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Area forecast discussion 
National Weather Service Taunton Massachusetts
1002 PM EDT Wednesday Jul 29 2015

Synopsis...
another very warm and humid day is in store for Thursday. An
approaching cold front will trigger showers and embedded
thunderstorms Thursday afternoon and evening with locally heavy
rainfall...especially across the interior. Not as warm and less
humid weather is expected Friday into the weekend and probably into
early next week. There may be some scattered showers and a few
isolated thunderstorms from time to time this weekend into early
next week as weak weather systems move across.

&&

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

10 PM update...

Forecast remains on track this evening. Dry weather will prevail as
upper level ridge axis moves over the region. A sticky night is
ahead as dewpoints are in the upper 60s to low 70s. This combined
with light winds will help fog become another issue tonight. Right
now low stratus is sitting just off the coast of ack and could
move onto the Cape. May need to watch the cape and islands for
widespread fog.

Previous forecast...
given high dewpoints and light winds...will once again see some
patchy fog develop in the typically prone locations. Low clouds
may develop across the far southeast New England coast...but with
southwest flow should not advance much further northwest than
that.

Low temperatures for most locations will only drop to between 70 and 75
with a few upper 60s possible in northwest Massachusetts.

&&

Short term /6 am Thursday morning through Thursday night/...
***showers and embedded thunderstorms will bring heavy rain and the
potential for localized street flooding Thursday afternoon and
evening especially across interior southern new england***

***a secondary concern will be for a few strong to marginally severe
thunderstorms late Thursday afternoon/early evening across western
Massachusetts and northern ct***

Thursday and Thursday night...

Southwest flow aloft and at the surface will transport deep moisture
into southern New England. Both the GFS/NAM show precipitable waters exceeding 2+
inches and a southwest low level just of 25 to 30 knots. We may see
some peeks of sunshine in the morning...but should see clouds begin
to dominate in the warm air advection moisture. Given the deep
moisture in place...scattered showers and isolated thunderstorms
could break out anywhere across the region by Thursday afternoon and
perhaps even earlier. Locally heavy rainfall will be possible with
this activity.

The main show will arrive late Thursday afternoon and evening in
association with a pre-frontal trough and associated cold front.
Poor middle level lapse rates and cloud cover will limit instability to
some degree. Nonetheless...we should be able to develop around 1000
MLCAPES across the interior given 70+ dewpoints in place. 0 to 6 km
shear is rather marginal...but does increase to between 30 and 35
knots across our northwest zones towards 00z. A lot of the
mesoscale models show a line of showers and embedded thunderstorms
working into western Massachusetts/northern CT sometime late Thursday
afternoon/evening. That activity weakens as it moves east into an
environment with less instability which is typical with southwest
flow aloft. Bulk of showers and embedded storms should exit the
coastal plain by midnight...but lingering activity is possible
across the cape and islands.

So to sum up...heavy rain with the potential for localized street
flooding across the interior will be the main threat with these
storms. However...a few strong to perhaps marginally severe
thunderstorms are possible mainly across western Massachusetts and northern CT.
The main concern would be localized strong to damaging wind gusts.
The hail threat is rather low given 500 mb temperatures of around -6c and
poor middle level lapse rates.

One little nuance we wanted to mention was the low risk for a brief
weak tornado across western Massachusetts and northern CT. There is about 25
to 30 knots of wind off the deck with rgem/NAM showing 0 to 1 km
helicity values near or over 100. Given 70+ dewpoints and low local/S
there is a low risk for that.

High temperatures Thursday should mainly be in the upper 80s to near 90...but a
few places across eastern New England may end up a few degrees
warmer if they see a longer period of sunshine. Either way it will
be very humid with 70+ dewpoints. Low temperatures Thursday night will be in the
60s to near 70 and areas of fog will likely develop in the typically
prone locations late.

&&

Long term /Friday through Wednesday/...
synoptic overview and model preferences...
medium range models continue to signal anomalous 500 mb cutoff vortex
across Hudson and James bays extending into Quebec during this
timeframe. This will push the long wave trough slowly east out of the
Great Lakes toward New England around the Tuesday-Wednesday timeframe. This
will push the hot...very humid air S of the region. Expect
generally seasonable but drier conditions from late this weekend
Onward.

Several weakening short waves will slide around the base of the
trough and push toward the region...but will tend to weaken as
they cross with generally weak instability in place. Will see
periods of scattered showers/isolated thunderstorms...though timing is in
question especially toward the middle of next week.

Used a blend of available guidance into Sunday with good
continuity...then transitioned over to the gefs/ecens means which
kept good timing of features from the previous forecast.

Details...

Friday...
cold front pushes further offshore Friday morning. Any leftover
showers will push off the cape and islands early...then will see
improving conditions moving in. Drier air also pushes in as dewpoints
fall away from the S coast. Winds will be light so with a weak
pressure gradient so will see some patchy fog develop late Friday night
in the normally prone inland locations as well as along the S
coast where higher dewpoints will linger. Highs on Friday will
generally be in the 80s.

