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Area forecast discussion 
National Weather Service Taunton Massachusetts
428 PM EDT Friday Jul 31 2015

seasonably warm this weekend with a risk of scattered showers and
widely scattered thunderstorms middle to late Saturday afternoon.
Warm weather continues into early next week along with the risk of
thunderstorms both Monday and Tuesday. Not as warm and less humid
conditions arrive middle to late next week.


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

Although evidence of a weak short wave...think activity now over
western New York will not be able to overcome dry air over our region
along with any forcing of consequence staying north. Thus...have
gone with a dry forecast through tonight. Have stayed with a model
consensus for temperatures tonight. Dewpoints give some space for
radiational cooling but starting the descent at rather high
values...upper 80s most areas...and so expect lows near to a
little above average for tonight. Winds have been a bit gusty over
land to 25 to 30 miles per hour but should settle down fairly quickly with


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

Main issue for this time period is whether or not we will see
any convection Saturday afternoon/early evening. A short wave trough
and relatively weak surface cold front will have a marginally
unstable air mass to work with and fairly notable vertical wind
shear of 40 to 50 knots. Think the NAM is a little too robust with
its instability as is a common bias but nonetheless other
models...including the higher resolution arw and nmm...provide at
least some support for widely scattered thunderstorms. Think we
may lack sufficient moisture but most models do try to produce at
least a little quantitative precipitation forecast. Relatively cool 500 mb temperatures are a
concern. Experience has shown that we have a tendency to
overproduce at this time of year with cold temperatures aloft. The
vertical wind shear of 40 to 50 knots suggests that its not out of
the question that one or two storms...if they are able to get
going...could produce locally strong wind gusts and hail. Although
some variation from model to model...inclined to think best
instability and chance for convection will be across southeast Massachusetts...S
central Massachusetts along and S of the masspike...northern Rhode Island and NE CT.
Have gone widely scattered to scattered. This is a relatively low
confidence situation and for the most part Saturday should be a
dry Summer day with temperatures in the 80s. Have gone with model
consensus for Saturday temperatures.


Long term /Sunday through Friday/...

* seasonable temperatures and lower humidity for the first half of the week
* pattern change by middle week bringing below average temperatures
* hit or miss showers/thunderstorms through the period


00z guidance is in good agreement for most of the period. Issues lie
within the small scale and timing. Strong upper level low will
continue to spin over Hudson Bay keeping the northeast in
southwesterly flow from elongated trough. Several waves will move
through this flow keeping the chance for showers and thunderstorms
in the forecast. Upper level low will begin to shift eastward due to
amplified ridge over the central Continental U.S. And northwesterly low
strengthening. This shift in the pattern will drop heights and temperatures
across the northeast...leading to below average temperatures.


Sunday through Wednesday...moderate confidence.

Middle-level ridge will build across the region Sunday into Monday.
Most of the area should remain dry but cannot rule out a few spot
showers or airmass thunderstorms. Best region will be across
northwest zones due to the higher terrain. Otherwise temperatures
will at or slightly above average. Highs will be near 85f to 90f
with lows between 60-70f.

Potent shortwave will move through the flow on Tuesday. Anticipate
showers and thunderstorms to develop ahead of the wave across
upstate New York on Monday and over southern New England Monday night into Tuesday. Some
modest instability and Li values below -4c leads to the potential
for overnight thunderstorms. Low confidence on strong to severe.

Temperatures on Tuesday will be slightly cooler but still near
seasonable as dry air from the west moves into the area.

Wednesday and beyond...high confidence in temperatures...low confidence in

Closed low aloft will shift eastward pushing a potent shortwave over
the region. This wave will develop a coastal low over the middle-
Atlantic and move close to the benchmark....grazing the South Coast
with precipitation. However exact placement can change...depending on if
pattern amplifies more. Otherwise anticipate cooler conditions as
upper level trough takes hold over the northeast sending several
waves to reinforce the cooler airmass.


Aviation /20z Friday through Wednesday/...
forecaster confidence levels...

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

Short term /through Saturday/...high confidence except only low
to moderate confidence in development of any convection Saturday

Rest of this afternoon...VFR for all terminals.

Tonight...VFR with perhaps just a little patchy fog in a few
interior low spots.

Saturday...VFR but risk of widely scattered thunderstorms in the
afternoon...with highest chance across interior southeast Massachusetts...S central
Massachusetts along and S of masspike...northern Rhode Island and NE CT.

Kbos terminal...high confidence in taf. Surface wind should diminish
toward sunset. For Saturday afternoon...widely scattered thunderstorms may
develop across bos area late Saturday afternoon but not enough
confidence to reflect in taf at this time.

Kbdl terminal...high confidence in taf. Isolated thunderstorm not
out of the question Saturday afternoon.

Outlook /Sunday through Tuesday/...moderate confidence.

VFR much of the time with a risk for scattered showers and thunderstorms Monday
into Tuesday morning. A few thunderstorms could be strong late Monday
afternoon/evening...especially west of a afn-orh-ijd line.


forecaster confidence levels...

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

Short-term /through Saturday night/...moderate confidence.

Tonight...tranquil conditions with generally good visibility and light
SW wind.

Saturday and Saturday night...enough of a SW fetch ahead of a
cold front that seas are projected to build to near 5 feet across
the outer S coastal waters. Think that the wave guidance is
overdone but nonetheless probably still enough fetch ahead of a
weak cold front to get those 5 foot seas and hence have raised a
Small Craft Advisory from late Saturday morning to Saturday night.
Also...isolated thunderstorms are possible Saturday evening ahead
of the cold front.

Other issue for Saturday afternoon is that there looks to be
enough in way of incoming seas to produce pockets of moderate rip
current activity across the exposed southern Rhode Island
shoreline...especially Block Island.

Outlook /Sunday through Tuesday/...

Fairly tranquil boating weather this period with modest SW
winds...good visibility and mainly dry weather.

Low risk of scattered showers and T-storms late Monday.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas from 11 am Saturday to
2 am EDT Sunday for anz255-256.


near term...Thompson
short term...Thompson
long term...dunten

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