775
FXUS61 KBOX 121115
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
715 AM EDT Mon Aug 12 2024

.SYNOPSIS...
Isolated to scattered shower or thunderstorm this afternoon,
otherwise dry and comfortable today and Tuesday. Other than
scattered showers on Thursday, much of the workweek is dry with
seasonable temperatures. A frontal system brings our next best
chance at widespread rains either this weekend or into early
next week.

&&

.NEAR TERM /UNTIL 7 PM THIS EVENING/...
705 AM Update:

No major changes needed with this update.

Mostly clear skies begin the morning with low humidity levels
and current temps in the upper 50s to mid 60s. Should see at
least a few hours of full sun, until we start to feel effects
of a potent shortwave disturbance in mid-levels that is evident
in water vapor imagery over Lake Huron. This feature and its
cold pocket of air aloft has been responsible for producing a
band of lake- enhanced rain seen in composite radar imagery
coming off Lake Ontario. As this feature nears our area this
afternoon, expect an increase in cloud cover toward partly to
mostly cloudy conditions. Shallow instability in conjunction
with the added dynamics should be enough to produce low-topped
showers in scattered coverage during the afternoon hrs; the
strongest of these could produce occasional lightning and also
the potential for graupel or pea- size hail given the seasonably
cold temps aloft and low wet-bulb zero heights. Overall we`re
not anticipating anything necessarily impactful or significant.
This activity then moves offshore by early tonight before
trending drier. Not a washout, and while there will be some
showers to dodge, several hrs of dry weather are also expected.
Highs mid 70s to lower 80s still look on track with no changes
there.

Previous discussion:

Updated: 2:50AM

Highlights:

* Few showers possible mid to late afternoon as a robust shortwave
  passes through the region. Otherwise it`s a dry and comfortable
  afternoon with highs 70s to lower 80s.

A quiet start this morning with mainly clear sky conditions. Today
is mainly dry, though there will be iso`d to sct`d rain/thunder this
afternoon. It`s been mentioned there is a robust mid-level low
pressure system centered in southwest Quebec. Shortwave ejects into
southern New England this afternoon and promotes development of
clouds and showers/low top thunderstorms. BUFKIT forecast soundings
indicate these showers will be shallow, but thunder and maybe small
pea-size hail is possible due to the cold pool aloft. The forecast
sounding also showed an inverted `V` profile, which means there may
be a few stronger gusts/outflow from any thunderstorms. Timing it
out, generally starting 1-3 pm across western-half of southern New
England and 4-6pm across the eastern-half. Not anticipating heavy
rain as PWATs are near climatology to perhaps the 75th percentile
which is around 1.2" to 1.4". An isolated amount of 0.25" to 0.50"
is possible but most locations receive much less. Showers diminish
after sunset, CAMs do show an isolated shower or two may linger
through 9-11pm.

A cooler afternoon with dew points in the 50s, refreshing, or is it
an early fall-like feel? Recall, temperatures aloft are cooler than
normal and will result in lower than normal highs. Many locations
are in the upper 70s to lower 80s, but terrain AOA 750 feet are
likely in the middle 70s, 73-76 degrees, coolest will be highest
terrain of the east slope of the Berkshires.

West to west/northwest wind today around 10 mph, with occasional
afternoon gusts to 20 mph.

&&

.SHORT TERM /7 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Updated: 2:50AM

Tonight:

Nearly a carbon copy of the previous night. Showers end and clearing
sky cover, the departing shortwave provides another reinforcing shot
of cooler and drier air. Light northwest winds overnight across the
interior, but the boundary layer remains mixed enough to continue
those winds near the coast. Where the winds are light, should have
falling temperatures into the 50s, while the urban centers are still
warm-ish in the lower 60s.

Tuesday:

All around a nice day across the region with surface high pressure
building in from the southwest. Aloft, flow is out of the northwest
to the north, reinforcing the lower dew points and humidity. A good
amount of sunshine with fair weather clouds mixed as there is a weak
shortwave moving through mid to late afternoon, but with low PWATs
likely only see added clouds rather than any rain.

Seasonably warm with highs in the upper 70 and lower 80s. Northwest
winds 5 to 10 mph.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Updated: 2:50AM

Highlights:

* Other than a chance for showers on Thurs, much of the workweek is
  dry, with seasonable temperatures.

* Next chance for widespread rains is with a frontal system moving
  in either on the weekend or early next week.

