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Area forecast discussion 
National Weather Service Taunton Massachusetts
631 am EST sun Nov 29 2015

high pressure building north of the region into the Gulf of Maine
brings a period of chilly dry weather through Monday. High
pressure shifts offshore Tuesday allowing for some moderation of
temperatures. A storm coming out of the western USA will bring
rain to New England late Tuesday into Wednesday. High pressure
then builds dry and seasonable weather for the late week.


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

630 am update...
cloud shield hangs over CT-RI-se mass although most of the low
clouds are along the South Coast. Cloud shield is trending east
and should move off the South Coast around midday. Morning amdar
soundings show a deep inversion over the region...but room enough
for some mixing today...and temperatures aloft that would support
maximum surface temperatures in the middle 40s to near 50.

Previous discussion...
overall dry quiet weather beneath high pressure building out of the
N/W. North-winds prevailing and seasonable temperatures forecast. Highs
around the middle- to upper-40s. Only issues are across the cape and
islands with scattered to broken low cloud decks per ocean-effect
processes. A cooler airmass aloft across a warmer ocean ... clouds
subsequent of boundary-layer mixing aided by decent north-fetch beneath
a dry-inversion around h95-925. Similar mixing does occur across the
interior resulting in dewpoints to drop into the teens with relative
humidity values in the 30s.

Will see a reinforcing cold front work into the area late with much
colder air to the rear. Northwest-winds shifting north/NE becoming breezy in
response to a tightening pressure gradient as high pressure shifts east
up against low pressure to the S.


Short term /6 PM this evening through 6 PM Monday/...
tonight ...

High pressure remains north as it shifts east. NE-winds increase with the
isallobaric-gradient response as low pressure begins to organize off
the middle-Atlantic and colder air aloft shunts S across the region. Of
concern is for some snowy activity across the cape and islands.

Forecast consensus is for boundary-layer mixing of moisture beneath
a h9 dry-inversion all within a relatively uniform layer of NE-winds
around 20 miles per hour and decent saturation. With ocean temperatures around
50-degrees / 10 celsius with a 15-20 degree celsius difference
with the top of the mixed-layer ... there are some decent ocean-
induced cape values up to 250 j/kg with ncape values close to
0.18. So in other words there is the potential for rain/snow
shower activity across the cape and islands. Believe there may be
some challenges in precipitation staying as all snow considering flow off
the warmer ocean. Not the greatest cold sink in play. Ground
temperatures are also warm in the 40s. Altogether ... unless
something gets really going there is a low confidence of any snow
accumulation. Will go with chance probability of precipitation.

Chilly night with lows around the middle-20s ... warmer along the coast
with NE-onshore flow and coolest spots north/west mass over high terrain.

Monday ...

High pressure pushes out over the Gulf of Maine. Cold airmass still
in place will make it one of the coldest days of the season with
respect to high temperatures forecast around the upper-30s. Winds
turn east onshore while becoming light. The well-mixed boundary layer
persists across the waters ... and as winds turn east ... though snow
chances conclude for the cape and islands ... marine stratus is
pushes onshore with the mean flow. Looking at the east-half of S New
England to be encompassed in clouds with the west-half remaining fair
with decent sunshine. Believe this will moderate the highs somewhat.


Long term /Monday night through Saturday/...
big picture... blocked flow over the western USA breaks. Closed low
pressure ejects east and northeast...guided by a 150 knot jet in the
southern stream. The upper low crosses the Great Lakes midweek and
New England on Thursday. High pressure ridge builds over the
northeast USA Friday-Saturday.

Models handling of upper flow and key surface features is similar
and has run-to-run consistency. Moderate to high confidence in a
blend of long range solutions.

The dailies...

Monday night...

High pressure over the region Monday night moves offshore Tuesday
morning. Expect fair skies and light wind...radiational cooling.
With dew points in the 20s...inland areas should fall into the 20s
with coastal areas in the 30s.


Approaching upper jet brings increasing high level clouds. The jet
will push the plains surface low into the Great Lakes. The jet will
also create a zone of upper venting along the middle Atlantic coast
which will support formation of a coastal low by Tuesday. This low
will move up the coast Tuesday afternoon and evening. Low level jet
of 30-40 knots wrapping around the low will mostly aim for the
Delaware-Maryland-Virginia and Jersey coastline during the day...shifting toward the
south New England coast toward evening. This suggests the combined
low level lift and upper venting will increase during the day but
remain focused to our south until late in the day. This is slower
than depicted in the model pop data but more in line with the GFS
and European model (ecmwf) quantitative precipitation forecast data. This brings chance probability of precipitation from southwest to
northeast during the afternoon/evening.

