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Area forecast discussion 
National Weather Service Taunton Massachusetts
1006 PM EST Friday Jan 30 2015

Synopsis...
low pressure developing southeast of Nantucket late today will
intensify over the Gulf of Maine tonight bringing periods of snow
to eastern Massachusetts. Blustery and very cold conditions
beginning tonight and continuing into the weekend. Low pressure
will pass south of New England Sunday night and Monday...but
likely bringing another accumulating snowfall to the region. Cold
conditions will continue through most of next week. Yet another
low may develop around next Wednesday or Thursday with a threat for
snow...though forecast confidence is low at this time.

&&

Near term /until 6 am Saturday morning/...
10 PM update...
light snow confined to east Massachusetts this evening. Middle level trough across
new eng will close off overnight as it moves east of Cape Cod. This
will result in the comma head possibly rotating back across
portions of Cape Ann and Cape Cod with a period of somewhat
heavier snow. Latest quantitative precipitation forecast guidance suggests not more than an inch
or 2 for Cape Ann and Cape Cod with a low risk for 3 inches over
the Outer Cape. Thus...we will drop the advisory for Essex County
but keep it for Cape Cod. Elsewhere...no more than a coating to
one half inch across east Massachusetts.

The bigger weather concern tonight will be as the coastal low
over the Gulf of Maine bombs Arctic air poised over western and
northern New York into northern New England gets drawn southward into
our region. This Arctic air will combine with gusty northwest winds up to
45 miles per hour to yield bitterly cold wind chills overnight with values of
-10f to -20f across western-central Massachusetts and CT. Therefore wind
chill advisories remain posted into Sat morning. In addition given
the magnitude of the winds a Wind Advisory has been posted for the
entire coastline including Cape Cod and the islands where
downslope component should yield the highest speeds.

&&

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

Comma-head snows linger over Cape Ann and especially Cape Cod till
12z-15z. Storm total snowfall will range between 2-4" with
highest amounts across the Outer Cape. After 15z clearing trend
develops.

Big weather story for tomorrow remains bitterly cold wind chills
along with gusty northwest winds up to 50 miles per hour with highest winds over Cape
Cod and islands. Highs only in the teens but wind chills -5 to +5.
Dry conditions prevail.

Saturday night...

Winds begin to subside but still bitterly cold with mins in the
single digits for most locations away from the coast and urban
areas. Dry weather prevails.

&&

Long term /Sunday through Friday/...
*/ Saturday night through Monday night...

Highlights...

- plowable snow anticipated for Sunday night into Monday night
- impacts to travel during the Monday morning/afternoon commute
- enough confidence from consensus to go with a Winter Storm Watch
- Winter Storm Watch in effect for locales along and S of Mass-Pike

Overview...

Moderate confidence forecast.

And here we go again with a storm. Going down all the guidance ever
known. Like a drifter I am lost about this storm. So i've made up my
mind. I'm ensemble blending this time. So here we go again.

With this forecast am not going to invest in one individual stock of
forecast guidance. Will diversify with a portfolio blend of ensemble
weighted guidance...evaluating risks and potential impacts which are
outlined in the discussion below.

Neutral-tilt open-wave trough above 850 mb sweeps across S New England
Sunday night-Monday night...progressing towards a negative-tilt late
in the period. Surface low emerges from the Ohio River valley Monday
morning sweep S of New England Monday-Monday night as it intensifies
in response to the isallobaric wind enhancing the baroclinic zone in
our proximity and the trough aloft undergoing negative-tilt.

Focus is within the anticyclonic branch of the warm-conveyer-belt
/wcb/ where a baroclinic-Leaf setup is anticipated with broadscale
isentropic/deep-layer forcing beneath rrq/lfq jet coupling of upper-
level jet streaks. Convergence of the wcb along north-S slantwise ascent
against tightening isothermal packing /subsequent of the enhancement
of the baroclinic zone/ will likely yield east-west mesoscale banding out
ahead of the storm and notably within the NE-quadrant of the 850 mb low
in regions of strong frontogenesis. Neighboring -epv /potential
instability/ there is the indication as suggested by sref means of
snowfall rates of around 1 inch per hour.

Yet uncertainty...

