Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KBOX 032145

Area Forecast Discussion
National Weather Service Taunton MA
445 PM EST Sat Dec 3 2016

High pressure builds across the area allowing for clear
conditions and light winds Sunday. A period of accumulating snows
is forecast from early to mid Monday morning as a weather
disturbance sweeps across the region. High pressure returns Monday
night with mainly dry conditions into Tuesday. Low pressure off
the mid Atlantic coast may bring some mixed light rain and/or snow
into southern New England Tuesday night into Wednesday night,
though timing and track remain uncertain. A polar front crosses
the region Thursday with rain showers possibly changing to snow
showers. Very windy and cold conditions Friday and next Saturday
with wind chill indices in the single digits and teens at night.


Into this evening...

Gradual pressure rises as high pressure builds in from the W as
low pressure exits E. Slight dampening of the winds but remaining
blustery out of the NW with gusts up to 30 mph. Scattered to broken
cloud decks continue as mid-level energy continues to rotate through
the overall cyclonic flow. Plenty of moisture and steep lapse rates
below H8-7.


A quiet, cold night of weather. Scattered to broken cloud decks are
forecast to continue across the N/W high terrain of S New England
and over the Outer Cape given N/NW flow relaxing through the night
as high pressure builds in from the W. Given the breezy conditions
somewhat cautious of the coldest guidance. Should be clear over S/E
interior S New England and should winds become light, especially
within the sheltered valleys, then it should drop off. So with a
combination of cold air advection and/or radiational cooling, most
locations will see lows in the 20s. Add in the winds, going to feel
like the teens for several locations by Sunday morning.



Pleasant but cool day on tap. Surface high pressure building into
the region as heights rise aloft, winds should dampen beneath the
anti-cyclonic flow. Clouds dissipating giving all of S New England
mostly clear conditions. Recent dousing rains along with a h925
airmass aloft around -4 to -6C, hesitant to go with the warmest of
guidance but believe we will come close. Thinking highs around the
upper 30s with warmest locations around the low 40s across the lower
CT Valley and interior S/E portions of S New England. Light NW wind.

Sunday Night into Monday...

 * Snow and impacts anticipated for the Monday morning commute.
 * Takeaways: reduced visibilities at times, slippery conditions.
 * Light accumulations forecast, coating up to 1 inch.
 * Highest snow accumulations possible above an inch over the east
   slopes of the Berkshires.

Mid to upper level feature flattening while becoming sheared by the
strong W flow aloft. Overall weakening as synoptics stretch, there
is still a measure of lift of a continental tropical airmass over-
running, especially along the 285-295K theta surfaces (H9-7), across
a diffuse warm frontal boundary beneath a measure of mid to upper
level forcing, enough to generate some low to mid level fronto-
genesis, squeezing the available moisture out of the atmosphere as a
mix or rain or snow. Went closely with the EC with this forecast.

One thing for certain is the environment ahead of inclement weather.
Prior to clouds on the increase W to E, conditions will be clear as
winds will be light allowing 2m temperatures to drop into the 20s.
Much of the area except along the immediate coast will be below
freezing before onset of precipitation towards early Monday morning.
Also will be fairly dry dewpoints as well.

But as to the availability of moisture aloft, especially within the
snow growth region (-12 to -18C), there is some uncertainty. Dry air
will be eroding the continental tropical airmass especially within
the stronger W flow. Anticipating top-down drying with mechanical
mixing given the faster flow aloft. Aside, will lean towards the
presence of ice (thinking its availability down to -8 to -10C).
Will keep any and all wintry precipitation as snow, no freezing rain.

So altogether, looking at a window of impacts around early to mid
morning Monday, roughly 4 am to 10 pm. Moistening low levels with
time, ran a wetbulb procedure closer to temperature with this event
given how light it is, but keep it below freezing longer along with
the presence of snow. A consensus of forecast solutions along with
ensemble probabilistics, at least a coating for much of interior S
New England with highest amounts of a tenth or two inch over W New
England with up to half an inch over the N/W high terrain.

