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Area forecast discussion 
National Weather Service Taunton Massachusetts
159 PM EDT Tue Sep 27 2016

Synopsis...
a cold front will cross the region today with a period of showers.
This front will stall near the coast late today and tonight
keeping the threat for showers along the South Coast, Cape Cod and
the islands through tonight. A cool, dreary and drizzly pattern
maintains into Saturday. Some partial improvement into Sunday
prior to return of high pressure from the north with cooler air.

&&

Near term /until 6 PM this evening/...
2 PM update...
showers have shifted south of the coast and will affect mainly
ack through the afternoon. Modified pops for current radar
trends.

Previous discussion...
band of showers pushing across cape/islands and South Coast as
drying is moving in from the west. Model timing is reasonable and
shows mid level drying reaching the South Coast by early afternoon
so expect partial sunshine developing from west to east,
especially interior with clouds lingering southeast new eng. Precipitable water plume
and deep moisture axis stalls just offshore and will keep threat
of showers into the afternoon for Cape Cod and for much of the day
over ack. Adjusted pops accordingly.

With developing sunshine, temps should reach the lower 70s for
much of the region, except a bit cooler cape/islands. Winds
diminishing over the cape/islands as low level jet moves east.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
tonight...

High pressure will build down the coast from the Gulf of Maine,
bringing a wind shift to NE as well as gusty winds mainly after
midnight from Cape Ann down to Plymouth. Scattered showers will
linger across southeast mass/Rhode Island tonight, but may start to see some
showers and patchy drizzle develop and move inland as the onshore
winds develop. Some question as to how far inland the shower
activity may push, which will be dependent upon a digging long
wave trough across the Great Lakes into the Ohio Valley. Held chance
pops across eastern areas, but can not rule out a few showers
further inland overnight though precip amounts will be light. Will
also see redevelopment of patchy fog. Overnight lows will range
from the upper 40s across the higher inland terrain to around 60s
along the immediate coast.

Wednesday...

Some questions as to how far the moisture plume off the ocean
will push inland during the day. Lower confidence on timing and
placement of the moisture, though looks like the best shot for any
shower activity will continue along with coast. Quantitative precipitation forecast amounts could
be up to 0.25 inches across the cape and islands. Gusty NE winds
will make for a raw fall day. Highs will run around 5 degrees
below seasonal normals for late September.

&&

Long term /Wednesday night through Monday/...
*/ highlights...

- a cool, dreary, drizzly pattern through Saturday
- possibly salvage a decent day on Sunday prior to a cold front
- high pressure and cooler air for next week
- monitoring invest 97l

*/ discussion...

Some interesting signals interpreted from the north hemispheric
pattern. Within the west hemisphere, contributing negative signals
from both the epo and pna are yielding a prevailing trough
pattern over the west and central Continental U.S.. meanwhile over the east
hemisphere, a subtle positive trend in the ao / nao signals a S
Greenland / icelandic low. Between the two: higher heights and
ridging prevail. Any energy that wobbles out of the progressive
flow regime becomes cut off as is the case for much of the
forecast period outlined below. There are also implications upon
the North Atlantic high and subsequent steering flow of the tropics,
pertinent when monitoring invest 97l.

A lot of unknowns in the forecast especially out through the
longer term. A forecast consensus is warranted though greater
weight is given towards ensemble probabilistics. Details below.

*/ Details...

Wednesday night through early Saturday...

Cut off low across the Ohio River valley east of which expect
roughly S to north low to mid level isentropic upslope along the
300-315k surfaces of sub-tropical air off the northwest Atlantic with
pwats up to 2 inches and decent Theta-E content. This both north and
aloft of a kinked warm frontal occlusion lying S and offshore of
New England as shallow, surface cold air damming prevails along
with a component of north flow from high pressure situated over southeast
Canada.

An over-running event with some impetus of deep-layer forcing per
individual waves of mid-level energy rotating north across the region
round the broader cyclonic flow of the cut off low, beneath mid to
upper level diffluence. But closer to the surface, up against
cooler drier air associated with high pressure to the north. New
England lying within the battleground of airmasses and thus
forecast guidance having difficulty coming to consensus on
rainfall outcomes. Welcome probabilistic datasets in this instance
yielding confidence as to where wet weather is most likely.

