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fxus61 kbox 201938 

Area forecast discussion
National Weather Service Boston/Norton Massachusetts
338 PM EDT sun Oct 20 2019

south coastal skirting rain overnight associated with the
remnants of Nestor. Majority clearing out Monday however clouds
lingering across the cape and islands. Dreary conditions
returning out ahead of an approaching cold front Tuesday, with
a period of showers Tuesday night into early Wednesday. Dry and
seasonably mild conditions follow Wednesday afternoon into
Friday although a cold front may bring a few showers Friday
afternoon and night. High pressure builds in for next weekend.


Near term /until 6 am Monday morning/...
2 PM update...

S-coastal skirting rain. Already ongoing, Nestor tropical remnants
upsloping along the 295-305k isentropic surfaces, drawn north and upward
through the atmosphere preceding a weak 500 mb-7 shortwave open-wave 500 mb
trof axis to the right-rear-entrance of a 300 mb jet streak along the north-
periphery of the east-moving mid-upper level ridge. Looking at radar it
looks like widespread stratiform rain is right on our doorstep. Yet
however heights stable if not subtly rising out ahead of a North-Plains
cyclone, surface high pressure and dry air is maintained over the southeast
Canadian Maritimes. A north/NE isallobaric-wind undercutting isentropic
upslope keeping lower levels dry (h925-7 thetae fields especially)
with surface high pressure acting as a bumper, consensus of model
forecast guidance, with the 12z high-res coming into agreement with
the global model guidance, keeping Nestor and its parent heavy rain
and deep moisture S and out over the waters. Rain mainly for the S-
coastal regions of New England into Monday morning.

It may look like rain is going to push right over US, but observed
in the okx / chh 12z sounding there's a lot of low-level dry air and
already its working to chew up the leading edge of rainfall into the
New York Hudson River valley. Chance pops to the Massachusetts Route 2 corridor and
that might be generous. Confident some trace-0.01 rainfall across
the Berkshires but across central Massachusetts down into north CT and north Rhode Island the north
low-level winds are likely to cut down on outcomes. Likely pops for
the S Rhode Island and S Massachusetts coastline and out over the S/southeast waters. Rainfall
amounts around 0.1-0.2 for those areas with likely pops, around 0.5
for Nantucket. Breezy east/NE winds not only with isallobaric-wind but
also the gradient wind subsequent of nestor's close approach. Gusts
up to 30 mph are possible towards Monday morning across the cape and
islands, sustained 10 to 15 mph.


Short term /6 am Monday morning through Monday night/...
2 PM update...

Monday into Monday night...

Nestor remnants not going far. North-Plains cyclone occludes, tightens
towards 990 mb, the mid-upper level ridge downstream builds across
the NE Continental U.S. Pushing the mid-latitude flow northward resulting in a
wobbling, cut-off Nestor lingering S/east of the 40n/70w benchmark. An
east-fetch drawn from the wrapping tropical low-level moisture round
Nestor back towards the approaching midweek occluded front, riding
beneath a dry-inversion settling down around h8-9. Moisture pooling,
saturating, while partial clearing is expected on Monday, going into
Monday night forecasting lowering conditions with nocturnal cooling,
brought inland by a Stout east low-level jet, upsloping, can't rule out
some drizzle as well for east/se-coastal Massachusetts. So dry and seasonable for
Monday with highs getting into the low 60s for most of New England
but east/se-coastal Massachusetts with onshore flow and lingering clouds. Then
overnight it turns dreary with lows in the 40s.


Long term /Tuesday through Sunday/...

* low clouds Tue with light rain or patchy drizzle at times
* period of showers Tue night into early Wed then improving
* dry and mild weather Thu/Fri
* continued mainly dry and cooler for next weekend

Tuesday into Wednesday...

