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Area forecast discussion 
National Weather Service Taunton Massachusetts
210 PM EST Tuesday Jan 27 2015

Synopsis...

A crippling and historic winter storm/blizzard will gradually loosen
its grip on eastern New England this evening. Drier weather follows
Wednesday afternoon into early Thursday. Low pressure will bring
another chance for snow Thursday night and Friday. Dry but very cold
air looks to follow for next weekend.

&&

Near term /through tonight/...
highlights...

* blizzard continues across eastern Massachusetts/Rhode Island this afternoon with
gradual improvement tonight

* snow diminishing across western Massachusetts/northern CT this afternoon but
some blowing and drifting snow continues

* destructive winds continue on the cape/Nantucket through the
afternoon with winds gradually diminishing tonight

1235 PM update...

Just lighter snowfall remained across northern CT and western Massachusetts at
around noon. Therefore...have downgraded northern CT to a Winter
Storm Warning. Any additional snow accumulations in this region
should be light with it all pretty much over by early this evening.
However...gusts between 25 and 35 miles per hour will result in blowing and
drifting snow and poor visibilities at times.

Meanwhile...1 to 2 inch per hour snowfall rates continue across
eastern MA/RI. This a result of well developed storm and a good middle
level deformation zone. Moderate to heavy snow will continue in
this region for another few hours...before tapering to lighter
snowfall by early evening. Blowing and drifting snow will continue
to result in blizzard conditions and near zero visibility through the
afternoon. Gradual improvement occurs this evening and especially
tonight.

Conditions across the cape and islands are life threatening.
Northerly wind gusts between 55 and 70 miles per hour with heavy snow and
near zero visibility continue to affect the region. Snow will
diminish some in intensity by late afternoon/early evening...but
blowing and drifting snow will continue right through tonight.
Winds will remain powerful with strong northerly low level jet
through the afternoon...so it will take until this evening to
diminish some although they will remain strong.

Tonight...
as middle level low lifts north from east of Cape Cod...expect snow
to gradually wind down and end from west to east. Some minor
additional accumulate possible. Otherwise very cold with lows down
into the single numbers...except teens immediate coast. Expect
subzero wind chills developing and approaching wind chill
threshold of -15 over the higher terrain in western and northern
Massachusetts.

&&

Short term /Wednesday through Thursday/...
Wednesday...
expect coastal storm to drift NE through the Gulf of Maine across
Nova Scotia during the day. Last of light snow will push off the
coast Wednesday morning...with improving conditions. However...will
still see blustery northwest winds behind the departing low along the
coast as tight pressure gradient lingers through midday before
diminishing. Brief shot of cold air moves across with 850 mb temperatures
down to -10c to -12c. This will translate to high temperatures only in
the 20s across the region...possibly only in the upper teens
across the interior higher terrain.

Wednesday night...
weak 500 mb ridge builds across along with associated north-S elongated
high pressure. As ridge axis moves across after midnight...winds will
drop off to light/variable or calm. This...along with mostly clear
skies away from the coast and the new snow pack...expect overnight
lows inland to drop to between zero and -5 across the colder
inland valleys...ranging to 5 to 10 degrees for most other areas
except holding around 20 across the Outer Cape and Nantucket.

Thursday...
progressive upper pattern brings another 500 mb short wave/clipper
surface low in this west-northwest flow. Ridge early Thursday morning will push
east as low shifts out of the Great Lakes and Ohio Valley. Will see
increasing clouds during the afternoon. Some light snow may sneak
into the east slopes of the Berkshires late in the day. Winds back to
SW...so will bring somewhat milder air to the region. Expect highs
to recover to the upper 20s to middle 30s...mildest along the S
coast.

&&

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

* clipper low may bring more measurable snow Thursday night and Friday
* much colder early next week

Overview...

Noting rather good agreement on synoptic features on the 00z
model suite into the upcoming weekend...though some questions lie
in the details. Continue to see signal for possible low pressure
moving out of the lower Mississippi Valley toward the region late
next weekend or early next week...but timing is in question. Used
a blend of available guidance along with ensembles for a consensus
forecast.

Details...

Thursday night and Friday...
expect clipper low to cross the region during this timeframe.
Noting a couple of weak 500 mb short waves which are not well
organized and surface system remains on the weak side. However...
fairly good quantitative precipitation forecast associated with the system so could see a plowable
snowfall.

Friday night through Monday...
low pressure and short wave exit the region during Friday night...though
timing the exit of the precipitation across eastern areas is still
somewhat in question. However...noting another shot of very cold
air working in as 850 mb temperatures dive to -18c to -22c by 12z Sat.
Should be dry by midday Sat but very cold.

High pressure looks to cross during Sunday...then timing issues come
into play with another possible system out of the lower
Mississippi Valley for Sun night and/or Monday. Low confidence as
uncertainty on timing and track continue.

&&

Aviation /19z Tuesday through Sunday/...
forecaster confidence levels...

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

Short term...through Tuesday night...

This afternoon and tonight...

Radar shows most of the snow is now east of the CT valley. The
heaviest snow is concentrated in eastern mass and to a lesser
extent in Rhode Island. Most ceilings and visibilities within this snow band
should be at or below 1000 feet and below 1 mile. Based on the
location of the storm center east of Nantucket...expect the snow
band will linger over eastern mass/Rhode Island through the afternoon with
an improving trend after 22z. Strong wind gusts continue in the
east with 50-60 knot gusts Cape Cod and islands. Low level wind
shear continues this afternoon on the cape and islands before
shifting offshore.

