Area Forecast Discussion
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183
FXUS61 KBOX 280806
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
406 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/...
Upper level confluent flow and subsidence behind departing
shortwave will bring very dry air in the mid levels with weak
cold front likely washing out across SE New Eng and becoming
overwhelmed by developing seabreezes. Mainly dry weather today
with pt-mosunny skies developing after any stratus burns off.
Models generating some marginal instability south of the Pike
today where low level moisture is a bit higher. Low risk for an
isold afternoon shower across RI and SE MA in the vicinity of
weak convergence assocd with seabreezes. But no thunder given
very dry air above 750 mb with good mid level cap.

850 mb temps 13-14C supports highs into the low and mid 80s but
cooler immediate coast where seabreezes develop. A bit humid
with dewpoints low to mid 60s.

&&

.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 /07Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Through 12z...Highly variable conditions across SNE from
IFR/LIFR to VFR. MVFR/IFR will be most prevalent in the CT
valley and SE New Eng coast.

Today...Moderate confidence.
Any morning IFR-MVFR conditions will lift to VFR during the
morning. An isold afternoon shower is possible across RI and SE
MA.

Tonight...Moderate confidence.
Mainly VFR cigs with isolated shower threat in the evening may
trend toward MVFR toward daybreak along the south coast as rain
lifts north into the region. Patchy fog may develop across SE
New Eng.

Saturday...Moderate confidence.
Highest confidence of rain and MVFR conditions will be near the
south coast with mainly VFR and dry conditions further to
north, especially Mass Pike northward. Increasing NE winds along
the coast with gusts to 25-30 kt developing.

KBOS Terminal...High confidence. Sea breeze should develop by
midday.

KBDL Terminal...Low confidence on IFR cig potential through 12z.
High confidence after 12z.

Outlook /Saturday Night through Tuesday/...

Monday...MVFR and possibly IFR south coast including islands and VFR
elsewhere.

Tuesday...VFR.

&&

.MARINE...
FORECASTER CONFIDENCE LEVELS...

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

Short Term /through Saturday/...

Today...High confidence. Light winds becoming SE in the
afternoon with seabreezes over the nearshore waters. Tranquil
seas.

Tonight...High confidence. Winds become NE overnight increasing
to 20-25 kt toward daybreak. Light rain overspreads southern
waters overnight.

Saturday...Moderate confidence. Gale watch continues. Potential
for NE gusts to 35 kt, especially southern and SE waters but
confidence not high enough to upgrade to a warning as models
have trended south with the storm. Seas may build to 10+ ft over
the eastern waters. Vsbys reduced in rain and fog, especially
southern waters.

Outlook /Saturday Night through Tuesday/...

Confidence...Moderate

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
SHORT TERM...KJC
LONG TERM...Thompson
AVIATION...KJC/Thompson
MARINE...KJC/Thompson



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