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Area forecast discussion 
National Weather Service Taunton Massachusetts
915 PM EST sun Feb 1 2015

Synopsis...
a major winter storm will affect the region tonight into Monday
evening with heavy snow for many locations. Bitterly cold wind
chills follow later Monday night into Tuesday morning. A cold
front swings through New England Wednesday night but may linger
close enough to affect the coast on Thursday. High pressure brings
another dose of very cold air starting Thursday night. Another
cold front moves through on Saturday.

&&

Near term /until 10 PM this evening/...
9 PM update...
leading edge of light snow still back across southeast New York and New Jersey. Hrrr
seems to have a decent handle on the onset and brings the snow
into the CT valley 10 PM-midnight reaching eastern Massachusetts 1-3 am. Snow
will be light initially but will become heavy at times 09-12z. In
fact there is a pretty strong signal for a period of heavy snow
lifting north from CT/Rhode Island and southeast Massachusetts around 12z before any changeover.
Intense 850 mb frontogenesis associated with overrunning of a very
tight thermal gradient with -epv and fairly steep middle level lapse
rates. Could see snowfall rates 2-3"/hour with isolated thunder snow.

The big challenge is timing of the changeover Monday morning as warm
air surges north and how this affects snow accumulate. Some of the
guidance is pretty quick with changeover 13-15z across CT/Rhode Island and
southeast Massachusetts but could see a decent front end thump before this. No
changes to current accumulate right now. Will reevaluate with 00z
model suite but may need to lower a bit near the South Coast.

&&

Short term /10 PM this evening through Monday night/...
highlights...

* major winter storm very late tonight into Monday evening
* heavy snowfall expected for much of the region especially during the
morning hours
* still some uncertainty for snowfall amts across Rhode Island and southeast Massachusetts due
to ptype issues

Overview...

Open wave bringing snow over Chicago and rest of the Midwest will
make its way eastward through the day and become negatively tilted
tomorrow afternoon. This wave will eventually cut-off at 700mb but
looks as if that will occur once it moves up to the Maritimes
allowing for US to miss some of the back-edge wrap around banding by
Monday night.

At the surface...low pressure will track across the lower Great
Lakes and pass across Long Island and over Nantucket tomorrow. With
Arctic high in place to the north...plenty of low level cold air in
place but warming aloft will make for a tricky snowfall forecast
near the S coast. Overall 12z model trend is to continue to nudge
the low a little farther north bringing in the potential for a 2-4c
warm layer over southeast mass and into southern Rhode Island. The 18z NAM is
just slightly cooler that the rest of the envelope with the 12z GFS
being the warmest. Trended the thicknesses with a blend of the
ec/GFS/NAM which put the forecast in the middle of the guidance
suite. The other concern is that the system is speeding up just
slightly...so have moved precipitation onset time accordingly. This is
typical in these overrunning precipitation set-ups. Overall not to many
changes from previous forecaster...just nudge everything northward
slightly and converted marine headlines to warnings.

1) timing and ptype

Snow will begin to overspread into CT and western mass between 10 PM
and 1 am then across the remainder of southern New England by 4 am.
At the onset...guidance shows very good lift within the snow growth
region and with negative epv and descent f-general looks like a good
thump of snow will occur. In fact sref guidance is hinting at
snowfall rates 2 inches per hour. Believe this could be true thanks
to the incredible thermal packing. These high snowfall rates will
last for several hours so we could see a quick 6 inches within 3 to
4 hours. This will unfortunately occur before and during the morning
commute dropping visibilities and making roads very treacherous for
commuters as plows could struggle to keep up.

Warm air will begin to work its way into southeast mass during the
middle-morning hours. Expect a mixture of sleet and freezing rain
making its way up to ijd to ply and points southward. In fact there
could be a period where most of the cape is all rain for a short
time. Have a lower confidence if rain will work up to the southeast
coastal plain due to the large snowpack on the ground...but it is
certainly possible especially if models continue to nudge the system
northward.

