Area Forecast Discussion
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000
FXUS61 KBOX 281401
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1001 AM EDT Fri Jul 28 2017

.SYNOPSIS...

Mainly dry weather today with seasonably warm temperatures and
humidity. Low pressure emerging off the Mid Atlantic coast
tracks south of New England Saturday, likely bringing some rain
to the immediate south coast along with cool temperatures and
gusty NE winds, but mainly dry weather further to the north.
A couple of slow moving low pressure areas off the mid Atlantic
coast will keep the region in a persistent northeast flow and a
risk of more rain early in the week across southeast zones. A
cold front may approach the region late Thursday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

10 am update...

Mostly dry day with seasonably warm conditions. Dense fog has
burned off this morning with the late-July sun. The boundary
layer destabilizing within light surface winds per weak high
pressure beneath mid to upper level confluent, subsiding flow,
brought about by NW flow round the polar low over SE Canada and
SW flow out ahead of the mid-level trough disturbance which will
be the main weather story for Saturday.

Should see sea-breezes develop along which it`s possible a spot
shower could develop with low-level convergence, yet suppressed
from deeper development along with the abundance of mid to upper
level dry air building in from the N. Areas of potential impact
mainly across interior CT into RI and SE MA where there is greater
low-level moisture availability and subsequent higher surface-
based instability.

Most locations dry today with a mix of sun and clouds (should
see mostly pancake cumulus), seasonable highs around the low
80s, cooler along the shores and across the high terrain.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...

Tonight...
Low risk for an evening shower, otherwise dry weather for much
of the night. However, as mid level low moves east from the Ohio
valley, coastal low will emerge off the mid Atlc coast late
tonight with deeper moisture lifting north toward the south
coast. As a result, some light rain may overspread the south
coast toward daybreak.

Saturday...
Models have continued a southward trend with coastal storm.
Highly anomalous late July pattern as strong vortex across SE
Canada maintains enough confluence to suppress coastal storm
south of the benchmark with heavy rainfall remaining mostly to
the south, although Cape Cod and especially the islands could
get into some heavier rainfall on Sat. Still some uncertainly
as there is a sharp moisture/QPF gradient along the northern
edge so a subtle shift back to the north would bring heavier
rainfall back in play for a larger portion of the SNE. For now,
we followed model consensus of confining highest pops across
Cape/Islands with mainly dry weather north of HFD-PVD-TAN.
Expect some sunshine developing in the interior and north of the
Mass Pike with partial clearing late in the day into the
coastal plain.

Anomalous NE low level jet will bring gusty NE winds to the
coast with gusts 25-35 mph with potential for 40 mph gusts over
the islands. Coolest temps in the 60s will be found across SE
New Eng with 70s further inland across the CT and Merrimack
Valleys. But lower confidence temp forecast across SE New Eng on
the northern fringe of the storm.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

Highlights...

* Persistent NE flow coastal areas with possible rough surf and high
  rip current risk
* Risk of another bout of rain south coastal areas early next week
  but considerable uncertainty

Overview...

Ridge persists over the western USA and over the west central
Atlantic. Southern New England looks to continue to lie in an area
of mid tropospheric weakness between and somewhat susceptible the
more pronounced upper high pressure centers. One closed upper level
trough over the mid Atlantic states results in a couple of
associated surface low pressure waves, which in turn introduces some
uncertainty for our forecast. There is confidence of a persistent NE
surface gradient but less confidence on NW extent of rain shield. As
the upper level trough lifts to the NE early next week, an
associated surface low pressure may lift far enough north to bring a
period of rain across some southeastern zones during Monday into
early Tuesday but higher than average uncertainly. Westerly zonal
flow dominates across southern Canada later in the week with signs
on operational models and ensembles of a short wave trough and
associated cold front approaching the forecast area late Thursday.

Periods of Focus...Sunday through Tuesday and Thursday.

Sunday through Tuesday...A persistent NE flow may result in a long
duration of fairly rough surf for this time of year as well as high
temperatures likely remaining a little below normal across the
coastal zones. As the mid Atlantic upper low pressure lifts to the
northeast, a surface low pressure center may also lift far enough
north to spread an area of rain into southeast zones.  Given the
uncertainty and 00Z ECMWF trend, have only chance POPs for those
southeastern zones and slight chance POPs elsewhere. Persistent NE
flow will likely result in rough surf and possibly elevated rip
current risk, especially as the periods begin to increase.

