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Area forecast discussion 
National Weather Service Taunton Massachusetts
749 PM EDT Friday Apr 24 2015

Synopsis...
unseasonably cool weather continues through this weekend with
spotty showers or sprinkles. Periods of unsettled weather and
below normal temperatures will continue through most of next
week as well.

&&

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

735 PM update...
diurnal isolated showers that developed across western areas earlier
this afternoon have dissipated as seen on latest NE regional 88d
radar mosaic. Remainder of low and middle clouds associated with
short wave moving across are shifting NE and dissipating via
latest infrared satellite trends.

Will see clouds continue to dissipate from S-north as well as shift NE
as they rotate around the northwest-southeast oriented upper low extending from
west central Quebec through Maine/north New Hampshire to the Gulf of Maine.
So...expect dry conditions with diminishing winds overnight. Cold
pool aloft along with light winds and clearing skies /mainly
around or after midnight/ will allow temperatures to fall.

Have updated near term conditions to bring conditions and
incorporated into trends for the remainder of the night. This left
only minor adjustments to previous forecast.

Previous discussion...

Tonight...
lingering cloud shield under the upper low and cold pool...but
this should start to lift out to the north and east somewhat. So
we expect at least partial clearing tonight with the best chance
over Connecticut. Pressure gradient stays enough to keep the air
moving...so frost is not likely except possibly in the most
sheltered of locations that clear. On the other hand temperatures
will be similar to last night or perhaps a degree or two cooler.
Expected range is in the upper 20s and 30s...and freezing temperatures in
parts of the active growing zone /CT-RI-southeast MA/. We plan on
converting the existing freeze watch to a freeze warning for
northern CT and northwest Rhode Island.

&&

Short term /6 am Saturday morning through Saturday night/...
Saturday...upper cloud shield and cold pool will be focused over
northern New England but close enough to affect US. Daytime
heating and a shortwave cycling around the low may push clouds
back our way during the day. The surface layer will be drier...so
most attempts at precipitation should evaporate on the way down.
Temperatures at 850 mb are forecast around -2c...which supports maximum surface
temperatures in the 50s. Winds aloft in the mixed layer reach 20
knots...so expect another day of gusts either side of 20.

Saturday night...

Weak ridge builds over southern New England providing clearing
skies and light winds. Radiational cooling with dew points in the
30s...so min surface temperatures should be in the 30s.

&&

Long term /Sunday through Friday/...
highlights...

* below normal temperatures through at least the middle of next
week
* scattered diurnal showers this weekend into middle-next week
* low confidence on coastal system Thursday or Friday

Overview and model preferences...

Persistent upper level blocking pattern remains in place across
the lower 48 with few changes expected into the middle of next
week. However...noting some subtle changes toward next Thursday/Friday
which are showing up at least on the last couple of medium range
operational runs of both the GFS and European model (ecmwf) that are starting to
signal the breaking down of the upper trough pattern. The gefs
and ec ensembles continue to keep slow progression of systems...so
still quite a bit of timing and track issues to contend with this
forecast cycle.

Negative nao/ao pattern remains in place...keeping below normal
temperatures and periods of unsettled weather through at least the middle
of next week as cutoff 500 mb low pressure continues to sit and spin
across the northeast into eastern Quebec and the Maritimes. Models
signaling a stronger short wave that will drop S across the region
out of eastern Canada in the upper flow will drop across the
region bringing a better chance for showers along with an enhanced
north-NE wind flow. Once this short wave moves S...the upper system
may start to shift east but timing is still very much in question due
to wide model solution spread beyond Tuesday.

Another question at this point is the potential coastal system
that works off the southeast U.S. Coast late Wednesday or Thursday. The 12z model
runs continue to keep the blocking across the northeast which may
actually shunt the coastal system S of the region. Noting a rather
strong system on the 12z European model (ecmwf)...which tends to develop and slow
the system as it passes S of New England Thursday night or Friday...
while the GFS is a more open wave but still pushes offshore. Will
still need to watch future model trends before writing this one
off for now.

Used a blend of available guidance into Tuesday...which showed
good consistency with the previous forecast...then transitioned
over to ensemble guidance through the remainder of next week.

Details...

