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Area forecast discussion
National Weather Service Taunton Massachusetts
104 PM EST Sat Dec 16 2017

Synopsis...
blustery and cold conditions today with less wind Sunday as
high pressure builds across the region. A weak warm front may
bring some light snow Sunday night and mixed rain/snow Monday.
Temperatures will be milder on Tuesday ahead of a cold front,
then turning blustery and colder Wednesday into Thursday.
Temperatures will moderate again on Friday as light rain moves
in ahead of another cold front.

&&

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

100 PM update...

Clouds have increased across the region early this afternoon
leading to filter sunshine. Temps have climbed to above freezing
for several locations in southern New England therefor have
increased high temps for today. Clouds will thicken this
afternoon thus limiting diurnal heating for the remainder of the
day.

Isolated snow showers are beginning to move across update New York
and into western Massachusetts. Expect snow showers to expand across the
region as northern stream shortwave pushes through. Best chance
for a dusting remains across western MA, CT, Rhode Island and the South
Coast. Went ahead and updated the snow potential for the region.
Also have seem some indications for a few snow squalls which
could limit vsbys this afternoon. Confidence isn't high, but
something to monitor. Aside from a few minor changes, the bulk
of the forecast remains on track for the rest of day.

Previous discussion...

Another northern stream shortwave drops south across new eng
this afternoon. Sunshine will give way to more clouds in the
afternoon as area of low and mid level moisture moves into the
region ahead of the shortwave. While most of the day will be
dry, a few snow showers are possible, mainly in western new eng
where column moisture is a bit greater. The shortwave will also
result in some gusty winds today and a reinforcement of the
colder airmass with 850 mb temps holding around -12c to -13c.
Highs will range from upper 20s to mid 30s. Gusts to 25-30 mph
developing.

&&

Short term /6 PM this evening through 6 PM Sunday/...
tonight...
gusty winds will gradually diminish tonight as high pres
approaches from the northwest. Good drying moves in which will result
in clearing skies although a few high clouds may move in from
the SW. Another cold night with lows down into the single
numbers in western Massachusetts where winds will decouple sooner, with
mostly teens elsewhere.

Sunday...
high pres builds to the north resulting in light winds but a
cold day as 925 mb temps around -8/-9c. With northerly winds
and cold start to the day, temps will only recover to the mid
20s to lower 30s, mildest near the South Coast. Expect lots of
sunshine but high clouds will be increasing in the afternoon.

&&

Long term /Sunday night through Friday/...
overview...

Continue to see a broad, progressive mid level steering flow
across most of the lower 48, especially over the northern tier
states, while cutoff 500 mb low tries to set up across the SW states
through Monday. Another stronger 500 mb short wave dives southeast out of
central Canada by mid week, but the question will be whether
some of its associated moisture will work far enough south to
bring another round of precipitation across.

Broad long wave ridge moves across the northern tier states by
around Thursday as another surface high moves quickly across.
Once again, another short wave in the steering flow. An
associated warm front may push across late next week as 500 mb
heights rise and winds shift to W-SW. Low pressure may also
form across the Great Lakes, with some precip trying to shift east.

Temperatures will start off below seasonal normals early next
week, then will briefly warm on Tuesday as the low passes north of
the region. Readings drop below normal again around mid week.
Beyond Wednesday, models showing a broad model solution spread,
so have below average confidence with the forecast.

Details...

Sunday night and Monday...

Weak, elongated short wave moves quickly eastward out of the
Ohio Valley, bringing some light precip with it. Still some
model solution spread in handling this short wave, with the GFS
and NAM being weak and diffuse while both the ggem and European model (ecmwf) are
showing a more organized albeit weak low moving across the
region with a more robust moisture field. Noting the quantitative precipitation forecast remains
light, with most of the higher amounts pushing in north and west of
the region late Sun night and Mon as the surface low moves
across northern New England Monday.

Do see the layer moistening up rather well, as seen on both the
GFS and NAM BUFKIT soundings, reaching through the dendritic
growth zone (which was generally between 850 and 650-700 hpa).
So, should see light snow developing across the region by around
midnight across central and western areas, pushing east after
midnight. At this point, looks like snow amounts will generally
be below an inch though some spots could reach an inch across
the east slopes of the Berkshires as well as over portions of NE
mass. May see precip taper off to patchy drizzle briefly as the
main area shifts east during Monday.