By late afternoon...the mixing potential begins to collapse as low
begins to retreat northeastward and cold air advection rushes into southern New England. Expect the
region to turn to all snow by 3-5 PM. This could also make the
evening commute a tad tricky as snow may limit visibilities for a time.
Snowfall rate will be less than what we are expecting for the
morning...yet could still see another inch or 2 during this time.

This is still a very tricky ptype forecast due to the strong temperature
gradient so any shift in the track could add or subtract just a few
inches.

2) snowfall accumulations and headlines

Kept with the warnings and advisories for now with this package as
did not see a reason to adjust even before the first Snowflake
begins to fall. Have high confidence that 10-14 inches of snow will
occur north of the Mass Pike where precipitation type will remain as all
snow. Lower confidence across Rhode Island and southeast mass where p-type
issues will occur...but generally think 6-10 inches are possible.
Across the cape could see amounts just shy of 6 inches but with the
onset of heavy snow in the morning believe the warning is still
justify. Have the lowest confidence for the islands especially across ack
where perhaps just 1-2 inches of snow and sleet may occur. Just
remember...that the slightest shift in the track or if surface temperatures
are just a hair off...snowfall amounts can change a couple of
inches.

3) strong winds and blowing and drifting snow

Northeast wind gusts of 30 to 40 miles per hour expected along the immediate
eastern mass coast on Monday as storm intensifies and pressure
gradient increases. This will result in poor visibility along with
blowing and drifting snow. Its possible that a few locations along
the coast could see near blizzard conditions for a very short
time...but storm doesn/T seem to warrant those type of headlines.
Everywhere else should see generally 15-25 miles per hour.

4) temperatures

A very strong coastal front will set up on Monday with temperatures in the
teens north of I-84 to I-90 corridor and west of I-495...while temperatures
will reach the lower to middle 30s southeast Massachusetts. These cooler temperatures will
create a more fluffy snow factor where as closer to the coastal
front we could see a heavy wet snow.

A flash freeze is likely across southeast coastal Massachusetts and cape/islands in
the evening as the coastal front moves through and temperatures plummet
from the 30s down to teens in the matter of just 2-3 hours. This
will ice up any wet surface outdoors. Motorist and pedestrians will
need to use caution.

Monday night...

System will exit out of the region on Monday night bringing in very
frigid air. In fact with winds decoupling...skies clearing and a
fresh snowpack on the ground we could see temperatures drop well below zero
in many locations by early Tuesday morning. This will result in wind
chills values between 15 and 25 below zero. Wind chill advisories
will likely be needed.

&&

Long term /Tuesday through Sunday/...
big picture...

Contour fields Tuesday show a flat flow across the eastern USA
with northern and southern jet streams. The next significant
system gets stitched together from three pieces: polar shortwave
diving south through western Canada...Pacific shortwave moving
ashore in British Columbia Monday...and remnants of Baja California upper low ejecting
east late Tuesday. All three phase over the eastern USA Wednesday-
Thursday with the trough axis crossing New England Thursday night.
Later...northern stream trough sweeps across eastern Canada over
the weekend. Trailing trough develops off the entrance region of
the supporting jet and approaches southern New England late Sunday
night.

Normal contour heights for Jan-Feb period are 5400-5450 meters.
Forecast contour heights are normal to slightly cooler than normal
most of the period...except much colder than normal Thursday
night through Friday night.

Good agreement among the models through 12z Thursday. Past that
there is agreement on the overall pattern but differences in the
details. We used a blend of the data.

Dailies...

Tuesday... high pressure along the East Coast will provide a dry
day. Diminishing northwest winds along the coast with over-water
speeds of 12-16 knots. These winds will combine with an air-water
temperature Delta of 18-20c to maintain ocean effect snow showers just
outside of Outer Cape cod in the morning but with a diminishing
trend along with the wind. Temperatures aloft will be equivilent to -20c
to -24c...supporting chilly maximum surface temperatures in the middle teens to lower
20s.