But where exactly all these ingredients come together and where the
greatest amount of forcing lies remains suspect. Associated energy
is just coming ashore in British Columbia Canada and there is some
question as to the S-stream energy that is captured from the low
center over the SW Continental U.S. / Mexico. Lots of uncertainty given by the
latitudinal / enhancement spread of forecast guidance upstream over
the Ohio River valley. Just like the run-up to the recent blizzard
models vary in placement of best east-west banding and thermal profiles.
Subtle shifts even on the order of 5 to 10 miles will result in
significant snowfall amounts and precip-types. Evaluating Storm Prediction Center sref
plumes show graphically just that extent of spread of possibilities.

Its incredibly difficult to nail the specifics down at this time but
feel that there is enough weighting to go with a Winter Storm Watch.
Wish to better inform/alert both the public and state / local govts.
Feel messaging the threat prior to the weekend and the fact that
there is a ton of snow on the ground gives everyone time to prepare
and to act accordingly for the potential of a significant snowfall.

No two storms are alike just like no two snowflakes are alike. Yet
we can draw comparisons from analogs. Noting cips-analogs...from the
60-hour NAM-forecast and 72-hour GFS-forecast...both key upon a swath of
east-west snow across the NE-Continental U.S. With at least 60% of analogs agreeing
upon storm-total snowfalls in excess of 8-inches...and yes noting
that the mean-median east-west snowfall is north of the Mass-Pike. What is
important to take away is that it is there and the probabilities
suggest seeing snowfalls in excess of watch-warning criteria. Other-
wise along the S-fringe of the banding is the likelihood of seeing
mixing with a freezing rain potential. Perhaps some strong gusts
across the cape / islands in excess of 35 miles per hour...otherwise majority
of analogs signal no issue with winds.

Snow...

Models differ on north-S placement of east-west banding. Just too far out and
too much uncertainty to make any specific guesses. Went with a broad
spread based on ensemble means and analogs. Would venture to believe
that the heavy snow potential and highest accumulations will exist
around and S of the Mass-Pike in line with wpc-thinking. Amounts up
to a foot are possible...some of this dependent on the fluff-factor
of the snow. Snow-ratios anticipated to be higher S to north with lesser
intrusion of warmer air aloft around 800 mb. So would figure a more wet-
snow to the S...fluffier north. Can not rule out thundersnow potential
but believe the less chances in comparison to the recent blizzard.

Main take-away: travel will be impacted during both the morning and
evening commute on Monday. Motorists should be aware of adverse
weather conditions that will be changing through the event with
respect to the pace of snowfall and possible near-zero visibilities.

Precipitation-type

May also contend with a east-west mixing line in proximity to the S-shore.
Warm intrusion around 800 mb pushed north by wcb may lend to a transition of
rain/snow with perhaps a wintry mix between of freezing rain/sleet
albeit thinking very thin. Focus of the narrow band of mixing would
occur with the approach and passage of the low in proximity to S New
England during the aforementioned timeframe. Forecast guidance split
but question whether a Micro-climate and the Arctic air spilling S
will keep US all snow. Altogether...main focus for potential wintry
mix...if any...is along the immediate S-shore.

Winds...

Blustery out of the north in response to the approaching / deepening low
pressure center through the day Monday into Monday evening. Will see
strong northwest-winds in wake of the storm. Could be contending with gusts
on the order of around 20-30 miles per hour for some locations...especially for
the shores. Adding to the potential fluff-factor of the snow...that
adds to the potential of blowing and drifting which has the impact
of generating near-zero visibilities.

Take-away: at this time it appears winds will remain below wind-advection
criteria.

Coastal flooding...

Middle-morning high tides are not astronomically high and late-evening
tides are much lower. Estimating around a foot of surge in response
to the storm...low confidence at this time of any coastal flooding.

*/ Tuesday Onward...

Highlights...

- another round of snow possible Thursday-friday; low confidence

Overview...

Cold high pressure is forecast to move over New England on Tuesday
behind the departing storm with highs only forecast to make it into
the teens most locales.

Next in the series of shortwaves is shown by the global models to
move onshore the northwest Pacific coast Tuesday night. This looks to be the
next piece of energy to watch in the long term. GFS/European model (ecmwf) show
coastal low development occurring Wednesday night or Thursday /slightly delayed
from model runs yesterday/ and threatening yet another impact to
New England centered on the Thursday-Friday timeframe. Large spreads in
the models/ensembles...no surprise 6-7 days out in time. The mean
shows a weaker storm compared to the Monday one...with the latest
30.12z operational runs either a glancing blow or a complete miss.
Too soon though to lean on a hit or a miss to southern New England.
Bitter cold looks to follow in the wake of this potential late week
storm.

