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Area forecast discussion 
National Weather Service Taunton Massachusetts
1021 PM EDT Friday Apr 17 2015

Synopsis...

Milder weather returns Sat ahead of a cold front which moves
through during the afternoon. Canadian high pressure brings
cooler weather Sunday. Then a coastal low delivers a wind swept
soaking rain to the region late Monday into Monday night. Cooler
weather should dominate next week with a few showers from time to
time.

&&

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

10 PM update...

With conditions clearing across the interior and winds becoming
light as a weak area of high pressure envelops the region...
attention focuses on anticipated low temperatures and potential
development of fog. Dewpoints at maximum heating of the day were
around the upper-40s...and with several locations likely to fall
below such crossover values with radiational cooling proceeding am
expecting dense fog to become an issue over interior valleys of S
New England...in addition to southeast Massachusetts which was the last to see rain
earlier today and had the least amount of time to dry out as the
weak frontal boundary and cloud conditions stalled across the
region. Dewpoints in the 50s and any clearing will easily result
in fog development for southeast Massachusetts. Forecast updated accordingly. Lows
down around the middle- to low-40s with coldest spots along the
S-shore adjacent to colder waters.

&&

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

Saturday...

Robust middle level shortwave swings through northern new eng during
the afternoon with 500 mb temperatures near -30c which is focused to
the north. Surface instability is marginal at best but confined to north new
eng where sbcapes less than 500 j/kg. Tt spike into the middle 50s
along with steep middle level lapse rates over 7 c/km but this also
across north new eng. Thus...best chance for any convection Sat
afternoon will be to the north. Instability parameters drop off
considerably across southern New England. We will have 20-30 percent probability of precipitation for
showers across northern and east Massachusetts associated with modest qg forcing
with the shortwave...but best chance in southern New England will be across NE Massachusetts.

After frontal passage moves through in the afternoon...deep mixing above
850 mb will promote gusty northwest winds...especially interior where a
few gusts to 35-40 miles per hour possible. Brief stronger winds near the
coast possible late afternoon/early evening. Maximum temperatures will
reach upper 60s to lower 70s...but cooler along the coast where
seabreezes are likely. Temperatures may struggle to 60 across the Outer
Cape and portions of NE Massachusetts.

For more on potential fire weather conditions...please consult
the fire weather discussion below.

Saturday night...

Strong high pressure builds to the north with mainly clear skies and
diminishing northerly winds. Min temperatures dropping into the
30s...except lower 40s along the coast and urban centers.

&&

Long term /Sunday through Friday/...

Highlights...

* cooler temperatures for Sunday
* wind swept soaking rain late Monday into early Tuesday
* cooler with periods of showers middle to late next week

Overview...

Overall the 12z guidance is in good agreement within the medium and
long range. However exact timing and strength of each system
especially middle to late next week still needs to be worked out. Upper
level ridge will move overhead Sunday and exit the region by the
overnight hours. Upper level low will move over the Great Lakes
pushing several shortwave over the region. This low becomes cut-off
by middle-week pinwheeling between the Great Lakes and New England
through the rest of the period. This will yield to a more showery
and cooler forecast for next week.

Details...

* Sunday...high confidence.

High pressure overhead will allow for plenty of sunshine and dry
weather. Temperatures will warm into the middle 50s to upper 60s. Anticipate
sea breeze development as winds aloft will be quite calm allowing
for temperatures along the coastline to be in the low 50s.

* Monday into Tuesday...higher confidence.

Guidance continues to show middle-Atlantic triple point low developing
and moving towards southern New England late Monday into Tuesday.
This system is very potent with strong 60kt 925mb southeasterly jet
and good moisture flux streaming into the flow. Precipitable water values reach
around 1.5 inches...which is about 2 Standard deviation's away.
Better dynamics of this system come in around the Monday evening
commute...but cannot rule out light rain ahead of it during the
afternoon hours.

Overcast skies during the day on Monday will limit diurnal heating
such that highs will struggle to get into the 50s. Also anticipate a
few gusts from the strong jet to mix down so we could see 20-30 miles per hour
gusts in the late afternoon. This will make for a very
cool...windy...wet day. Temperatures will begin to warm up overnight as
warm front associated with low pressure approaches the region
bringing a good slug of rain. Expect quantitative precipitation forecast values to range between 1-2
inches as rain will continue into early Tuesday.

There is a low probability that locations south of the Mass Pike may
see some isolated thunder by Monday evening into Tuesday within the
warm sector. Showalters drop below 0 and total totals will be above
50. Kept thunder out of the forecast for now as confidence is low.

