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Area forecast discussion 
National Weather Service Taunton Massachusetts
434 am EST Tuesday Jan 27 2015

Synopsis...
a crippling and historic winter storm / blizzard will impact the
region into tonight. 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...

* crippling and potentially historic blizzard with 1 to 2 feet of
snow...locally higher amounts
* strong to damaging winds / hurricane force across southeast New England
* moderate to major coastal flooding / severe beach erosion

WV loop shows deepening middle level low south of Long Island with
well defined comma head with warm conveyor belt/trowal lifting northward
into new eng. Rapid cyclogenesis in progress with surface low down to
984 mb. There are subtle differences in the track...but general
agreement of a track close to the benchmark as a sub 980 mb
storm around 12z. Only slow movement north during today as the
low gets captured by the upper level system which will prolong
occasional heavy snow through today.

Snowfall / banding / blizzard...
very intense mesoscale band setting up across north CT through
central/NE Massachusetts associated with the strengthening middle level
frontogenesis with the deepening middle level low producing strong
Omega through the dendritic growth zone. Probably seeing 2-4"/hour
snowfall rates in this band. Meanwhile...pulses of heavier snow
bands which are convective in nature continue to move from the
ocean across southeast Massachusetts. Very heavy cluster over the islands will be
moving up across southeast Massachusetts next 1-2 hours. Middle level lapse rates over
6 c/km across southeast new eng suggesting potential for upright
convection and thunder snow. Snowfall rates 2-3"/hour will be
developing in southeast Massachusetts and portions of Cape Cod.

How these bands evolve today will be critical to the snowfall
forecast and this will be tricky. GFS/European model (ecmwf) keep the best middle
level frontogenesis across east Massachusetts while NAM is further west across
central Massachusetts into CT. NAM seems to be handling this the best and
keep this band in the same general area before weakening and
moving east. Meanwhile...low level convergence and frontogenesis
associated with the coastal front across southeast Massachusetts will result in a
secondary maximum in eastern Massachusetts including Cape Cod with occasional
heavy snow.

We have only made slight modifications to the snow accumulate...
lowering slightly in the Berkshires and increasing across Cape
Cod...especially near the canal. Still looking for maximum snowfall
across NE CT through central Massachusetts...with secondary maximum across east Massachusetts
to the Cape Cod canal. Around 2 feet expected in this area...locally
30-36 inches possible where persistent bands set up. Lesser
amounts in between bands.

Combination of heavy snow and strong wind will result in blizzard
conditions...especially across eastern half new eng with
considerable blowing and drifting. In addition...wind chills will
be down into the single numbers above and below zero adding to the
severity and life threatening aspect of the storm. Travel will be
nearly impossible.

Wind...
core of strongest winds will be occurring through about 18z for
the cape/islands to coastal southeast Massachusetts as low pressure deepens near the
benchmark. Low level jet around 75 kts persists in this region.
Soundings show potential for near hurricane force gusts to 75 miles per hour
in this region...with gusts to 50-60 back to the I-95 corridor and
30-40 further in the interior. Expect wind damage and widespread
power outages across portions of southeast Massachusetts and especially the
cape/islands where heavy wet snow will add to Load.

Temperatures...
coastal front currently across southeast Massachusetts with temperatures in the teens west
of the front and 20s to lower 30s to the east. Expect temperatures to
remain in the teens to near 20 today for most of the region...and
eventually falling into the teens and lower 20s southeast coastal Massachusetts this
afternoon as the coastal front moves through.

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 /09z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term...through Tuesday night...

Tonight...
significant snowstorm is moving into the region. Heavy snow will
move up after midnight with 1-3 inch per hour rates...and local 4
inch per hour rates possible. North northeast surface winds will
increase through the night with gusts 30-40 knots in the CT valley
and central mass...40-50 knots in the bos-pvd coastal plain
area...and 50-70 knots cape/islands/South Coast. Even stronger
winds aloft move in at 2000 feet above ground level leading to low level wind
shear.

