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Area forecast discussion 
National Weather Service Taunton Massachusetts
643 PM EST Monday Nov 24 2014

Synopsis...

After a wet and mild day...a weak cold front will move across the
region overnight. This will allow for a quiet and mild Tuesday with
some gusty SW winds. Nor'easter for Wednesday into Thursday. Gradually
turning colder into the weekend.

&&

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

7 PM update...

Still a lot of low-level moisture across the region maintained by
continued blustery flow. Can see the weak cold front progressing east
across upstate New York / PA...with notably some lightning present along
the New York / Canadian border. Quite the impressive warmth continues
prior to the cold front which sweeps the region overnight. Expect
a mix of low clouds and fog...the worst of which will be across
the S-coastline including Cape Cod / islands. As the front sweeps
the region...again not expecting much in the way of precipitation
but mainly a dry push. Conditions clearing behind the front into
Tuesday morning. Again...remaining mild with near steady temperatures
prior to the front...dropping off thereafter. Gusty SW-winds ahead
with gusts around 15-20 miles per hour...stronger more so over the coastal
plain and adjacent waters.

&&

Short term /6 am Tuesday morning through Wednesday night/...

Tuesday into Tuesday night...

High pressure will begin to slide in on Tuesday allowing for a quiet
weather day. Still a descent jet aloft so will continue to see gusty
winds around 15-25 miles per hour during the day. Cold air advection will begin to pool in so
temperatures will be cooler than today with highs in the middle 50s to low
60s...still slightly above average. Quiet overnight.

Wednesday through Thursday morning...

*/ highlights...

- Nor'easter will impact New England Wednesday into Wednesday night
- significant impacts which will disrupt travel
- plowable snows across the interior
- potential heavy rain across southeast New England /Cape Cod - islands/
- strong NE-winds across east Massachusetts / Cape Cod / islands

*/ overview and model consensus...

Overview...

Individual model solutions narrowing in on a focus of a storm track
around the 40n/70w benchmark. But it continues to be difficult to
resolve specific details across the region. Again...we really may
not know the true outcomes till just a day or two prior.

Weighed preference upon the 24.15z sref / 24.12z GFS ... and now the
24.12z European model (ecmwf) has finally come aboard...hooray! Now with a consistent
storm-track...impacts begin Wednesday morning...increasing into the
evening with the height of the storm. Model consensus has the storm
winding down Thursday morning.

Synoptically...

Based on a preferred model consensus above: low pressure intensifies
from the Gulf Tuesday NE across the 40n/70w benchmark S of Nantucket
around midnight Thursday. Accompanying 850 mb low passes NE in the
vicinity of the Cape Cod canal to northwest of the 40n/70w benchmark.

During Wednesday...baroclinic Leaf / over-running pattern of broad-
scale ascent yields top-down moistening dynamically cooling with
time. With surface interior north-flow with coastal NE-flow...and drier
air N/W...am expecting wetbulbing towards the dewpoint to around the
freezing mark the division of which may be along a possible coastal
front setup immediately north/west of the I-95 corridor. Expect initial
rains for interior locales changing over to snow through the day...
as to the timing of that transition remains uncertain at this time.

Into Wednesday night...intensifying low sweeps NE around the 40n/70w
benchmark S of Nantucket. With a progressive flow-pattern /+nao/ and
absence of a closed-low above 850 mb /more emphasis of an anti-cyclonic
branch of the warm conveyer belt/...with low pressure troughing over
the Great Lakes associated with a strong polar-low holds Arctic air
rearward across c-Canada /+ao/...expecting thermal profiles around
the freezing mark over interior S New England...while mild over the
immediate coast with continued thinking of maintained coastal-front
setup prior to storm passage.

Precipitation outcomes...

A front-end thump is anticipated with slantwise forcing per fronto-
genesis northwest of 850 mb low extended east...along with indications of weak
trowaling toward the northwest-quadrant of the 850 mb low. Beneath enhanced
ascent per middle-level impulse and rrq of the upper-level-jet...strong
deep-layer lift through moist dendritic zones should yield a northwest-southeast
precipitation gradient across S New England with heaviest precipitation
immediately northwest of the surface low which again sweeps NE around the
40n/70w benchmark.

Could be talking storm-total precipitation amounts around 1.5-2.0
inches for southeast New England with lessening amounts north/west with up to
around 0.75-inches for northwest Massachusetts and SW New Hampshire. See details below in the
thermal setup discussion that breakdown what those amounts could
equate to in terms of snow. Again...initial precipitation will likely start
out as rain for some interior locations before changing to snow.

F-general SW-NE banding is evident northwest of the 850 mb low yet with minor
indications of static/inertial instability per -epv. Can not rule
out the possibility of SW-NE bands of heavier returns per WSR-88D
radar during the event that will yield locally higher
precipitation amounts. Its likely we will have better handle in
analyzing such outcomes when near-term high resolution guidance
becomes available.

Thermal setup / snowfall amounts...

If a coastal front setup emerges beneath near-isothermal profiles
around -5c up to 700 mb then would expect snow-to-liquid ratios ranging
from 10:1 to 15:1 as sref meteograms suggest across the interior...
with coastal rains.

Quite a range that has significant implications on snowfall amounts.
Challenges of snowfall rates during the time of day /likely will see
difficulty in accumulating snows during the day with marginally cold
surface temperatures/...also wet-bulbing to equilibrium within the
first 1 kft above the surface...and where we will effectively wet-
bulb and/or where areas are overcome by heavy snowfall rates.

