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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
914 PM EST Sat Nov 16 2019

Synopsis...
high pressure will shift east across northern New England
tonight, keeping dry conditions and cold air across the region.
As the high pushes away Sunday, temperatures will gradually
moderate but remain below normal. A coastal storm will then bring
rain and strong coastal winds late Sunday night into Monday,
with some light icing in the interior at the onset. The storm
moves to the Maritimes Tuesday with high pressure building south
of New England Wednesday and Thursday. A cold front may bring a
round of showers sometime Thursday night into Friday.

&&

Near term /until 6 am Sunday morning/...
915 PM update...

Clear skies across much of southern New England this evening but some lower
clouds have developed on the upper cape and there are clouds
just offshore and flirting with ack. Cross sections show
increasing low level moisture across eastern new eng where skies
will likely become mostly cloudy late tonight and toward
daybreak. But remaining mostly clear further into the interior.

Clear skies, light wind and dry airmass with strong high pres to
the north will result in excellent radiational cooling
conditions away from the coast. Lows here will bottom out in
the single numbers and teens, coldest across western Massachusetts. Along
the coast, a NE wind will keep temps mostly in the 20s with low
to mid 30s Outer Cape/islands where gusts to 20-30 mph expected
overnight as a coastal front develops. In fact temps will
likely rise into the 30s across east coastal Massachusetts as NE winds
increase.

&&

Short term /6 am Sunday morning through 6 PM Sunday/...
Sunday...

Will see east-NE winds continue to increase through the day as the
northern periphery of the moisture from the southeast low pres works
toward the region. Clouds will continue to increase and lower,
especially during the afternoon.

Some question how quickly the moisture will work up the coast,
which will be dependent upon how quickly the high across New Hampshire and
Maine lifts to the Maritimes. At this point, should remain dry
across the majority of the region through the day, but will
start to see the leading edge of the light rain reach the S
coast around or after 21z.

Temps will recover especially along the coast with the
persistent onshore winds. Readings will top off in the lower-mid
40s along the shore, ranging to the mid-upper 30s well inland,
coldest across the higher inland terrain.

&&

Long term /Sunday night through Saturday/...
highlights...

Coastal low and potential impacts Sun night into Mon:

* light icing/light freezing rain likely at the onset across parts
of the interior late Sun night/Mon am before ptype changes to rain

* periods of rain late Sun night and Mon which may be heavy at times
especially across eastern Massachusetts/Rhode Island

* northeast wind gusts of 35 to 45 mph with a few gusts up to 50
mph possible across the immediate coast late Sun night/Mon

* minor coastal flooding possible along the eastern Massachusetts coast on Mon

Tuesday through Saturday...

* dry and seasonable weather follows Tue/Wed and into Thu

* a round of showers possible sometime Thu night into Fri

Details...

Sunday night into Monday...

The main concern continues to revolve around a coastal low pressure
system Sun night into Mon, which will pass east of Nantucket.
The high resolution models tend to be faster and further
northwest when compared to the ec/GFS. We think there will be
somewhat of a compromise in the models, so blended the timing
for now. Thinking that much of sun evening may end up dry other
than some light drizzle along the coast. However, should see
precipitation overspread the region from southeast to northwest
after midnight.

1) interior light icing potential:

Ptype should mainly be rain in most locations. However, given
the low pressure system tracking offshore and lingering high
pressure over eastern Canada some light icing/freezing rain is
likely across portions of the interior at the onset. We are most
confident in this occurring across the high terrain of the
Worcester Hills and east slopes of the Berks. Up to one tenth of
an inch of ice accretion is possible and untreated roads will
be icy for the morning commute. There also is a possibility for
a brief period of light freezing rain across the lower
elevations of interior northeast Massachusetts and into parts of CT, but
it also could end up a few degrees too warm. Regardless, ptype
should change to rain Mon morning in all locations.

2) strong wind potential along the coast:

Offshore low pressure tracking east of Nantucket will be associated
with a modest northeast low level jet of 45 to 55 knots across eastern Massachusetts and
Rhode Island. This should result in northeast wind gusts of 35 to 45 mph with
a few gusts near 50 mph along the coast. The strongest of these
winds will be late Sun night into Mon especially across the
cape/islands. Since we do not have a rapidly bombing low pressure
system or anomalously high surface pressures in eastern Canada,
think this will mainly be a Wind Advisory event along portions of
the eastern Massachusetts coast. Fortunately, given most leaves are off the
trees these wind speeds should not cause too many issues other than
a few downed tree limbs etc.

3) rainfall:

Given we have a well developed coastal low pressure system tracking
east Nantucket, periods of rain will impact the region late Sun
night into Mon. The guidance continues to differ with rainfall
amounts given uncertainty how close the system tracks to the
coast. With a closed 700 mb low expecting a general 0.50 to 1.50
inches of rainfall with the higher amounts across eastern Massachusetts
and Rhode Island. We may see some 2 inch amounts across eastern Massachusetts and RI,
depending on the exact track. Regardless, rainfall amounts are
not expected to be high enough to result in any fresh water
flooding issues.

