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Area forecast discussion 
National Weather Service Taunton Massachusetts
943 PM EDT Tuesday Oct 21 2014

Synopsis...
scattered showers tonight into the first part of Wednesday will
turn into a soaking rain later Wednesday into early Thursday in
association with a coastal low pressure system. Showers will
linger Friday as the storm slowly pulls away from New England.
Mainly dry weather expected this weekend with seasonable
temperatures.

&&

Near term /until 6 am Wednesday morning/...

930 PM update...

Cluster of heavy showers with embedded thunder over western
Worcester County has finally dissipated. Thus Flash Flood Warning
and Flood Advisory have been allowed to expire. Big difference
between dual pol which estimated a storm total of up to 5.9 inches
near Ware...while legacy much less at 2.9 inches. Legacy matches
up better with surrounding radars and it probably more accurate
than the dual pol given the low freezing level this evening /7
kft/.

As for the remainder of this evening and overnight...water vapor
imagery indicates closed middle level low over western PA with
multiple short waves rotating around this large circulation. This
will translate to scattered showers overnight. 00z upstream sounding
at okx Long Island indicates a very deep layer of moist adiabatic
lapse rates. This will continue the risk of an isolated
thunderstorm with heavy rain overnight. Previous forecast captures
these nicely so no major changes with this update.

&&

Short term /6 am Wednesday morning through Wednesday night/...

***a soaking rain late Wednesday into early Thursday with the
heaviest amounts expected across northeast massachusetts***

Wednesday and Wednesday night...

Areas of light rain and showers will continue to expand from north
to south through middle afternoon Wednesday...as moist onshore
northeast flow increases. The widespread soaking rain will wait
until later Wednesday afternoon and particularly Wednesday night.

The soaking rain will develop as low pressure and its associated
closed middle level centers lifts northeast. A strong easterly low
level jet of 30 to 40 knots will provide plenty of moisture and
strong lift for a widespread heavy rain event. The core of the
strongest low level jet will setup across our northeast
zones...which is where we expect the heaviest rain. Overall...
expect a widespread 1 to 2 inches of rain across most of our region
through early Thursday. The exception might be our far northeast
zones...where 2 to 3 inch rainfall amounts seem reasonable. There
is a low probability of some 4 inch rainfall amounts in our far
northeast zones...mainly in Essex County. If this were to
materialize...we might have some flooding issues depending on how
fast it falls. However...since its a low probability and a 3rd and
4th period event did not issue any flood headlines at this time.
Will need to monitor things closely...especially if model trends
slide the axis of heavy rain a bit further south than currently
indicated. Regardless...expect typical nuisance poor drainage
street flooding issues.

Finally...we did note some elevated instability late Wednesday into Wednesday
night. Included a slight chance of thunder in the forecast...but do
not expect anything widespread.

&&

Long term /Thursday through Tuesday/...

* long duration coastal storm will bring rain Thursday
* lingering showers possible on Friday
* mainly dry and seasonable weather this weekend

Overall models are in fairly good agreement through the long term.
There are some discrepancies with a couple of features as well as
some differences in the mesoscale details but those are to be
expected. The main weather story will be the long duration coastal
storm early in the period. After the coastal storm moves away from
southern New England...the weather dries out and becomes more
seasonable. Upper level flow flattens out late in the weekend into
early next week with more zonal flow expected.

Thursday...expect widespread rain to continue as a coastal low
pressure system slowly moves up the coast to Maine. An additional
half to inch and a half of rain is expected across the majority of
the area Thursday. As the low pressure moves into the Gulf of Maine
and then the Maritimes...expect highest amounts to occur along the
immediate East Coast of Massachusetts...particularly on Cape Cod and
Cape Ann where rain will last the longest. With the higher precipitable waters
and low level jet strongest across northern New England...expect the
heaviest rain and the strongest winds to occur there. The one
exception could be along Cape Ann where there may be some strong
northeasterly winds off the ocean. Cool...onshore flow and overcast
skies will keep temperatures in the 50s to low 60s during the day
and in the 50s overnight.

Friday...could see some lingering showers as low pressure moves up
into the Maritimes but winds shift to the northwest bringing
somewhat drier air into the region. Overall expect drier weather
and a gradual improvement as the day GOES on.

Saturday through Monday...another upper level trough moves over the
northeast but here is where we see some discrepancies between the
European model (ecmwf) and the GFS. The European model (ecmwf) has a strong negatively tilted upper
trough over southern New England while the GFS has a more neutral
upper trough. In both models low pressure in Quebec will pull a
cold front through at least a portion of southern New England. The
GFS is more aggressive with the front and has more moisture
associated with it...resulting in a greater chance of showers with
the front. Expecting dry seasonable weather Sunday and Monday as
high pressure builds along the eastern Seaboard and then slides
south of southern New England.