So in addition to the initial start/changeover to snow...speed of
the system and impacts to precipitation amounts...and range of snow-
to-liquid ratios...it is an incredibly huge challenge to nail down
snowfall amounts. One key to this entire forecast is the track of
the 850 mb low along with h925 temperatures at or below -2c.

The dividing freezing line is varied among preferred model solutions
but narrowing down in vicinity of the area between the CT I-395 to
the I-90/I-290/I-495 Massachusetts corridor to the I-95 corridor.

So after pulling out all my hair...intangibles noted above make the
snowfall forecast tedious. Feel during the day snow accumulations
will occur at 32-degrees or below with snow occurring at 36-degrees
or lower. This lowered snowfall amounts from the prior shift. In
collaboration with wpc...broad area of 6+ inches within the watch
area west of northwest Massachusetts to northwest Rhode Island encompassing all of CT except coastal
communities. Amounts around 8-10 inches possible across the higher
elevations with locally higher amounts.

Continued thinking that there will likely be wiggle room of the rain-
snow band due to uncertainty in thermal profiles in the forecast.
Expect changes within snowfall amounts along the gradient advertised
around the area immediately west of the I-95 corridor.

Winds...

Consistent NE-flow over east Massachusetts including Cape Cod and the islands.
Gusts exceeding 45 miles per hour are possible but dependent on how strong the
storm actually gets...which again is uncertain. Wind Advisory head-
lines may be needed...but if they are would expect that it would be
on the low-end of criteria with gusts around 50 miles per hour.

Coastal flooding...

Forecast tides of 10 feet expected at Boston shortly after midnight
Thursday. Anticipating a short-residency time of the storm...perhaps
a minor surge and maybe some splashover if the NE-winds discussed
above verify.

&&

Long term /Thursday through Monday/...

Thursday night through Monday...

Medium range models in good agreement that series of weak shortwaves
will rotate around broad trough in place over eastern states. This
will maintain dry weather and below average temperatures into
weekend...although expect some cloudiness from time to time. We
should see brief moderation in temperatures sun as SW flow develops
ahead of next cold front...which will bring reinforcing shot of cold
next Monday. May see few showers with passage of front Sun night/Monday
morning...but should be isolated at best.

&&

Aviation /00z Tuesday through Saturday/...

Forecaster confidence levels...

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

Short-term /through tomorrow/...moderate confidence.

0z update...

Cold front /unv-syr-mss/ sweeps the terminals overnight around 9z.
Expect a mix of MVFR-IFR conditions lowest along the S-shoreline
with IFR-vlifr ceilings/visibilities along with gusty SW-winds ahead of the
front around 25-30 kts initially gradually relaxing. The breezy
flow should keep the majority of fog away.

Improving VFR through Tuesday morning and into the day with
continued west/SW winds gusts up to 20 kts.

Kbos terminal...moderate confidence. Specific timing as to
improvement over the terminal is not entirely certain.

Kbdl terminal...moderate confidence. Expect a gradual improvement
with ceilings lifting towards 8z. May lift faster than forecast.

Outlook...Tuesday night through Friday.

Wednesday into Thursday...moderate confidence.

Nor'easter anticipated. Significant accumulation snows over interior
terminals immediately west of the I-95 corridor. +Sn possible.
Around 40 knots NE-winds across east Massachusetts / Cape Cod / islands...along
with +ra. Mix of IFR-vlifr conditions.

Friday...VFR. Moderate confidence.

&&

Marine...

Forecaster confidence levels...

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

Short term /through tomorrow/...moderate confidence.

7 PM update...

Southerly flow will continue overnight with gusts around 25 to
30 kts. Weak cold front will sweep the waters towards Tuesday
morning switching the winds to a more SW. Will gradually drop the
gales converting to small-craft advisories. Seas remaining choppy.

Southwest winds will continue tomorrow as high pressure builds.
Yet with weak cold air advection aloft expect gusts to remain up to 20-25 kts.
Seas will be slow to response. So Small Craft Advisory will likely be needed.

Outlook...Tuesday night through Friday.

Wednesday into Thursday...moderate confidence.

Nor'easter anticipated passing NE around the 40n/70w benchmark S of
Nantucket midnight Thursday. Likely NE gales over east Massachusetts / Cape Cod /
islands...and all waters. Heavy rain lending to reduced visibilities
at times.

Friday...moderate confidence.

Small Craft Advisory conditions should persist on outer waters due to 25kt gusts
and 5 feet seas.

&&

Box watches/warnings/advisories...

CT...Winter Storm Watch from Wednesday morning through Thursday
morning for ctz002>004.
Massachusetts...Winter Storm Watch from Wednesday morning through Thursday
morning for maz002>006-008>012-026.
New Hampshire...Winter Storm Watch from Wednesday morning through Thursday
morning for nhz011-012-015.
Rhode Island...Winter Storm Watch from Wednesday morning through Thursday
morning for riz001.
Marine...Small Craft Advisory until 4 am EST Tuesday for anz232>234-251.
Small Craft Advisory until 1 am EST Tuesday for anz230-236.
Small Craft Advisory until 10 PM EST this evening for anz231.
Small Craft Advisory until 7 PM EST Tuesday for anz235-237-255-
256.
Gale Warning until 10 PM EST this evening for anz250-254.

&&

$$

Synopsis...dunten/sipprell
near term...dunten/sipprell
short term...dunten/sipprell
long term...jwd
aviation...dunten/sipprell/jwd
marine...dunten/sipprell/jwd

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