* Monitoring developments regarding Potential Tropical Cyclone Five
  east of the Lesser Antilles. See NHC Advisories on this system for
  more details. Increasing risk for high surf and rip currents from
  later this weekend, but any other specifics remain too uncertain
  to pinpoint at this time.

Details:

No significant changes were noted in today`s 00z guidance through
the remainder of the upcoming workweek, with pretty good consistency
run-to-run and across modeling systems. Broad cyclonic flow aloft
with surface high pressure will govern our weather pattern through
the rest of the workweek. This should bring a mix of clouds and sun
during the day, and while most of the workweek is generally dry,
there is a better chance at showers on Thurs as a weak vort maxima
rotating around a broad upper trough sparks shallow convective
development especially in/near the higher terrain. No significant
impacts are expected from any showers which develop, however.
Temperatures begin around seasonable levels with a modest warming
trend toward late week, but highs in the upper 70s to lower to mid
80s pretty common.

Still looks as though the next best chance at more widespread rain
chances is with a pretty robust frontal system moving in from the Gt
Lakes either this weekend or early next week. Previously the GFS was
at odds with the international guidance suite on this frontal
system. There are now more members from the 00z GEFS as well as the
00z GFS which lend support to at least the existence of this frontal
system nearing Southern New England. However pretty large
disagreement on its timing, with the Canadian GEM holding off until
early next week, the GFS late in the weekend, while the ECMWF is the
most pessimistic in showing rains developing Sat and continuing
through Mon. For now left a rather general broad-brushed Chance PoP
for the weekend into early next week, but that will need refinement
once there`s better agreement on the timing.

Finally, will be continuing to keep close monitor of developments
regarding what is now Potential Tropical Cyclone (PTC) Five located
near the Leeward Islands. For the latest on PTC 5, see the latest
advisories from the National Hurricane Center. Most available track
model forecasts indicate PTC 5 - forecast to become a strong
tropical storm or hurricane in the next five days, with the next
named system to be Ernesto - making a northward to northeast pass
well offshore east of 70W longitude late this weekend. However we
need to be cognizant of adjustments in storm track as it is still
very early in this system`s lifecycle. It thus remains way too early
to provide specifics/effects to Southern New England, if any, due to
that uncertainty. However, long-period swell well ahead of this
system may stand to increase the risk for rip currents and high surf
as we move into the weekend. This is supported by the ECMWF Wave
guidance, which shows 5-9 ft swells reaching our southeastern coast
around Sat night and Sun.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

12z TAF Update:

Today...High Confidence.

VFR. Increasing clouds this afternoon, but remain VFR with
clouds bases around 5,000 to 7,000 feet. Dry in the morning,
then scattered brief afternoon showers, have included PROB30 for
western terminals; -SHRA at BDL & BAF between 18z/22z, here is
where there is highest confidence in rain. Elsewhere VCSH in
the rest of the terminals, except Cape Cod and the Islands.

Very low prob (5-10%) of isolated thunder, but too low to
include in the TAF. WSW to WNW winds 10-15 kt. Could have some
higher gusts between 18z-23z up to 20 knots. Cape and Island
winds are SW 10-15 kt and gusts to 20 knots.

Tonight and Tuesday...High Confidence.

Dry & VFR. WNW winds are 5-15 kt.

KBOS TAF...High Confidence.

Mainly VFR, although risk for SHRA between 17-02z could bring
MVFR visby for a brief period of time. WNW winds around 10 kt
begin a slow backing to WSW with gusts 18-20 kt this aftn,
before shifting to NW around 10 kt after 02z Tue.

KBDL TAF...High Confidence.

Mainly W to WNW winds 5-15 kt and dry weather through this
morning. Then VCSH this afternoon, mainly 18z-22z.

Outlook /Tuesday Night through Friday/...

Tuesday Night through Wednesday Night: VFR.

Thursday: VFR. Slight chance SHRA, isolated TSRA.

Thursday Night through Friday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Updated: 2:50AM

Through Tuesday...High Confidence.

Tranquil boating weather with persistent SW winds 5-15 kt through
today, could have few stronger gusts to 20 knots for the near
shore waters off of the coast of RI and southeast MA. Wind
shifts to WNW tonight into Tuesday. Dry weather with the
exception of a few brief showers, an isolated thunderstorm this
afternoon, dissipating with sunset.

Outlook /Tuesday Night through Friday/...

Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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