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Area forecast discussion 
National Weather Service Taunton Massachusetts
655 am EDT Friday Mar 27 2015

Synopsis...
cold front offshore has an area of showers moving along it up the
coast into New England. This will move offshore later this
morning. A second cold front in the St Lawrence Valley will move
across New England today and offshore toward evening. Weak low
pressure moving up the coast may bring some light snow to southern
New England tonight and Saturday. High pressure will push south
of New England Sunday. Another batch of precipitation is possible
late Sunday night into Monday ahead of a cold front.

&&

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

700 am update...

Cold front has moved offshore this morning. Heavy rain showers
continue to move across southern New England this morning. The
showers can be heavy at times reducing visibilities and allow for ponding
on roadways. Motorist should use caution if traveling. 1 hour quantitative precipitation forecast
amount ranges between 0.05-0.10 inches.

Across the northwest portion of the region...spotters as well as
ASOS report snow mixing into the rain. Expect this trend to
continue from northwest to southeast this morning as 850mb temperatures aloft continue
to cool and surface temperatures will be near the middle 30s. If the precipitation
is heavy enough could see a quick coating across the higher
elevations of the Berks and orh hills.

Aside from minor tweaks to adjust for current trends...bulk of
the forecast remains on track for this morning.

Previous discussion...

This morning...
area of showers moving up the front aligns well with the right
entrance region of the upper jet. This jet moves off into the
Maritimes by afternoon...so this area of rain/showers should move
off by midday. Timing from the regional radar mosaic would
suggest the showers move off around middle morning...which lines up
well with the model dynamics.

This afternoon...
airmass dries out a bit during the afternoon. Model cross sections
show the drier air around 700 mb while moist air lingers below 850
mb. So we expect lingering clouds but precipitation tapering off most
areas. Exception is along the South Coast and islands where there
would be a lingering chance. Temperatures at 950 mb support maximum temperatures in
the 40s.

This evening...
another upper jet maximum approaches up the East Coast with southern
New England in the left exit region. This along with a weakening
of the dry layer would suggest an re-expanding chance of precipitation in
southern New England. We have shown chance probability of precipitation returning in Rhode Island
and CT by 00z.

&&

Short term /6 PM this evening through 6 PM Saturday/...
upper trough over the Great Lakes shifts east during this time.
This brings cold advection aloft destabilizing the airmass. The
upper jet initially provides upper venting and lift tonight. All
of this suggests a chance of precipitation during the night and lingering
into Saturday morning.

The models continue to show a wave of low pressure forming along
the cold front well offshore. They also show an inverted trough
extending up along the east Massachusetts coast. We saw this
during the snow blitz last month...indicating an increased chance
of snow showers in eastern mass overnight and Saturday morning.
Model moisture fields are marginal. Temperatures favor snow
during this time...although more marginal for snow than our
previous experience. All-in-all most places should see less than
an inch of snow. But the extra support from this trough could
yield a slushy 1-2 inches accumulation. Temperatures of 25-35 are
borderline for this accumulation...so confidence in those numbers
is low- moderate.

Temperatures will warm a little during Saturday morning and should be
enough to change any snow over to rain by midday. Temperatures aloft
support maximum temperatures in the 30s.

&&

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

* ocean enhanced snow showers Saturday night
* a weak cold front will move through on Monday bringing scattered showers
* moderating Spring-like temperatures into next week
* Alberta clipper moves through Tuesday night into Wednesday

Overview...

Unfortunately an active pattern appears to be setting up over
southern New England beginning this weekend into next week. Deep
trough will move over southern New England on Saturday pushing the
Carolina low south of the benchmark and towards the Maritimes. A
quick moving ridge and associated high will follow on Sunday before
northwest flow sets up as ridge build over The Rockies. This will
allow for several waves to push through with the first moving from
the Great Lakes into northern New England dragging a cold front with
it on Monday. Next an Alberta clipper will dive into southern New
England by late Tuesday into Wednesday. Lastly a northern and
southern stream merger appears to approach by late Thursday into
Friday.

Overall guidance is in good agreement until day 7 where they are
split in timing on the Thursday system as the ec is more progressive
than the amplified GFS. Still mesoscale scale details and thermal
profiles to work out but it does look like there is the potential
for some snow showers into next week.

Details...

* Saturday night...moderate confidence.

Temperatures overnight will fall well below normal with lows around the
teens to low 20s with the coolest spots out west as skies will
begin to clear as high pressure begins to build in.

