Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 171555
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1055 AM EST Fri Nov 17 2017

.SYNOPSIS...
Intensifying low pressure over the Maritimes yields a dry but
blustery and chilly day across New England. High pressure crests
across the area tonight providing dry but cold weather.
Strengthening low pressure will push across the St Lawrence
River Valley this weekend as gusty southwest winds develop
Saturday afternoon and night. A cold front will cross the region
by Monday morning, with another shot of cold and blustery
conditions. Dry conditions will prevail from Monday through
Thanksgiving. Temperatures will fluctuate daily, from mild to
below average in the fast flow aloft.

&&

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

no major changes to the forecast this morning, but did bring it
back in line with observed trends. The main concern remains the
winds. Decided to hold off on a Wind Advisory for this morning.
Wind speeds are just beneath criteria and the spotter reports
are only indicating isolated minor damage.

Previous Discussion...

Closed mid level low and surface cyclone over Nova Scotia continues
to intensify today given trough amplification and associated height
falls. This results in modest CAA into southern New England with 850
temps lowering to -6C this morning, about -1 standard deviation
colder than climo. This combined with tight pres gradient will
result in a chilly morning across the region with NW winds gusting
up to 35 mph.

Cold air advection peaks this morning then eases this afternoon
as mid level trough moves offshore replaced by height rises
across the region. Thus not as windy this afternoon. However
temps will only rebound to 40-45, upper 30s across the high
terrain, almost 10 degs cooler than normal.

Scattered to broken cold air advection strato-cu this morning will
give to mostly sunny conditions this afternoon as temps begin to
warm aloft in response to height rises.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
330 AM update...

Tonight...

Ridge of high pres builds across the area from west to east,
resulting in a cold night especially outside the urban areas as
mostly clear skies combine with light winds and a very dry airmass.
For whatever reason MOS has been running too cold in these
radiational cooling events this past month so we will follow a model
blend here to offset the colder MOS guid. Nonetheless most locations
fall into the 20s tonight, upper teens northwest MA and closer to 30
for Boston. Will have to watch mid and high clouds spilling into the
area late tonight, which may have an impact on temps with mins
possibly not quite as cold.

Saturday...

Chilly start to the day but low level WAA commences with increasing
SSW winds during the afternoon and especially late in the day. Some
morning sunshine thru high clouds possible, but will fade behind
increasing clouds during the afternoon as mid level trough and 985
mb surface cyclone exits Great Lakes. All global guidance including
ensembles keep dry weather across the entire region thru 18z Sat.
Thereafter showers overspread the area especially western MA/CT.
Will have to see how later model runs trend but it`s possible much
if not the entire day remains dry across RI and eastern MA.

Low level WAA should result in highs in the 50s across the coastal
plain including the Boston to Providence corridor, with 40s farther
inland where it will take longer to modify shallow cold air.

SSW winds will increase as low level jet approaches the region.
Model soundings suggest wind gusts up to 40 mph along the south
coast by late in the day Saturday.

&&

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

* Gusty SW winds Saturday night will shift to W-NW Sunday into
  Monday, with some strong gusts during each day
* Milder air moves across the region Tuesday, only to exit as
  another cold front brings colder air and gusty winds at mid
  week
* Early outlook for Thanksgiving appears to be dry but cool

Overview...

Progressive mid level steering flow continues through this
forecast period across the lower 48. Noting a couple of fast
moving low pressure systems in the northern stream, though it
appears that the steering flow pushes further N into southern
Canada early next week.

Rather strong winds accompany two passing systems, which could
produce wind advisory level winds from Saturday night into
Monday. The stronger of the two systems passes across southern
Quebec Sunday, with gusty SW winds Sat night into Sunday
shifting to W-NW Sunday night and Monday.

As the pattern flattens out Monday night, will see another system
move across central Quebec closer to Hudson Bay around mid week.
Most of the mid level energy and moisture will be well N of the
region, so expect dry conditions as another shot of cooler air
moves in. High pressure appears to keep fair weather across the
region for Thanksgiving though it will be cool with temps
running 5 to 10 degrees below seasonal levels.

Details...

Saturday night...

Will see temps rising during the night on mild SW winds. H925
temps rise to +11C to +12C during the night. Will also see gusts
up to 35-40 kt possible, highest along the S coast. May get
close to Wind Advisory levels, but will monitor as marginal low
level lapse rates in place except along the immediate S coast.
Have used a non-diurnal temp trend through the night. As cold
front moves into western areas toward daybreak, could see some
brief higher gusts, up to 45 kt, as winds start to shift to W.

Showers move across through the night, and could see a few
heavier downpours across western areas after midnight. This
could also help mix some higher winds down with the precip.
QPF amounts could reach up to 0.3 to 0.5 inches from central
Mass and NE CT westward through the night.