4) minor coastal flooding potential:

Fairly decent east/NE fetch combined with several hours of strong winds
should bring a storm surge of 1.5 to 2.0 feet with Monday afternoon
high tide in eastern MA, which is a little higher than storm surge
guidance from estofs/etss. Astronomical high tide is (10.3 ft
at Boston and 3.7 ft at Nantucket harbor) so this would bring
the potential for pockets of minor coastal flooding to
much of the eastern Massachusetts coast including Nantucket and Martha's
Vineyard. Seas offshore of 14-18 ft are not expected to
significantly add to the impact along coast but may bring minor
beach erosion. So in a nutshell, while some pockets of minor
coastal flooding seem reasonable do not think winds/storm surge
will be enough to result in a significant coastal flood event.

Monday night and Tuesday...

The system departs Monday night into early Tuesday morning. It is
possible there is a touch of wintry precipitation on the backside of
the system across the high terrain of western Massachusetts. Any amounts
though should be light. Otherwise, dry weather expected for most of
Tue with highs recovering into the 40s to the lower 50s.

Wednesday through Saturday...

Another low pressure system and associated cold front may bring a
period of showers sometime Thu night into Fri. Otherwise, dry
weather expected with seasonable temps dominating. The exception
might be Fri as we may have a period of mild temps in the warm
sector ahead of the next cold front.

&&

Aviation /02z Sunday 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.

Tonight...

Mainly VFR, but some MVFR cigs develop across eastern new eng
overnight. NE wind gusts increase to 20-30 kt across the
cape/islands overnight.

Sunday...

Low end VFR to MVFR cigs dominate sun. Lowest of the ceilings
expected across eastern New England. East-NE winds increase along
the coast during the day, up to 20-25 kt with gusts to around 30
kt across Cape Cod and the islands around or after 18z. Gusts
up to 35 kt by around 00z in vicinity of kack.

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Sunday night through Thursday/...

Sunday night: MVFR/IFR conditions possible. Strong winds with
gusts up to 40 kt. Rain likely. Chance freezing rain across parts of the
interior.

Monday: mainly IFR, with local MVFR possible. Strong winds with
gusts up to 40 kt. Ra, patchy fog. Freezing rain likely in the morning
across parts of the interior.

Monday night: mainly MVFR, with areas IFR possible. Windy with
gusts up to 35 kt. Chance rain showers.

Tuesday: mainly VFR, with local MVFR possible.

Tuesday night: VFR.

Wednesday through Wednesday night: VFR. Breezy.

Thursday: mainly VFR, with local MVFR possible. Breezy. Slight
chance shra, slight chance freezing rain.

&&

Marine...
through tonight...

Expect NE winds to briefly diminish to 15-20 kt this evening,
then will become east-NE 20-30 kt, highest on the southern outer
waters mainly after midnight. Gusts will increase to around 35
kt on the southern outer waters, where gale warnings remain in
place. Seas will build to 5-8 ft on the outer waters. Good
visibility.

Sunday...

Expect east-NE winds will increase to gale force across the waters
east and S of Cape Cod as well as the southern near shore waters
from midday through the afternoon. Gale warnings are in effect
there. On the eastern waters, winds will gust up to 25-30 kt.
Seas will build up to 6-10 ft, highest on the southern outer
waters. Good visibility continues, but will see light rain
reach the southern waters toward nightfall.

Outlook /Sunday night through Thursday/...

Sunday night: moderate risk for gale force winds with gusts up
to 40 kt. Rough seas up to 18 ft. Rain. Local visibility 1 to
3 nm.

Monday: moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 17 ft. Rain, patchy fog. Visibility
1 to 3 nm.

Monday night: low risk for gale force winds with gusts up to
35 kt. Rough seas up to 13 ft. Chance of rain showers.

Tuesday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 10 ft.

Tuesday night: winds less than 25 kt. Seas up to 5 ft. Slight
chance of rain showers.

Wednesday: low risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas up to 5 ft.

Wednesday night: moderate risk for Small Craft Advisory winds
with local gusts up to 30 kt. Areas of rough seas.

Thursday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Gale Warning from 4 PM Sunday to 7 PM EST Monday for
anz231>235-237.
Gale Warning from 3 am to 5 PM EST Monday for anz230-236.
Gale Warning from 10 PM Sunday to 10 PM EST Monday for anz250-
251.
Gale Warning from 1 PM Sunday to 10 PM EST Monday for anz254.
Gale Warning until 7 PM EST Monday for anz255-256.

&&

$$
Synopsis...Frank/evt
near term...kjc

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