Main focus on Saturday night is the snow potential. NAM/GFS are very
bullish in their quantitative precipitation forecast compared to the conservative ec. Inverted
trough will begin to slide eastward during the evening hours as
surface low moves towards the Maritimes. However secondary shortwave
will continue to trigger lift aloft and with Delta ts near 20 degree
difference expect ocean effect snow showers to develop/enhance
ongoing snow showers. This is also supported by north/northeast
winds and very steep lapse rates. Went with HPC quantitative precipitation forecast to play
conservative but generally could see 1-2 inches additional from what
falls during the day on Saturday. Will need to watch this set-up
closely as we could have a surprise 3 to 4 inch amounts somewhere
along the east mass coastline.

* Sunday...high confidence.

Sunday is a transition day as deep trough begins to pull offshore
and upper level ridge moves into the region. Warm air advection will
begin to push in late in the day allowing for temperatures to eventually
warm into the middle 40s. Expect mostly clear skies in the morning but
they will begin to cloud up during the afternoon as the next system
approaches from the west.

* Monday into Tuesday...moderate confidence.

Next upper level disturbance will impact southern New England late
Sunday into Monday. Still some spread amongst the guidance for
timing with the GFS being 6hrs faster then rest of the guidance.
Therefore trended towards ec/HPC on this portion of the forecast.
Surface low across the Great Lakes will pass just north of
southern New England...dragging associated cold front with it. Temperatures at the onset
look to be cool then warm up during the day on Monday prior to
frontal passage. At the onset of precipitation...expect a few snow
showers...but then transitioning to rain fairly quickly as temperatures
warm up. Moisture is marginal so coverage may be more scattered along the
front.

* Tuesday night into Thursday...low confidence.

Next short wave will quickly dive through the flow from Canada and
move across or just south of southern New England. The ec is more
amplified/stronger with this system cutting off the 850 mb low
compared to the GFS which keeps an open wave. Timing is also an
issue as if it pass overnight then temperatures will be cool enough for
snow showers...vs a daytime passage. Still a good amount of time to
watch this system but depending on the placement of the low...we
could see another 1-2 inches of snow across the area.

Weak ridge will follow behind the system before next low pressure
impact southern New England either Thursday or Friday. Ec is less
amplified and more progressive compared to the GFS. Still plenty of
time to watch this system as well.

&&

Aviation /12z Friday through Tuesday/...
forecaster confidence levels...

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

Short term...tonight and Friday...

Today...moderate confidence.

Rain showers this morning will taper off this afternoon. Observed
values LIFR in the east and mixed VFR/MVFR in CT and western mass.
Expect the LIFR to linger in the east with MVFR in CT and western
mass. Conditions improve this afternoon with VFR in the west and
MVFR ceilings in the east.

Tonight and Saturday...moderate confidence...
another area of showers moves in with MVFR ceilings and MVFR/IFR
visibilities. Temperatures cool enough during the night to change any
rain to snow. Most of the IFR visibilities should be concentrated in
eastern mass and possibly Rhode Island. This continues into Saturday
morning. Temperatures Saturday should warm into the 30s which
should change the snow to rain in the coastal plain...while the
interior remains snow.

Kbos taf...moderate confidence in taf.

Kbdl taf...moderate confidence in taf.

Outlook...Saturday night through Tuesday...high confidence.

Saturday night into Sunday...VFR conditions likely. Scattered MVFR along
and southeast of I-95 due to ocean effect snow showers. Visibilities may be
reduce if heavy band of snow sets-up.

Monday...VFR dropping to possible MVFR in scattered rain showers as weak
cold front moves through.

Tuesday...VFR.

&&

Marine...
forecaster confidence levels...

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

Short term...tonight and Friday...moderate confidence.

Today...
north winds 10 to 15 knots with gusts to 20 knots. Lingering seas
of 5 to 9 feet on the outer waters and Rhode Island/Block Island
sounds. Small Craft Advisory continues on these waters.

Tonight...north winds pick up as colder air moves south and a
distubance passes well offshore. Expect winds gusting to 25 knots
on the outer waters with seas lingering at 5-6 feet.

Saturday...continued gusty winds reaching 25 knots on the outer
waters. Continued rough seas 5-7 feet on the outer waters. There
is potential for winds gusting to 25 knots on Cape Cod Bay and
Nantucket Sound as well.

Small craft advisories for the outer waters and Rhode Island waters have
been extended until Saturday evening.

Outlook...Saturday night through Tuesday...

Moderate confidence into Tuesday.

Saturday night...surface low will pass well south and east of the
benchmark. However this will increase winds up to 25-30 kts and
build seas through the night. Small Craft Advisory will be needed.

Sunday through Monday...high pressure quickly builds in on Sunday
allow for winds and seas briefly subside. By Sunday night...winds
back to SW and with approaching cold front on Monday will see seas
increase in response. This will allow for Small Craft Advisory to continue through
the period.

Tuesday...weak lull in between systems however winds will be gusty on
the backside of the front reaching near 30kts. This will keep seas
up above Small Craft Advisory.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 6 PM EDT Saturday for anz235-237-
250-254>256.

&&

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

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