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Area forecast discussion 
National Weather Service Taunton Massachusetts
1059 PM EDT Friday Oct 31 2014

Synopsis...
an intensifying coastal storm will move up the coast Saturday and
pass offshore Saturday night and early Sunday potentially bringing
damaging winds and rain to the region. High pressure builds over
the eastern USA early next week. One or two cold fronts may cross
southern New England Wednesday through Friday.

&&

Near term /until 6 am Saturday morning/...
1040 PM update...
bands of light rain and showers continue to fan across CT into west
Rhode Island at 02z. Main band of rain remains just off the Outer Cape and
Nantucket coast. Have adjusted the pop forecast just a bit to
indicate a few more breaks through 06z-07z due to wide temperature/dewpt
spreads continuing across the middle and lower CT valley...then
should become steadier as dewpoints begin to rise as the lower levels
become more saturated.

Looking at radar trends down the coast...looks like steadier rain
trying to develop east of the middle Atlantic coast while spotty showers
continue to develop off the New Jersey coast to Long Island. This appears
to be on track from the previous forecast...and should continue to
see this fill in overnight.

Have adjusted forecast to bring current to current trends.

Previous discussion...
strong high pressure in the Great Lakes will combine with low
pressure moving northeast towards southern New England to result in
winds continuing to increase overnight. Northeasterly winds will
pick up to around 15 miles per hour by early Saturday morning. With the
increasing onshore flow...expect temperatures not to fall...though will
lower a few more degrees through daybreak.

&&

Short term /6 am Saturday morning through Sunday/...
***strong to damaging winds are likely with an intensifying coastal
storm Saturday night and sunday***

31/12z models are in fairly good agreement on an intensifying low
pressure system moving up the coast from North Carolina and passing
just outside the 40/70 benchmark Saturday night. This is associated
with a digging trough moving eastward from the Great Lakes and a
couple of shortwaves rotating around the east side of the trough.
This combined with a strong high pressure system that will move from
the northern plains into the Great Lakes region will result in a
tight pressure gradient across southern New England.

Wind: this is a fairly high confidence forecast for wind. The tight
pressure gradient...along with a northeasterly 50 knots low level jet
bringing much colder air over the relatively warm ocean waters will
result in strong to damaging wind gusts across much of southern New
England Saturday night into Sunday. The colder air will allow lapse
rates to steepen and winds to easily mix down to the surface.

The most likely location for wind gusts to reach 58 miles per hour or greater
is across coastal Plymouth County...the cape...and islands where we
have issued a High Wind Warning. Expect that much of eastern
Massachusetts and Rhode Island will likely have winds gusting to at
least 50 miles per hour and that with partially to fully leaved trees... damage
may be done to trees and power lines. Have kept the high wind watch
up for these areas and allow the next shift to evaluate another
round of model data before deciding how to upgrade. The wind in
these areas is expected to pick up Saturday evening and continue
through much of Sunday.

Across the remainder of southern New England /Connecticut...southern
New Hampshire...and western and central Massachusetts/ expect wind
gusts to reach up to 45 miles per hour. However...rather than being associated
with the low level jet...these winds will be more a result of strong
cold advection into the region on Sunday. Wind advisories will
likely be needed for these areas but given that winds are not expected
to increase until Sunday...felt we could wait for another model
run.

Coastal flooding: please see tides/coastal flooding section below
for more information.

Rain: moderate confidence. Expecting rainfall amounts of generally
an inch or less west of Interstate 95. Amounts may be a bit higher
east of 95 but should still remain under 2 inches. There is a
possibility that drier air may work its way in at the middle levels and
cut off precipitation for a period and that would undercut rain
totals a bit.

Snow: low confidence. While not a high probability...there is a
possibility that our rain will end as a brief period of snow Sunday
morning in some areas. The most likely location for this is
actually along the Interstate 95 corridor where the cold conveyor
belt wraps around the low pressure Sunday morning. This may provide
enough dynamic cooling to result in some wet snowflakes falling. If
it were able to accumulate at all...it would be a coating to less
than an inch. There is also a possibility that some snow may fall
in the higher terrain of the Monadnocks and Worcester Hills. This
is also a low probability but if it occurs could result in one to
maybe two inches of accumulation. Again this would only be at the
higher elevations.

&&

Long term /Sunday night through Friday/...
big picture...

The long term period starts with a closed low over the northeast USA
a trough over The Rockies...and a ridge in between. The closed low
lifts northeast into the Maritimes early in the week. The ridge and
trough to our west move east...but the overall flow becomes more
zonal with time with a detached southern stream wave near the
Mexican border. Heights start the period below normal due to the
closed low...then climb to normal or a little above normal in the
zonal flow. Depending on timing...could be cooling back to below
normal late in week.

This suggests a cold start to the week but quickly trending back to
normal middle week...then cooling at end of week. Once the upper flow
becomes zonal...confidence in the timing of individual waves in the
flow and their associated surface systems will be reduced.

The dailies...

Sunday night-Monday-Tuesday... the axis of the upper low and cold
pool start Sunday night overhead and move off through the Maritimes
by Monday. Drier air moves in at all levels Sunday night and remains
overhead Monday. Fair mixing should reach to around 900 mb. Temperatures
of zero to -1c at that level translate to maximum surface temperatures in the
upper 40s and around 50. The high moves off to the east Tuesday
with milder air moving in especially aloft. Cross sections show
increasing moisture at middle and high levels...so expect some middle
and high clouds together with the sun. Temperatures warm up a little but
mixing will be shallower...950 mb temperatures support maximum temperatures middle 50s.

