Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 222320

Area Forecast Discussion
National Weather Service Taunton MA
720 PM EDT Sat Oct 22 2016

A strong upper level disturbance sweeping across New England will
usher in colder air and blustery, potentially damaging-winds through
Sunday. Wind advisories and gale warnings posted. Upper trough and
possibly weak surface low pressure will pass south of New England
Monday morning. Dry and cool northwest flow will persist Monday
afternoon through Wednesday. High pressure will drifts east of New
England late Thursday followed by a front and possible showers
late Thursday night into Friday.



7 PM Update...

Rain and wet snow mixed over the higher elevations of the
Berkshires with a dusting to perhaps localized half inch or so
above 1500 feet. Could see a few wet snowflakes mixed in over the
Worcester hills late evening into early morning hours but no
accumulation expected. Coastal plain is expected to remain dry
especially with help of some downsloping winds. Otherwise,
blustery with strong enough wind gusts to bring branches down and
perhaps an isolated tree here and there, especially if not
healthy. Gusts mostly 35 to 45 mph expected with peak values over
high exposed terrain and southeast coastal areas. Wind Advisory
continued. Temperatures appear to be fairly close to the forecast
so far.

4 pm update...

*/ Highlights...

 - Rain moving out, winds picking up quickly out of the W
 - Low pressure deepening, winds increase, temperatures drop
 - Gusts up to 50 mph possible Sunday
 - Wind Advisory in effect, event-driven with leafed trees

*/ Discussion...

Through this evening...

Negatively tilted trough continues to lift N/E across the region
as a prominent dry slot wraps into the system. Along the leading
edge, a well-defined line of moderate rain with embedded heavier
showers pushing N, exiting over the next couple of hours. To the
W, a dynamically driven environment of low to mid level QG forcing
yielding an area of rain and a low risk of a rumble of thunder.
This area will pivot N/E across S New England for the remainder
of the afternoon, exiting out during the evening hours, lingering
the longest across the high terrain.

Colder air rushing in and numerous reports of snow accumulation
across the high terrain well to the N/W over Upstate NY into VT /
MA. Already reports of nearly an inch in Peru, MA as of 4 pm.
Given the dynamic situation and likely many to be caught off guard
with the first snow of the season, will go ahead with the issuance
of a SPS for the high terrain along the E slopes of the Berkshires.


Blustery W winds with the possibility of wind-related damage. Wind
Advisory for all of Southern New England. Surface low deepening to
980 mb as it lifts northeast through Maine. Tightening pressure
gradient and isallobaric component. This as cold, dry air pushes
across the region. Expect the shallow airmass to result in boundary
layer mixing up to H9 throughout allowing the mix-down of faster
momentum aloft, with the top of the mixed-layer blowing out of the
W around 45 mph. While highest confidence of reaching wind advisory
criteria is across the high terrain and along the immediate coast
adjacent to warmer waters, the entire area is included given fully
foliated trees and their susceptibility to potential impacts even
with winds of 30 to 40 mph. Likely to see some down branches, trees,
overall issues that will lead to isolated-scattered power outages.

This as showers linger across the high terrain as the main comma-
head vort-lobe associated with the negatively-tilted trough axis
lifts N/E along with better QG-forcing and trowaling moisture. Do
anticipate broken to overcast cloud decks to linger with cold air
advection proceeding at the surface with milder, dry air aloft.
Likely PoPs for the high terrain. Cold air advection pushes lows
down into the upper 30s to low 40s.



Wind-related threats continue with the possibility of gusts up to 50
mph. Clouds clearing out allowing for abundant sunshine and boundary
layer mixing up to H85 where forecast soundings suggest winds at the
top of the mixed layer will be around 50 mph. Ensemble probabilities
support a wind advisory threat over all of Southern New England with
W gusts up to 45 mph, with highest confidence of strongest gusts
over the high terrain and immediate coast adjacent to warmer waters.
Question as to whether there is the additional threat of downsloping
winds into river valleys given cold air within the low levels with
H85 temperatures around -2C warming to 0C towards late in the day.

Going to keep winds blustery throughout much of the day though
the timing of greatest impacts looks to be around mid to late
morning through early afternoon. Given temperatures aloft, looking
at a cooler than average day with temperatures around the mid to
upper 50s.

Sunday night...

Wet-weather expected overnight. Moistening low levels and increasing
clouds associated with isentropic upslope of a continental-polar
airmass along a leading warm-frontal boundary. This associated with
mid-level forcing per stretched vort lobe through a broadly open-
wave trough and accompanying reinforcing surface cold front. Looking
at showery weather moving into S New England after midnight and into
the Monday morning period. Could be a moderate W to E band parent to
greatest forcing and low to mid level frontogenesis though. Tough to
nail down but the consensus of forecast guidance and ensemble probs
have the bulk of wet-weather activity S of the Mass Pike. Remaining
mild with S winds. Lows forecast to fall down around the low to mid


*/ Highlights...

  * Quick moving short wave trof and moisture plume brings chance
    of rain southern zones Mon morning

  * Series of cold nights Mon through Wed nights may trigger
    Frost/Freeze headlines for some zones not yet turned off

  * Potential rain event late Thursday night into Friday

*/ Overview...

