606
FXUS61 KBOX 152347
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
747 PM EDT Mon Jul 15 2024

.SYNOPSIS...
Dangerous heat and humidity will continue through Wednesday with
little nighttime relief expected. Scattered showers and
thunderstorms will decrease in coverage tonight, but another
risk for thunderstorms are expected both tomorrow and on
Wednesday. A cold frontal passage late Wednesday into Thursday
will give way to a much more comfortable airmass to end this
work week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Buoyancy continued to decrease rather rapidly towards sunset,
with 6-hour changes of -200 to -600 J/kg of CAPE. KBOX radar
also showed showers and storms were done, for a little while at
least.

Attention now turns to an approaching convective complex over NY
state and northern PA. Latest timing brings this complex, in a
much weakened state, to the east slopes of the Berkshires
between 10 PM and midnight. Currently thinking showers may make
is as far east as Worcester County before finally falling apart
late tonight (~2-4 AM).

Tweaked temperatures and dew points to reflect observed trends.

400 PM Update:

West to east broken line of showers and thunderstorms has
developed along or near the Massachusetts Turnpike eastward to
northeast of Boston. A subset of these storms have become
strong, especially along the Worcester to Springfield area and
are also re- developing over the same general locations. These
storms are developing in a weakly-sheared setting but one with
high mixed-layer CAPE values around 2000 J/kg per SPC`s
mesoanalysis. These storms are capable of producing copious
amounts of rainfall in a short period of time given their
tendency to move across the same general areas, and the
strongest of cells could be capable of localized straight-line
wind damage from water-loaded downdrafts of wind. Additional
storms are possible into northern CT as activity over the Lower
Hudson Valley Given poor lapse rates between 700-500 mb and the
absence of stronger wind shear, the coverage and intensity of
storms stands to decrease after sundown.

The more uncertain/unclear element of the forecast comes from a
second area of storms developing well to the west over far
western NY. This is associated with a bit more apparent mid-
level trough in far southern Ontario. Most guidance shows this
activity weakening as it nears our western counties later
tonight (after 9 PM) and instability also is forecast to be
weaker as well. Vast majority of the area otherwise is dry,
although stratus and fog are likely to re- develop along the
south coast, Cape and Islands.

Lows remain in the lower to mid 70s tonight and it will still be
quite muggy, offering little relief.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
400 PM Update:

Tuesday and Tuesday Night:

Tuesday is essentially a persistence type forecast. Heat and
humidity will continue to be the main story on Tuesday, with
heat advisories continuing. It looks at though Tuesday could be
the hottest stretch in terms of heat indices with values around
the upper 90s to lower 100s away from the South Coast, Cape and
Islands. Otherwise, morning low clouds and fog along the South
Coast, Cape and Islands should disperse early in the morning,
with several hours of full sun expected. Daytime highs in the
lower to middle 90s.

Still a risk for another round of thunderstorms and some of
those may become strong too as another weak disturbance around
the broader cyclonic flow aloft to our northwest rotates
through. While areas north and west of I-95 seem more favored
for another round of thunderstorms, latest high res models show
some loose consensus with storms arriving later in the day than
today. Details regarding the location and timing of this
disturbance aloft as well as any/additional triggering
mechanisms for storms is still uncertain with storms now
ongoing. There certainly could be changes regarding the timing
and development pending those details, but it is difficult to
provide those specifics with any degree of confidence.

We should see decreasing trends in storm coverage and intensity
into the evening hours, with stratus along the South Coast of
RI and MA again as we get deeper into the evening hrs, with lows
in the low to mid 70s.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Key Points...

* One more day of dangerous heat and humidity Wed
* Scattered showers and thunderstorms late Wed/Wed night
* Relief from heat and humidity Thu/Fri/Sat with seasonable
  temperatures

Wednesday and Wednesday night...

One more day of dangerous heat and humidity is on tap ahead of
an approaching cold front. Current timing places this front
close to southern New England during peak heating Wednesday
afternoon and evening, leading to a risk for showers and
thunderstorms. The timing is not yet certain, and some changes
may be needed with later forecasts. CSU machine learning
probabilities still highlight a wind threat as the primary
concern. Some question as to how long past sunset any
thunderstorms may linger, but showers are expected to persist
into Wednesday night.

Thursday through Sunday...

Some showers may linger into the first part of Thursday
depending on the timing of the cold front. Otherwise, high
pressure building in from the midwest behind the cold front will
result in significant relief from the heat and humidity with
mainly rain-free conditions Friday through Sunday.

Temperatures are expected to drop to near to slightly above
normal levels, especially Friday, before starting to slowly
rise this weekend into early next week. Dew points are expected
to fall to much more comfortable levels across the interior, but
may still be closer to higher humidity along the immediate
coast.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Tonight: High confidence in trends, though moderate on timing.

Any TS should dissipate shortly after sundown. We do have to
watch storm activity now developing over far western NY for the
western airports after 03z Tue, but would be in a weakened
state if it makes it this far east at all. Otherwise, generally
VFR, though IFR-LIFR anticipated again tonight for the Cape and
island airports. SW winds around 10 kt.

Tuesday and Tuesday Night: High confidence.

Any IFR-LIFR over the south coast, Cape and Islands erodes by
mid morning (~12-15z) with generally VFR conditions. There is
another risk for SHRA/TS again Tue aftn to early night, with
perhaps a better chance from ORH westward, but left out of the
TAFs due to lower confidence on development and coverage.
Weakening after sundown with generally VFR conditions, although
stratus and fog at sub-VFR levels again expected for the Cape
and Islands. SW winds around 10 kt.

KBOS TAF...High confidence in TAF. Possible SHRA/TS again on
Tue, but left TSRA out of the TAF due to low confidence. SW
gusts ease after sundown, then redevelop Tue.

KBDL TAF...High confidence in TAF, moderate on storm timing.
Possible SHRA/TS again on Tue, but left TSRA out of the TAF due
to low confidence. SW gusts ease after sundown then redevelop
Tue.

Outlook /Wednesday through Saturday/...

Wednesday through Wednesday Night: Mainly VFR, with local MVFR
possible. Breezy. Chance SHRA, slight chance TSRA.

Thursday: VFR. Chance SHRA.

Thursday Night through Saturday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight through Tuesday Night: High confidence.

A ridge of high pressure off the Atlantic coast will continue
to result in persistent SW winds across the waters through Tue
night. Small craft advisories remain in effect for portions of
the nearshore waters through this afternoon, and may be needed
again for Tue in the same areas.

There is a risk for thunderstorms on the northeastern waters
through sundown. The other issue will be overnight and early
morning fog with the focus across the southern waters.

Outlook /Wednesday through Saturday/...

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 25 kt. Local rough seas. Slight chance of rain showers.

Wednesday Night: Winds less than 25 kt. Local rough seas. Rain
showers likely, slight chance of thunderstorms.

Thursday: Winds less than 25 kt. Local rough seas. Chance of
rain showers, isolated thunderstorms.

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.

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

Friday Night through Saturday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT Wednesday for CTZ002>004.
     Air Quality Alert from 11 AM to 11 PM EDT Tuesday for CTZ002.
MA...Heat Advisory until 8 PM EDT Wednesday for MAZ003>007-010>019-
     026.
     Heat Advisory until 8 PM EDT Tuesday for MAZ020-021.
RI...Heat Advisory until 8 PM EDT Wednesday for RIZ001>005.
     Heat Advisory until 8 PM EDT Tuesday for RIZ006-007.
MARINE...None.

&&

$$

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