Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 050848
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
348 AM EST Mon Dec 5 2016

.SYNOPSIS...
Brief period of light to moderate snow during the morning commute
will result in snow covered roads especially across CT...western
and central MA. Steadiest snow occurs early this morning then mix
and/or change over to rain toward midday from south to north. Then
partial clearing late in the day. Dry Monday night into Tuesday
with high pressure. Low pressure off the mid Atlantic coast may
bring some mixed light rain and/or snow into Southern New England
Tuesday night into Wednesday. A polar front crosses the region
late Thursday or Thursday night, with the chance for rain and
snow showers. Very windy and cold conditions are then expected for
Friday and next Saturday.

&&

.NEAR TERM /THROUGH TODAY/...

345 am Update...

*** Brief period of snow and slippery travel during the morning
 commute ***

Snowfall...

Warm advection snows entering NJ into eastern NY at 3 am. Column
cold enough to support snow across all of southern New England.
Bulk of the short wave energy tracks northwest of southern New
England. Thus best forcing for ascent tracks across NY state into
northern New England. Hence upward vertical motion is modest
across our region. In addition system is very progressive limiting
duration of precip. Furthermore deep layer moisture is lacking.
This may be why bulk of guidance only has likely pops and not
categorical. All of these parameters will limit snowfall
potential.

Both NAM and GFS show modest omega in the snow growth region from
09z to 12z across southern New England from west to east this
morning. However during this time low level dry air hangs tough
and by the time the column saturates dry air aloft is rapidly
advecting eastward into the snow growth region. This will limit
duration of steady/moderate snow to about only an hour or two (3
hrs at the most) this morning from 09z to 12z west to east. Given
this leaned toward the lighter qpf from the 00z GFS/EC and RGEM.
This yields snowfall potential of a coating to an inch across RI
and eastern MA...before mixing or changing to rain later this
morning before ending this afternoon.

Farther inland (north and west of I-95)...given snow band is
expected to weaken from west to east...slightly more snow inland
with 1-2" likely. Low risk for a few spots receiving up to 3"
across western CT/MA before snow band weakens eastward. Also low
risk for a few interior spots receiving a brief period of freezing
drizzle later this morning as dry air advects into the snow growth
region...eroding ice crystals with supercooled droplets in warmer
clouds below dominating. So in a nutshell some slippery travel
for the morning commute along and northwest of I-95 corridor in RI
and eastern MA. Southeast of this region duration of snow will be
very brief.

Temperatures...

Cold this morning but once precip ends temps will rise into the
upper 30s and lower 40s this afternoon. May even see a few breaks
of sunshine mid to late afternoon CT...western-central MA and
toward sunset RI and eastern MA. Winds will be fairly light today
given weak pgrad, so not much of a wind chill to speak of.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/...

345 am update...

Tonight...

Strong mid level subsidence behind departing short wave which
yields deep layer drying thru the column across southern New
England tonight. Thus dry weather with mostly clear skies. Modest
cold air advection behind this wave with blustery NW winds
developing along the coast including Cape Cod and the islands.
Seasonably cold with lows in the 20s...low 30s in Boston,
Providence and the remainder of the immediate coastline including
Cape Cod and the islands.

Tuesday...

Short wave ridging over the area will yield sunshine much of the
day. However progressive upper air pattern with southern stream
system approaching New England late in day resulting in clouds on
the increase from SW to NE. Temps slightly colder than normal with
highs in the upper 30s and low 40s. However it will feel
seasonable given lots of sunshine and light winds with weak high
pressure overhead.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights...

* Mixed precipitation possible Tuesday night into Wednesday
  morning
* Very strong front crosses the region Thu or Thu night
* Windy and cold into next weekend with strong gales over the
  waters


Tuesday night through Wednesday night...Moderate confidence.

Models continue to show a fast moving, weakening mid level short
wave in SW flow moving thru our area, while a weak low pressure
system emerges off the mid Atlantic coast Tuesday night. A potential
secondary low pressure in southern Great Lakes region is expected to
weaken as it moves E. Mid-Atlantic low center is forecast to track
well south of 40N/70W, with our area having relatively light QPF
totals.

Best chance for measurable precip should be Tuesday night into
Wed morning, then as low moves further offshore, precip becomes
more spotty/diminishing for Wed afternoon. At this time thinking
there is the potential for a wintry mix of light rain and snow to
all light snow across much of the area Tue night, then on Wed
precip winding down but a changeover to light rain at least along
the coastal plain.

Wednesday night should be mainly dry with our area in between
systems.

Thursday and Friday...Moderate confidence.

