Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 180312
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1012 PM EST Tue Jan 17 2017

.SYNOPSIS...

A mixed bag of wintry weather will continue to impact S New England
into Wednesday morning. Could see leftover spotty showers lingering
Wednesday. High pressure builds over the region for Thursday through
the weekend with mainly dry and seasonably mild conditions. Low
pressure developing off the Carolinas Saturday should remain well
south of the region. A more significant storm may affect New England
Mon into Tuesday with rain and/or mixed precip/ice along with strong
coastal winds.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

10 pm update...

Not many forecast updates. At this point we`re in it to win it.
Tackling a lot of precipitation-type issues when ascertaining the
current state of the atmosphere. Three things we`re evaluating as
we go into the overnight period, handling a very tricky forecast:

1) Dry air invading through the W through the dendritic growth
zone, the favorable region of ice. Interrogating this along with
colder air holding stout to the N (more on that shortly). Appears
drier air moves across the region overnight, however a positively-
tilted H5 trough with attendant mid level forcing may yield ascent
to keep RH values within the dendritic zone favorable towards the
development of snow rather than freezing rain at the surface. The
near-term high res guidance is a bit mixed on outcomes.

2) Surface wet bulb temperatures along with the coastal front SW
to NE across NE MA (roughly along the 495 beltway). Temperatures
fluctuating with the intensity of precipitation, dropping a degree
or two when it is more moderate, in some cases heavy, subsequent
of dynamical cooling, coming up when precipitation turns light.
Seeing locations wobble back and forth between precipitation types.

3) Low level thermal profile. Critical thicknesses have lowered
at 1000-850 mb with ongoing cold air damming. N MA a battleground
of the H925-85 freezing line parallel to the E flow up against the
warm intrusion around H8 discerned from 0z Albany sounding.

Will be watching this overnight. Already 3 mb surface pressure
falls in 3 hours S of New England at this hour. The magnitude and
depth of the cold air that is drawn S from the 1030+ high over SE
Canada, this could keep ice present in the low-layers thus making
the precipitation outcomes either rain or snow. High-res guidance
signals such a cold push S closer to morning. Things may be
evolving a bit faster with the secondary low development.

Albany 0z sounding characterizes the juxtaposition of warm and
cold layers below H7, their depth and magnitude of which is
critical for interpreting precipitation type at the surface.

Overall...

Continue to agree with the previous forecast discussion. N/E will
see snow mixing in with sleet as the low levels cool overnight.
Whereas S/W with warming aloft, will see rain with those areas at
or below freezing experiencing freezing rain, especially over the
interior where cold air remains locked in. N winds funneling
through the CT River Valley definitely aiding in the maintenance.

Continued thinking that the biggest threat of snowfall is over
N/NE MA while the biggest threat of icing is across the high
elevations of W MA and W CT, namely the Berkshires into Litchfield
Hills, places in NW Hartford County CT included.

Headlines...

Configuration of advisory still looks valid. Thus current headlines
are still valid.

Snow Potential...

A general swath of 2-4" north of the MA Pike and west of I-495 with
possibly some higher amounts over extreme N Worcester, NW Middlesex
and NW Franklin counties. To the S towards the CT border a general
Coating to an inch is possible. Elsewhere less than an inch of
snow and sleet across northern CT/RI into Metro-West Boston. SE
MA and S RI mainly rain.

Freezing Rain Potential...

Mid level warming combined with shallow cold air will setup across
the CT River Valley especially high terrain of Hartford county into
W/SE MA. A trace to a tenth of an inch of ice is possible with a
tenth to a 0.25" possible across the high terrain of this region,
namely the Berkshires and Litchfield Hills including N/W Hartford
County CT. Can not rule out some icing atop the Tolland Hills into
S Worcester County. Within areas of heavier icing, isolated power
outages are possible.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...

3 pm update...

Nasty day for much of the region with a a cold wind swept rain
during the morning for much of eastern MA and RI as secondary 1009
mb low well established near the 40N/70W benchmark. This combined
with 1028 mb high over eastern Quebec will provide a gusty northeast
winds into the region.

Still could have snow falling across northern MA including
interior northeast MA away from the coastline such as Lowell and
Lawrence MA to the NH line.

Best lift moves offshore after 12z so lighter precip the remainder
of the day with any snow confined to the higher terrain. By the
late day commute just looking at light spotty nuisance type
precip. Chilly day with highs 35 to 40 but feeling colder along
the coast given the gusty onshore winds.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...

Highlights...

* Mainly dry with above normal temperatures Thu through the weekend
* A storm may bring rain and/or mixed precip/ice Mon into Tue

Overview...