Rain will begin to end Tuesday afternoon from southwest to
northeast as cold front passes through and low moves offshore.

* Wednesday into Friday...moderate confidence.

Strong cut off low will spin over the northeast during this time
period. Could see a few waves develop but the increasingly stacked
upper low pressures will mean a decrease in precipitation intensity.
However may see a lot of diurnal cumulus and diurnal showers developing
as cold pool aloft will be overhead. Lastly expect temperatures to be
about 5-10 f below average for the week thanks to the slow-moving
upper-level low and its associated cold pool.

&&

Aviation /02z Saturday through Wednesday/...

Forecaster confidence levels...

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

Short term /through Saturday night/...

3z update...

Tonight...

IFR-LIFR fog remains an issue for S/southeast Massachusetts and likely to develop
overnight across Interior Valley terminals of S New England. With
light winds forecast...the problem is anticipated to persist into
the morning hours by which point winds increase and scour out the
low visibilities.

Saturday...high confidence. VFR. Chance of afternoon showers NE
Massachusetts to Cape Cod. Increasing northwest winds developing in the interior in
the afternoon with gusts to 30 knots. Seabreezes likely along east
coastal Massachusetts into the afternoon...becoming northwest late afternoon.

Saturday night...high confidence. VFR.

Kbos taf...high confidence. Fog should not be an issue for the
terminal. Seabreeze developing by 15z Sat then winds shift to northwest
around 21z.

Kbdl taf...moderate confidence. IFR-LIFR visibilities with fog are
forecast to develop after midnight towards Saturday morning.

Outlook...Sunday through Wednesday...

Sun...VFR and diminishing winds. High confidence. Sea breeze
along the coast.

Monday...MVFR/IFR developing in rain/fog by afternoon. East/southeast wind
gusting to 25-30kt near coast. Moderate confidence.

Tuesday...MVFR possible in scattered showers. Moderate confidence.

Wednesday...mainly VFR with scattered MVFR in diurnal cu/showers. Moderate
confidence.

&&

Marine...

Forecaster confidence levels...

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

Short term /through Saturday night/...high confidence.

10 PM update...

Patchy dense fog is forecast over the waters into Saturday morning
in combination with light winds. Visibility restrictions
anticipated. Will see low clouds and fog scour during the morning
period as winds increase. Seabreezes likely across nearshore
waters during Sat afternoon. A period of stronger northwest winds
will develop Sat evening bit speeds mostly below Small Craft Advisory. However...a
period of north wind gusts to 25 knots possible over southeast waters
overnight.

Outlook...Sunday through Wednesday...

Sunday...high confidence.

High pressure moves across New England. Light winds and subsiding seas.

Monday...moderate confidence.

Increasing east/southeast winds expected Monday with building seas...probably
requiring Small Craft Advisory with gusts reaching 25-30kt. Outside chance of
reaching marginal gales /35kt/. Seas could reach as high as 8-11 feet
on outer waters Monday night. Rain and fog will limit visibility Monday
afternoon and and Monday night.

Tuesday...moderate confidence.

High seas will continue through the day as low pressure system exits
the region. Anticipate Small Craft Advisory to continue well into the
afternoon/evening fro choppy seas. Westerly wind gusts will slowly
diminish throughout the day.

Wednesday...moderate confidence.

Seas and wind will slowly subside but with another approaching
system...seas may remain choppy. Small Craft Advisory may be needed.

&&

Fire weather...

After collaboration with surrounding weather forecast offices and fire weather
officials...we have issued a Fire Weather Watch for interior
Massachusetts...north CT and northwest Rhode Island. Rainfall this morning was under 0.25" and
very dry conditions and gusty winds will develop Sat afternoon.
Deep mixing will result in wind gusts to 35 miles per hour across the
interior with relative humidities dropping to near 25 percent
leading to critical fire weather conditions.

High pressure moves in on Sunday keeping the winds gusts at Bay...
but allowing for relative humidity/S to drop near 25 percent again.

Conditions will turn more wet by next week with several chances of
showers and cooler weather throughout the work week.

&&

Box watches/warnings/advisories...

CT...Fire Weather Watch from Saturday afternoon through Saturday
evening for ctz002>004.
Massachusetts...Fire Weather Watch from Saturday afternoon through Saturday
evening for maz002>005-008>012-026.
Rhode Island...Fire Weather Watch from Saturday afternoon through Saturday
evening for riz001.
Marine...none.

&&

$$

Synopsis...kjc/dunten
near term...kjc/dunten/sipprell
short term...kjc
long term...dunten
aviation...kjc/dunten
marine...kjc/dunten
fire weather...weather forecast office box staff

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