Area Forecast Discussion
Issued by NWS Boston, MA

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448
FXUS61 KBOX 011525
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1025 AM EST Thu Dec 1 2016

.SYNOPSIS...
Dry, breezy and mild conditions later this morning and afternoon.
Other than the risk of a few snow showers or flurries Friday
night, expecting mainly dry conditions through much of this
weekend, with a trend toward cooler temperatures. Weak low
pressure may bring spotty light rain and/or snow showers Sunday
night into Monday. Into the middle of next week, there is some
potential for wintry precipitation Tuesday night into Wednesday,
but timing and track remain uncertain.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1030 AM Update...

Made some tweaks to the forecast this morning. Drier air has been
moving in a bit quicker, leading to mostly sunny skies. Some
clouds still spilling over the Berkshires across portions of
western MA and northern CT. Precipitation has largely ended for
today across southern New England. Can`t completely rule out a
stray sprinkle as long as the clouds persist across the western
half of southern New England.

Adjusted temperatures to reflect observed trends.

Previous Discussion...

Lead short wave and associated triple point low pushes to the Gulf
of Maine with rapid clearing/drying from west to east. This will
be accompanied by a wind shift to the west. Winds will immediately
become gusty as modest pressure-rise fall couplet enhances wind
gusts potential. Model soundings supports west winds gusting up to
35-40 mph after sunrise...then settling back to 20 to 30 mph this
afternoon.

Sunshine returns by mid-late morning. This, coupled with a mild
start and CAA delayed to later today, highs of 55-60 will be
common across RI and eastern MA...50-55 elsewhere with coolest
readings over the high terrain. Normal high for Dec 1st is 42F-48F
for southern New England.

Not as much sunshine across the hilly terrain as strato-cu
overspreads this area later this morning and continues thru the
afternoon. This cloudiness holds off until mid to late afternoon
farther east across RI and eastern MA. So overall not very winter
like for the 1st day of Dec.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Tonight...

Dry but cooler with 850 temps falling to about -3C. This combined
with a modest west wind will make it feel noticeably cooler. Temps
will fall back into the 30s but still running 5-8 degs above
normal for early Dec. Some cloudiness expected across northwest MA
as lake effect clouds spill up and over the Berkshires. However
mainly dry conditions should prevail.

Friday...

CAA continues and low level flow veers more to the west. This
trajectory may be more favorable for lake effect clouds to impact
northern MA and possibly farther southward. Both NAM and GFS have
increasing low level lapse rates of 6.5C/km to 7.0C/km in the
925-700 mb layer. Given this layer is nearly saturated along with
cyclonic flow aloft...could see some lake effect streamers make it
over the Berkshires into northern MA. Thus have including very low
probs of light showers/sprinkles with snow showers/flurries for
the high terrain.

Otherwise a typical early Dec day with highs in the mid to upper
40s along with a chilly west wind of 15 to 25 mph. More clouds
across northern MA with some partial sunshine expected over CT/RI
and southeast MA.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights...

* Mainly dry conditions with cooling temperatures through the
  weekend
* Low confidence in wintry precip Sunday night into Monday
* Another low may approach sometime Tuesday night or Wednesday,
  but low confidence on timing and track continue

Overview...

00Z models and ensembles were in fairly good agreement through
this weekend in keeping mainly dry conditions in place, though
will see temperatures cool through this timeframe as the cutoff H5
low spins across Atlantic Canada. Should see mainly dry
conditions through Sunday.

From Sunday night onward, uncertainty continues with regards to
how the models handle the ejection of cutoff mid level low
pressure out of the SW U.S. as high amplitude H5 ridge builds
across the eastern U.S. into eastern Canada. Noting wide model
solution spread as next system works its way across the midwest
and Ohio Valley early next week. One weak low looks to approach
Sunday night into Monday, but not a lot of moisture with this
system. The surface system associated with the progressive cutoff
mid level system may approach around the late Tuesday into
Wednesday timeframe, but with low consistency with the track and
timing of this system, low confidence at this time, but could see
a wintry mix depending upon the temperature regime as the system
approaches.

Details...

Friday night through Sunday...Moderate to high confidence.

Cutoff upper level low over Quebec will shift into the Maritimes,
but broad troughing extends westward across northern New England
into N NY state through Saturday. May see some widely sct snow
showers across the E slopes of the Berkshires Fri night into early
Sat morning.

