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

Synopsis...

The blizzard winds down this evening across eastern New England.
Other than a few ocean effect snow showers on Wednesday across the
cape and Nantucket...it will be dry and cold for the rest of the
region as the cleanup begins. Plains low pressure will bring
another chance for snow Thursday night and Friday. Dry but very
cold air looks to follow for the weekend. A third storm may
affect the region Sunday night and Monday.

&&

Near term /until 6 am Wednesday morning/...

Highlights...

* blizzard winds down this evening across eastern New England
* winds gradually diminish across the cape/islands tonight
* dry and cold Wednesday except lingering snow showers cape/Nantucket

4 PM update...

Vertically stacked system and trowel structure was allowing
deformation axis of snow to continue across eastern
MA/RI...especially Plymouth and Barnstable counties where it was
locally heavy. The powerful storm will continue to slowly lift to
the northeast...allowing bulk of accumulating snow to end across
eastern Massachusetts/Rhode Island between 6 and 8 PM...but will last a few
hours longer across the cape and islands.

Low temperatures will range from the single digits to the lower teens
across much of the region. This will result in wind chill values
between zero and 10 below zero.

Cape and islands...

As mentioned in the previous paragraph...improvement will be slowest
across the cape and islands. Northerly wind gusts between 40 and 60
miles per hour across this region will gradually diminish tonight as storm
slowly moves to the northeast. Steady snow should end across the
cape/islands by late evening...but ocean effect snow showers with
north-northwest winds will persist into the overnight hours. In addition...
considerable blowing and drifting snow will continue throughout the
night resulting in reduced visibility and hazardous travel.



&&

Short term /6 am Wednesday morning through 6 PM Wednesday/...

Wednesday...

Scattered ocean effect snow showers will remain possible across the
cape/Nantucket into the afternoon with north-northwest winds and an 850t/ocean
differential of 20c. Any additional accums will be rather light in
this region. Across the rest of the region...high pressure will
slowly build in from the west. Partial sunshine should develop from
west to east later in the morning and into the afternoon. High
temperatures will only be in the lower to middle 20s as the cleanup begin

&&

Long term /Wednesday night through Tuesday/...
big picture...
northern and southern streams will push shortwaves across the USA.
One northern stream shortwave entered the Pacific northwest today
and will reach New England Thursday night/Friday. A southern
stream shortwave from California may merge with it Wednesday or
Thursday. Another pair of shortwaves dig over the plains over the
weekend and approach the East Coast Sunday night/Monday.

The various models are similar in the broad portrait of weather
systems these next seven days but differ on details such as
timing. We opted for a blend of model data for this forecast.

The dailies...

Wednesday night-Thursday...high confidence
high pressure moves across the region and should provide a period
of clear skies and light winds. Dew points will be in the single
numbers below zero which should allow the colder locations to a
similar range overnight. If there are potential problems in the
forecast...it would be that mins may be 2-4f too warm in the
normal cold spots of the east if they radiate more effectively.

The high will shift offshore Thursday but still provide plenty of
dry air for New England. As it shifts offshore...a southwest flow
aloft will bring in increasing moisture aloft and thus increasing
middle and high clouds. Any precipitation should hold off until after dark.

Thursday night-Friday...low-moderate confidence
clipper and supporting shortwave race east to the Great Lakes
Thursday and then redevelop along the New England coast. The GFS
has the redevelopment in the Gulf of Maine while the European model (ecmwf) and
ggem show this closer to 40n/70w. The southern solution is closer
to the dynamically favored left exit region of the upper jet...and
may result in more precipitation if it occurs. Temperature profiles favor
snow although some warm intrusion may warm the cape/islands into
the upper 30s and provide a brief change to rain. This will need
to be monitored. The differences in model placement of the surface
low lead to the reduced confidence in this part of the forecast.

