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Area forecast discussion
National Weather Service Boston/Norton Massachusetts
1254 am EST Tue Nov 19 2019

Synopsis...
the coastal storm will continue to bring spotty light rain and
strong winds along the coast tonight. The rain may become a
wintry mix across the interior high terrain late tonight into
Tuesday morning. Mainly dry and seasonably chilly weather
follows Tuesday afternoon into early Wednesday. Low pressure
passing south of the region may push some rain and snow showers
across central and eastern areas from midday Wednesday into
Wednesday night. Dry conditions and seasonable temperatures for
Thursday. An approaching front will bring a chance for showers
on Friday, then dry but colder conditions Friday night into
Saturday. Another system may approach Saturday night into
Sunday, but the details remain uncertain.

&&

Near term /until 6 am this morning/...
10 PM update...

Radar mosaic shows enhanced area of precip in the lower Hudson
Valley in New York and into New Jersey/east PA. This is on the nose of
stronger 500 mb height falls/mid- level diffluence associated
with upper low which per WV imagery is roughly analyzed over the
eastern West Virginia Panhandle. This feature is expected to
move north/neward towards southern New England overnight with
steadier precipitation resuming mainly around/just after
midnight in the west, and likely into the overnight/pre-dawn hrs
across central/eastern Massachusetts-CT and Rhode Island.

In the interim, shower coverage has really diminished to either
intermittent showers or drizzle especially from eastern
CT/central Massachusetts eastward. This appears to be due to a dryslot
on the eastern extent of the upper low, with better mid-level
moisture prevalent over eastern New York into western CT/western Massachusetts.
Showed rain and drizzle thru first part of the overnight from
eastern Massachusetts/Rhode Island to east- central Massachusetts/eastern CT.

00z radiosonde observations at okx/alb showed a prevalent warm nose with maximum
warm-nose temps between +3.5c at alb to +7c at okx, underlying
cool though still above- freezing below-warm nose temps. With
cool advection taking some time to erode the warm nose, rain
should initially predominate but the potential for northerly
drainage flow to advect cooler wet-bulb temps across the higher
elevations in the Berks, idea of an expected transition from rain
to ice pellets/brief freezing rain looks on track before things become a
clumpy wet snow into the morning. Winter Weather Advisory still
looks valid for light wintry mix leading to some Road impact
overnight, though will reassess the end timing with the morning
package.

Did tweak hourly temps somewhat to account for current obs and
near-term trends, though these changes were small.

Previous discussion...

Through the overnight hours, the next round of precipitation
approaches. This is associated with a potent mid level trough
lifting north out of the Delmarva, ushering out today's coastal
low, while bringing another slug of moisture with it. Pwats
>0.75" together with potent mid-level energy and favorable jet
dynamics aloft will bring fairly widespread rain showers to all
of southern New England generally after midnight into Tuesday
morning, with the greatest quantitative precipitation forecast amounts in western MA/CT.

Surface temperatures have been adjusted slightly warmer in line
with the latest hi-resolution guidance which has lessened the
magnitude of caa, decreasing the risk of appreciable snow/icing
overnight. However, in the highest elevations of the Berkshire
slopes, temperatures will hover at or near freezing, so can't
rule out a coating of snow or light glaze of ice early Tuesday
morning. For the possibility of some light freezing rain, a
Winter Weather Advisory continues through Tuesday morning for
western Hampshire and Franklin counties.

&&

Short term /6 am this morning through 6 PM Wednesday/...
Tuesday starts wet before drying out by late morning/afternoon.
By 15z (10am) the core of the upper low is over Maine, along
with the bulk of the moisture. Looking through the column we see
some drier air working in in the mid and upper levels which
should allow for peeks of sun Tuesday afternoon. This will help
warm temperatures a bit too, even in the cold air advection pattern. High temps
should reach into the 40s for most, which, with light winds and
the emerging sun will be a nice change from today's wet, raw
weather. Tuesday night into Wednesday morning things stay dry
but we'll see increasing clouds. This as a deep mid level trough
digs to our south, eventually wrapping around enough moisture
to bring some rain and snow showers on Wednesday. Cold air advection pattern
will be evident overnight (850mb temps down to -2 to -3c), with
surface lows about 5 degrees colder than the night previous, in
the upper 20s and low 30s.