There has been model consistency over the last couple of nights
in the development of ocean effect showers over the eastern waters
as colder air works across the warmer waters. They have been
trying to bring some isolated showers into outer Cape Cod Sat into
Sat night, though some question whether they will get in with a
mainly NW flow in place. Usually need a more northerly flow to get
the moisture to work across the arm of the Cape. Kept only slight
chance POPs going for this aspect.

Noting a fairly tight pressure gradient across the region during
this timeframe between the exiting low and strong high pressure
building out of the Ohio River valley to the mid Atlantic states.
Will see gusty winds especially along the coast, up to 30-35 mph
at times mainly Saturday into Saturday night.

Temperatures on Saturday will be close to seasonal normals for
early December, then will be cooler as mid level heights lower.

Sunday night through Wednesday...Low confidence.

High pressure will build across the region early Sunday night. May
see as weak low approach Sunday night into Monday morning. Lack
of good support or moisture should mean spotty light precip if
that. Still uncertain on the evolution of this system as it
approaches. At this point, have slight chance POPs in the
forecast.

Beyond this, H5 ridge looks to build over the northeast U.S. into
eastern Canada, while SW U.S. cutoff low becomes captured by this
building ridge in the developing SW flow aloft. This may approach
the region around the Tuesday to Wednesday timeframe, but very
uncertain on this track and timing. With the building ridge,
temperatures should moderate somewhat but will need to monitor for
possible cold air damming that may set up as any precip
approaches. Will continue to monitor.

&&

.AVIATION /15Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday/...

Today...High confidence.

Mainly VFR conditions. Winds shift to W and will briefly gust up
to around 25 kt as low pressure exits to the Gulf of Maine. May
see some gusts up to 30 kt through midday. Diurnal clouds will
redevelop by mid-late morning across western areas, with BKN deck
at 3000-4000 ft, which will move across the remainder of the
region through this afternoon. Less confidence on CIGS developing
across the eastern half of southern New England.

Tonight...High confidence.

VFR but areas of MVFR cigs across the higher terrain. West winds 5
to 10 kt except 15 to 25 mph along the coast and especially Cape
Cod and the Islands.

Friday...moderate confidence with some uncertainty on extent of
lake effect snow/rain showers entering MA/RI/CT.

Marginal VFR-MVFR cigs as lake effect rain/snow showers spilling
over the Berkshires into northern MA and eventually CT/RI and
southeast MA later in the day. West winds somewhat gusty up to 25
kt.

KBOS TAF...Rain shield moving rapidly eastward with dry weather
and IFR cigs improving to MVFR by 09z-11z. Moderate confidence.

KBDL TAF...Rain shield moving rapidly eastward with dry weather
and IFR cigs improving to MVFR by 08z-10z. Moderate confidence.

Outlook /Friday Night through Monday/...

Friday night through Sunday...High confidence. Mainly VFR. May see
some spotty light -SHRA Friday night into Saturday across outer
Cape Cod, with spotty -SHSN over the E slopes of the Berkshires
Fri night. W-NW wind gusts up to 25-30 kt Fri night into Sat
night, mainly along the S coast.

Sunday night and Monday...Low confidence. May see patchy MVFR
conditions in spotty -SHRA/-SHSN Sunday night into Monday morning,
then should be mainly VFR. Timing is uncertain, though.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Friday/...

Today...
S-SE winds shift to SW through mid morning across the eastern
waters as low pressure moves NE of the waters. Winds then become
W later this morning at 20-30 kt. A few gusts to 35 kt possible
near shore. Showers and fog move offshore and improve with the
wind shift around sunrise.

Tonight...

West winds 20-25 kt. Mainly dry weather and good vsby.

Friday...

More of the same...west winds 20-25 kt along with mainly dry
weather and good vsby.

Outlook /Friday Night through Monday/...Moderate confidence.

Friday night through Saturday night...Expect NW winds gusting up
to 25-30 kt across most of the waters /except Boston Harbor and
Narragansett Bay/. Seas will range up to 5-6 ft over the outer
waters. Winds should diminish after midnight Sat night.

Sunday through Monday...Seas may linger around 5 ft early Sunday,
otherwise winds and seas should diminish below small craft
criteria. N winds may gust up to 20 kt late Mon on the outer
waters.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 6 PM EST Friday for ANZ231>235-237-
     250-251-254>256.
     Small Craft Advisory until 7 PM EST this evening for ANZ230-
     236.

&&

$$
SYNOPSIS...Nocera/EVT
NEAR TERM...Belk/Nocera/EVT
SHORT TERM...Nocera
LONG TERM...EVT
AVIATION...Belk/Nocera/EVT
MARINE...Nocera/EVT



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