Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 120251
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
951 PM EST Mon Dec 11 2017

.SYNOPSIS...
Low pressure in the Ohio Valley will move across New England
Tuesday and northeast of the region Wednesday. It will bring
a mixed bag of weather with snow northwest, a mix to rain
central, and rain southeast late tonight and Tuesday. A shot of
arctic air follows Wednesday and Thursday with a period of
strong winds and bitterly cold wind chills. Another low pressure
system may bring more snow to the region sometime in the
Thursday night to Friday night timeframe, if it tracks close
enough to the coast. Somewhat milder weather will arrive by the
end of the upcoming weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

10 PM update...

Not much change from previous forecast. New 00z
NAM/RGEM/ARW/NMM/RAP and HRRR continue to have onset of precip
across western and central MA 4 am - 7 am, although low level
dry air may linger long enough to delay precip until 9 am - noon
across RI and southeast MA. Thus may have to push back onset
times across this area. Also given the lack of cloud cover this
evening along the south coast has allowed good radiational
cooling 930 pm temps in the mid to upper 20s across Cape Cod and
Nantucket. Therefore will adjust hourly temps to reflect this
current trend however temps will level off and then rise
overnight in the coastal plain with increasing cloud cover and
onshore winds developing. Otherwise previous forecast is on
track.

Previous discussion...

A strong short wave trough seen on water vapor over IL will be
rapidly moving east tonight and to eastern NY late tonight.
Low pressure at the surface over Ohio will move into New York
state overnight. Warm air advection cloudiness will increase
across our region overnight and snow is likely to break out in
northwest MA before daybreak. There is a chance that
precipitation could reach as far as northern CT and central MA
by daybreak. Although 850 mb temperatures are cold enough for
snow, the 925 mb temperatures warm enough such that a few hours
of freezing rain are possible in northern CT, northwest RI, and
into southern Worcester and Middlesex Counties in MA within a
few hours of daybreak. This could be a problem for the morning
commute.

We have expanded the Winter Weather Advisory southward and
eastward a bit, to include Hartford, Tolland, Windham (in CT),
northwest Providence County (in RI), and central and northwest
Middlesex Counties (in MA). In these areas, a thin
coating...less than one tenth of an inch...of ice is possible
before daybreak. The Advisory remains in effect for the
remainder of western and central MA.

Lows tonight will be in the 20s except low to mid 30s Cape Cod
and the islands. Light winds becoming southeast. Temperatures
may begin to rise late in southern areas as southeast winds
become established.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...

Tuesday...

Any freezing rain should be short-lived but it could be a factor
during the morning commute in the Hartford, Springfield, and
Worcester areas, as well as the northwest suburbs of Providence.
925 mb temps warm very rapidly on strong southerly low level
winds, so it should change to plain rain across most of southern
New England during the morning. In fact, high temperatures will
reach 50 degrees in RI and southeast MA!

In the higher terrain of northern Worcester County and in the
slopes of the Berkshires, snow will be moderate to heavy for a
few hours in the morning, with total accumulations ranging from
2 to 4 inches, with local amounts of 5 or 6 inches in the
extreme northwest corner of Franklin County, MA. Even there,
some sleet and freezing rain may mix in during the afternoon.

Southeast winds will become gusty...with up to 25-35 mph gusts
possible along the coast. We have discounted the NAM, which has
what appears to be way too strong of a LLJ of 80 kt at 850 mb
and 50-60 kt gusts at the surface. All other models are more
like 40-50 kt at 850 mb.

Tuesday night...

Winds shift to the west behind the departing storm system.
However, as a vigorous upper level low approaches, scattered
snow showers or squalls are possible, which could add some
light accumulations, especially in western sections toward
Wednesday morning.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Wednesday...

There is a chance of snow squalls continuing into Wednesday
morning as an arctic front progresses across Southern New
England. Very little snow accumulation is expected with these
passing showers, likely up to an inch at most west of the
Worcester Hills.

Winds will pick up in the afternoon as there is an impressive upper
level jet overhead. Models are in agreement with 40kts at 925mb
mixing down to the surface Wednesday afternoon. The GFS suggests
the strongest winds will be over the northern tip of the Cape
and extend into Mass Bay. Wind gusts between 40 to 50 mph are
not out of the question. Winds will likely peak by 00Z Thursday
as the upper level jet sits directly over the region.

Wednesday night temperatures will range in the teens due to the
arctic airmass now over the region. With the combination of the
arctic airmass and strong surface winds, wind chills are likely
to hover near zero degrees overnight. With minimal cloud cover
as well, radiational cooling will add to the low apparent
temperatures.

Thursday and Friday...