Surface pressure falls as the storm deepens offshore. This will
tighten the pressure gradient and bring increasing northwest winds
on the trailing side of the storm. Cold air then gets drawn in
across New England Friday. Temperatures aloft will support maximum temperatures in
the 30s during the morning-midday and 20s by sunset.

Friday night-Saturday-Sunday...
strong winds trailing the storm bring incoming cold air with
airmass temperatures reaching the single numbers. This will bring wind
chills below zero. Northern and western wind chills should go
below 10 below zero and may require a Wind Chill Advisory.

High pressure builds over the region on Saturday with dry weather
and gusty northwest winds. Temperatures at 925 mb will be -13c to
-17c...so maximum temperatures Saturday will be challenged to reach the 20s
most places...best chance will be in Rhode Island and southeast mass.

The high moves offshore on Sunday...again creating increasing
moisture aloft while dry near the surface. This will mean
increasing clouds during the day with temperatures a little less cold
than on Saturday.

Sunday night-Monday...
next pair of shortwaves approach. The southern stream shortwave
generates an inverted trough in the western Gulf/Mississippi
Valley region. The northern shortwave helps generate low pressure
in this trough and swings it northeast toward New England. All
move precipitation into New England and consensus keeps temperatures cold enough
for snow. But differences in track ranging from across the
Berkshires /ECMWF/ to across the 40n/70w benchmark /ggem/. And
this is a day 5 forecast. So confidence remains low.

Tuesday...
high pressure builds over the region with 925 mb temperatures again
falling to around -15 to -17c. Another chilly dry weather day.

&&

Aviation /21z 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 /Wednesday night through Sunday/...low to moderate
confidence.

Wednesday night-Thursday...VFR with light northwest wind becoming
light south on Thursday.

Thursday night-Friday...ceilings lower to MVFR with MVFR-IFR visibilities in
snow. Conditions improve to VFR Friday afternoon. Winds also shift
to northwest with gusts of at least 25 knots.

Saturday-Sunday...VFR. Gusty northwest winds 25-30 knots
Saturday...lighter winds Sunday.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday/...high confidence.

***Gradual improvement tonight but conditions will remain dangerous
for mariners until wednesday***

Powerful storm slowly pulls away from the region and finally lifts
into the Canadian Maritimes on Wednesday. Storm force wind gusts
continue for the first part of the night...but should see things
lower to gales near midnight. Gales then lower to Small Craft Advisory headlines Wednesday
morning as pressure gradient slowly weakens. 25 to 30 foot seas
across the the eastern waters will gradually diminish tonight and
finally drop below 10 feet sometime Wednesday afternoon.

Outlook /Wednesday night through Sunday/...moderate confidence.

Wednesday night-Thursday...

Diminishing northwest winds through the night. Could be some 25
knot gusts in the evening but otherwise winds should be less than
that threshold. Lingering 5 to 7 foot seas on Massachusetts Bay
and the outer waters will diminish overnight. Conditions remain
below small craft thresholds on Thursday.

Friday...
cold front moves through with areas of reduced visibility in snow.
Once the front moves across the waters...winds shift to northwest
and increase to 30-35 knots. This is close enough to the gale
threshold so that low-end gales are a possibility. This will be
monitored.

Seas will also increase to 5 to 8 feet on the exposed waters. The
northwest winds will bring in plenty of cold air. This will cause
ocean effect snow showers off Outer Cape cod...and freezing spray
will again develop Friday night.

Saturday...northwest gales expected with potential for a light freezing
spray. Seas remain high...possibly up to 7-9 feet on the exposed
waters.

Sunday...winds and seas at Small Craft Advisory levels but
diminishing through the day.

&&

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 10 PM EST this evening for anz231>234-250-
254-255.
Freezing spray advisory until 8 am EST Wednesday for
anz231>235-237-251.
Small Craft Advisory until 7 PM EST Wednesday for anz230-236.
Gale Warning until 1 am EST Wednesday for anz235-237-251-256.

&&

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

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