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Area forecast discussion 
National Weather Service Taunton Massachusetts
1002 am EST Sat Feb 6 2016

Synopsis...
high pressure brings dry weather this weekend with above normal
temperatures by Sunday. Two developing coastal storms may bring
accumulating snow Monday and Tuesday especially across eastern
Massachusetts. An Arctic cold front brings much chillier air for the end of
the week.

&&

Near term /until 6 PM this evening/...

10 am update...

No major changes to previous forecast. Confluent flow over the
region today positions high pressure at the surface just south of New
England. This will result in winds becoming west-southwest this afternoon and
helping temperatures recover to 35 to 40. So other than adjusting hourly
temperatures a bit previous forecast remains on track.

Previous discussion...

Weak upper level trough begins to set up over the region
today. A passing high to our south will tighten the pressure gradient
across the region for this afternoon. Anticipate gusts between 15-20
miles per hour. Weak shortwave will will also bring some middle-level moisture
into the area resulting in a filtered sunshine. Guidance does
indicate temperatures in the upper 30s to low 40s but with the fresh
snow pack that may be a bit to optimistic.

&&

Short term /6 PM this evening through 6 PM Sunday/...
tonight...

High pressure will mainly dominate resulting in quiet weather.
However pressure gradient will be slow to relax which will limit
radiational cooling overnight. Temperatures will drop into the 20s with
perhaps low readings in areas where the wind will be calm.

Sunday...

Low pressure system to the north will drag a weak cold front through
the region on Sunday. This front will be dry but may bring in some
clouds. Westerly flow will dominate in the afternoon which will
allow for temperatures to warm in to the 40s. Help aid in melting
some of the snow.

&&

Long term /Sunday night through Friday/...
big picture...

Longwave pattern shows ridge west/trough east as before...with
increasing amplitude early week and decreasing amplitude late week.
Overall a cold and unsettled pattern for southern New England. At
shorter wave scales we see three shortwaves affecting the pattern.
The first is in the lower miss River Valley and generates coastal
low pressure off the Carolinas Sunday. This swings wide of our
area...crossing about 4 degrees south of the 40n/70w benchmark...and
then sweeps northeast just south of Nova Scotia. The second
shortwave is moving ashore in the Pacific northwest and will carve a
deep cold trough over the eastern USA during the early week. The
third shortwave is along the Arctic Ocean coastline and will drop
south into the USA midweek.

Operational guidance mass fields are similar on the broad scale most
of the period. But there are differences in the details...especially
regarding the second shortwave and its developing coastal system
Tuesday. This second shortwave was just coming ashore at measurement
time last night. The 12z Saturday models should have a better read
on the shortwave and its effects. We continue to favor a model blend
especially using the GFS and European model (ecmwf).

The dailies...

Sunday night-Monday... coastal storm passes well offshore...some 4
degrees south of the benchmark. Normally that would mean a swing and
a miss for strike three. But high pressure builds south from Quebec
and establishes a pressure gradient that should bring a northeast
marine flow with Delta of 13-15c. This should at least bring
increasing clouds overnight and Monday. Less confidence on precipitation
given mediocre forcing and changing run-to-run amounts.

Models have backed off on quantitative precipitation forecast during Monday with main focus on cape
and islands...possibly eastern mass. We have backed off onset of
probability of precipitation until 06-12z Monday and value of probability of precipitation by about 20 percent. This
still brings potential for several inches in eastern mass with
highest amounts Cape Cod/Plymouth Colorado area.

Monday night-Tuesday... second shortwave digs over the Midwest with
surface low redevelopment along the middle Atlantic coast. This new
coastal low then moves past New England. Better dynamics and
resulting lift should be in place and with deeper moisture would
expect this to be a better chance of precipitation than the Monday offshore
system. But the responsible shortwave is just now moving ashore as
noted above. So still some uncertainty with this system and its
potential. We will bring a period of likely probability of precipitation as the system moves
through.