&&

Aviation /03z 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/...moderate confidence.

3z update...

North-S band of -sn with MVFR impacts and locally IFR confined to east Massachusetts
and especially Cape Ann and Cape Cod overnight. Prevailed
conditions in fmh / hya...tempo over bos as impacts may skirt
terminals.

VFR elsewhere. Otherwise strong northwest winds with gusts up to 40
knots...highest along the coast. May need to contend with blowing and
drifting snow impacts.

Saturday...any MVFR-IFR in snow bands over extreme east Massachusetts in the
morning will improve to VFR by afternoon. Elsewhere VFR prevails.
Strong northwest winds with gust up to 45 knots over Cape Cod...25-35 knots
elsewhere.

Sat night...VFR along with diminishing winds.

Kbos taf...moderate confidence. Potential for MVFR snow bands
into early morning Saturday. Have gone with a tempo for the
potential.

Kbdl taf...high confidence. VFR.

Outlook /Sunday through Tuesday/...

Sunday...high confidence.

VFR. Northwest winds gusting to 25-35 knots Saturday...highest along the
coast. Lighter winds Sunday.

Sunday night into Monday night...moderate confidence.

Deteriorating conditions to IFR-vlifr with snow. Blustery north-winds
with gusts up to around 30 kts. Conditions improve late as winds
back northwest.

Tuesday...moderate confidence. Mainly VFR. May see gusty northwest winds
early.

Wednesday...moderate confidence. VFR.

&&

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.

630 PM update...no major changes to the forecast.

Tonight...gale center develops over Georges Bank and then into Gulf
of Maine. Northwest gales develop all waters along with moderate freezing
spray near shore. Snow showers later tonight will limit visibility eastern
Massachusetts waters.

Saturday...gale center lifts into the Maritimes with northwest gales
continuing over the Massachusetts and Rhode Island waters. Moderate freezing spray
likely. Snow showers reduce visibility over eastern Massachusetts waters in the
morning.

Saturday night...gale center pulls farther away with winds finally
becoming sub-gale over Massachusetts and Rhode Island waters. Visibility improves with snow
showers well offshore.

Outlook /Sunday through Tuesday/...

Sunday...moderate confidence.

Expect winds and seas remain at small craft levels. Light
freezing spray likely.

Sunday night into Monday night...moderate confidence.

Area of low pressure sweeping west-east across the S-waters. Will see
winds out of the north increase to gale-force. Waves increasing 10-12
feet on the S/southeast waters as the storm intensifies to the east and winds
back out of the northwest late in the period.

Tuesday...moderate confidence.

Northwest winds relax around departing storm with seas subsiding...
though still forecast to remain at Small Craft Advisory levels.

Wednesday....moderate confidence.

Winds forecast to turn SW and pick up with seas into Small Craft
Advisory levels again. Few snow showers possible.

&&

Box watches/warnings/advisories...
CT...Winter Storm Watch from Sunday evening through late Monday
night for ctz002>004.
Wind Chill Advisory from 1 am to 9 am EST Saturday for ctz002-
003.
Massachusetts...Wind Advisory from 1 am to 9 PM EST Saturday for maz022>024.
Wind Advisory from 1 am to 6 PM EST Saturday for maz007-015-
016-019>021.
Winter Storm Watch from Sunday evening through late Monday
night for maz009-011>013-015>022.
Wind Chill Advisory from 1 am to 9 am EST Saturday for maz003-
004-010-011.
Wind Chill Advisory until 11 am EST Saturday for maz002-008-
009.
Winter Weather Advisory until 10 am EST Saturday for maz022.
Rhode Island...Wind Advisory from 1 am to 9 PM EST Saturday for riz008.
Wind Advisory from 1 am to 6 PM EST Saturday for riz005>007.
Winter Storm Watch from Sunday evening through late Monday
night for riz001>007.
Marine...freezing spray advisory until 6 PM EST Saturday for anz231>235-
237-250-251.
Gale Warning until 6 PM EST Saturday for anz232-250-254-255.
Gale Warning until 6 PM EST Saturday for anz230-231-233-234-
251.
Gale Warning from 1 am to 1 PM EST Saturday for anz236.
Gale Warning until 6 PM EST Saturday for anz235-237-256.

&&

$$
Synopsis...nocera/sipprell/gregoria
near term...kjc/nocera
short term...nocera
long term...sipprell
aviation...nocera/sipprell/gregoria
marine...nocera/sipprell/gregoria

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