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Area forecast discussion 
National Weather Service Taunton Massachusetts
341 am EST Monday Jan 26 2015

Synopsis...
a historic winter storm will affect the region tonight into
Tuesday night...travel may become impossible and life threatening.
Drier weather follows Wednesday afternoon into early Thursday...but
low pressure will bring another chance for snow Thursday night and
Friday. Very cold air likely follows for next weekend.

&&

Near term /until 6 PM this evening/...
modest and cold high pressure settles across qc and northern New England
today. With drier and colder air gradually pulling north. However...it
is thanks to this block...and the colder air in place than there
was with the weekend storm...that will allow low pressure...newly
developing off the Virginia/NC coastline to rapidly deepen and slow as
it approaches the benchmark by this evening.

Although light echos are already apparent S of Li this
morning...the dry air in place where dewpoint depressions of 10-15f
will likely keep much of the initial echos from reaching the
surface...locking the colder air in place...and holding off snowfall
until mainly the afternoon and early evening hours. Quantitative precipitation forecast is light
during this time...so any accumulations should generally be a
couple inches or less.

The only caveat though...is the potential for slightly heavier
snows along and near the East Coast of Massachusetts. This will be the result of
ocean effect snowfalls...developing off of the cold Gulf of Maine
as winds shift to the NE. This may enhance snowfall rates during
the earlier commute ahead of the impending storm...so areas in the
bos metropolitan and north and S shores will need to be watched through the
morning as mesoscale guidance shows these snow showers developing
not long after sunrise.

&&

Short term /6 PM this evening through Wednesday/...

*** potentially historic winter storm ramps up tonight ***

* blizzard conditions expected
* up to 2 feet of snow for many areas with higher amounts possible
* damaging winds likely coast especially cape/islands...gusts 60 to 75 miles per hour
* pockets of major coastal flooding possible along the eastern Massachusetts
coast

Overview...
confidence remains high for a historical blizzard impacting
southern New England beginning late in the day today.
However...that does not mean there are not some mesoscale
differences which will need to be monitored as we approaches. At
issue at this point...are differences in the final low pressure depth
prior to the occlusion process ranging from 978 hpa on the NAM/CMC
to 984 on the GFS. At odds also...is the likelihood of two
distinct banded snow features...the first...a long and significant
deformation/f-gen band stretching from coastal main into interior
southern New England...the tip of which could range anywhere from the
CT valley to metropolitan-west and the Merrimack valley. Available WRF
outputs are in disagreement here...with the nmm further west with
the heavier banding...while the arw is suggesting the east. The other
area will likely be form central Rhode Island through about the S shore/bos
metropolitan of mass as a coastal front develops and wavers inland. So it
is likely that there will actually be two bullseyes of snow
totals to watch...where storm total snowfall is likely to exceed 2
feet. Finally...this banding location will likely be dependent on
final track...which are still in some mesoscale-scale dispute with the
GFS remaining more progressive and outside the 40/70 benchmark
while the ecwmf/NAM are just inside and much slower...stalling the
low pressure only about 50 nm southeast of ack. Therefore...the banding and
axis of 2.5-3.0 inch total quantitative precipitation forecast amounts are likely to waver a
bit...and will need to be updated as the event is unfolding. Will
try to show this two-bullseye snowfall somewhat with this
update...but given that this will be high impact storm across all
of southern New England wholesale changes will note be made.

Details/impacts...

Precipitation type...
models continue to indicate the chance of a changeover to rain
briefly especially for ack...with the h92 0c line inching close
/but staying mainly S with the 00z runs/. NAM is coldest while
European model (ecmwf) remains the coldest of the operational models. Given the
slight cooling shift of recent runs and examining BUFKIT profiles
and based on impact potential...will be upgrading ack to a Winter
Storm Watch this this update...as initial snow...followed by back
end after the potential changeover...could still exceed warning
criteria.

Total snowfall/blizzard...
as mentioned above..we are already noting some potential for
ocean effect snow showers to be potentially impacting portions of
the north and S shores /bos metropolitan also/ around the time of afternoon
rush. Given the storm prep...it/S possible more could be on the
Road. Therefore...may actually see some modest accumulations
before the main precipitation shield moves up from the SW between 18z and
00z. By 00z it should be snowing...although lightly to start
pretty much across all of southern New England with any totals likely
falling below an inch or two.

