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Area forecast discussion 
National Weather Service Taunton Massachusetts
102 am EST Monday Nov 24 2014

Synopsis...
a warm front will bring a brief period of heavy rain and strong
winds along the southeast coast Monday morning...followed by
unseasonably mild conditions Monday afternoon. Quiet and mild
Tuesday with some gusty SW-winds. Storm system anticipated Wednesday
into Thursday morning...yet specific outcomes remain uncertain.
Gradually turning colder into the weekend.

&&

Near term /through today/...
1255 am update...
leading edge of showers across east PA and New Jersey will be moving into CT
and west Massachusetts by 08z then reaching east Massachusetts 10-12z. Made minor adjustments
to probability of precipitation for onset of rain...otherwise forecast on track. Areas of
fog across cape/islands will dissipate rapidly as low level
approaches.

Previous discussion...

***brief period of heavy rain Monday morning along with strong winds
across southeast new england***

Tonight and Monday morning...

1) brief period of heavy rain

Dry conditions will prevail this evening...but the weather will
rapidly deteriorate from southwest to northeast between 6z and 12z
Monday. Low pressure working up towards the Great Lakes will
induce a strong southerly low level jet. This will transport deep
moisture northward as precipitable waters climb to between 3 and 4 Standard
deviations above normal. That combined with strong forcing should
yield a brief period of heavy rain. Thunder indices are marginal
but enough forcing could generate and isolated thunderstorm or two
across the far southeast New England coast. Fortunately the system
is fairly progressive...so expect the steady/heavy rain to be over
by Monday afternoon. Rainfall amounts should be on the order of
0.50 to 1 inches in most locales...but can/T rule out some locally
higher amounts...especially if we can generate any isolated
convection in our southeast zones. So not concerned about any
significant flooding...other than typical nuisance poor drainage
street flooding which will unfortunately coincide with the Monday
am rush hour.

2) strong wind gusts potential across the southeast coast

The other concern will be the potential for a period of strong
southerly wind gusts across southeast New England...especially
Monday morning. Given the inversion...its always tricky to see
how much wind will be able to make it down to the ground. Low
level jet at 850 mb is around 80 knots along the southeast New
England coast between 12z and 16z. Taking half of that often can
get you in The Ball park of what will be realized at the surface.
This would result in Wind Advisory criteria being met across our
southeast zones. Therefore...have hoisted a Wind Advisory for
southern Rhode Island and far southeast Massachusetts Monday morning. This is
for the potential for a period of southerly wind gusts of 40 to 50
miles per hour. If we can get a fine line going...confidence would increase
more in being able to bring the strong winds down to the ground.
Nonetheless...still thought it was Worth the advisory.

Monday afternoon...

The strong middle level lift/moisture will have lifted to our northeast
by Monday afternoon. Therefore...the steady and heavy rain will
have come to an end. We will still have a lot of low level
lift/moisture around for a few passing showers so maintained some
probability of precipitation. Otherwise...it looks like a very mild day in store for the
region with 850 mb temperatures on the order of +10 to +12c. Despite a
lot of clouds...strong southerly flow should allow highs to surge
well into the 60s. Not sure if we will see much sun given so much
low level moisture...but if we end up with more than expected some
locations could reach or exceed 70. Regardless...will actually
feel a bit muggy for late November standards...with dewpoints
close to 60! Also...there is a lot of wind just off the deck into
Monday afternoon. We could see gusts of 30 to 40 miles per hour develop even
in the interior...depending on if we can muster any peeks of
sunshine.

&&

Short term /tonight through 6 PM Tuesday/...
Monday night...

Strong southwesterly low level jet will not allow winds to decouple.

This combined with unseasonably warm 850 mb temperatures will result
in an unseasonably mild night. Low temperatures will hold in the
50s in most locations! Much of the night will be dry...but a few
spot showers will be possible during the first part of the night.

&&

Long term /Tuesday night through Sunday/...
*/ highlights...

- dry and mild Tuesday
- storm Wednesday into Thursday...travel impacts
- turning colder into the weekend

*/ overview and model consensus...

Main focus is on the Wednesday - Thursday timeframe. In agreement
with wpc: continued spread of guidance upstream resulting in the
poor resolving of downstream impacts. Individual model solutions /
ensembles still undecided on the relative track / strength of down-
stream energy across the NE-conus. Difficult to resolve details
across the region of which we may not know the true outcomes till
about 2-3 days prior.