Tuesday night-Wednesday... two parts to this midweek storm. Part one
is the coastal low spun up by the upper jet. Part two is the cold
front that the system swings east. The coastal low moves past
Nantucket Wednesday morning bringing strong low level lift and 1.25
inch precipitation water values...1.5 near Nantucket. Expect rain
overnight and into the day Wednesday. This is well above average for
Dec 1-2 and likely past the 90 percent exceedance values. So could be
some locally heavy downpours Tuesday night/Wednesday morning
especially cape/islands/southeast MA/RI. There may be a short
break in precipitation as the coastal low moves off to the Maritimes...but
then another chance as the cold front sweeps through during
Wednesday afternoon/evening. Some concern for a cold air damming
signal in our interior...but forecast temperature profiles remain
warm enough for rain most of the storm. Cold air moving in after
the cold front Wednesday night may bring mixed rain/snow in
western mass just before the storm ends.

Thursday... upper low and cold pool move overhead Thursday.
Sufficient moisture expected in the cold pool to generate diurnal
clouds...possibly an isolated snow shower in western mass. Winds at
850 mb will be west-northwest around 40 knots...with gusts 20-30
knots reaching the surface.

Friday-Saturday... high pressure builds over the northeast. The
European model (ecmwf) is suggesting an upper trough drops down from Canada Friday
night/Saturday. But the GFS and continuity do not show we
are staying with a dry forecast for now.


Aviation /11z Sunday through Thursday/...
forecaster confidence levels...

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

Short term /through Monday/ ... high confidence.

Today ...

Improving VFR under north-winds as clouds drift offshore in the south.
Scattered-broken VFR to MVFR ceilings linger across cape and islands. North-winds
back NE late and increase with gusts up to 20 kts.

Tonight ...

Overall VFR and breezy NE-winds. Main concern is southeast mass.
Northeast winds bring cold air across the warmer waters and ashore
in southeast mass. This would support a low deck of clouds along
with a chance of rain/snow showers. On average MVFR ceilings with
adverse weather. Best chance after midnight.

Monday ...

Winds back east and onshore. From the Worcester Hills west mainly VFR.
To the east a mix of low-end VFR to MVFR ceilings. East-winds gusting up to
20 kts.

Kbos terminal ... chance of MVFR conditions building back into
the terminal late tonight or early Monday with east-onshore flow.

Kbdl terminal ... VFR should hold through a majority of the
forecast period with north/NE-winds prevailing.

Outlook /Monday night through Thursday/...

Monday night-Tuesday... high confidence.
VFR. MVFR ceilings/visibilities in rain possible toward sunset late Tuesday.

Tuesday night-Wednesday... moderate confidence.
IFR/LIFR in rain and fog...occasionally heavy downpours with poor
visibility. East to southeast winds 30-40 knots at 2000 feet above
the surface Tuesday night/Wednesday morning which may cause some
low level wind shear. Additional rain/showers move across from the
west during the afternoon/evening with a cold front. Behind the
cold front winds become west to northwest Wednesday night and
conditions will improve to VFR.

Thursday...moderate confidence.
VFR. West-northwest winds gusting 20-30 knots.


forecaster confidence levels...

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

Short term /through Monday/ ... high confidence.

High pressure shifts from Quebec into the Gulf of Maine as low
pressure becomes better organized off the middle-Atlantic coast
through Monday. This will result in north-winds presently to back out
of the NE tonight and out of the east Monday. The increase in the
pressure gradient will result in gusts up to 25 kts tonight that
will gradually relax into Monday beneath the stronger influence of
high pressure. Small-craft-advisories amended accordingly with
anticipated wave action of 5 to 7 feet.

One final concern is the possibility of rain shower activity over
the waters tonight with breezy NE-winds. Much of this due to ocean-

Outlook /Monday night into Thursday/ ... confidence.

Monday night-Tuesday... high pressure over the waters moves off to
the east. Winds and seas will remain below small craft thresholds.

Tuesday night-Wednesday... coastal low pressure moves up the coast
past Nantucket Wednesday morning. This will bring east-southeast
winds 25-30 knots overnight and Wednesday morning. Seas will build
from the south...reaching 5-8 feet on the exposed waters. Shifting
winds Wednesday...becoming west in the late afternoon as a cold
front moves through. Small Craft Advisory may be needed due to
winds and seas.

Thursday...strong west to northwest winds behind the midweek storm
with gusts to 30 knots. Gusts to 35 knots are possible...but
continue at low confidence. Seas will continue at 5 feet or higher
on the outer waters but subside during the afternoon. Small Craft
Advisory may be needed.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory from 3 PM this afternoon to 1 PM EST
Monday for anz231-250-251.
Small Craft Advisory until 4 PM EST Monday for anz254>256.


near term...wtb/sipprell
short term...sipprell
long term...wtb

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