Models in agreement that persistent SE CONUS ridge will build
northward along the east coast through the end of the week and into
the weekend as active Pacific jet sends series of waves into the
central CONUS. By the weekend southern stream system with Pacific
origins will evolve into a closed low then lift toward the NE early
next week. Given energy will not reach the west coast until this
weekend, expect varying model solutions next several days. However,
with lack of deep cold air snow will be difficult to come by with
most of the precip likely in the form of rain or interior ice
depending on positioning of downstream high pres and track of sfc
low. Temps will remain above normal through the period.

Details...

Wednesday night into Thursday...

Coastal low pres will move offshore in the evening. Abundant low
level moisture persists Wed night so at the very least we expect
lots of clouds during the night. Some light rain or interior snow
may linger into the evening then sfc ridging should take control
overnight Wed night into Thu. Morning clouds Thu should give way to
partial sunshine in the afternoon as the column begins to dry.
above normal temps with highs mostly in the 40s.

Friday through Sunday...

Surface high pres in control for much of the period as ridging aloft
builds into the region. Result will be mainly dry weather but low
level moisture will result in lots of clouds at times. Above normal
temps trending cooler Sun as high pres sets up in the Maritimes with
cold air damming signature. Coastal low emerging off the NC coast on
Sat should remain far enough south to keep it dry.

Monday into Tuesday...

Inherent low confidence at this time range. Potential for a
significant QPF event as southern stream system approaches but
details unknown. EPS and GEFS probs for greater than one inch QPF
are quite high at this time range with moderate probs greater than 2
inches. Potential for snow is low given lack of deep cold air but
ice remains a threat in the interior given the presence of high pres
downstream which could provide a source of low level cold air if sfc
low can track south of New Eng. Variability in model solutions
is likely until energy reaches the west coast this weekend.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...

Forecaster Confidence Levels...

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

3z Update...

Short Term /through Wednesday/...Moderate Confidence.

Tonight...

Mix of MVFR to LIFR lowering overnight with mixed precipitation
types. SN/PL for the N/E with more FZRA/PL towards the SW across
the interior while RA for the coastal plain terminals and along
the shores. Intermittent visibility impacts as cigs are trending
lower. Biggest concern continues to be FZRA impacts to BDL and BAF
during the overnight period, possibly into the Wednesday AM push.

N flow through the CT River Valley with a N/NE flow to the E. Will
see winds turn N and increase into the morning hours.

Wednesday...

MVFR with LIFR/IFR across the high terrain. Rain most terminals
but rain and/or snow high terrain. Gusty NE winds eastern MA
coast.

Specific Terminals...

KBOS TAF...bulk of precip will be rain but snow and sleet may mix
in during the overnight hours. Gusty NE winds late tonight into
Wednesday.

KBDL TAF...Wintry mix of SN/IP/FZRA. Light snow / ice accumulations
are forecast with snow on the order of several tenths and several
hundreds of an inch of icing.

Outlook /Wednesday Night through Sunday/...

Wednesday night into Thursday...Moderate confidence. MVFR/IFR cigs
Wednesday night and early Thursday, improving to VFR from west to
east during the day. NE gusts 25-30 kt Cape/Islands Wed evening
diminishing overnight. Light winds Thu.

Friday through Sunday...Moderate confidence. Areas of MVFR cigs
possible at times, otherwise VFR.

&&

.MARINE...

Forecaster Confidence Levels...

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

10 pm Update...No major changes to the forecast.

Short Term /through Wednesday/...Moderate Confidence.

Tonight...

ENE winds gradual increase tonight to 30 kt or so by morning,
strongest wind vicinity of Cape Cod and Nantucket waters. Vsby
lowering in rain.

Wednesday...

ENE winds up to 30 kt with strongest winds across the Cape Cod and
Nantucket waters. Low risk for a few gusts up to gale force...35
kt. Vsby reduced at times in rain and fog.

Outlook /Wednesday Night through Sunday/... Moderate confidence.

Wednesday night...High confidence. Lingering NE gusts to 25-30 kt in
the evening, diminishing overnight. Seas gradually subsiding.

Thursday through Sunday...Moderate confidence. Light winds for much
of the period as high pres builds over the waters. Lingering 5 ft
seas over the outer waters Thu subsiding below SCA by Fri.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...Winter Weather Advisory until 7 AM EST Wednesday for
     CTZ002>004.
MA...Winter Weather Advisory until 7 AM EST Wednesday for
     MAZ002>006-008>012-026.
RI...None.
MARINE...Gale Warning from 8 AM to 4 PM EST Wednesday for ANZ231-232-
     254-255.
     Small Craft Advisory until 7 PM EST Wednesday for ANZ230-
     233>237-250-251-256.

&&

$$

SYNOPSIS...KJC/Nocera
NEAR TERM...KJC/Nocera/Sipprell
SHORT TERM...Nocera
LONG TERM...KJC
AVIATION...KJC/Nocera/Sipprell
MARINE...KJC/Nocera


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