential
rainfall/localized flash flood potential will be sometime
Friday/Friday night along a frontal boundary.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Main concern into this evening is the potential for convection.
Still mixed messages from the environment. Most-unstable CAPE
values were analyzed at 1,000-2,000 J/kg with 40-50 kt of shear.
However, the mid level lapse rates were not very supportive of
strong updrafts. Expecting any storms will need to be watched
going into this evening, but the threat of severe weather across
southern New England is low into this evening.

Expecting convection to diminish with sunset, leaving some
clouds behind. Stratus resurges back across portions of our
region overnight. Also with areas of fog, much like the past
couple of nights.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Not much change in airmass Wednesday into Wednesday night. Heat
and humidity continue. Maintained the Heat Advisory, and even
expanded it for areas that will probably meet the lower 2-day
criteria Wednesday.

Still a risk for strong to isolated severe thunderstorms
Wednesday. Much like today however, mid level lapse rates are
not expected to be all that supportive. Thus, these stronger
storms should be few and far between. More concerned about the
potential for downpours and localized flooding. The greater
focus should be farther to our north, but our region will not be
that far away from the warm front across northern New England.

A cold front associated with post-tropical cyclone Beryl should
approach from the west late Wednesday night. This will provide a
better focus for triggering rainfall.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Key Points...

* Warm & Humid weather continues Thu & Fri

* Warmer than normal temperatures continue through Tuesday.
  Humidity remains but likely not as humid as late week.

* Main threat for widespread showers/t-storms with torrential
  rainfall & localized flash flooding will be sometime late Fri
  or early Saturday but confidence in exact timing is low to
  moderate.

Details...

Thursday...

A lingering upper level ridge over the western Atlantic
continues to direct tropical moisture up the east coast into New
England on Thursday, fortunately directing the bulk of Beryl`s
remnants further to our north and west. Thus, the bulk of the
showers and downpours should remain over northern New England in
closer proximity to the good forcing. However, a handful of
storms are possible, especially closer to the MA/NH/VT border
and any storm that forms will be capable of producing a heavy
downpour and localized flooding. Plenty of moisture to work with
as dewpoints rise into the mid 70s! It will feel very humid
paired with temperatures in the upper 80s. Can`t rule out that
the Heat Advisory will need to be expanded into Thursday.

Friday and Saturday...

This period looks to be the most active of the extended
forecast though a good deal of uncertainty remains as to the
exact timing of the heaviest rainfall. A shortwave moves up the
east coast on Friday bringing with it an even deeper moisture
plume with PWATs over 2 inches Friday night into early Saturday.
This combined with placement beneath the right rear quadrant of
a 70kt upper jet will provide amble synoptic lift together with
a surface boundary for widespread moderate to heavy rainfall
late Friday into early Saturday. Still looking like some drying
out is possible for the latter half of Saturday but if things
slow down we could see showers continuing much of the day.

Sunday through Tuesday...

Warmth and humidity continues to be with us through at least
the early part of next week. Guidance is quite divergent on how
the pattern evolves beyond Saturday with the GFS introducing
another shortwave in the zonal flow for unsettled weather
throughout while the ECMWF brings in a drier ridge. Ensemble
guidance is less excited about rainfall, with anywhere from a
10-50% chance of measurable precip on Sunday. For now sticking
with a dry forecast for the latter half of the weekend into
early next week.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

Tonight...Moderate confidence.

Any isolated to scattered convection that is able to develop,
mainly across western and northern MA, should diminish by mid-
late evening. Otherwise, IFR/LIFR conditions in low clouds and
fog likely return to the south/southeast coast as the boundary
layer cools. But the northward extent of the MVFR-IFR conditions
remains uncertain, but thinking primary risk will be near and
especially south of I-90.

Wednesday...Moderate Confidence.

Any lower cigs/vsbys should improve to mainly VFR away from the
south coast. MVFR/IFR may linger into the afternoon near the
immediate south coast, Cape and Islands. A few showers or
t-storms are possible again Wed with the main risk probably
across western and northern MA again. Winds becoming more
south/SSW at 10 to 15 knots.

Wednesday Night...Moderate confidence.

MVFR-IFR should redevelop once again. South winds continue.

KBOS TAF...High confidence in TAF.

Scattered showers and thunderstorms are expected west of I-495,
so there is a low chance that a storm could make it to the
terminal this evening (22-01Z). Confidence in this actually
occurring is too low for any mention of thunder in the latest
TAF.

KBDL TAF...High confidence in TAF.

Confidence in thunderstorm activity is higher across north/west
MA and less so for CT, so there is no mention of thunder in the
latest TAF update, but there is a low risk. Mentions of -TSRA
may appear in future updates if confidence increases.

Outlook /Thursday through Sunday/...

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

Thursday Night: VFR. Breezy. Chance SHRA.

Friday: VFR. Breezy. Chance SHRA, isolated TSRA.

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

Saturday: VFR. Chance SHRA, isolated TSRA.

Saturday Night: VFR. Slight chance SHRA.

Sunday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Wednesday Night:

Warm/humid air mass will support areas of fog over the coastal
waters, especially during the overnight hours. Otherwise,
expect winds to prevail out of the south/southwest with modest
seas up to three feet over the outer marine zones. Can`t rule
out an isolated afternoon/evening storm over the eastern marine
zones both this evening and Wednesday afternoon.

Outlook /Thursday through Sunday/...

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

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 20 kt. Local rough seas. 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.

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

Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.

Sunday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Wednesday for CTZ002>004.
     Air Quality Alert until 11 PM EDT this evening for CTZ002.
MA...Heat Advisory until 8 PM EDT Wednesday for MAZ003>007-010>019-
     026.
     Air Quality Alert until 11 PM EDT this evening for MAZ005>007-
     010>016.
RI...Heat Advisory until 8 PM EDT Wednesday for RIZ001>004.
MARINE...None.

&&

$$

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