Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 271120

Area Forecast Discussion
National Weather Service Taunton MA
720 AM EDT Tue Sep 27 2016


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.



730 am update...

Rain with embedded heavier downpours sweeping quickly across S
New England, moving through a tad faster than the latest HRRR.
Rainfall amounts of around half an inch have been observed. Not
too shabby. Expecting a drying trend W to E during the morning
hours with shower activity lingering S/E offshore, perhaps the
islands and outer Cape for the afternoon as the front stalls up
against the Atlantic high as per latest RAP guidance. Storm total
rainfall amounts of around half an inch, perhaps higher over SE
portions of New England as the front slows up and there is, in
addition, the slight risk of a thunderstorm though low confidence
so did not go with a mention.

Attendant cold front with the N to S band of rain sweeping across
the region behind which winds back W/SW and sunshine emerges.
Anticipating highs to warm up around the low 70s especially over
the W and Central portions of S New England.




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 SE Mass/RI 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 CHC
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.


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. QPF 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.



*/ 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 N Hemispheric
pattern. Within the W Hemisphere, contributing negative signals
from both the EPO and PNA are yielding a prevailing trough
pattern over the W and Central CONUS. Meanwhile over the E
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 N 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 E of which expect
roughly S to N low to mid level isentropic upslope along the
300-315K surfaces of sub-tropical air off the NW Atlantic with
pwats up to 2 inches and decent theta-e content. This both N 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 N flow from high pressure situated over SE

An over-running event with some impetus of deep-layer forcing per
individual waves of mid-level energy rotating N 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 N. 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 N-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 N into the
progressive flow regime, deamplifying and transitioning into a
positively-tilted trough axis. Offshore warm frontal occlusion
kicks back N 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 W 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 W/Central CONUS. 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



Forecaster Confidence Levels.

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

Short Term /through Wednesday/...

12z update...

Today...Moderate confidence.

Low-end VFR / MVFR cigs, possibly a brief period of IFR as already
seen out in the CT River Valley as of 11z, as -RA sweeps W to E
across the terminals this morning, lingering over SE terminals
midday into afternoon. TEMPO vsby impacts down to IFR with RA/+RA.
Gusty S winds upwards of around 25 kts ahead of the front especially
over the coastal terminals gradually veering out of the W/SW.

Tonight and Wednesday...Moderate confidence.

Deteriorating trends. Lowering MVFR-IFR that expands E to W during
the overnight period. SCT SHRA developing as well. Perhaps some
improvement over W and Central terminals of S New England during
the day Wednesday. Winds continuing to veer out of the NE, increasing.

KBOS TAF...RA moving through as of 11z, likely to persist to around
13z before conditions improve. Will hold cigs at MVFR at lowest.

KBDL TAF...Drying trend through the remainder of today. Conditions
improving to VFR.

Outlook /Wednesday Night through Saturday/...Moderate confidence.

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

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



Forecaster Confidence Levels.

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

Short Term /through Wednesday/...High confidence.

7 am major changes to the forecast.

Today...Have extended small crafts through midday across the
south bays and sounds as S-SW winds gust up to 25-30 kt. Expect
the gusts to diminish by early afternoon. Seas build up to 5-6 ft
mainly on the southern waters to east of Cape Cod which will
continue through the afternoon on the outer waters. Visibility
restrictions in areas of showers and patchy fog, which will
linger through the day on the southern waters to east of Cape
Cod. Low risk for a few thunderstorms over southern waters.

Tonight...S-SW winds shift to NE from N-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 SE waters. Small crafts will be needed again late

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 N/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 E/SE waters and over the far SW waters. Visibility restrictions
more than likely given dreary, drizzly conditions forecast with
embedded scattered to widespread showers.



MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ232-
     Small Craft Advisory until noon EDT today for ANZ233-234.
     Small Craft Advisory until 4 PM EDT this afternoon for ANZ250.
     Small Craft Advisory until 5 PM EDT Wednesday for ANZ254>256.



NEAR TERM...Sipprell/EVT
LONG TERM...Sipprell
MARINE...Sipprell/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.