May be too bullish on amounts as latest forecast has on average a
half an inch for much of S New England. But aside, snow is expected
and the main takeaway is that travel will become hazardous given the
timing of the event during the Monday morning commute and should
roads become snow covered. At a minimum snow will result in reductions
in visibility.

Towards midday conditions should quickly improve with winds becoming
breezy out of the W and conditions clearing out. Temperatures remain
stable during the morning given cloud cover and W winds. More than
likely by midday into afternoon with clearing we`ll see temperatures
bounce to highs around the upper 30s, low 40s.

Monday night...

Turning quiet and once again cold. High pressure building back into
the region parent with rising heights aloft. Winds should become
light out of the N as conditions become mostly clear. Especially for
those areas with any snow cover, should see radiational cooling
proceed resulting in lows well down into the 20s, perhaps teens for
the high terrain. Leaning with the coldest MOS guidance.



* Very active weather pattern
* Mixed precipitation possible late Tuesday night and Wednesday
* Very strong polar front blasts through on Thursday
* Windy and very cold into next weekend with strong gales over
  the waters

Tuesday... High confidence.

High pressure over eastern Quebec and
northern New England will provide a mostly sunny day. However
there will be cool northeast to east winds and increasing high and
mid cloudiness from the southwest during the afternoon. Highs only
upper 30s to lower 40s.

Tuesday night through Wednesday night...Moderate confidence.

The upper level closed low from the southwest states will have
opened up and what is left aloft will be moving across the Mid-
Atlantic states then passing the south of New
England. Meanwhile a strong upper low will be moving across
western Ontario. The net effect will be to cause a splitting of
the flow over us. Low pressure at the surface off the VA/NC coast
will cause cloudiness and some light precipitation to spread into
mainly western and southern portions of southern New England
Tuesday night. The precipitation could be a mix of snow and rain
in northern CT and central/northeast MA and mainly light snow in
northwest MA...with rain elsewhere.

On Wednesday...GEFS and ECMWF ensembles all show the main low
moving straight east and passing well to our south. However...with
light moist easterly flow over the area we should remain cloudy
and there could still be some light rain southeast and a light
rain/snow mix northwest. Not expecting any more than an inch of
snow in the northwesternmost areas. Highs upper 30s northwest to
mid 40s southeast. The light precipitation may continue into
Wednesday night with the best chances of light snow still in the
slopes of the Berkshires especially in northwest MA. Some light
accumulations still possible there Wednesday night.

Thursday and Thursday night...Moderate confidence.

Still some big timing differences in models regarding the
progression of a very sharp upper level trough and arctic cold
frontal passage. The GFS and its ensembles are roughly 12-24
hours quicker than the ECMWF and its members. We have taken a

Southerly winds ahead of the front will cause temperatures to rise
to the upper 30s northwest and upper 40s southeast Thursday.
Showers are likely ahead of the front. They will mainly be rain
showers, but if the front enters northwest MA before evening, the
rain showers could change over the snow showers there late in the

The arctic front should pass through Thursday night, accompanied
by a chance of snow showers across most of the region, except rain
in southern RI, Cape Cod, and the Islands. Lows 25 to 30 except
mid to upper 30s Cape Cod and Islands.

Friday and Saturday... Moderate confidence.

Ensemble means show low pressure bombing out over southeastern
Canada...anywhere from Labrador to Nova Scotia. A very strong
pressure gradient over New England will cause northwest winds to
gust to 25-35 mph inland and to 35-45 knots over the coastal
waters, with perhaps some 50 knot gusts over the waters. Depending
on timing, the max winds could be Friday afternoon or Friday
night. Highs Friday will struggle to rise through the 30s except
lower 40s Cape Cod and Islands. Models are indicating that lake
effect snow showers from the eastern Great Lakes may actually make
it over the Berkshires and into portions of western and central
Massachusetts. Have gone with 20-30 percent PoPs for those areas.