As stated there is the likelihood of two banding locations...one
from typical middle-level deformation and negative epv...with the other
closer to the surface in vicinity of of the coastal front across Rhode Island-southeast Massachusetts or
near the I-95 corridor. While nailing these down is difficult
almost 24 hours out...mesoscale models do at the very least
indicate that within either of these bands...dendritic growth will
likely be near a maximum and with bands of very negative epv...2-3
in/hour snowfall amounts within either of these bands are likely
beginning late tonight...and continuing well into the day on Tuesday
as these bands slowly pivot and begin a slow shift to the east. Given
the slow movement...this also suggests that some areas could see
snowfall amounts of about a foot in 6 hours or even less.

Therefore...feel the mention of 2+ feet of total snowfall across
interior to east Massachusetts/Rhode Island and even northern CT is possible...with a few
spots approaching 3 feet not out of the question. Regarding the
blizzards...BUFKIT mixing profiles still support winds near blizz
criteria along with this potentially heavy snow bands within the
current blizzard warnings...so not planning on making any
adjustments at this time.

With the chance for lower snow ratios nearer to the coastal front
locations...colocated with the stronger winds...will have to watch
portions of southeast Massachusetts /particularly near the coast/ for the higher
likelihood of damage/power outages. Higher ratios further inland
/colder air/ are expected.

It appears ocean enhancement will likely delay the end time
especially for portions of the S shore...southeast Massachusetts and east Rhode Island late Tuesday
into Wednesday...which may snow until after noon on Wednesday. However...by
Tuesday night...expect slowly diminishing snowfall rates from west to east.

Winds...
GFS has backed down a bit on the low level jet...now supporting 65 knots at
h92 from southern Rhode Island through bos and points southeast. However...NAM/ECMWF
continue lean closer to 70-80 knots. BUFKIT mixing profiles support
at least 75-80 percent of this momentum being mixed especially
closer to the coastlines. Therefore...can still support wind gusts
approaching hurricane velocity near the shore...particularly the
outer arm of Cape Cod and Nantucket although this tapers
inland...still could see some wind gusts 50-60 miles per hour as far inland
as Rhode Island and the I-95 corridor. As mentioned above...where this
coincides with lower ratio /more water laden/ snow...could produce
more tree damage and therefore potentially more power outages.

Coastal flooding...
for more on this...please see the coastal flooding section below.

&&

Long term /Wednesday night through Sunday/...
lingering snow showers should come to an end Wednesday morning across most
of eastern New England as powerful low pressure lifts into the
Canadian Maritimes. A few ocean effect snow showers may linger into
the afternoon or perhaps early evening across the cape and islands.
Otherwise...partial sunshine develops as the day wears on across the
region. It will remain cold and breezy with highs mainly in the 20s.
High pressure builds in Wednesday night and with deep snow pack in
place/diminishing wind some outlying locations should fall below
zero.

Another low pressure quickly moves in from the west Thursday night and
Friday. This system won't compare to what we will see over the next 48
hours...but shortwave looks fairly impressive. If the energy ends
up going north of US will just have a round of snow showers. A
track to our south would result in accumulating snow. It remains
uncertain at this time but something will have to watch.

Behind that system a shot of very cold air will follow for next
weekend with well below normal temperatures.

&&

Aviation /08z Monday through Friday/...
forecaster confidence levels...

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

Short term...through Tuesday night...

Through 21z today...high confidence in trends...lower confidence
in timing.
VFR remains through about 15z this morning...at which point a slow
dip with MVFR ceilings are expected to move in from the S. Snows
mainly hold off until about 18-21z...but will be light to start.

Tonight into Tuesday night...high confidence.
Significant storm is expected. Conditions overnight tonight begin
to dip from MVFR to vlifr with the likelihood of airports reaching
minimums during the early morning Tuesday. This will be the result of
heavy-blowing snow with the possibility of some airports seeing
2-3 inch or more per hour snowfall rates. This will be associated
with very strong winds...40-50 miles per hour inland at times...with the
potential for 70-80 miles per hour winds especially near Cape Cod and the
islands. Aside from this...low level wind shear is likely as winds at 2kft are
likely to reach 70-80 knots.

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 Friday/...

Wednesday...moderate to high confidence. Conditions improve to VFR
from west to east...although MVFR ceilings may linger cape/islands.
Northwest wind gusts to 25 knots.