Nevertheless...continue to weigh preference upon the west-envelope of
forecast solutions. Believe the 23.6z / 23.12z GFS and the 23.12z ec
ensemble mean offer the most reasonable NE-track of the system in
the vicinity of the 40n/70w benchmark S of Nantucket. Agree with wpc
noting there has been a wide spread of ec deterministic solutions on
the west-half of the guidance along with the UKMET...while the Canadian
remains to the right.

Expect a moderate development of the system which will result in
impacts across the region...though there remains a significant
amount of uncertainty on both the strength and the exact track of
the system. Aside...expecting some sort of rain and / or snow band
somewhere across S New England...with a climatological preference of
rain over coastal communities and snows for the interior.

The only certainty to the forecast is the timing of the system of
which impacts are anticipated to begin during the day Wednesday...
increasing into the evening with the height of the storm around
midnight Thursday. Model consensus has the storm concluding Thursday
morning.

Details...

Tuesday into Tuesday night...

Dry and mild. High pressure in control beneath the dry-slot rearward
of the departing low over the St Lawrence River valley in Canada. Am
expecting blustery SW-flow with gusts 30-35 miles per hour along the S-coast.
Winds relaxing into the evening. Light flow overnight could make for
a good radiative cooling setup. But anticipating middle- to high-level
clouds to increase from the S into Wednesday morning limiting the
potential.

Wednesday into Wednesday night...

Synoptically...successive Pacific-impulses maintain an open-wave 500 mb
trough into the Gulf. Undergoing a negative-tilt across the east-Continental U.S.
Initiates and intensifies an area of low pressure from the north-Gulf NE
over the west-Atlantic across the 40n/70w benchmark S of Nantucket by
midnight Thursday. No appreciable downstream blocking signifies a
progressive-flow pattern /+nao/ resulting in the absence of a closed-
low pattern above 700 mb /less emphasis of a cyclonic branch of the warm
conveyer belt/...while low pressure troughing over the Great Lakes
associated with a strong polar-low holds Arctic air rearward across
c-Canada /+ao/ resulting in thermal profiles around the freezing
mark over S New England.

Towards evening...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 modest
west-component of ageostrophic flow...and drier air north/west initially...am
expecting wetbulbing towards the dewpoint around the freezing mark
the division of which may be along a possible coastal front setup.

Overnight...intensifying low sweeps NE in the vicinity of the 40n /
70w benchmark S of Nantucket. With a progressive flow-pattern and
lack of a closed low above 700 mb...much of the emphasis is with the
anti-cyclonic branch of the wcb. Nevertheless a front-end thump is
anticipated with slantwise ascent / forcing per frontogenesis northwest of
850 mb low extended east...along with indications of weak trowaling toward
the northwest-quadrant of the 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 SW-NE band signature
across S New England...though where exactly remains uncertain as is
the exact track as well as the depth / strength of the storm.

If a coastal front setup emerges beneath near-isothermal profiles
just below freezing up to 700 mb per the preferred model solutions noted
earlier...then would expect interior snows /with a near 1:10 ratio/
and coastal rains. Key to this entire forecast is the track of the
850 mb low along with h925 temperatures at or below -2c. The dividing
line is varied among preferred model solutions. Cips analog guidance
does weigh some indication per probabilities of > 2 inches of snow.

Low confidence forecast. 23.12z ec / UKMET continue to be on the
warmer-end of solutions. If the 23.12z GFS / gefs and 23.15z sref
are correct with the track of the 850 mb / surface low...which is in
the middle of the guidance spread /Canadian the far east solution/ then
would expect a plowable snow across the interior north/west of the I-95/495
corridor...keeping in mind there is likely wiggle room of the rain /
snow band due to the uncertainty in thermal profiles this far out in
the forecast. So with that being said...will not issue out any snow-
fall graphics with this forecast. There is absolutely no certainty
as to snow-outcomes.

Cips analogs have toned down on the wind probabilities. But with the
aforemention model preference...will need to watch the 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.

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. All sorts of dependencies and intangibles. Its a hard
knock life.

Thanksgiving and beyond...

Continued Pacific energy rotating through the broader open-wave 500 mb
trough will to need to be monitored as to whether middle-level impulses
invoke another offshore low around Friday. Once the 500 mb trough pushes
through the region...expect the return of below-average temperatures
ushered by NW-flow.