Wednesday through Friday... upper trough with its cold pool aloft
and cloud shield linger Wednesday. The Arctic shortwave then swings
through on Thursday. Expect quite a few clouds during this period
with a chance of snow showers. Clipper low then drops southeast from
northern Ontario Friday and bringing more clouds and scattered snow
showers. Mixed layer reaches either side of 925 mb each day...a
little higher Thursday behind the Arctic shortwave and surface
front. Temperatures aloft at the top of the layer support 30s
Wednesday...20s west/32 east Thursday...and 20s to near 30 Friday.
As noted earlier...cold and unsettled.

&&

Aviation /15z Saturday through Wednesday/...
forecaster confidence levels...

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

Short term /through Sunday/...

10 am update ... no major changes from 12z tafs. Previous
discussion below.

Today...high confidence. VFR. Winds shift to the SW. A few gusts
between 15-20 miles per hour are possible in the afternoon.

Tonight into Sunday...high confidence. VFR.

Kbos terminal...high confidence in trends.

Kbdl terminal...high confidence in trends.

Outlook /Sunday night through Wednesday/...

Two potential storms during this period...either could bring
IFR/LIFR ceilings and visibilities in snow. The first chance for this will be
Monday...with best chance on Cape Cod and islands. North-northeast
winds will gust to 35 knots along the eastern mass coast. The second
chance will be Monday night and Tuesday with all of southern New
England under the gun. Conditions improve Wednesday to MVFR ceilings
with scattered snow showers.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday/...high confidence.

10 am update ... no major changes from previous forecast. Chop
seas develop this afternoon as west-southwest winds oppose easterly swells
across the ocean waters of Rhode Island and Massachusetts. Earlier discussion below.

======================================================================

Lingering swells and seas will begin to subside today. Small Craft Advisory lingers for
a portion of the day...but may be able to be dropped sooner.

High pressure will build over the waters through the weekend. An
increase in the gradient will allow for some gusty winds across the
northern waters late this afternoon into tonight. Seas will build in
response. Small Craft Advisory may be needed tonight and into tomorrow for building
seas in response to gusty winds.

Outlook /Sunday night through Wednesday/...moderate confidence...

Sunday night-Monday...a developing gale center will pass well
offshore southeast of Nantucket...but strong winds will extend an
unusual distance out from the weather system. Northeast winds over
the waters will increase to gale force. This will build seas of 7 to
11 feet on the exposed waters. A Gale Warning will eventually be
needed for late Sunday night and Monday. Also expect reduced visibilities
in rain and snow.

Monday night-Tuesday...a second weather system will develop along
the middle Atlantic coast and move outside Nantucket. This will bring
another period of northeast winds with gusts over 25 knots. There
remain many questions about this next system...as well as low
potential for winds reaching 35 knots. Seas will remain at 7 to 11
feet.

Wednesday... winds diminish as the second coastal storm moves off.
Wind speeds should go below 25 knots. Rough seas will linger much of
the day especially on the southern exposed waters.

&&

Tides/coastal flooding...
Monday...

There is a fairly high astro tide of 11.2 in Boston late Monday
morning. Northeast wind gusts of 30 to 40 knots from large
circulation of the intensifying ocean storm will likely result in a
1 to 1.5 surge. Seas should be built up to between 10 and 15 feet
by then...so feel there is a decent shot for pockets of minor
coastal flooding along eastern Massachusetts coast. There is a low risk for
pockets of moderate coastal flooding...if the storms ends up a bit
faster and tracking further west than current guidance indicates.

Monday night and Tuesday...

Main concern is if we end up with a second area of strong low
pressure tracking up the coast...which could impact additional high
tide cycles. Large spread in the guidance on whether or not this
happens. If so...will have to watch the Tuesday noon high tide
cycle across eastern Massachusetts as Boston has an 11.5 astro tide.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 1 PM EST this afternoon for anz250.
Small Craft Advisory until 7 PM EST this evening for anz254-
255.
Small Craft Advisory until 10 am EST this morning for anz256.

&&

$$
Synopsis...wtb/dunten
near term...wtb/nocera/dunten
short term...dunten
long term...wtb
aviation...wtb/nocera/dunten
marine...wtb/nocera/dunten
tides/coastal flooding...

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