Thursday and Friday...moderate confidence. Another round of MVFR-
IFR conditions in some snow sometime Thursday night and/or Friday.

&&

Marine...
forecaster confidence levels...

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

Short term /through Tuesday night/...high confidence.

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

A rapidly strengthening low pressure system will move up the
coast...slowing near southeast New England through tomorrow. This
will generate wind gusts of 55-65 knots out of the NE. Expect seas to
approach 30 feet over the east waters as well. Hurricane force wind
warnings continue for the open waters...with storm warnings closer
to the shore. It is encouraged that mariners return to port by
this afternoon.

Conditions improve somewhat Tuesday night into Wednesday...although a period
of gales are possible until conditions drop down to Small Craft
Advisory thresholds.

Outlook /Wednesday through Friday/...

Wednesday...moderate to high confidence. Any left over gale force
northwest wind gusts early in the morning will quickly diminish to
small craft levels. Seas will continue to lower but still remain
well above small craft thresholds across the eastern waters.

Thursday and Friday...moderate confidence. High pressure nearby
will keep winds/seas below small craft thresholds Thursday into early
Friday. Depending on the track of an approaching low pressure see
Small Craft Advisory conditions develop later Friday or Friday night.



&&

Tides/coastal flooding...
*** a period of hurricane force wind gusts possible Tuesday am ***

Significant coastal flooding is expected during the early Tuesday
morning high tide along the Massachusetts East Coast. High tide
occurs between 4 and 6 am along most of the coastline. In Boston
high tide is at 430 am. We will continue with the coastal Flood
Warning for the Tuesday am high tide and have kept the watch in
place for the Tuesday late afternoon high tide.

For the Tuesday am high tide...anticipate the storm surge to be 3 to
3.5 feet and still rising to possibly 3.5 to 4 feet by the time of
the later Tuesday morning low tide. By the Tuesday early am high
tide...anticipate seas to have built to between 20 and 25 feet just
offshore...highest east of Cape Cod and Nantucket. NE surface winds
anticipated to be gusting between 50 and 60 knots by the time of the
early Tuesday am high tide. These seas will be high to splash over
seas walls for overwash to be an issue in those places typically
prone to it. Severe beach erosion is likely in a few spots given the
elevated water levels...wave runup and strong wave action. This is a
storm that could produce one or more new inlets along exposed east
and northeast facing barrier beaches.

The Tuesday late afternoon high tide is about a foot lower
astronomically but the surge could be about the same or slightly
higher than at the Tuesday am high tide. Also seas could be still 25
to 30 feet just offshore at the time of the Tuesday late afternoon
high tide.

We will have to watch closely the exact timing of the strongest
winds /gusts to 70 knots possible!/ And surge...which appear to occur
around the time of low tide late Tuesday morning into midday. Given the
time difference between low tide and high tide is only 6 hours there
isn/T much margin for error here. If the strongest winds and surge
coincide with one of these high tides major coastal flooding would
occur.

&&

Box watches/warnings/advisories...
CT...Blizzard Warning from 7 PM this evening to 1 am EST Wednesday
for ctz002>004.
Massachusetts...Blizzard Warning from 7 PM this evening to 1 am EST Wednesday
for maz005>007-012>021.
Coastal Flood Warning from 3 am to 7 am EST Tuesday for maz007-
015-016-019-022>024.
Coastal Flood Watch from Tuesday afternoon through Tuesday
evening for maz007-015-016-019-022-024.
Winter Storm Warning from 7 PM this evening to 1 am EST
Wednesday for maz002>004-008>011-024-026.
High Wind Warning from 7 PM this evening to 1 am EST Wednesday
for maz024.
Blizzard Warning from 7 PM this evening to noon EST Tuesday
for maz022-023.
Rhode Island...Blizzard Warning from 7 PM this evening to 1 am EST Wednesday
for riz001>008.
Marine...hurricane force wind warning from 7 PM this evening to 7 PM
EST Tuesday for anz231>235.
Storm Warning from 11 PM this evening to 7 PM EST Tuesday for
anz230-236.
Storm Warning from 7 PM this evening to 7 PM EST Tuesday for
anz237-251.
Hurricane force wind warning from 1 am to noon EST Tuesday for
anz250-254>256.

&&

$$
Synopsis...Frank/doody
near term...doody
short term...doody
long term...Frank
aviation...Frank/doody
marine...Frank/doody
tides/coastal flooding...fn

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