&&

Long term /Wednesday night through Monday/...
highlights...

* light rain and/or snow showers push across central and
eastern areas Wed into Wed night as an offshore low passes.
Gusty northerly winds develop across the coastal waters.

* High pressure brings dry, seasonable weather on Thursday

* mild temperatures make a brief return ahead of an approaching
front, bringing showers Thu night and Fri, then dry but
colder weather late Fri night into Sat

* model solution spread lending to low confidence forecast for
potential approaching system sometime next weekend

Overview...

An amplified but progressive mid level steering pattern
continues across the lower 48. 500 mb trough may bring some
unsettled conditions around mid week, but should push steadily
offshore. Will see a brief dry and seasonal day as progressive
500 mb ridge pushes across the eastern Seaboard. Cutoff 500 mb low
crosses eastern Ontario/Quebec, with a trailing surface front
swinging across Fri night into Sat.

Solutions amongst the 12z model suite signaling increasing
spread next weekend. This lends to rather low confidence as
another system may approach during this timeframe.

Details...

Wednesday and Wednesday night...

An amplified long wave trough, with a cutoff 500 mb low passing
close to or S of the region, will lift east-NE Wed afternoon into
Wed night. Looks like moisture will shift back across central
and eastern areas during the midday and afternoon hours before
moving offshore. May see some light snow showers across north
central areas, with mainly rain showers across eastern mass.
Mainly northerly winds in place, but temps will top off in the
upper 30s to lower 40s as most of the colder air holds back
until the trough shifts east.

Leftover showers linger across the mid and Outer Cape Wed
evening, then will exit rather quickly as drier air moves in on
northwest winds. Temps will bottom out in the mid-upper 20s well inland
to the mid- upper 30s along the immediate coast, which are
close to seasonal normals. Will see winds gusts up to 20-25 kt
across the Outer Cape and Nantucket, as well as across the
coastal waters.

Thursday and Thursday night...

500 mb ridge will steadily shift E, along with large surface high
pressure that will cross the eastern Seaboard. Northwest winds will
start off gusty especially along the coast, but will diminish as
the ridge builds east. Highs will range through the 40s.

As the ridge shifts offshore Thu night, will see light/variable
winds to start then becoming S-SW. This will allow temps to
bottom out Thu evening, then will slowly rise through the
remainder of the night. Clouds will also increase during the
night as the next system approaches. May see scattered showers
develop and move across mainly around or after midnight, with
the best chances across central and western mass, possibly into
north central CT.

Friday through Sunday...

Looks like showers will be scattered across the region through
Friday as the front pushes across, though there is some question
on the timing of this feature with increasing model solution
spread. Ahead of the front, temps will be mild. Expect readings
topping off from the mid-upper 40s across the higher inland
terrain to the lower- mid 50s across the coastal plain.

A lot of question remain in place for the upcoming weekend
weatherwise. Model solutions are spread out, mainly with how
each member is handling a potential southern stream system that
may try to lift NE. This is likely due to wide spread in the
handling of the mid level features, namely how fast the next
northern stream system moves along as well as a possible
southern stream short wave that may merge with the northern
stream system. For now, have started off dry, then could see
unsettled conditions. However, quite a bit of uncertainty so low
confidence forecast.

&&

Aviation /06z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Wednesday/...moderate confidence.

06z taf update:

Rest of the overnight...

Generally IFR/LIFR from orh/pvd eastward, with MVFR/IFR toward
baf/bdl. For bdl/baf, expect an increase in steadier precip over
the next couple hrs with a p-type transition from rain to wet
snow moving into the pre-dawn/early morning. Periods of drizzle
and intermittent light rain now from orh/pvd eastward, though another
round of steadier rains will move in between 09-12z. North to northwest
winds 4-10 kts, generally strongest furthest east and lighter
west. Will see a continued decreasing trend areawide, along with
a slow shift to NW/WNW.