Tuesday...low pressure moving through the Great Lakes and into
Quebec may bring a cold front through southern New England late
Tuesday and Tuesday night. Another chance of some showers possible
with this front but plenty of uncertainty.

&&

Aviation /02z Wednesday 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/...

930 PM update...

No major changes from 00z tafs. Earlier discussion below.

=================================================================

Tonight...moderate confidence. Conditions gradually will lower to
MVFR from east to west tonight. We then expect further lowering to
mainly IFR by daybreak Wednesday...but timing remains uncertain.
Areas of light rain and drizzle will expand overnight in areas north
of the Massachusetts Turnpike...but a few showers are possible just about
anywhere. Patchy fog may also develop.

Wednesday and Wednesday night...moderate to high confidence. Low
end MVFR to IFR conditions expected. Areas of light rain...showers
and drizzle will be common for the first part of Wednesday across
the northern zones and gradually expand south. Widespread moderate
to heavy rain expected later Wednesday into Wednesday night. Northeast wind
gusts of 20 to 25 knots develop on the coast Wednesday night...but near 30
knot gusts are possible across northeast Massachusetts coast.

Kbos...moderate confidence in taf but low confidence in trends.

Kbdl...moderate confidence in taf but low confidence in trends.

Outlook...Thursday through Sunday...

Thursday...high confidence. MVFR/IFR conditions likely in rain and
possibly some isolated thunder. NE winds gusting up to 20 to 25 kts
across S New Hampshire and NE Massachusetts.

Friday...high confidence. Slow improvement to VFR expected in
clearing skies.

Saturday and Sunday...moderate confidence. VFR. Low probability of
scattered showers Saturday.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday night/...

***high seas and gale force northeast wind gusts possible Wednesday
night across our northeast Atlantic waters***

945 PM update...

No major changes from previous forecast. NE winds will increase
toward morning across the Cape Ann waters with gusts of 25-30 knots
possible. Earlier discussion below.

======================================================================

Tonight...moderate to high confidence. East to southeast winds will
shift to the northeast later tonight as low pressure lifts northeast
off the middle Atlantic coast. Winds across most of the waters will
remain below Small Craft Advisory thresholds...except for the northeast waters where
gusts to 25 knots possible toward daybreak.

Wednesday and Wednesday night...moderate to high confidence. Low
pressure will lift northeast as an intensifying easterly low level
jet develops. At the surface...should see northeast Small Craft Advisory wind gusts
overspread most of our waters during the day Wednesday. The core of
the strongest jet will be north our waters Wednesday night. Still
the potential for a period of northeast 35 knot wind gusts across
out far northeast waters. Therefore...have issued a gale watch for
this location. Also...seas may build to around 15 feet in our
extreme northeast Atlantic waters.

Outlook...Thursday through Sunday...

Thursday...high confidence. 10 to 15 foot seas on the northeastern
waters will slowly diminish through the morning and into the early
afternoon...5 to 10 foot seas elsewhere will do the same.
Northeasterly winds 20 to 25 kts will slowly diminish through the
day as well. Small craft advisories will likely be needed for most
waters for at least a portion of the day.

Friday and Saturday...high confidence. Mainly quiet boating weather.
Winds and seas increase slowly late Saturday night.

Sunday...moderate confidence. Seas and winds increase gradually on
the southern waters...briefly reaching small craft criteria.

&&

Tides/coastal flooding...
fortunately astronomical high tides are rather low over the next 48
hours and the core of the strongest winds will be to our north.
Therefore...the risk of even minor coastal flooding is quite low.
However...there is the potential for some minor beach erosion along
the Salisbury and Plum Island coasts during the high tides Wednesday
night and Thursday. No coastal flood headlines are anticipated
though for this upcoming event.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory from noon Wednesday to 8 am EDT Thursday
for anz231>235-237.
Gale watch from Wednesday evening through late Wednesday night
for anz250.
Small Craft Advisory until 8 PM EDT Wednesday for anz250.
Small Craft Advisory until 8 am EDT Thursday for anz251-
254>256.

&&

$$
Synopsis...Frank/rlg
near term...Frank/nocera/rlg
short term...Frank
long term...rlg
aviation...Frank/rlg
marine...Frank/rlg
tides/coastal flooding...

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