Wednesday through Friday... two shortwaves move across the northeast
and eastern Canada during middle to late week. The first wave lifts
through Quebec with limited curvature in New England. The second
wave digs deeper over the Great Lakes and sweeps across New England
24-36 hours later than the first. As the upper flow is roughly
zonal...exact timing of the two passages is low confidence at this
time.

With the first wave directed through Canada and the upper flow
remaining southwest...there is a good chance the surface front
stalls over or near southern New England. The second deeper wave
turns the upper flow northwest and should push a cold front well
offshore with colder air then flowing in. We will go with chance
probability of precipitation north of the Pike late Wednesday/night with the first wave and
front...then more widespread chance probability of precipitation Thursday with the second
wave and front. Timing on this will likely change somewhat with
successive model runs.

&&

Aviation /03z Saturday through Wednesday/...
forecaster confidence levels...

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

Short term /through Sunday/...

Tonight...high confidence in events...moderate confidence in
timing. VFR to start...but conditions deteriorate through the
night to MVFR-IFR from south to north with lowest conditions
along the coast. Expect scattered showers south of the Mass Pike
with the greatest chance of steadier rainfall along the South
Coast.

Saturday through Sunday...moderate to high confidence. MVFR/IFR
conditions continue through 12z Sunday when ceilings start to rise
from west to east as low pressure pulls away from southern New
England. Northeasterly winds increase through the period...peaking
in the 40 to 50 knots range Saturday night into Sunday morning for
the eastern terminals. Windspeeds will be lower across the western
terminals but still gusting up to 35 to 45 kts peaking more on
Sunday. Widespread rain expected through Sunday morning most
locations and continuing on the East Coast...cape...and islands
into Sunday afternoon.

Kbos...high confidence in taf trends. Lower confidence on exact
timing of onset of rain and higher winds.

Kbdl...high confidence in taf trends. Lower confidence on exact
timing of onset of rain and higher winds.

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

Sunday night through Tuesday...VFR. Northwest winds Monday will gust
25 to 30 knots during the day.

Wednesday...VFR. Possible brief MVFR ceilings/visibilities in showers late
in the day and at night.

&&

Marine...
forecaster confidence levels...

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

***Dangerous coastal storm for mariners expected this weekend***

High confidence through Sunday.

Northeasterly winds will increase...reaching 25 kts after
midnight. The wind will continue to steadily increase through
Saturday and Saturday night as an intensifying low pressure passes
southeast of Nantucket. Winds are expected to increase to storm force...
particularly on the waters east of Massachusetts. Have upgraded
the storm watch to a Storm Warning on those waters. Less confident
on the potential for storm force winds south of New England.
Therefore have kept the storm watch with the peak of the winds
expected Saturday night into Sunday. This will likely need to be
upgraded to either a Storm Warning or possibly high end gales
depending on the track of the low.

With northeasterly winds gusting to 50 kts...seas will increase
substantially reaching 15 to 20 feet easily on the eastern coastal
waters. There is a possibility that they increase to as much as 25
feet east of Cape Cod.

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

Sunday night and Monday...gusty northwest winds at gale force early
Sunday night. Winds then diminish but remain 25 to 30 knots through
Monday. Seas diminish Sunday night but linger 5 to 10 feet
through Monday.

Tuesday...winds and seas will remain below small craft levels.

Wednesday...seas will remain below 5 feet. Southwest winds will
increase with frequent gusts 20 to 25 knots.

&&

Tides/coastal flooding...
a coastal Flood Watch continues for the Saturday evening and early
Sunday morning high tide cycles for the eastern Massachusetts coast...including
the north facing portion of Cape Cod and Nantucket. This is for the
potential of minor to isolated pockets of moderate coastal flooding
possible along with beach erosion.

Astronomical high tides are rather low Saturday evening and again
early Sunday morning. However...strong north to northeast wind gusts
up to 50 knots may result in seas building to around 20 feet over
the open waters. Still some uncertainty as to how strong the winds
will get...but the potential is there for a 2 to 2.5 storm surge
along with significant wave action. Based on the latest data...we
are most concerned about the Saturday evening high tide cycle. The
winds appear strongest at that time with a little more of an
easterly component to the wind.

The highest risk areas appear to be Hull and Scituate. We also have
to be concerned with the typical hot spots...such as Salisbury and
Plum Island which are very susceptible to beach erosion. Finally...
will also have to keep an eye on Nantucket Harbor...as strong
northerly winds can cause issues for them.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...high wind watch from Saturday afternoon through Sunday morning
for maz005>007-013>018-020.
High Wind Warning from 5 PM EDT Saturday to 4 PM EST Sunday
for maz019-021>024.
Coastal Flood Watch from Saturday evening through Sunday
morning for maz007-015-016-019-022-024.
New Hampshire...none.
Rhode Island...high wind watch from Saturday afternoon through Sunday morning
for riz001>008.
Marine...storm watch from 6 am EDT Saturday through Sunday afternoon
for anz232>237-255-256.
Storm Warning from 6 PM EDT Saturday to 5 PM EST Sunday for
anz230-231-250-251-254.

&&

$$
Synopsis...wtb/rlg
near term...wtb/rlg/evt
short term...rlg
long term...wtb
aviation...wtb/rlg
marine...wtb/rlg/evt
tides/coastal flooding...staff

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