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Area forecast discussion
National Weather Service Taunton Massachusetts
1033 PM EST Thu Feb 23 2017

Synopsis...
high pressure offshore of New England will bring unseasonably
warm conditions through Saturday. A warm front may trigger a
few showers across northern Massachusetts late tonight and
Friday morning, with light spotty drizzle elsewhere. Otherwise
mainly dry weather prevails. A strong cold front will cross the
region Saturday night, bringing areas of rain and patchy fog.
There will be a low chance for isolated thunderstorms as the
front passes. Dry but blustery conditions return on Sunday into
Monday with normally cool temperatures. A couple of fast moving
low pressure areas may bring unsettled conditions to the region
around the middle of next week.

&&

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

Surface obs at 10 PM and satellite trends show South Coast fog
bank breaking and shifting offshore. Obs still show patches of
light fog in the CT valley and clear skies/light winds in the
interior. We also continue to see onshore southwest winds at the
coastaline, bringing air with dew points in the mid and upper
40s coming off water temps near 40. This continues to threaten a
period of coastal fog/low clouds along the South Coast
overnight.

Surface obs at 10 PM also show a weak cold front moving through
northern New England. This may reach northern Massachusetts overnight, but
building upper ridge and southwest flow aloft will both work to
slow any forward progress.

Temperatures in the airmass leading the front are mild with dew
points in the 40s. This continues to be a good target for
overnight temperatures.

A broad cloud shield, indicating return flow lift over the
front, is located out in the Great Lakes including PA and
western New York. This will shift east overnight and so we may have
increasing mid and high clouds later tonight. Otherwise a dry
night. No changes planned with the forecast grid fields.

&&

Short term /6 am Friday morning through Friday night/...
updated 410 PM...

Friday...

Warm front across northern Massachusetts in the morning lifts slowly north.
Thus at least some sunshine across CT/Rhode Island and southeast Massachusetts with more
clouds across northern Massachusetts especially in the morning. This boundary
may yield some spotty light rain over northern Massachusetts in the morning
along with spotty light drizzle elsewhere, but the trend will be
towards drier weather for the afternoon.

Given we'll remain in the warm sector expecting another day of highs
in the 60s across CT/Rhode Island along and south of the Massachusetts Pike. Route 2
corridor northward to the Vermont/New Hampshire border will be slightly cooler with
highs in the upper 50s given cool side of the boundary. Boston and
the North Shore may have seabreezes that limit highs to the 50s.
However let's keep in mind it's still late Feb when normal daytime
highs should be only in the lower 40s. Thus Spring fever continues
and 60s possibly lingering into Sat too!

Friday night...

More of the same, warm sector airmass remains over the region so
very mild conditions prevail with temps only falling into the 40s
along with another round of patchy fog and drizzle.

&&

Long term /Saturday through Thursday/...
highlights...

* mild with showers late Saturday and Saturday night
* blustery and seasonably cool Sunday and Monday
* progressive steering pattern around the middle of next week
may bring a few weather systems and unsettled conditions

Overview...

12z model suite remains in pretty good agreement through Sunday,
then model solutions diverge greatly after this timeframe thanks to
a redeveloping broad upper level steering pattern across the lower
48 through the middle of next week. Have low confidence in timing
and track of individual systems from Mon through Thu due to the fast
flow aloft.

Strong 500 mb short wave moves quickly across the region late Sat and
Sat night, with its associated cold front. Will see normally cool
but blustery conditions move in for Sunday and Monday as high
pressure moves across. Beyond this, really tough resolving sensible
weather with low continuity amongst the model suite through the
middle of next week. Monday is a good example, with the GFS
continuing to develop a wave of low pres in the developing SW flow
aloft, while the Canadian ggem and European model (ecmwf) keep dry conditions. Do
note some model to model consistency with a couple of systems during
the Tue night to Thu timeframe, but timing is still in question.

Used a blend of available guidance through Sunday with rather good
confidence. Into next week, transitioned to the model ensembles
which showed a bit better continuity than individual model
solutions.

Details...

Saturday into Saturday night...

Models continue to signal strong short wave moving quickly
eastward as it wraps around cutoff 500 mb low over western Hudson
Bay during this timeframe. Its associated surface cold front
will cross the region during Sat night.

Will continue to see low clouds and areas of fog Sat morning,
which may break briefly as S-southeast winds increase with the
increasing pres gradient ahead of the cold front during the
afternoon. Clouds look to linger through the day, along with
some scattered showers as low level moisture remains underneath
the inversion. May also see some patchy drizzle mainly along the
S coast where best low level moisture pooling will take place
with the onshore wind.

Strong low level S jet will push toward the region during Sat,
increasing to 35-45 kt at h925 up to 50 kt at 850 mb by 00z sun as
front approaches. Best mixing is noted behind the front, but
some of this could mix down with any moderate rain that may push
across.

Southern stream swath of higher pwats sweep into the region on
the strong winds aloft. While the pwats are only about 1 inch,
this is about 2 South Dakota above climo for late February. Noted that
the higher quantitative precipitation forecast amounts have shifted a bit further north into north New
England and upstate New York with the 12z run, along with the faster
forward progress of the front once it reaches the region
overnight. At this point, expect about 0.25 to 0.5 inches with
highest amounts across the east slopes of the Berkshires, with
around 0.1 inches or less along the coast.

