Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 112059

Area Forecast Discussion
National Weather Service Boston/Norton MA
359 PM EST Tue Dec 11 2018


Mainly dry and cold weather prevails into Thursday, except for some
scattered ocean effect snow showers Wednesday, mainly across
the outer-Cape. Mild temperatures arrive Friday and continue
into early next week with the best chance for rain Friday night
into Saturday in association with low pressure.



Dry weather will continue throughout the day as a high pressure
remains over the region. Light veering winds with clear skies
will dominate into the evening, apart from ocean effect clouds
that continue to linger over the outer Cape, as well as
Nantucket. Clouds will also increase along the south coast and
SE Mass overnight as a tongue of moisture at 925mb pushes

Overnight temperatures will be 5 to 10 degrees below normal
once again, with areas at higher elevations possibly seeing lows
into the teens.



A shortwave will move southeast across the region overnight,
providing enough instability for ocean effect snow along the
outer Cape tomorrow morning. Models support ocean effect snow
tomorrow along the outer Cape. As winds turn out of the NNW by
12z tomorrow, combining with the instability and moisture aloft,
ocean effect seems likely after 12Z.

Looking at model soundings, it looks like the temperature
difference between an inversion aloft and the sea surface temps
will be between 15C and 20C, which will support strong snow
showers during the time period. Snowfall accumulations look to
be between 1 to 2 inches along the outer Cape, but less than 1
inch is possible into Falmouth and southern Plymouth county.

Elsewhere across the region will be mostly sunny and dry.

Snow will likely last throughout the day, however, some models
are showing pockets of dry air moving in aloft after 18z, which
may cut off the snow showers earlier than expected.

A strong high pressure builds into the northeast Wednesday
night. With mostly clear skies and light northerly winds,
overnight temperatures will be more than 10 degrees below
normal. Northern Massachusetts could see lows in the single




* Dry but cold Thursday
* Milder Friday with a period rain focused Fri night into Sat
* Low confidence forecast early next week



High pressure overhead will result in mostly sunny skies but another
cold day.  After a very cold start...light winds and the low
December sun angle will only allow afternoon high temperatures to
recover into the lower to middle 30s.

Thursday night...

Dry weather should prevail...but we may see some mid level
cloudiness overspread parts of the region overnight.  This a result
of high pressure moving off the coast and warm advection aloft.
Still expect to see low temps bottom out mainly in the upper teens
to lower 20s with rather light winds.

Friday into early next week...

A pattern change to milder weather expected as an active Pacific jet
flushes out the cold weather we have experienced over much of the
last month. Given the pattern transition and active sub-tropical
jet...the forecast going forward remains low confidence into early
next week.

We do think that warm advection ahead of southern stream energy will
result in a period of rain...focused Friday night into Saturday.
A low risk for a period of freezing rain at the onset can not be
ruled out...but generally expecting a rain event.

The other big issue is the track/timing of the surface low. This
will all come down to the location/strength of both the northern and
southern stream energy.  If the southern stream energy gets pulled
northward, precipitation chances would continue into Sunday and/or
Monday...but if it gets shunted south our region will mainly be dry.
If we do see precipitation Sun into Mon...ptype would favor rain
given the overall milder regime. However...a low risk for some
wintry precipitation can not be completely ruled out. The storm
would have to track near the Benchmark and would also require enough
marginally cold air to work down from the north.


Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...High confidence.

Overall VFR. Exception is Cape and Islands, as well as portions
of Southeast MA as SCT-BKN -SN is forecast Wednesday with SCT-
BKN low-end VFR to MVFR CIGs. Potential VSBY issues down to IFR
with -SN. With -SN, winds shifting N / NW, becoming breezy with
potential gusts up around 20 kts late.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: VFR.

Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance

Friday Night: Mainly MVFR, with local IFR possible. Breezy. RA.

Saturday: Mainly MVFR, with local IFR possible. RA likely.

Saturday Night: Mainly MVFR, with local IFR possible. Windy
with areas gusts to 30 kt. Chance RA.

Sunday: Mainly MVFR, with local IFR possible. Windy with local
gusts to 30 kt. Chance RA.


Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...High confidence.

Rather tranquil boating conditions through this evening with
good visibility. Northerly flow increases across the waters
late tonight into Wednesday. Rough seas expected to develop
across the outer coastal waters as a result. A Small Craft
Advisory has been issued for the waters along the Cape due to
high seas and strong gusting winds. In addition to the winds,
ocean- effect snow showers may reduce visibility at times to
less than 3 NM late tonight into Wednesday across the eastern
coastal waters.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft.

Thursday Night: Winds less than 25 kt.

Friday: Winds less than 25 kt. Chance of rain.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas locally approaching 5 ft. Rain.

Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Rain likely.

Saturday Night: Moderate risk for Small Craft Advisory winds
with local gusts up to 30 kt. Rough seas up to 11 ft. Chance of

Sunday: Moderate risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 12 ft. Chance of rain.


MARINE...Small Craft Advisory from noon Wednesday to 1 PM EST
Thursday      for ANZ250-254-255.


NEAR TERM...Correia
SHORT TERM...Correia
MARINE...Correia/Frank is the U.S. government's official web portal to all federal, state and local government web resources and services.