Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 101529
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1029 AM EST Sun Dec 10 2017

.SYNOPSIS...
Mainly dry and cool conditions are expected this afternoon and
Monday. Low pressure will approach from the west late Monday
night into Tuesday. This will likely bring a period of
accumulating snow mainly to the northwest of the Boston to
Providence corridor, while southeast New England should be mild
enough for mostly rain. A shot of arctic air follows Wednesday
and Thursday along with a period of bitterly cold wind chills.
Another low pressure system may bring more snow or mixed
precipitation to the region sometime Thursday night/Friday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Last of the snow moved offshore earlier this morning. clouds
continuing to diminish over land, but persist across the eastern
outer coastal waters. Plenty of sunshine expected to help the
melting process this afternoon. Minor tweaks to bring the
forecast back in line with observed trends.

Previous Discussion...

There were just a few lingering snow flurries across the
southeast New England coast early this morning, which should end
shortly. Main concern through mid morning are untreated
roads/walkways will be slippery with patchy black ice. These
conditions should improve later this morning and afternoon as
temps rise above freezing. A mixture of sun and clouds is
anticipated with high temps well up into the 30s to near 40.
Gusty west winds will make it feel a bit colder.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
Overnight...
Upper lvl shortwave, linked to weakening cold front will
approach through the overnight hours. As mentioned above, most
of the moisture associated with this wave/front is aloft and
minimal, so mainly increase in clouds is expected. Cannot rule
out an isolated SHSN, however these will be few and far between,
and relatively light. Once again, leaned on NIL to low end
slight chance POPs. Mins will be limited thanks to increase in
cloud cover overnight, but should still dip below freezing, into
the mid 20s thanks to a cool start.

Mon...
High pres builds in behind the weakening wave, allowing winds to
once again shift to the W. Mainly dry after any lingering SHSN
early. Highs once again remain cooler than they otherwise could
thanks to cool air aloft and lingering snowpack. Expecting
mainly mid 30s, with a few spots near 40 where less SN is
observed.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Highlights...

* Accumulating snow may impact Tue AM rush hour...mainly northwest
  of the BOS-PVD corridor and especially interior northern MA

* Arctic air follows Wed/Thu along with a period of bitterly
  cold wind chills

* Some more snow or mixed precipitation possible late Thu night/Fri

Details...

Monday night and Tuesday...

The main concern late Monday night into Tuesday revolves around snow
potential and possible impact to the morning rush hour...mainly
north and west of the Boston to Providence corridor.  Northern
stream shortwave energy will be diving south towards the Great Lakes
along with an initial surface low tracking to our northwest.  The
result will be a decent southerly LLJ developing which will increase
the forcing for ascent.  The antecedent airmass is cold, but given
southeast winds blowing off the ocean in early December is not
usually a recipe for much snow along the coastal plain.  While a
brief period of snow can not be ruled out, unless guidance changes
significantly would be tough to get more than an inch.

The forecast is more complex to the northwest of the Boston to
Providence corridor and particularly across interior northern MA.
The cold antecedent airmass should result in at least a period of
snow, but whether accums are minor or several inches hinges on a few
things.  Some of the 00z guidance has trended a bit quicker with
secondary coastal development, which would slow down or limit the
mid level warm surge.  A very small change in thermal profiles can
make a difference from some areas receiving an inch vs 5 inches of
snow. While this remains uncertain, the potential for several inches
of snow is highest across interior northern MA.  Regardless, the
Tuesday morning rush hour will likely be impacted to some degree.
Will also have to watch for a band of ice in the transition zone as
low level cold air will be tough to scour out. The bulk of the
precipitation should be over by late afternoon.

Wednesday and Thursday...

The main story will be a shot of arctic air as a deep upper trough
sets up over New England.  While dry weather will dominate other
than a brief passing snow shower or two, temperatures will be well
below normal.  Lows should be between 5 and 15 above and highs only
in the 20s. It also should be rather windy for a time which should
result in wind chills dropping to between 5 above and 10 below zero
late Wednesday night/Thursday morning.

Thursday night and Friday...

Low confidence at this point given time range and model
disagreement.  However, will have to watch for shortwave/low
pressure system that may bring a period of snow and/or mixed
precipitation to the region.

Next Weekend...

It looks like we should see some moderation in temps by the end of
next weekend, but the extent of that and low long it lasts is
unknown at this point.

&&

.AVIATION /16Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Monday/...

Today...High confidence. VFR, but some lingering FEW/SCT clouds
between 1000-1500 feet across the outer Cape and Nantucket.
Lower clouds continue to move offshore late this morning.
Westerly wind gusts of 20 to 25 knots develop into this
afternoon.

Tonight...High confidence. Mainly low end VFR despite a broken
deck of mid level cloudiness. Brief marginal MVFR conditions in
a spot snow shower possible late.

Tomorrow...High confidence. Mainly VFR. W winds 10-15
kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: Mainly VFR, with local MVFR-IFR possible toward daybreak
as SN moves into the region with some RN along the coastal plain.

Tuesday: Mainly IFR, with areas MVFR possible. Breezy. RA, SN.

Tuesday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHSN.

Wednesday: Mainly VFR, with areas MVFR possible. Windy with
gusts to 35 kt. Slight chance SHSN.

Wednesday Night: VFR. Strong winds with local gusts to 40 kt.

Thursday: VFR. Windy with 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 Monday/...High confidence.

W winds will briefly shift to the SW tonight, but gusts to 25 kt
are likely right into early Mon. Meanwhile seas, which currently
run 8-9 ft offshore will linger, only diminishing as winds recede
on Mon. Therefore, most small craft advisories will continue
into tomorrow.

Outlook /Monday Night through Thursday/...

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain.

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

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Areas of rough seas. Slight chance of
rain showers, slight chance of snow showers.

Wednesday: Moderate risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Slight chance of snow showers.

Wednesday Night: Moderate risk for gale force winds with gusts
up to 40 kt. Rough seas up to 11 ft. Slight chance of snow
showers.

Thursday: Low risk for gale force winds with gusts up to 35 kt.
Local rough seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 PM EST Monday for ANZ231>235-237-
     250.
     Small Craft Advisory until 7 AM EST Monday for ANZ251.
     Small Craft Advisory until 7 PM EST Monday for ANZ254>256.

&&

$$
SYNOPSIS...Frank/Doody
NEAR TERM...Belk/Frank
SHORT TERM...Doody
LONG TERM...Frank
AVIATION...Belk/Frank/Doody
MARINE...Frank/Doody



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