With the precip mainly near and behind the front, colder air
will work in while some of the precip is across the region. Will
see mix/changeover to snow mainly across the higher terrain of
the Berkshires and northern Worcester Hills. Will still see
precip quickly shut off as system clears the coast between 06z
and 09z sun. Expecting mainly a dusting of snow, with an outside
shot of up to 1/2 inch, which could occur near the border with
Berkshire County. May see some lingering rain along the east mass
coast toward daybreak.

Still noting good instability as the front approaches, with tt
into the lower 50s, Lis at or just below zero and tq values in
the upper teens to around 20. Some signals for elevated
convection, considering low level capping in place on BUFKIT
soundings until the front approaches. May see some brief heavy
rainfall near the Berkshires into parts of the northern CT
valley, which could also bring brief strong wind gusts down.
Have kept isold thunder in the forecast from about 22z through
06z.

One other aspect after this system passes will be rising water
levels across the watershed into early next week. Much if not
all the snowpack has or will have melted across this region, but
still much more upstream that will push into the headwaters and
head downstream. Will need to monitor in case some river levels
approach action stage.

Sunday through Tuesday...

High pressure builds to the mid Atlantic coast Sunday, keeping
good shot of cold air advection working across in the west-northwest wind
flow at the surface and aloft. 850 mb temps drop from -4c (east)
to -10c (west) at 12z Sunday down to -9c to -11c at 18z. Excellent
low level mixing also works in, with a 50 kt jet at 850 mb moving
across Sunday, and 30-35 kt jet at both h9 and h95. So, will
likely see wind gusts up to 30-35 mph during the day Sunday,
highest gusts across the higher terrain and along the coast. At
least skies will be mainly sunny.

Remains seasonably cool and blustery on Monday, but some big
model differences especially on the 12z GFS. This model
continues to signal a fast moving weak system working NE around
the backside of the departing high pres off the mid Atlantic
coast Mon night and Tue. Low confidence continues.

Most models showing a bit better continuity with another system
in the Tuesday timeframe. Looks like good lift ahead of another
warm front as low pressure moves across the Great Lakes. Again,
looks like the ggem and European model (ecmwf) are in better agreement with the
GFS the outlier. Went with chance pops with this system, though
low confidence remains.

Wednesday-Thursday...

Upper level pattern remains progressive, with 500 mb trough
migrating across the central U.S. During this timeframe. Timing
of the associated low pres and cold front still in question, but
looks like another decent shot of precip with it some time late
Wednesday into Thursday. Lower than average confidence during
this timeframe.

&&

Aviation /03z Friday through Tuesday/...
forecaster confidence levels...

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

Short term /through Friday night/...

Tonight...low to moderate confidence. Patchy fog along the South
Coast thinned at 10 PM, but sufficient low level moisture to
expect at least patches of MVFR vsbys in fog overnight. Areas of
LIFR cigs and MVFR/IFR vsbys in fog still possible along the
South Coast overnight.

Friday...moderate confidence.
Combination of IFR-MVFR in the morning with slow improvement to
from south to north. Low risk of some spotty light rain across
northern Massachusetts.

Friday night...MVFR likely with light spotty showers/drizzle
possible.

Kbos taf...moderate confidence in taf after 06z.

Kbdl taf...moderate confidence in taf after 06z.

Outlook /Saturday through Tuesday/...

Saturday...moderate confidence. MVFR-IFR conditions in areas of
fog and low clouds. May see spotty drizzle along the S coast
Sat morning. Isolated thunderstorms approach the east slopes of the
Berkshires around 21z-22z, then shift steadily east Sat evening.
Brief heavy rain possible across west mass with any thunder. Precip
mixing with or changes to -sn around midnight or so across the
higher inland terrain ending after 06z. May see local IFR-LIFR
conditions in any -sn. Conditions improve rapidly toward
daybreak across central and western areas. West winds gusting to
20-25 kt after midnight.

Sunday...moderate confidence. VFR conditions. Northwest winds gusting
to 25-30 kt, highest along the immediate coast and across the
higher terrain.

Monday...low confidence. Mainly VFR conditions. SW winds gusting to
around 25 kt, highest along S coast. May see local MVFR in isold
-shra mainly S of the Mass Pike Mon afternoon/night.

Tuesday...low confidence due to timing of weather features. May see
scattered -shra with local MVFR conditions. May mix with or change
to -shsn during the nighttime hours mainly across the higher terrain.

&&

Marine...
forecaster confidence levels...

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

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

South-southwest winds continue overnight and Friday. Brief gusts
near 25 knots still possible overnight, but mostly 15 knots or
less. Biggest concern will be vsby lowering to below a mile at
times in patchy fog overnight thru Fri night.

Outlook /Saturday through Tuesday/...

Saturday...moderate confidence. Southeast winds shift to S Sat night
gusting to 25-30 kt. Seas build up to 6-9 ft, highest on the
outer waters. Reduced visibilities in areas of fog and scattered
showers Sat, then in rain Sat night and patchy fog Sat night.
Low chance of isold thunderstorms Sat evening through around
midnight. Winds shift to west after midnight Sat night, gusting to
25-30 kt. Conditions improve with the wind shift.

Sunday...high confidence. West-northwest winds gusting to 25-30 kt across
the open waters. Low chance for gale force gusts on the eastern
outer waters. Seas up to 6-9 ft, though will slowly subside as
winds diminish Sun night. Good visibilities.

Monday-Tuesday...low confidence due to timing of weather features.
SW winds may gust to around 25 kt at times on the outer waters
Mon and Mon night, then diminish Tue. Local visibility restrictions
possible in scattered showers Mon night-Tue, though timing in
question.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...wtb/nocera/evt

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