With clearing skies Friday forecasting temperatures to
drop to below model consensus guidance levels...into the upper
teens in the Worcester hills and slopes of the Berkshires with 20
to 25 elsewhere and upper 20s to near 30 Cape and Islands.
Winds will still be 20-30 mph and this causes some single digit
wind chill index values in northwestern Massachusetts Friday night.

High pressure builds into the Mid-Atlantic states on Saturday, but
despite sunshine it will still be blustery and cold across
southern New England. Highs will only reach the upper 20s to mid
30s. Wind chill indices Saturday night could dip to near zero in
northwest Massachusetts.


Forecaster Confidence Levels...

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

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

Remainder of today...
VFR. SCT-BKN low-end VFR cigs over N/W MA and CT high terrain as
well as across the Outer Cape. Low risk MVFR. NW winds gusting as
high as 35 kts with highest gusts over high terrain, coastline.

VFR. NW winds diminishing but initially blustery. Gusts up around
25 kts dampening. Cigs dissipating.

VFR. Mostly clear with light NW winds.

Sunday Night into Monday...
Mostly -SN with coastal -RA for the Monday morning push. Will see
conditions deteriorate around 9-15z to IFR with -SN as VSBY will
most likely be impacted. Cigs mainly MVFR, IFR for the high terrain.
W winds around 5 to 10 kts. Improving VFR beginning around 18z Monday.
Snow accumulations possible, at least a coating, for all interior

Monday Night...
VFR. SKC. Light NW winds.

KBOS TAF...Gusty NW winds continuing around 25 to 30 kts.
Diminishing through the overnight period.

KBDL TAF...Gusty NW winds continuing around 25 to 30 kts.
Diminishing through the overnight period.

Outlook /Tuesday through Thursday/...

Tuesday...High confidence. VFR.

Tuesday night through Wednesday night... Low to moderate confidence.
MVFR to local IFR ceilings in light rain RI and southeast MA...
a mix of rain and snow northern CT, central and northeast MA, and
light snow northwest MA.

Thursday... Low to moderate confidence. Mainly MVFR ceilings in
areas of light rain showers ahead of an approaching arctic cold
front. Depending on timing, rain showers could change to snow
showers with local IFR conditions in western MA late in the


Forecaster Confidence Levels.

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

Short Term /through Monday Night/...

Through Sunday...

High pressure building into the waters will allow winds and seas
to relax. Initially, NW gusts up to 30 kts expected, dropping out
overnight into Sunday morning. Wave action dampens through Sunday.
This will allow small craft advisories to conclude. Ocean effect
rain showers likely to be an issue throughout, especially over the
outer waters.

Sunday night into Monday night...

Weak disturbance will sweep W to E across the waters during the
early to mid Monday morning period. Winds will overall be light
and out of the W. Expect showers, perhaps some slight reductions
in visibility. Winds increase late going into Tuesday morning out
of the NW, could see some gusts up to 20 kts. Waves remaining
below 5 feet throughout.

Outlook /Tuesday through Thursday/...Moderate confidence.

Tuesday through Wednesday night...Winds and seas remain below
small craft criteria for most of the waters. NE to E winds may
gust to 15 to 20 knots at times. Seas may build to near 5 ft
over the southern outer waters by Wednesday night.

Thursday...Small craft advisories will likely be needed. Ahead of
an approaching Arctic front, winds will shift to the southeast to
south and may gust up to 25 to 30 kt by late Thursday afternoon.
Seas will be building to 5 to 7 ft over the outer waters.

Attention mariners... Although it is just beyond this current should be aware that northwest to west strong gales
with some potential for storm force gusts are expected to develop
Friday into early next weekend. Stay tuned to the forecast.


MARINE...Small Craft Advisory until 10 AM EST Sunday for ANZ230>237-251-
     Small Craft Advisory until 4 PM EST Sunday for ANZ250-254-255.


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