Strong winds will continue into Thursday morning but begin to
dissipate throughout the afternoon and evening.

Both the ECMWF and NAM point towards a weak system that brings
light snow to the islands and southern coast of New England
Thursday afternoon. The system will likely not linger off the
coast for very long, resulting in minimal snow accumulations, if
any at all.

The arctic airmass remains over the region through Thursday and
Friday resulting in much below normal afternoon temperatures. With
the winds diminishing by Thursday evening, wind chills should not be
an issue, however overnight temperatures will continue to range in
the teens across much of the region.

Friday night and Saturday...

A coastal low is expected to clip the region Friday/Saturday
resulting in periods of heavy snow along the 95 corridor.
Unfortunately, the models are not in agreement with timing or
position for when it does make its way up to Southern New
England.

Going with guidance from the ECMWF and NAM, precipitation will push
north across the region starting at 18z. As the low moves further
northeast, east of the 95 corridor will likely see the most
accumulation. The coastal low is expected to push offshore by
Saturday afternoon.

Sunday...

A ridge builds in Sunday morning behind the coastal low. Winds will
turn to the southwest, advecting warmer temperatures into the region
by midday. Dry and seasonable temperatures will continue through
early next week.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short Term /through Tuesday Night/...

03z update...

No major changes to 00z TAFs. Precip begins approximately 09z-
12z across western and central MA, 14z-17z remainder of the
area. Previous discussion below.

==================================================================

Tonight...Moderate confidence.
VFR to start, will give way to MVFR early AM Tue as CIGS lower
and light SN/FZRA moves in mainly after 06Z along and north of
route 2. SN accums would be light. Light winds shift around to
the E, except SE along the coast.

Tuesday...Moderate confidence. Mixed MVFR and occasional IFR
conditions in a mix of SN/FZRA giving way to all RA through
sunrise into midday Tue. Risk for NW MA to remain SN long
enough for accums to reach 3-6 inches with little or no snow
accumulation southeast of a Hartford to Boston line. Period of
FZRA before the change to RA. Conditions improve after 20Z.
Winds gusting to 20-30 kt along the coast.

Tuesday night...Moderate confidence. MVFR ceilings and scattered
snow showers moving from west to east across the region. Local
IFR in any heavier snow showers, especially in western sections.
West winds gusting to 20-25 kt at times.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF. Potential for wintry mix
between 12Z-14Z.

Outlook /Wednesday through Saturday/...

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

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

Thursday through Thursday Night: VFR. Breezy.

Friday: Mainly VFR, with local IFR possible. Chance SN.

Friday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SN.

Saturday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Tonight...High confidence. Winds are slowly diminishing. Seas
will slowly subside...to below SCA criteria over the southern
waters by this evening. Quiet boating weather tonight, but that
will be very temporary.

Tuesday...Moderate confidence. Winds gradually shift around to
the SE. Gusts 25-30 kt expected on the S waters with 35-40 kt
possible on the E waters. Gale Warnings are in effect for the
eastern waters with Small Craft Advisories posted for all other
waters. Rough seas of up to 5 to 10 ft on the outer waters.

Tuesday night...Winds shift to the southwest to west. Winds
still gusting to 25-30 kt and seas still quite rough, especially
over the southern outer waters.

Outlook /Wednesday through Saturday/...

Wednesday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 14 ft. Slight chance of snow showers.
Visibility 1 to 3 nm.

Wednesday Night: Moderate risk for gale force winds with gusts
up to 40 kt. Rough seas up to 14 ft.

Thursday: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Local rough seas. Local visibility
1 to 3 nm.

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

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of snow. Areas of visibility 1 to 3 nm.

Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Chance of snow. Visibility
1 to 3 nm.

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Local visibility
1 to 3 nm.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for
     CTZ002>004.
MA...Winter Weather Advisory from 4 AM to 1 PM EST Tuesday for
     MAZ005-010>012.
     Winter Weather Advisory from 4 AM to 4 PM EST Tuesday for
     MAZ002>004-008-009-026.
RI...Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for
     RIZ001.
MARINE...Small Craft Advisory from 9 AM Tuesday to 6 AM EST Wednesday
     for ANZ231>234.
     Small Craft Advisory from 1 PM to 7 PM EST Tuesday for ANZ230-
     236.
     Small Craft Advisory until 6 AM EST Wednesday for ANZ235-237-
     255-256.
     Gale Warning from 10 AM to 7 PM EST Tuesday for ANZ250-251-254.

&&

$$
SYNOPSIS...Correia/GAF
NEAR TERM...Nocera/Correia/GAF
SHORT TERM...GAF
LONG TERM...Correia
AVIATION...Nocera/Correia/GAF
MARINE...Correia/GAF



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