&&

Aviation /06z Monday through Friday/...
forecaster confidence levels...

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

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

Through today...conditions deteriorating to MVFR/IFR SW to NE
08-12z as widespread rain...locally heavy overspreads the region.
Rain will be exiting 14-16z with a few showers possible in the
afternoon...but MVFR/IFR ceilings will persist. S wind gusts to
35-40 knots possible across southeast new eng and especially cape/islands
12-16z...then SW gusts to 25-35 knots during the afternoon. Low level wind shear
likely as 2k feet winds 45-55 knots.

Tonight...MVFR-IFR conditions gradually improve to VFR in the
evening across west and north terminals...but not until after 06z across
southeast new eng. Blustery SW wind gusts 25-35 knots in the evening
diminishing overnight.

Kbos terminal...moderate confidence. Kept ceilings above IFR with
gusty S winds...but a brief period of IFR possible.

Kbdl terminal...moderate confidence. Low level wind shear will be of great
concern in the morning with southerly low level jet and weaker east/southeast flow
near the surface.

Outlook...Tuesday through Friday.

Tuesday through Tuesday night...moderate confidence.

West/SW-flow diminishing through Tuesday with gusts of around 30 kts
over southeast-coastal terminals initially Tuesday morning. VFR.

Wednesday into Thursday morning...low confidence.

Significant storm anticipated. Possible threats of a plowable snow
over interior S New England...with strong NE winds over east Massachusetts / Cape
Cod / islands...maybe even +ra. Mix of IFR-vlifr anticipated. Storm
impacts beginning Wednesday enhancing Wednesday night. Height of the
storm around midnight Thursday...concluding into Thursday morning.

Later-Thursday into Friday...low confidence.

Improving VFR. But much of this depends on storm morphology.

&&

Marine...
forecaster confidence levels...

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

Short term /through Monday night/...moderate confidence.

7 PM update...no major changes to the forecast.

Deepening low lifting towards the Great Lakes will induce strong
winds aloft Monday morning. While potential mixing to the surface
will be limited...still think there is a decent shot of southerly
35-40 knots gusts. Such gale-force wind gusts may continue into
Monday evening out of the SW.

Gale warnings hoisted for all waters except Boston Harbor. Seas
should build to between 10 and 15 feet across the southern waters.

Outlook...Tuesday through Friday.

Tuesday into Tuesday night...moderate confidence.

Winds turning west/SW remaining blustery with gusts around 30 kts for
Tuesday morning...relaxing through the day. Waves around 10 feet on
the outer waters Tuesday morning...diminishing thereafter.

Wednesday into Thursday...low confidence.

Significant storm anticipated passing near the 40n/70w benchmark S
of Nantucket. Possible threats of strong NE gales over east Massachusetts / Cape
Cod / islands...including all adjacent and outer waters. Heavy rain
lending to reduced visibilities at times. Storm impacts beginning
Wednesday enhancing Wednesday night. Height of the storm around
midnight Thursday...concluding into Thursday morning.

&&

Tides/coastal flooding...
astronomical tides are fairly high during the Monday morning high tide
cycle. With southerly gales expected...a storm surge of 1-2 feet is
likely along the South Coast. This may bring a few locations to
minor flood. The main threat for minor coastal flooding will be
along Narragansett Bay and Westport Harbor due to southerly fetch.
Coastal flood advisories have been issued for the South Coast. No
flooding is expected along the East Coast.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...Wind Advisory from 5 am early this morning to 2 PM EST this
afternoon for maz018>024.
Coastal Flood Advisory from 7 am to 11 am EST this morning for
maz020>022.
New Hampshire...none.
Rhode Island...Wind Advisory from 5 am early this morning to 2 PM EST this
afternoon for riz003>008.
Coastal Flood Advisory from 7 am to 11 am EST this morning for
riz002-004>007.
Marine...Gale Warning from 5 am early this morning to 10 PM EST this
evening for anz231>235-237-250-251-254>256.
Small Craft Advisory from 5 am early this morning to 10 PM EST
this evening for anz230.
Gale Warning from 5 am early this morning to 2 PM EST this
afternoon for anz236.

&&

$$
Synopsis...Frank/sipprell
near term...kjc
short term...Frank
long term...sipprell
aviation...kjc/sipprell
marine...Frank/sipprell
tides/coastal flooding...

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