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Area forecast discussion 
National Weather Service Taunton Massachusetts
700 am EST Monday Dec 22 2014

Synopsis...

A wave of low pressure will bring periods of wet weather mainly late
tonight into Tuesday night...which may begin as a brief period of
frozen precipitation across northwest and north central
Massachusetts. A much stronger storm passing well to our west
Wednesday into Christmas morning will bring heavy rain...gusty winds
and probably minor coastal flooding. Dry weather with above normal
temperatures expected Christmas afternoon into Saturday. Low
pressure may bring a return to unsettled weather by next Sunday.

&&

Near term /until 6 PM this evening/...

7 am update...

Despite upper level ridging aloft...east to southeast flow just off
the deck was enough to result in low level lift for scattered rain
showers just east of the Massachusetts coast. Based on radar imagery and
latest mesoscale models...opted to increase probability of precipitation today
across eastern New England for scattered showers. Ptype...on
eastern Massachusetts coast mainly rain showers but a few flakes could mix in
across northeast Massachusetts this morning. Further inland...across the
interior it will be cold enough for a few snow showers/flurries but
main focus will be on the eastern Massachusetts coast. Therefore...just
expect a few snow showers/flurries and much of the day will be dry
across the interior.

As for high temperatures...low level northeast flow and cloudy skies
probably keep highs in the middle 30s across the interior. Onshore
flow will allow coastal locations to see highs in the upper
30s to the lower 40s...with even middle 40s on cape and islands.

&&

Short term /6 PM this evening through 6 PM Tuesday/...
tonight into tomorrow...

*light freezing rain is possible across the interior northwest and
northern Worcester hills*

A weak area of low pressure develops along a warm front off the middle
Atlantic...drifting northward toward the area. This low remains weak
as the warm front moves slowly northward tonight into tomorrow.
Decent warm advection ahead of this wave with several hi-res
guidance models shows a potential for cold air damming across the
interior into Tuesday morning. Biggest question will be the
moisture potential...is there enough to develop precipitation especially tonight?
Guidance does show enough lift ahead of approaching surface low per
the GFS/ec so anticipate precipitation to develop and overspread across
southern New England. If this plays out with cold air damming and
warm air advection...then we could see freezing rain/drizzle across
the interior northwest and northern Worcester Hills very late
tonight into Tuesday morning. A Winter Weather Advisory may be
needed.

As surface low continues to move northward...and high pressure over
eastern Canada...anticipate an increasing low level jet. This southeasterly
jet will continue to feed moisture into the region and with
soundings show a very saturated profile could see numerous showers
with perhaps a few heavy downpours. Noticed guidance has
increased the quantitative precipitation forecast over the past few days. As the weak surface low
moves north of southern New England...warm front will lift
northward so all precipitation by the late morning will be in the liquid
form.

We could also see some minor coastal flooding concerns on Tuesday
with due easterly flow increasing to about 20 to 25 miles per hour. See below
for more details.

&&

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

* periods of rain Tuesday night into xmas morning will be heavy at times
* dry by Christmas afternoon but windy
* temperatures around 60 for some late Wednesday into Christmas morning
* dry but above normal temperatures continue Friday and Sat
* unsettled weather may return by sun but low confidence

Details...

Tuesday night into Christmas...

Strong shortwave will dig across the central U.S. And allow deep
south to southwest flow aloft across southern New England. This
will send and anomalous mild airmass into southern New England for
late December. Gefs showing precipitable waters 4 to 5 Standard deviations above
normal by Wednesday night across our region. While heavy rain is still
expected...the models have cut down on the quantitative precipitation forecast in the last few runs.
The main low still passes well to our west across Great Lakes...but
their slower and weaker with secondary development across our
region. This results in a weaker low level jet...hence less quantitative precipitation forecast.
Given anomalous precipitable waters in place...do not want to completely let our
guard down with the potential for flooding...but does appear
somewhat less of a risk than yesterday. Nonetheless...still expect
typical nuisance poor drainage street flooding.

As for timing...southerly flow aloft will result in scattered
showers Tuesday night. Bulk of the rain will occur Wednesday into early
Christmas day when strongest forcing coincides high precipitable water airmass.
Some of this rain will be heavy at times may result in nuisance poor
drainage street flooding. Still a low risk for more significant
flooding given extremely high precipitable waters ...but slower development of
secondary low pressure may be a limiting factor. Regardless...
expect 1 to 3 inches of rain. Will continue to mention a slight
chance of thunder with showalter indices near zero.

The bulk of the rain should come to an end Christmas morning with
temperatures probably around 60 for much of the region. While gusty
southerly winds are expected Wednesday night...inversion and weaker low
level jet will probably keep most areas below advisory criteria.
Still have to watch for a small window on the coastal plain especially if
temperatures can exceed 60...but higher confidence in wind on Christmas
afternoon and evening behind the system. Increasing westerly wind
aloft and steepening lapse rates will bring the potential for these
winds. Decent shot at a period of 35 to 50 miles per hour gusts behind this
system Christmas afternoon and evening. While the GFS is an
outlier...it would even suggest the potential for high wind criteria
to be met with 70 knots at 850 mb. That may be overdone...but
something will have to keep an eye on the next few days.