Saturday-Sunday...
another cold front approaches late Sat...crossing the region Sat
night. Front and precipitation with it tends to weaken as it moves into
more stable air...but will still see widely scattered showers and maybe
a thunderstorm or two. Looks like the best chance occurs across
the east slopes of the Berkshires into the western CT valley. Precipitation
will tend to dissipate after sunset Sat night...though can not
rule out a lingering shower across Cape Cod and the islands.

On Sunday...weak high pressure ridge builds across so will see dry
conditions with highs again in the 80s...though holding in the middle-
upper 70s across Outer Cape cod and Nantucket. A few showers might
approach far western areas well after midnight Sun night.

Monday through Wednesday...
models having a tough time with timing of short waves in the
slowly migrating upper flow across the northeast...as well as
which short wave will have more energy than others. For now...have
low chance probability of precipitation mentioned late Monday/Monday night as another front
moves across. Showers may linger into Tuesday...then noting drier
conditions for next Wednesday. Rather low confidence during this
timeframe due to wide model solutions.

&&

Aviation /02z Thursday through Monday/...
forecaster confidence levels...

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

Short term /through Thursday night/...

Tonight...moderate to high confidence. Mainly VFR conditions.
Will see patchy fog develop late in the typically prone locations.
In addition...low clouds may work onto the islands and Cape
Cod...but should not make it much further northwest than that with
southwest flow.

Thursday...moderate confidence. Probably VFR conditions dominate
into the middle afternoon...except the South Coast/cape and islands
where low clouds/fog patches will be at least nearby. Scattered
showers/isolated thunderstorms are possible in the warm air
advection pattern during the day. However...the main focus will be
a line of showers and embedded thunderstorms that will likely work
into western Massachusetts/northern CT by late afternoon/early evening. A few
of these storms may contain localized strong wind gusts and
torrential rainfall. In addition...southwest wind gusts of 25 to 30
knots are expected to develop along the coastal plain during the
afternoon.

Thursday night...moderate confidence. IFR ceilings/visibilities likely across
southeast New England coast with mainly broken MVFR to VFR ceilings
elsewhere. Showers and embedded thunderstorms will weaken as they
push into eastern Massachusetts and Rhode Island Thursday evening...but some locally
heavy rain is still possible. Bulk of activity over after midnight
except perhaps cape and islands...but patchy fog and low clouds may
develop.

Kbos terminal...high confidence through tonight. Sea breeze should
come to an end between 21z and 23z this evening.

Kbdl terminal...high confidence through tonight. Patchy fog may
affect the terminal for a few hours before daybreak Thursday.

Outlook /Friday through Monday/...

Friday...moderate to high confidence. Mainly VFR. Patchy fog may
develop in normally prone inland locations as well as along S
coast late Friday night with local MVFR-IFR visibilities.

Saturday...moderate confidence. Mainly VFR. Scattered showers/isolated
thunderstorms late Sat through around midnight Sat night. Local
MVFR-IFR conditions in any precipitation.

Sunday...moderate confidence for VFR conditions.

Monday...low to moderate confidence. Mainly VFR. Local MVFR-IFR
in any showers/isolated thunderstorms mainly away from S coast.
Showers linger into Monday night with brief local MVFR.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Thursday night/...

Tonight...high confidence. Weak pressure gradient should keep winds
and seas below Small Craft Advisory thresholds. May see some areas
of fog develop late across the southern waters.

Thursday and Thursday night...moderate to high confidence.
Developing low level jet will result in near shore southwest wind
gusts of 25 to 30 knots developing Thursday afternoon. In
addition...long southwest fetch will allow for seas to build to
between 3 to 5 feet across most open waters. Small Craft Advisory headlines go into
effect for all waters Thursday afternoon. Winds diminish Thursday
evening...but will need to keep headlines up through Thursday night for
the outer-waters through Thursday night from the left over swell.

Outlook /Friday through Monday/...

Friday...moderate confidence. SW winds may gust close to 20 knots
along southern waters. Seas 4 feet or less.

Saturday through Monday...general west-SW winds in place below small
craft criteria. May see gusts up to 20 knots on the southern waters
Sat night and again Monday/Monday night. With long SW fetch in place...
seas will build up to 5-6 feet on the southern outer waters during
this timeframe so small crafts may be needed.

&&

Climate...
here are the high temperatures for our climate sites today through 7 PM...

Boston 92 at 649 PM
Bradley 95 at 407 PM
Worcester 88 at 426 PM
Providence 93 at 434 PM
Milton/Blue Hill 91 at 510 PM /ASOS/

Record highs for today...

Boston 97 on 1933 & 1931
Providence 95 on 2002 & 1949
Bradley 96 on 1933
Worcester 94 on 1892
Milton/Blue Hill 97 in 1949

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...air quality alert until 11 PM EDT this evening for maz017>024.
Rhode Island...air quality alert until 11 PM EDT this evening for riz005>008.
Marine...Small Craft Advisory from noon to 7 PM EDT Thursday for
anz230>234-236-251.
Small Craft Advisory from noon to 11 PM EDT Thursday for
anz235-237.
Small Craft Advisory from noon Thursday to 8 am EDT Friday for
anz250-254>256.

&&

$$
Synopsis...Frank/evt
near term...Frank/dunten
short term...Frank
long term...evt
aviation...Frank/evt
marine...Frank/evt
climate...

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