Expect ceilings and visibilities to improve west to east the first part of
tonight. Western areas remain VFR through the night while eastern
areas become VFR after midnight. MVFR ceilings may linger on Cape Cod
and Nantucket. Northwest winds will diminish with all areas under
30 knots after midnight.

Wednesday...VFR most areas. Some lingering MVFR ceilings Outer Cape
cod and Nantucket. Northwest winds continue to diminish under 20
knots.

Kbos taf...high confidence in taf trends...lower confidence in
exact timing.

Kbdl taf...high confidence in taf.

Outlook /Thursday through Saturday/...

Thursday through Friday night...moderate confidence. VFR through
most of Thursday. Another round of MVFR-IFR conditions in -sn and
patchy fog Thursday night into Friday night...then improving from west-east
after midnight. Northwest winds becoming gusty after midnight Friday.

Saturday...moderate confidence. VFR. Leftover MVFR ceilings/visibilities
across east Massachusetts early. Northwest winds with gusts up to 25-35 knots possible.

&&

Marine...
forecaster confidence levels...

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

Short term /through tonight/...high confidence.

*** Powerful storm produce life threatening conditions ***

We still have northerly wind gusts of 45-60 knots with seas near 30 feet
still affecting our eastern waters. We did convert hurricane wind
warnings over to storm force wind warnings as winds have diminished
just enough...but dangerous and life threatening conditions will
continue across the waters into the evening.

Outlook /Wednesday through Saturday/...

Wednesday...high confidence. Any leftover gale force northwest wind
gusts early in the morning will quickly diminish to Small Craft
Advisory levels...then should subside below small craft Wednesday night.
Seas will continue to subside...but will remain well above small
craft thresholds across the outer waters.

Thursday and Friday...moderate confidence. Expect winds and seas
below small craft Thursday into Thursday night. West-northwest winds increase during
Friday. Low end gale gusts possible Friday night. Seas building.
Light freezing spray likely.

Saturday...northwest gale gusts remain possible on the outer waters along
with light freezing spray. Seas remain high...possibly up to 7-9
feet on the outer waters.

&&

Tides/coastal flooding...
*** late afternoon high tide will likely produce comparable
impacts to early morning high tide in many areas except probably
higher impacts north side of Cape Cod and Nantucket ***

Forecast for late afternoon high tide is tricky when it comes to
the details. The surge should be subsiding but not fast enough
to preclude problems. The issue is how fast the surge subsides.
Believe waves will be higher than at the time of the early morning
high tide but also starting to subside. There are a couple of
other factors to consider. Some shoreline defenses may have been
compromised with the early morning high tide and thus increasing
vulnerability for at least a few spots. Also...wave periods have
increased to the 13 to 15 second range and suggest greater energy
in the breaking surf this afternoon compared with early this
morning. And there are some areas which remain inundated from the
early morning high tide with the water unable to drain...an
unsettling situation for sure.

Greatest concern is the potential impact for Cape Cod and
Nantucket. Very strong onshore winds will just be starting to
diminish as we approach the time of high tide and so think the
surge will remain near 4.5 feet along the north side of Cape Cod
and near 4 feet in Nantucket Harbor. These values are well above
those from both the etss and estofs guidance. Expect a worse
impact for the north side of Cape Cod and probably at least a
little worse for Nantucket. Beach erosion is expected to be severe
in these same areas as well as the ocean side of Cape Cod from
Truro to Chatham.

Elsewhere along the Massachusetts East Coast...anticipate
comparable coastal flood impact for the shoreline from Hull to
Plymouth with runup and overwash as big or perhaps even bigger
factor due to the large waves. We are also thinking a comparable
impact for the shoreline from Salisbury to Rockport with large
waves and erosion playing a role there as well. In contrast...the
shift in the wind to be from the north or north-northwest is expected to result in
less impact along the North Shore from Boston to Gloucester.

Looking ahead to the early Wednesday morning high tide
cycle...generally between 530 am and 630 am...anticipate pockets
of minor coastal flooding along north and northeast facing
shorelines as well as some additional erosion. Impacts for the
early Wednesday high tide will be much less than what we have
experienced or will have experienced during the high tides today.

&&

Box watches/warnings/advisories...
CT...Winter Storm Warning until 8 PM EST this evening for
ctz002>004.
Massachusetts...Blizzard Warning until 8 PM EST this evening for maz005>007-
012>023.
Coastal Flood Warning until 8 PM EST this evening for maz007-
015-016-019-022-024.
Winter Storm Warning until 8 PM EST this evening for
maz002>004-008>011-026.
High Wind Warning until 1 am EST Wednesday for maz024.
Winter Storm Warning until 1 am EST Wednesday for maz024.
Rhode Island...Blizzard Warning until 8 PM EST this evening for riz001>008.
Marine...Storm Warning until 1 am EST Wednesday for anz232-255-256.
Freezing spray advisory until 8 am EST Wednesday for
anz231>235-237-251.
Storm Warning until 10 PM EST this evening for anz231-233-234.
Gale Warning until 7 PM EST this evening for anz230-235>237.
Storm Warning until 9 PM EST this evening for anz250-254.
Storm Warning until 7 PM EST this evening for anz251.

&&

$$
Synopsis...kjc
near term...Frank/kjc
short term...evt
long term...evt
aviation...wtb/evt
marine...Frank/kjc/evt
tides/coastal flooding...Thompson

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