After overnight lows in the upper teens and 20s, expect highs
to recover to the 30s across most areas, except 40-45 across the
S coast with the continued zonal flow aloft and corresponding
500 mb heights around 550 dm.

Tuesday through Thursday...

Digging 500 mb short wave in the west-northwest flow across central Canada
will dive southeast during Tuesday. Associated weak surface low
forecast to remain north of the region, but the southern edge of the
precip may push into central and northern areas. Light quantitative precipitation forecast
amounts are currently forecast. Temps will moderate, so should
see mainly light rain, but could mix with or change to snow
showers as it ends early Tue night.

Leftover precip should push offshore during the early morning
hours on Wed, then colder air returns with gusty west-northwest winds
during Wed. Gusts up to around 25 kt are possible during the
day, but possibly up to 30 kt across Cape Cod and the islands.

Broad high pressure will cross the region on Thursday with dry
conditions and temps running up to 5 degrees below normal.

Thursday night and Friday...

As the high moves offshore Thu night, will start to see a
change in the upper level pattern. Another long wave trough
will push into the central U.S., Extending to the 4 corners
region. This will cause the steering flow to shift to west-SW
during this timeframe with increasing 500 mb heights and milder
temps toward late next week.

Surface low pres develops the western lakes, with low level
southerly winds bringing moisture to the upper Mississippi
Valley during Thu. Will still see northwest flow early across New
England, but as the high moves offshore, winds shift to S-SW.
Temps will respond during Fri, with highs ranging from around
40 across the east slopes of the Berkshires into north central mass up
to around 50 along the S coast.

Big question during this timeframe will be whether moisture
from off the Carolinas will start to feed north as winds shift
ahead of the developing low to the W, bringing some precip
along with it. Model solution spread continues, to lower
confidence on timing and track of precip.

&&

Aviation /18z Saturday through Thursday/...
forecaster confidence levels...
low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short term /through Sunday/...high confidence.

Before 00z...VFR with iso MVFR from aqw to fmh in snow showers.
Gusty west winds near 25 kts higher along the coastline.

Tonight and Sunday...VFR with diminishing wind.

Sunday night...VFR to start with MVFR conditions expanding from
south to north towards daybreak. Chance of snow showers during
the overnight.

Kbos terminal...high confidence.

Kbdl terminal...high confidence. Cannot rule out the potential
for a snow shower this afternoon.

Outlook /Sunday night through Wednesday/...

Sunday night: mainly VFR, with areas IFR possible. Chance snow.

Monday: MVFR-IFR conditions possible. Chance snow. Chance rn S
coast in the afternoon.

Monday night: mainly VFR, with local IFR possible. Patchy br.

Tuesday: mainly VFR, with areas MVFR possible. Breezy. Slight
chance rain showers.

Tuesday night: VFR. Windy with local gusts to 30 kt. Slight
chance shra, slight chance shsn.

Wednesday: VFR. Windy with local gusts to 30 kt.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday/...high confidence.

Today and tonight...W-NW gusts to 25-30 kt, with a few marginal
gale force gusts near 35 kt possible over southern waters.
Strong winds lingering into this evening before diminishing
after midnight. Small Craft Advisory all waters.

Sunday...light northwest winds with seas below Small Craft Advisory.

Outlook /Sunday night through Wednesday/...

Sunday night: winds less than 25 kt. Slight chance of snow.
Areas of visibility 1 to 3 nm.

Monday: winds less than 25 kt. Chance of rain, chance of snow.
Areas of visibility 1 to 3 nm.

Monday night: winds less than 25 kt.

Tuesday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas locally approaching 5 ft. Slight chance of rain
showers.

Tuesday night: moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Local rough seas. Slight chance of rain
showers.

Wednesday: low risk for gale force winds with gusts up to
35 kt. Areas of rough seas.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 1 am EST Sunday for anz231>234-251.
Small Craft Advisory until 7 PM EST this evening for anz230-
236.
Small Craft Advisory until 3 am EST Sunday for anz235-237-250.
Small Craft Advisory until 6 am EST Sunday for anz254>256.

&&

$$
Synopsis...kjc/evt

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