Trof over Labrador remains anchored in place for a time and then
only slowly moves east over the North Atlantic. As a result,
southern New England remains in NW flow with steady supply of cold
air advecting into the region through at least mid week. There are a
couple of short waves to keep an eye on during this period. One fast
moving upper short wave trof with flat surface wave moves quickly
along or just south of the New England south coast Monday AM. A
second and higher amplitude short wave trof approaches the east
coast Thursday night into Friday. Medium range deterministic models
have come into better agreement for now and somewhat consistent with
prior ensembles. Nevertheless, the time period is still 5 to 6 days
out with energy still tracking across the Pacific. Hence, we may see
varying depictions of how the energy is handled as we get closer to
the end of the week. Some prior runs handled this energy differently
due to split flow upstream. Probably a cool and dry regime going
into the next weekend with early signals showing a tendency for one
long wave trof to set up over the far eastern Pacific and another
along or perhaps just east of the east coast.


Monday...Fast moving short wave energy rotating about the Labrador
vortex may have enough going for it to reflect a very flat surface
wave passing west to east just south of New England and deep enough
moisture to support a period of light rain...most likely across RI
and southeast MA. The south coast looks to be close to the left exit
region of a H250 jet streak passing through the mid Atlantic region.
At this time amounts look to be under a quarter inch. Since we do
not have all that much continuity on this feature, will just
indicate chance POPs for now. Clouds and rain could suppress
temperatures a few degrees over the Cape and Islands.

Monday night through Thursday...Looks dry and on the cool side
during this period with NW flow persisting. May be enough decoupling
Monday and Tuesday nights to allow temperatures to drop below
freezing in many northern interior locations, although the more
exposed areas may still experience some mixing. By Wednesday night,
winds should be quite light over the area as surface high pressure
drifts across the area, but the air mass will be starting to modify.

Thursday night and Friday...Short wave trof energy will likely
affect the area to at least some extent. Both the ECMWF and GFS
deterministic models indicate what may be a cold occlusion with
possible triple point moving across southern New England Friday
morning, but those details are subject to change between now and
then. At any rate, it seems prudent to depict chance POPs for that
time frame. Temperature forecasts for Friday could be quite
challenging with a high dependency on the timing of the system.

Saturday...Looks to be dry and somewhat cool in a NW flow behind the
departing surface front and upper short wave trof.


Forecaster Confidence Levels.

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

Short Term /through Sunday Night/...

20z update...

Tonight...High confidence. MVFR cigs improving to VFR, most areas
02Z to 06Z. Exception will be Berkshires where SCT SHRASN will
persist into the early AM hours. W wind gusts up to 40 kt with
highest confidence over high terrain and coastal terminals.

Sunday...High confidence.
Clearing during the morning to VFR. W gusts around 30 to 40 kts
during the day with strongest across the high terrain and coastal
terminals where 45 kts is possible.

Sunday night...Moderate confidence.
W winds taper into evening. Will see increasing low-end VFR to
MVFR cigs towards midnight and into morning associated with an
area of -RA/RA. Impacts mainly focused along and S of the Mass

KBOS TAF...West winds expected to gusst 30 to 35 KT overnight with
low chance of one or two gusts near 40 KT. Not enough confidence
for AWW at this time. Becoming VFR around or shortly after 03Z

KBDL TAF...While breezy tonight, the stronger winds will be across
the terminal on Sunday. Slight risk during the overnight period
that if winds decouple enough there could be an issue of LLWS as
winds 2 kft agl tonight will be out of the W around 35 to 40 kts.

Outlook /Monday through Thursday/...High confidence.

Monday...VFR except possibly MVFR cigs/vsbys in light rain and fog
during the morning along the south coast.

Tuesday through Thursday...VFR. NW wind gusts to 25 knots still
possible during Tuesday.

Thursday night into Friday...Areas of IFR to MVFR cigs/vsbys in
showers and areas of fog possible.


Forecaster Confidence Levels.

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

Short Term /through Sunday Night/...High confidence.

4 pm update...


A strong burst of winds out of the W/SW the last couple of hours
with gusts up to 45 kts associated with faster momentum moving
into the region and mixing down to the surface. Expect a general
trend over all waters overnight of wind gusts around 35 kts, as
high as 40 kts. Gale warnings ongoing. Seas becoming rough with
the enhanced wind stress. Visibilities improving with increasing


Gale force W winds continue with gusts up to 45 kts possible. Seas
remaining rough building upwards of 10+ feet on the outer waters.
Gale warnings continue.

Sunday night...

Gales taper and will see the conclusion of Gale Warnings as we go
through the period. Will also see an area of rain sweep the S
waters towards midnight and continue into the morning hours. Seas
remain rough due to the wind stress. Likely see Gale Warnings
converted to Small Craft Advisories.

Outlook /Monday through Thursday/...

Through Thursday...High confidence.

Small Craft NW wind gusts may persist over most of the waters
through Tuesday. Quieter conditions anticipated for Wednesday
through Thursday.

Friday...Moderate confidence.

Some uncertainty exists with the evolution of a weather system
for Friday, but it has the potential to have enough of a pressure
gradient to support wind gusts near the Small Craft Advisory
threshold of 25 knots.


CT...Wind Advisory until 2 PM EDT Sunday for CTZ002>004.
MA...Wind Advisory until 6 PM EDT Sunday for MAZ002>024-026.
RI...Wind Advisory until 6 PM EDT Sunday for RIZ001>008.
MARINE...Gale Warning until 2 AM EDT Monday for ANZ231>234-251-255-256.
     Gale Warning until 11 PM EDT Sunday for ANZ230-235>237.
     Gale Warning until 5 AM EDT Monday for ANZ250-254.


NEAR TERM...Sipprell/Thompson
SHORT TERM...Sipprell
LONG TERM...Thompson
MARINE...Sipprell/Thompson is the U.S. government's official web portal to all federal, state and local government web resources and services.