* Sunday...high confidence.

While the upper low continues to bring a few diurnal showers with
the cold pool aloft which actually looks to slowly shift east later
in the day. So...as has been the case over the last several
days...skies should start off partly to mostly sunny then clouds
develop along with a few spotty showers especially near and north of
the Mass Pike closer to the short wave that begins to shift out of
northern New England late in the day.

Expect temperatures to top off mainly in the 50s...but if a little more
sun works through the clouds across the lower CT valley...readings
may touch 60 in a few spots.

* Monday through Tuesday night...moderate confidence.

Rather potent 500 mb short wave and associated backdoor /of sorts/
surface reflection rotate SW across the region during this
timeframe. Looks like the best energy and precipitation chances will
push across Monday night through into Tuesday night. Winds also
shift to north-NE and increase. Gusts up to around 25 knots possible
mainly along east coastal areas. May see some appreciable rainfall
with quantitative precipitation forecast of 0.2 to 0.3 inches along the East Coast as low level
moisture increases with the onshore wind.

* Wednesday through Friday...low confidence.

Still quite a bit of uncertainty with southern stream system that
may make the turn up the eastern Seaboard. However...12z model
trends are tending to keep this system to the S thanks to the
upper level low that may push the southern system offshore. This
this was a recent trend though...did keep chance probability of precipitation going from
Thursday afternoon through a good portion of Friday due to the model/S
handling of the southern stream upper level system. Temperatures are also
trying to creep back closer to seasonal levels during this
timeframe as well.

&&

Aviation /00z 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/...

Tonight...high confidence. VFR. Leftover west-northwest wind gusting to 20
knots through 02z-03z inland then diminishing.

Saturday...high confidence. VFR. Possible brief MVFR in spotty
showers during the day Saturday. Northwest winds gusting around
20 knots.

Saturday night...high confidence. VFR with light wind.

Kbos taf...high confidence in overall taf.

Kbdl taf...high confidence in overall taf.

Outlook...Sunday through Wednesday...

Moderate confidence Sunday through Tuesday...low confidence
Wednesday.

Sunday...mainly VFR. May see brief MVFR conditions in scattered showers.
Sea breeze development possible along East Coast.

Monday-Tuesday...areas of MVFR ceilings/visibilities possible with better
chance for showers. North-NE winds increase especially along East Coast.
May see gusts to 20-25 knots from Plymouth County S to Cape Cod and
the islands mainly Monday night and Tuesday.

Wednesday...VFR with mainly dry conditions. Light north-northwest winds.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Saturday night/...

West-northwest winds gust 20 to 25 knots with strongest gusts
offshore. Seas linger near 5 feet on the outer waters through
Saturday and then subside. Seas below 5 feet all other waters
through the period.

Small Craft Advisory lingers on the outer waters through Saturday
morning due to seas and occasional gusts to 25 knots. Small Craft Advisory also
lingers on Rhode Island and Block Island sounds tonight mostly due to winds
at or near 25 knots.

Outlook...Sunday through Wednesday...high confidence.

Sunday...winds and seas below small craft criteria. Expect northwest
winds to shift to NE but remain below 15 knots. Sea breezes possible
along East Coast.

Monday...N-NW winds increase but remain below small craft. Seas
remain below 5 feet.

Monday night through Tuesday night...N-NE winds increase...gusting
to 25-30 knots. Seas build up to 5-7 feet...highest on the eastern
outer waters during Tuesday. Moderate probability for small craft.

Wednesday...winds become northwest and diminish. May see leftover gusts
to 25 knots early. Seas will remain at or above 5 feet mainly on the outer
waters.

&&

Box watches/warnings/advisories...
CT...freeze warning from 2 am to 8 am EDT Saturday for ctz002>004.
Massachusetts...none.
Rhode Island...freeze warning from 2 am to 8 am EDT Saturday for riz001-003.
Marine...Small Craft Advisory until 6 am EDT Saturday for anz235-237.
Small Craft Advisory until noon EDT Saturday for anz250-
254>256.

&&

$$
Synopsis...wtb/evt
near term...wtb/evt
short term...wtb
long term...evt
aviation...wtb/evt
marine...wtb/evt

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