Thursday...Model consensus suggests that an approaching cold front
may trigger scattered showers/thunderstorms during the late
afternoon and evening. Have chance POPs as well as a chance of
thunder 18Z Thu to 05Z Fri for much of area.  Mid level winds are
not all that strong so primary hazard may be locally heavy rain.

&&

.AVIATION /14Z FRIDAY THROUGH TUESDAY/...

Forecaster Confidence Levels...

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

Short Term /through Saturday Night/...

Today...High confidence.
SCT-BKN low-end VFR cigs around 4-5 kft agl. Low risk SHRA
mainly across interior CT, RI, and southeast MA. Light winds
allowing sea-breezes around 15-16z. MVFR-IFR linger offshore of
the S-shore and islands.

Tonight...Moderate confidence.
CIGs building back N overnight. Low-end VFR most locations with
a mix of MVFR-IFR along the S-coast and across the Islands. A
potential return of lower VSBYs over the mid-CT valley and along
the S-coast and Islands down to 1/2SM. Winds increasing out of
the NE with the potential for gusts up around 25 kts by morning.
Chance -RA up to the MA-pike, more likely along the immediate S
coast and across the Islands. Greatest impact on ACK.

Saturday...Moderate confidence.
NE flow persists with gusts up to 30 kts for shoreline terminals.
Will see CIGs scour from the N/W, lifting, while remaining BKN-
OVC along the S/SE-coast with IFR possible with more likely -RA.
Drying trends from the N/W, more likely chance -RA along and S/E
of BOS-BDL.

Saturday Night...Moderate confidence.
CIGs continuing to erode S/E. BKN-OVC MVFR-IFR lingers over SE New
England, mainly across the Cape and Islands, becoming SCT towards
Sunday morning. Continued NE winds with gusts up to 30 kts. With
CIG scouring, -RA chances and VSBY impacts conclude.

KBOS Terminal...Forecasting sea-breezes to develop around 15-16z.
SCT low-end VFR CIGs initially, eroding with the onshore flow.

KBDL Terminal...Light winds overall. -RA chances into the overnight
period, but eroding going into Saturday morning as winds increase
out of the NE with gusts up to 25 kts.

Outlook /Sunday through Tuesday/...

Sunday through Tuesday...
SCT low-end VFR CIGs. Continued breezy NE flow with gusts up to
25 kts, mainly across SE coastal terminals.

&&

.MARINE...

FORECASTER CONFIDENCE LEVELS...

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

*/ Headlines...

 - Rough boating conditions for small boaters developing tonight
   and continuing through Tuesday.

 - GALE WATCH remains in effect through late Saturday night.

 - Could potentially see rip current develop along the shores,
   perhaps even beach erosion with the prolonged NE fetch.

*/ Forecast...

Short Term /through Saturday/...

Today...High confidence.
Sea-breezes developing around midday along the near-shore waters.
Otherwise roughly 5-10 kts out of the SE. Tranquil boating weather
with seas remaining below 3 feet. Some low clouds and patchy fog
linger around the S-coast and Islands throughout.

Tonight...High confidence.
Winds turning and increasing out of the NE with gusts up to 25 kts
towards Saturday morning. Wind stress results in waves building up
to 5 feet towards morning as well. Increasing areal coverage of rain
over the S waters, adding to the likely redevelopment and/or increase
in extent of low clouds and fog lingering around the S-coast and
Islands.

Saturday...Moderate confidence.
GALE WATCH in effect. NE winds continuing with gusts up to 35 kts
possible over the S/SE waters. Waves building to 10 feet by the
end of the day as the areal extent of rain scours from the N/W,
lingering longest over the S/SE waters with patchy fog and visibility
restrictions at times.

Saturday night...
GALE WATCH continues. NE winds remain brisk with gusts up to 35
kts as waves greater than 10 feet, up to 12 feet, are possible
on the S/SE outer waters. Continued scouring of clouds and rain
from the N/W, looking at the conclusion of rain and fog issues
over the S/SE waters by Sunday morning.

Outlook /Sunday through Tuesday/...Moderate confidence.

Persistent NE flow will likely cause an extended period of rough
seas. Anticipate at least gusts to SCA levels across south coastal
waters into Monday, but seas will probably remain elevated through
at least Tuesday.  Have gone significantly above Wave Watch given
our experience with persistent NE flow situations.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from Saturday morning through late Saturday night
     for ANZ231>235-237-254>256.

&&

$$

SYNOPSIS...KJC/Thompson
NEAR TERM...KJC/Thompson/Sipprell
SHORT TERM...KJC
LONG TERM...Thompson
AVIATION...KJC/Thompson/Sipprell
MARINE...KJC/Thompson/Sipprell


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