There continue to be some timing and track differences regarding
polar front wrapping around cutoff upper low across Hudson Bay.
Digging mid level long wave trof will bring a surge of very cold air
into our area. GFS timing of front is Thu day, while ECMWF timing is
more Thu night. Will go with a model compromise for this
timeframe. Mainly chance pops since exact timing of frontal
passage is still uncertain. Chance for rain and/or snow showers
across most of the region.

Colder air will continue to sweep into the region during Friday as W-
NW winds quickly increase. While at this time most of Friday/Friday
night should be dry, cold air advection combined with WNW flow going
thru eastern Great Lakes Region could translate to a few snow
showers making their way into the east slopes of the Berkshires.
Also the potential exists for a tightening pressure gradient as a
low over the Canadian Maritimes intensifies, which could allow for
gusts of 25-35 kts. Wind chills Fri night dip into the
teens/single digits.

Saturday and Sunday...Moderate confidence.

While mainly dry conditions are anticipated for Saturday with
high pressure working eastward, may see lingering snow showers
across the east slopes of the Berkshires, as well as ocean effect
snow showers off the coast. Our area could still be caught in a
tight pressure gradient with a deepening low pressure over the
Canadian Maritimes. Thus could have winds gusting to 25-35 kt,
strongest winds along east coastal MA and the nearby coastal
waters.

During Sunday models show potential for a weak low pressure system
moving eastward towards/into our area. While moisture does not look
abundant with this feature, it could bring some light snowfall to
the area.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

09Z update...high forecast confidence on trends but some
uncertainty on exact timing of details.

Leading edge of precip on radar not reaching the ground due to
dry air eroding precip before reaching the surface. Snow
overspreads CT/RI/MA between 09z-12z from west to east.
Steady/moderate snow in MVFR-IFR for only an hour or two before
becoming lighter and intermittent between 12z-15z. Then snow
changes to rain 15z-18z across RI and eastern MA...possible much
of CT too. Before then snow accumulations of a coating to an inch
for RI and eastern MA...1-2" elsewhere with a low risk of a few
amounts up to 3" across western CT/MA. Also low risk for a period
of freezing drizzle 12z-15z across the interior. Precip ends 18z-
21z from west to east with conditions improving to MVFR/VFR 21z-
24z from west to east.

Tonight...high forecast confidence.

VFR likely along with increasing NW winds up to 25 kt across Cape
Cod and Islands. Lighter winds elsewhere. Dry weather prevails.

Tuesday...high forecast confidence.

VFR and diminishing winds. Dry weather prevails with any risk for
precip holding off until after sunset.

KBOS TAF...
MVFR with -SN around 12z-15z before mixing with and changing over
to -RA 15z-18z. Snow accumulations of a coating to an inch
possible. MVFR may improve to VFR toward 00z.

KBDL TAF...
MVFR in SN 09z-12z then possibly mixing or changing to rain 15z-
18z. Snow accumulations of 1 to 2 inches with a low risk of
snowfall amounts up to 3 inches. Also low risk for a period of
freezing drizzle 12z-15z.

Outlook /Tuesday Night through Friday/...

Tuesday night and Wednesday...Low to moderate confidence. MVFR to
local IFR ceilings Tue night into Wed morning in light rain RI/SE
Mass, a mix of rain/snow elsewhere. Improving to VFR Wed
afternoon/night.

Thursday...Moderate confidence. Mainly MVFR ceilings in areas of
light rain showers ahead of approaching polar front. Depending on
timing, rain showers could change to snow showers with local IFR
conditions Thu afternoon/night.

Friday...Moderate confidence. VFR except localized MVFR in
isolated snow showers far interior MA.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Tuesday/...

345 am update...

Today...high forecast confidence.

Main issue will be vsby restriction in snow early this morning
then snow changing to rain later this morning. Vsbys improve late
today from west to east. Otherwise light winds today.

Tonight...high forecast confidence.

Low pressure develops east of New England resulting in NW winds of
20-25 kt. Thus SCA posted. Dry weather and good vsby.

Tuesday...high forecast confidence.

Diminishing winds as high pressure builds over New England. Dry
weather and good vsby.

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

Tuesday night through Wednesday night...Winds and seas remain
below small craft criteria for most of the waters. NW winds Mon
night will shift to E, gusting up to 20 knots at times.

Thursday...Small craft advisories may be needed. Winds will shift to
the SW-W and may gust up to 25 to 30 kt by late Thursday
afternoon/night.  Seas will be building to 4-6 ft over the outer
waters.

Friday...Strong W-NW gales expected to develop. There is the
potential for some storm force gusts. Stay tuned for the latest
forecast updates.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 7 PM this evening to 7 AM EST
     Tuesday for ANZ231>235-237-250-251-254>256.

&&

$$
SYNOPSIS...Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...NMB
AVIATION...Nocera/NMB
MARINE...Nocera/NMB



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