Wednesday... axis of high pressure shift east early Wednesday
morning with increasing moisture aloft bringing increasing clouds.
Cold front then moves east through the Great Lakes Wednesday and
across New England Wednesday night. Two jet streams in place
Wednesday actually clash Wednesday...left entrance region of the
southern jet and right exit region of the northern jet...but models
show enough moisture and isentropic lift especially across
northern mass to expect some snow Wednesday morning followed by a
break in the afternoon and then snow showers along/ahead of the
cold front Wednesday night. Coastal areas such as Cape Cod and
islands could stay warm enough to mix with or change to rain.

Thursday...cold front moves offshore about the time that the upper
trough phases and deepens. Coastal New England and the offshore
waters will be under the left exit region of the combined upper jet.
This would suggest one or more waves developing along the cold front
after it moves offshore. This would maintain a chance of snow in Rhode Island
and eastern mass during Thursday. We continued a chance of snow
showers in these areas. General snow tapers off Thursday night as
the front and its wave move farther to sea. But cold air is drawn in
with air-water Delta of 18-20c and strong gusty north-northwest
winds. So expect more ocean-effect snow bands to develop
overnight...with a fetch that favors hits on the middle and Outer Cape.
The gusty north-northwest wind will also generate sub-zero wind
chills across most of southern New England with chills of 10 to 15
below across western and central mass.

Friday through Sunday... high pressure builds in on Friday with
clear skies inland and lingering ocean effect snow over or just east
of Outer Cape cod. Eastern Canada upper trough will drive another
cold front across New England on Saturday bringing another chance of
snow showers followed by cold air. This front stalls south of New
England Sunday. Attention then turns to the trough that may develop
to our southwest over the weekend. If it does...it is positioned
correctly to form another low along the stalled front. That low
would then move up the East Coast at the end of our forecast period.
As this comes at the end of day seven...we will keep probability of precipitation just to
our south and allow the model solutions to mature.

&&

Aviation /02z Monday through Friday/...
forecaster confidence levels...

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

Short term.../through Monday/...

Tonight into Monday...high confidence in trends but lower
confidence in timing.

VFR will deteriorate to IFR-LIFR ceilings/visibilities in moderate to heavy
snow. Snow will reach bdl/baf around 04-05z...orh/pvd 06-07z and
bos 07-08z. Ceilings and visibilities deteriorate quickly after onset of the
snow.

IFR/LIFR in moderate/heavy snow continues through the day Monday. Ptype
may transition to a period of sleet/freezing rain around midday
from hfd-pvd-pym south and changing to rain over the cape/islands.
NE wind gusts to 30-35 knots developing across east coastal Massachusetts
Monday...with 25 knots across Rhode Island and remainder of east Massachusetts. Snowfall
rates will average between 1-2 inch per hour and could be as high
as 3 inches per hour. High confidence in plowable snow across all
airports north and west of the canal.

Monday night...conditions will improve to VFR from west to east
though the overnight. Low confidence on exact timing.

Kbos taf...high confidence. Lower confidence in exact timing of
IFR conditions in snow.

Kbdl taf...high confidence. Lower confidence in exact timing of
IFR conditions in snow.

Outlook /Tuesday through Friday/...

Tuesday...moderate confidence... VFR. Northwest winds gusting to 20
knots in the morning diminishing in the afternoon.

Wednesday...low confidence... MVFR or brief IFR in snow showers.
Best chance is across northern mass.

Thursday...low confidence... VFR western mass and Connecticut. MVFR
or brief IFR in lingering snow showers for eastern mass and Rhode Island.

Friday...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 Monday/...high confidence.

Tonight into Monday...moderate to high confidence.

Winds/seas will be quiet tonight but ramp up tomorrow as low
pressure intensifies near the South Coast. Gale warnings have been
issues for gales in the morning and in the evening. The main focus
for gusts to 40 kts will be across eastern Massachusetts coastal
waters...especially north of Cape Cod...with lighter winds over
the south coastal water. Seas build to 15+ feet across our eastern
waters by late Monday afternoon/evening.

Very cold air mass will drop over the waters Monday night and with
choppy seas and winds still gusting freezing spray is def
possible. Therefor have issued a freezing spray warning for all of
the waters not including Boston Harbor and Narragansett Bay.

Outlook...Tuesday through Friday...low-moderate confidence.