Tuesday and Tuesday night...
significant snowstorm continues through the period with snowfall
rates of 1-3 inches per hour. Isolated thunder possible. Most
airports are expected to be at or below minimums during this
period with LIFR/vlifr conditions. Very strong wind continue with
gusts 70-80 knots cape and islands and parts of southeast mass.
Low level wind shear continues through Tuesday and diminishes
Tuesday night.

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

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

Outlook /Wednesday through Saturday/...

Wednesday...high confidence in trends...moderate confidence in
timing. Conditions improve to VFR from west to east...although MVFR
ceilings may linger across Cape Cod and the islands through midday or
early afternoon. Northwest wind gusts to 20-25 knots through
midday along the coast.

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 ***

Expect NE wind gusts of 55-65 knots with seas 30-35 feet over the east
waters as well. Hurricane force wind warnings continue for the
open waters...with storm warnings closer to the shore.

Conditions improve somewhat later today into tonight...although a
period of gales are possible until conditions drop down to Small
Craft Advisory thresholds.

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...
*** moderate to major coastal flooding today along the eastern Massachusetts
coast for both this morning and late afternoon high tide cycles ***

Powerful winter storm developing near the 40n/70w benchmark and
combining with Arctic high pressure over southeast Quebec to yield
hurricane force wind gusts this morning and into midday across
Nantucket...Cape Cod and coastal Plymouth County. Tide gauges along
the eastern Massachusetts coastline at 3 am indicating storm surge values
already 2.5 to 3.0 ft! This will yield moderate to major coastal
flooding with this morning/S high tide cycle. The highest impact
areas will likely be Nantucket/Cape Cod Bay communities and
northward along the coast into Plymouth County including the
communities of Hull/Marshfield and Scituate.

Coastal flooding will occur farther northward into Cape Ann however
the magnitude of the flooding should be slightly less than the South
Shore.

These high water levels will result in significant inundation of sea
water. Structural damage is likely as well given seas offshore have
already climbed to 18 to 22 feet and will only continue to increase.
Could see offshore seas 25 to 35 feet this afternoon! This will result
large waves battering seawalls and other shoreline structures. In
addition the high water levels will combine with the large wave
action to yield severe beach erosion.

As for the late afternoon high Tide...Water levels may be about a
half a foot lower however seas will be at least as large as this
morning or possible a few feet higher. Thus impacts will be similar
however the focus will shift to coastal Plymouth County southward to
Cape Cod Bay communities such as Sandwich Harbor. Thus less impact
for Nantucket than this morning. Nevertheless at least moderate
coastal flooding expected for Nantucket.

So in a nutshell...no changes to any headlines with coastal flood
warnings remaining in place for the next two tide cycles.

As for Rhode Island...the risk for minor coastal flooding has commenced with
high tide already occurring. Therefore the risk has diminished and
the advisory will be allowed to expire.

&&

Box watches/warnings/advisories...
CT...Blizzard Warning until 1 am EST Wednesday for ctz002>004.
Massachusetts...Blizzard Warning until 1 am EST Wednesday for maz005>007-
012>021.
Coastal Flood Warning until 7 am EST this morning for maz007-
015-016-019-022>024.
Coastal Flood Warning from 3 PM this afternoon to 7 PM EST
this evening for maz007-015-016-019-022-024.
Winter Storm Warning until 1 am EST Wednesday for maz002>004-
008>011-024-026.
High Wind Warning until 1 am EST Wednesday for maz024.
Blizzard Warning until noon EST today for maz022-023.
Rhode Island...Blizzard Warning until 1 am EST Wednesday for riz001>008.
Marine...hurricane force wind warning until 7 PM EST this evening for
anz231>235.
Freezing spray advisory until 8 am EST Wednesday for
anz231>235-237-251.
Storm Warning until 7 PM EST this evening for anz230-236-237-
251.
Hurricane force wind warning until noon EST today for anz250-
254>256.

&&

$$
Synopsis...kjc
near term...kjc
short term...evt
long term...evt
aviation...evt
marine...kjc/evt
tides/coastal flooding...nocera

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