Easterly flow Tue with considerable low level moisture
developing will result in low clouds overspreading much of the
region. Models generating light quantitative precipitation forecast moving in from the east.
This is likely a signal for some light rain or patchy drizzle
developing within moist easterly flow beneath dry air through
the mid levels. Then approaching shortwave and attending cold
front moves into the region Tue night. Deep moisture plume and
low level convergence will result in a period of showers moving
west to east across southern New England. The low level jet is somewhat fractured
and not particularly strong so not expecting an organized area
of heavy rainfall. But some locally heavier rain is possible Tue
night as a wave develops on the front which enhances low level
convergence. However, better chance likely across Maine on Wed
north of the developing surface wave where decent east/southeast low level
jet develops. Much of the shower activity should be east of new
eng by Wed morning, but can't rule out a few lingering showers
into Wed morning, mainly across eastern Massachusetts. Otherwise, expect
increasing sunshine Wed as good mid level drying moves in with
mild temps well into the 60s.

Thursday through Sunday...

High pres moves off the mid Atlc coast Thu with return flow
developing. Sunshine and seasonable temps for Thu. Models differ on
the pattern for the end of the week into the weekend. European model (ecmwf) showing
a split flow pattern with dominant northern stream into the weekend
with southern stream low pres approaching late in the weekend. GFS
has more of phased system with rain impacting southern New England on Sat. Leaning
toward European model (ecmwf) solution which has support of other global guidance
including UKMET/ggem. This supports a frontal passage late Fri/Fri
night which may be accompanied by some showers then high pres
building in for the weekend with dry and cooler conditions. Will
have to watch possible southern stream system approaching late in
the weekend. If timing speeds up then some rain may begin to impact
the region sometime Sunday, but going with a dry forecast for now.


Aviation /20z Sunday through Friday/...
forecaster confidence levels...

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

Short term /through Monday night/...

18z update...

Rest of today...high confidence.
VFR. Light winds. Increasing clouds lowering to low-end VFR over
southwest CT towards 0z Monday.

Tonight...moderate confidence.
Broken-overcast low-end VFR with MVFR over CT / Rhode Island / southeast MA, the
risk of IFR across the cape and islands, even perhaps the mid-CT
River Valley towards early Monday morning as cigs clear. An
increasing east/NE wind 10 to 15 kts along the coast, as high as 20
kts across the cape and islands with gusts as high as 30 kts that
heighten early morning Monday.

Monday...moderate confidence.
Low-end VFR - MVFR cigs eroding S/east through morning except out
across southeast Massachusetts. A NE wind persisting, MVFR broken-overcast cigs
linger across the cape and islands much of the day. Breezy east/NE
winds throughout especially along the coast, 10 to 15 kts, gusts
to 25 kts.

Monday night...moderate confidence.
Broken-overcast lowering cigs over all of S New England. Confident MVFR
however could see IFR issues. Winds becoming E, remaining 10 to
15 kts, strongest along the coast with gusts up to 25 kts.

Kbos terminal...
high confidence in taf.

Kbdl terminal...
high confidence in taf.

Outlook /Tuesday through Friday/...moderate confidence.

Tuesday: mainly MVFR, with local IFR possible. Breezy. Chance
ra, chance dz.

Tuesday night: mainly MVFR, with areas IFR possible. Rain showers

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

Wednesday night: VFR. Breezy.

Thursday through Thursday night: VFR.

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


forecaster confidence levels...

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

Short term /through Monday night/...

2 PM update...

Nestor remnants sweep North/East near and southeast of the 40n/70w benchmark
overnight, stalling and wobbling Monday into Monday night. With
high pressure settled north across New England into the southeast Canadian
Maritimes, the neighboring airmasses yield a Stout east/NE gradient
wind into S New England. Generally 10 to 15 kts with gusts up as
high as 30 kts Monday morning. Seas potentially building 6 to 8
feet over the S/southeast waters. Small craft headlines posted for those
outer waters up against the S-coast, Cape Cod and islands.

Rain overnight tonight, lower visibility with rain especially on
the S-waters. Partial clearing Monday, but lower conditions return
Monday night along with forecast drizzle.

Outlook /Tuesday through Friday/...moderate confidence.

Tuesday: winds less than 25 kt. Areas of rough seas. Chance of
rain, chance of drizzle.

Tuesday night: winds less than 25 kt. Areas of rough seas. Rain
showers likely.

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

Wednesday night through thursday: winds less than 25 kt. Seas
up to 5 ft.

Thursday night: winds less than 25 kt. Areas of seas
approaching 5 ft.

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


Box watches/warnings/advisories...
Rhode Island...none.



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