Tuesday... northwest winds gusting to 30 knots morning...diminishing
by afternoon. Seas start at 5-9 feet and should subside in the
afternoon. Heavy freezing spray in the morning will diminish as the
winds also diminish. Scattered snow showers east of the Outer Cape
in the morning will move out to sea by afternoon.

Wednesday...low pressure and cold front race east from the Great
Lakes. Expect less wind but also reduced visibilities in snow or rain
showers mostly in the afternoon and at night. Winds will shift to
northwest late at night as the cold front moves through. Seas start
the day below 5 feet but then increase to 5-8 feet on the outer
waters and on Rhode Island Sound by night. A Small Craft Advisory may be
needed.

Thursday...cold front moves east of the waters as winds increase
from the north and northwest. Cold air moves in behind the front and
may generate freezing spray by Thursday evening and Thursday night.
Low pressure may develop along the departing front and pass east of
the waters...but close enough to bring rain and snow...and increase
the wind to 25-30 knots. Seas of 5 to 8 feet will subside Thursday
night. A Small Craft Advisory may be needed.

Friday... north winds reaching 30 knots will diminish at night. Seas
should remain below 5 feet. Ocean effect snow showers will bring
areas of lower visibilities on the waters east of Massachusetts. A Small
Craft Advisory may be needed.

&&

Tides/coastal flooding...
*** pockets of minor coastal flooding possible during the late
Monday morning high tide cycle along Boston/S South Shore but no
major problems expected***

Seas will not really be ramped up in time for the middle to late Monday
morning high tide along the eastern Massachusetts coast. However...there may
be enough east to northeast wind to result in a 1 to 1.5 foot storm
surge. Its marginal...but may see some pockets of minor coastal
flooding mainly across Boston/S South Shore. While significant
problems are not expected...areas from Hull...to Scituate...to
Marshfield and Duxbury were hit very hard from last week/S blizzard.
Pockets of minor coastal flooding may delay some of the cleanup and
repairs on going in that region...so felt it was Worth issuing an
advisory for that region.

There is another astronomical high tide late Monday evening...but
its a foot lower and by then winds are already offshore.
Therefore...its really just the Monday morning high tide that were
concerned about and any issues from that will likely be very minor.

&&

Climate...
with extremely cold air moving in behind the departing low Monday
night...temperatures may fall back close to or surpassing record
levels early Tuesday morning. Expected high temperatures on Tuesday will
be chilly as well...but should stay above the record coldest maximum
temperatures for the date.

Here are the record lows for Tuesday 2/3...

Boston -5 set in 1881
Providence -6 set in 1961
Worcester -7 set in 1931, 1955 and 1971
Windsor Locks -3 set in 1955
Blue Hill observation -7 set in 1955

Here are the record low maximum temperatures for Tuesday 2/3...

Boston 14 set in 1917
Providence 12 set in 1917
Worcester 8 set in 1955
Windsor Locks 12 set in 1917
Blue Hill observation 9 set in 1917

&&

Box watches/warnings/advisories...
CT...Winter Storm Warning until 1 am EST Tuesday for ctz002>004.
Massachusetts...Winter Weather Advisory until 1 am EST Tuesday for maz023-024.
Winter Storm Warning until 1 am EST Tuesday for maz002>022-026.
Coastal Flood Advisory from 9 am to noon EST Monday for maz016-
019-022.
Rhode Island...Winter Weather Advisory until 1 am EST Tuesday for riz008.
Winter Storm Warning until 1 am EST Tuesday for riz001>007.
Marine...heavy freezing spray warning from 7 PM Monday to 7 am EST
Tuesday for anz231>235-237-250-251-254>256.
Gale Warning from 7 am Monday to 7 am EST Tuesday for
anz231>235-237.
Gale Warning from 7 am Monday to 1 am EST Tuesday for anz230-
236.
Gale Warning from 5 am Monday to 7 am EST Tuesday for anz250-
251-254>256.

&&

$$
Synopsis...wtb/dunten
near term...kjc/dunten
short term...dunten
long term...wtb
aviation...wtb/dunten
marine...wtb/dunten
tides/coastal flooding...
climate...

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