Lows will occur early, ranging from around 40 across the E
slopes of the Berks to the lower 50s along the immediate S
coast.

Sunday and Monday...

The cold front will push offshore by midday, but could see temps
top off in the mid-upper 50s across central and eastern areas
before frontal passage. Showers will move E during the day with
improving conditions during the afternoon. A few showers might
linger into Sunday evening across E coastal areas.

Another round of gusty W-NW winds will move in Sunday and and
continue into Monday. Will again have to monitor for Wind
Advisory level sustained winds and/or gusts, especially across
eastern areas. Best shot for strongest winds looks to occur
along the coast, but could also see some of the strong winds
across the higher inland terrain.

Temps will drop back to the 20s away from the coast, up to 30-35
on the shoreline Sunday night, with readings only recovering to
the 30s inland and 40-45 at the shore on Monday, running 5 to 10
degrees below seasonal levels.

Tuesday and Wednesday...

Low pressure moves E out of Ontario Tuesday, remaining across
central Quebec early Wednesday. Associated cold front sweeps
across the region Tue night. Most of energy and moisture will
remain N of the region, so will just see a wind shift push
across. After temps running up to 5 degrees above normal on
Tuesday, readings will dip closer to seasonal levels Wednesday.

Wednesday and Thanksgiving...

Mainly dry conditions expected through the holiday as mid level
storm track looks to remain N of the region. Winds shift to NW
early Wed morning as a dry cold front pushes offshore, followed
by large high pressure building E out of the central U.S. toward
the eastern seaboard on Thanksgiving. Noting some model
solution spread, though the 00Z GFS and ECMWF were pretty close
in their surface high pres position. Looks like temps will run
close to or a bit below seasonal levels.

&&

.AVIATION /16Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

Through Today...High confidence.

Low end VFR SCT-BKN clouds will lift through the morning. Clouds
will tend to dissipate from midday into this afternoon, but some
clouds will linger along E coastal areas. Main issue continue to
be gusty NW winds with speeds up to 30-35 kt, and low risk of
gusts up to 40 kt across higher inland terrain and along the
immediate coast.

Tonight...High confidence.

VFR. Dry weather along with diminishing winds.

Saturday...High confidence.

VFR, light winds and dry weather thru the morning. MVFR and rain
begin to increase from west to east, with current timing 21z-00z.
Also S-SW winds increase during the afternoon with gusts
approaching 35 kt by late in the day along the south coast
including Cape Cod and the Islands.

KBOS Terminal...
High confidence in TAF. Main issue today will be gusty NW winds
up to 30 kt.

KBDL Terminal...
High confidence in TAF. Main issue today will be gusty NW winds
up to 30 kt.

Outlook /Saturday Night through Tuesday/...High confidence.

Saturday Night: Mainly MVFR, with local IFR possible. Strong
winds with local gusts to 40 kt. SHRA, patchy BR.

Sunday: Mainly VFR, with local MVFR possible. Strong winds with
gusts to 40 kt. Chance SHRA.

Sunday Night through Monday: VFR. Windy with gusts to 35 kt.

Monday Night: VFR. Windy with local gusts to 30 kt.

Tuesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...High forecast confidence.

Today...

Replaced the Gale Warning for Cape Cod Bay a little earlier
than it would have expired with a Small Craft Advisory. That
will be the trend for today with the other coastal waters.
extended the Gale Warning a couple of hours for the outer
coastal waters south and east of the Cape and islands, where
latest buoys indicate gale force gusts continuing.

Previous discussion...

NW gales across open waters this morning, lingering to gale
force across the eastern waters this afternoon. Dry weather
and good vsby prevail.

Tonight...

Light winds as high pressure crest over the New England waters.

Saturday...

light winds to start the day but increasing SSW winds during the
afternoon and possibly reaching Gales by sunset across the RI and
southern MA waters. Showers may also arrive late in the day.

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

Saturday Night: Low risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Rain showers likely, patchy fog.

Sunday and Sunday night: Moderate risk for gale force winds
with gusts up to 40-45 kt. Rough seas up to 12-15 ft. Rain
showers likely Sunday.

Monday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 11 ft.

Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from Saturday afternoon through Sunday afternoon
     for ANZ232>237-255-256.
     Small Craft Advisory until 1 AM EST Saturday for ANZ231>235-
     237-256.
     Small Craft Advisory until 7 PM EST this evening for ANZ230-
     236.
     Gale Warning until 1 PM EST this afternoon for ANZ250-251-254.
     Small Craft Advisory until 5 AM EST Saturday for ANZ255.

&&

$$
SYNOPSIS...Nocera/EVT
NEAR TERM...Belk/Nocera/EVT
SHORT TERM...Nocera
LONG TERM...EVT
AVIATION...Nocera/EVT
MARINE...Belk/Nocera/EVT



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