Tuesday...
MVFR-IFR ceilings with VFR-MVFR vis initially as precip shield
lifts northward into Vermont/New Hampshire thru 12-16z Tue. Drying thereafter.
By afternoon, should see some improvement towards broken-overcast MVFR-
VFR - lowest ceilings mainly along and north of the Mass Pike.
Winds mainly west-northwest-west 3-6 kts, and may be light/variable at times
as p-gradient slackens.

Tuesday night...
ceilings likely to lower again to MVFR levels and eventually
MVFR-IFR from NE to SW as Tuesday night progresses. Late
overnight, shallow moisture from a distant coastal low could
bring a potential for unrestricted rain/drizzle or very light
snow, with low prob of light freezing drizzle. Best chance of
frozen precip mainly northwest of bed/orh. Light west-northwest/west winds initially,
though become northwest 3-8 kts, highest towards the cape/ack.

Kbos taf...high confidence in taf and trends.

Kbdl taf...high confidence in taf and trends. Rain may briefly
mix with snow showers early Tuesday am.

Outlook /Wednesday night through Saturday/...

Wednesday: MVFR/IFR conditions possible. Breezy. Slight chance
rain showers.

Wednesday night: mainly VFR, with local MVFR possible. Breezy.

Thursday: VFR. Breezy.

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

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

Friday night through saturday: mainly VFR, with local MVFR
possible. Windy with local gusts up to 30 kt. Slight chance
rain showers.

&&

Marine...
short term /through Wednesday/...moderate confidence.

10 PM update:

Made several changes to marine headlines.

Winds have largely subsided below gale criteria (though may
briefly ~ next hour be high end Small Craft Advisory/low-end gale on the
northeast offshore waters). With continued improvement/easing
north/northwest gusts, converted all prior standing gale
warnings to small craft advisories. So the biggest change is
that gale warnings are no longer in effect.

In the near-shore zones, existing scas (boston Harbor and
Narragansett bay) were allowed to expire as winds/seas per obs
and trends have fallen below Small Craft Advisory levels. However, per the recent
buzm3 ob indicating continued low-end Small Craft Advisory gusts, opted to
extend the Small Craft Advisory through midnight for The Vineyard Haven/Buzzards
Bay and Rhode Island Sound areas; further extension isn't likely with
continued improvement.

General idea is that winds will subside a bit quicker than will
the seas, with 10-15 footers into Tuesday for the offshore
waters. Steady rains have largely become intermittent and/or
drizzle, though visibilies will still be around 2-5 miles with
periods of mist/fog and intermittent rain showers into Tuesday
morning.

Expect west winds at 5-10 kts on Tuesday. Seas up to 5 to 9 ft,
highest on the eastern outer waters early, then slowly
subsiding but remaining at or above 5 ft through the day.

West-northwest winds at around 10 kt early Tuesday night will shift to north
after midnight, with gusts up to around 15 kt. Seas will linger
at 5 to 6 ft across the outer waters through most if not the
entire night.

Outlook /Wednesday night through Saturday/...

Wednesday: low risk for Small Craft Advisory winds with gusts
up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Wednesday night: moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain
showers.

Thursday: low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft.

Thursday night: winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.

Friday: low risk for Small Craft Advisory winds with gusts up
to 30 kt. Local rough seas. Chance of rain showers.

Friday night: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Slight chance of
rain showers.

Saturday: low risk for Small Craft Advisory winds with gusts up
to 30 kt. Areas of rough seas. Slight chance of rain showers.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...Winter Weather Advisory until 6 am EST early this morning for
maz002-008.
Rhode Island...none.
Marine...Small Craft Advisory until 7 am EST this morning for anz231-
232.
Small Craft Advisory until 6 PM EST this evening for anz250-
254>256.
Small Craft Advisory until 5 PM EST this afternoon for anz251.

&&

$$
Synopsis...evt/bw
near term...loconto/evt/bw

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