So in all, expect a cloudy, dreary, drizzly at times, cool
pattern for the period with unseasonable cooler than average
temperatures. Likely bouts of widespread showers with embedded
heavier downpours with the focus more towards the S. Chance to
likely showers north-S with little mention of thunder as the warm
frontal occlusion lies S. If all GOES well, some places over a 48
hour period could see upwards of +2 inches of rain, again greatest
confidence S of the Mass Pike. Bulk of the heavier rain Friday
into Saturday as mid level energy focuses convergence of deep
layer moisture along the lifting warm frontal occlusion towards
the S shore of New England.

Later Saturday through Sunday...

Drier air entraining as the cut off low is kicked back north into the
progressive flow regime, deamplifying and transitioning into a
positively-tilted trough axis. Offshore warm frontal occlusion
kicks back north perhaps giving US a decently mild day for Sunday
prior to the cold front sweeping the region late into Sunday
evening with some light showery weather and blustery west winds
during the transition process.

Next week...

A fair amount of weather features to evaluate. High pressure
builds S out of Canada along with some cooler air aloft towards
midweek. Coolest conditions around the early week period before
the airmass moderates ahead of a deep trough axis emerging out of
the west/central Continental U.S.. it's prior to this as the mid to upper level
low transition out that the combination of diurnal heating beneath
cyclonic flow aloft yields to daytime shower activity. Will keep
some pop chances for the Monday and Tuesday daytime timeframe.

Way too early to say much on invest 97l. Not ignoring track
guidance there still remains considerable spatial and temporal
spread within the breadth of guidance, though good agreement that
the system will strengthen into our next named tropical
disturbance. Keeping an eye on the system, staying situationally
aware and informed, but not jumping on any one particular
solution.

&&

Aviation /18z Tuesday through Sunday/...
forecaster confidence levels.

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

Short term /through Wednesday night/...

High confidence on trends and overall theme. Lower confidence on
exact details.

Through tonight...MVFR/IFR conditions over the cape/islands will
eventually expand inland from east to west across southern New England later tonight
with patchy fog developing as well. CT valley will be last to see
lower clouds. Occasional showers will persist across ack tonight
with areas of drizzle developing elsewhere after midnight.

Wednesday and Wednesday night...widespread MVFR cigs likely with
pockets of IFR possible. Areas of drizzle. NE wind gusts to 25 kt
developing along the coast.

Kbos taf...overall high confidence in taf. Expect IFR cigs
developing later tonight into Wed with slight improvement
possible Wed afternoon.

Kbdl taf...moderate confidence in taf. Mainly MVFR cigs developing
late tonight into Wed.

Outlook /Thursday through Saturday/...moderate confidence.

Overall a persistent north/NE flow with gusts up to 30 kts at times.
Expect a mix of MVFR-IFR with likely drizzle and scattered to
widespread rain showers activity, especially over S/SW New England
terminals.

Possible low level wind shear issues, more closer towards Saturday with winds at
the surface remaining out of the N, but out of the S at 2 kft agl.

&&

Marine...
forecaster confidence levels.

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

Short term /through Wednesday/...high confidence.

930 am update...
winds diminishing from west to east through midday with speeds
below 20 kt this afternoon. Small craft advisories will continue
over outer southern waters due to seas. Showers gradually exiting
with improving vsbys, but will persist over southeast waters through the
day.

Previous discussion...

Tonight...S-SW winds shift to NE from north-S as high pressure noses
across the waters from the north. Will see gusts up to around 25
kt after midnight, mainly on the eastern waters. Seas around 5 ft
on the southern waters, but beginning to build late on the eastern
waters. Expect reduced vsbys scattered showers and patchy fog,
especially southeast waters. Small crafts will be needed again late
tonight.

Wednesday...NE winds gusting to 25-30 kt, highest on the eastern
waters. Seas building up to 5-7 ft. Scattered showers with locally
reduced vsbys, along with patchy fog early.

Outlook /Wednesday night through Saturday/...moderate confidence.

Persistent north/NE flow with gusts to near gale force at times will
make for steady wave heights around 6 to 9 feet on the waters away
from inner harbors and sounds. Strongest wave action is likely over
the east/southeast waters and over the far SW waters. Visibility restrictions
more than likely given dreary, drizzly conditions forecast with
embedded scattered to widespread showers.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 2 PM EDT this afternoon for anz232.
Small Craft Advisory until 5 PM EDT Wednesday for anz254>256.

&&

$$
Synopsis...sipprell/evt
near term...kjc
short term...evt
long term...sipprell
aviation...kjc/sipprell
marine...kjc/sipprell

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