Friday and Saturday...

Upper level ridge off the southeast coast will keep keep US in mild
southwest flow aloft. Dry weather expected with forcing for any
precipitation will to our northwest. Highs mainly in the 40s to
lower 50s.

Sunday...

Confidence in the forecast GOES down considerably over this time.
Developing upper level ridging into Alaska will send the polar jet
southward into the central U.S. At the same time...upper level
ridge off the southeast coast will try to hang tough. The GFS
insists on dry and colder weather arriving...but were not convinced.
Given the Southeast Ridge...it may hold the cold air up and allow
developing low pressure to track near New England sun and Sun night.
This could bring rain or snow depending on its track...obviously a
week out so plenty of uncertainty but would lean towards another
system and away from the dry GFS.

&&

Aviation /12z Monday through Friday/...
forecaster confidence levels...

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

Short term /through Tuesday/...

7 am update...

Today...high confidence. Mainly MVFR conditions but some localized
IFR conditions possible along the coast and Worcester Hills. A few
showers expected along eastern Massachusetts coast with perhaps a passing
flurry/snow shower or two across the interior.

Tonight...moderate confidence. Mainly MVFR conditions continue in
scattered light snow showers. Light freezing rain possible late Monday night
across northwest Massachusetts.

Tuesday...moderate confidence. MVFR conditions may drop to IFR
within and heavy rain fall. Visibilities will be reduced to 5sm or less
as well.

Kbos terminal...moderate confidence.

Kbdl terminal...moderate confidence.

Outlook...Tuesday night through Friday...

Tuesday night into Thursday morning...moderate confidence.
Widespread low end MVFR to IFR conditions expected in periods of
heavy showers/low clouds and fog patches. A period of southerly
wind gusts of 30 to 40 knots expected on the coastal plain Wednesday
night. Low level wind shear also a concern for the entire region Wednesday into early Thursday.

Thursday afternoon into Friday...moderate to high confidence in
mainly VFR. However...a period of westerly 30 to 45 knot wind gusts
possible Thursday afternoon and evening.

&&

Marine...
forecaster confidence levels...

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

Short term /through Tuesday/...moderate to high confidence.

High pressure across Quebec and the Maritimes will result in
persistent northeasterly to easterly winds across the waters through
today. This will build seas to 5ft on the eastern waters despite
wind gusts up to 20 knots. Have continued Small Craft Advisory.

Approaching surface low pressure from the middle-Atlantic tonight will
help increase an easterly low level jet over the water tomorrow. This will
build the seas between 5-8 feet. Could see wind gusts between 20-30
kts as the front passes. Small Craft Advisory has been expanded accordingly.

Outlook...Tuesday night through Friday...moderate confidence

Tuesday night...long fetch easterly flow will continue to result in
Small Craft Advisory seas across the outer-waters with high pressure moving east of
the Canadian Maritimes. Winds should generally be below small craft
thresholds.

Wednesday into early Thursday...intensifying low pressure passing
well to our west will cause winds to turn southerly and become
gusty. Small craft wind gusts are a lock. The main uncertainty is
do we see southerly gales develop Wednesday night. Strong low level jet
present...but we will be dealing with an inversion over the
relatively cool ocean. Regardless...still should see at least a
period of near gale force southerly wind gusts.

Later Thursday into Friday...a period of westerly gale force wind
gusts appears likely in the cold advection pattern behind the storm
Thursday afternoon and night. Winds should diminish some on Friday.

&&

Tides/coastal flooding...
high astronomical tides occur Tuesday and Wednesday.

East Massachusetts coast:

Tuesday...high tide at Boston will be 11.6 feet at midday. Winds will
be from the east at 10 to 15 knots...so there will be onshore flow
during this high tide. While this is nothing too strong...given the
high astro tide expect some splash over/minor coastal flooding.
Certainly do not expect to see any significant issues.

Wednesday...high tide at Boston will be 11.7 feet at midday. Winds
will be from the southeast near 10 knots but there will be some
pressure falls with intensifying low pressure to our west. This
should be enough for more splash over/minor coastal flooding with
the high astro tides. However...do not expect any significant
problems given winds/seas should be held in check during the time of
high tide.

South coast:

Wednesday evening...southerly winds are expected and astronomical
tides increase along the South Coast. High tide in Providence will
be 5.2 feet that evening. 925 mb low level jet strengthens to 55-65 kts which
could push a 1 to 2 foot surge up along the South Coast during the
time of high tide. The low level inversion will probably hold the
strongest winds just above the ground...so thinking the risk is for
splash over and minor coastal flooding. There still is a low risk
for moderate coastal flooding...but that is often hard to get in a
non-tropical system along the South Coast.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 1 am to 7 PM EST Tuesday for anz231-
232-251-256.
Small Craft Advisory from 1 PM this afternoon to 7 PM EST
Tuesday for anz250-254.
Small Craft Advisory from 10 PM this evening to 7 PM EST
Tuesday for anz255.

&&

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

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