Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 180011

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

A mixed bag of wintry weather will impact much of S New England
from late this afternoon 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.


710 PM update...
Widespread precip overspreading SNE this evening. Evaporative and
dynamic cooling resulting in rain changing to snow across interior
northern MA while sleet is mixing in with the rain near the coast.
Thermal profiles indicate cooling in the low levels this evening,
especially far northern and interior NE MA where rain will change
to snow this evening, although sleet will mix in at times. Further
south and west, warming aloft is more pronounced and will support
mostly rain with areas of freezing rain in the interior where low
level cold air is locked in. Biggest threat for icing is across
the higher elevations in southwest MA with a secondary threat near
and south of the Mass Pike from central MA into the hills of NE

Forecast largely on track but we increased snow amounts across
interior NE MA where deep cold air hangs on for much of the night
supporting mostly snow in this region.

Previous discussion...

First short wave trough moving across the eastern Great Lakes
early this afternoon with parent surface low of 1008 mb over Lake
Erie. Warm advection precip associated with this feature was
across much of NY state into northern NJ/NYC and Long Island.
Latest meso analysis has pressure falls up to 4 mb in the past 3
hrs over the DC area. This will support secondary low pressure
developing off DE/NJ coast later this evening and overnight. This
combined with 1030+ mb high pressure over eastern Quebec will help
advect dry/cold air into southern New England.


Leading edge of precip continues to erode as it encounters very
dry air across the region. This is apparent on the 18z observed
sounding from ALY which reveals a very dry layer below 850 mb with
a -20C dew pt at 925 mb! This yields subzero wet bulb temps thru
the column except around zero just above 850 mb. This is a
snow/sleet sounding with lots of evaporative cooling potential
given magnitude of low level dry air.


Onset of precip looks to be 3pm-5pm across CT and western-central
MA...then moving east into RI and eastern MA 6-8 pm but possibly
not until 9 pm for Cape Cod and the Islands given stubborn dry air
below 850 mb.


Models in good agreement on burst of moderate to heavy precipitation
around 22Z-02Z. Good snow growth signature at this time with
strong lift in the DGZ. Where precip remains all snow could see
snowfall rates of up to an inch per hour. However mid level
warming as seen on the observed 18z ALY sounding just about 850 mb
supports a mix of sleet and rain south of the MA Pike into
northern CT and eventually freezing rain once surface wet bulb
temps are realized. Eastward into RI and southeast MA probably a
period of sleet given mid level warming. Farther northward into
eastern MA including Boston a mix of rain/snow and sleet is likely
with mainly snow north of the MA Pike and west of I495. This is
where the worst travel conditions will be experienced. The
heaviest precip will be this evening with somewhat lighter
intensity overnight.


Not much change from previous forecast guidance as well as latest
trends from radar and satellite imagery. Thus previous headlines
and configuration of advisory still looks valid. Thus will
continue will current headlines.

Snow Potential...

Looks like a swath of 2-4" north of the MA Pike and west of I495
with possibly up to 5 or 6" across the higher terrain in this
region...northern Worcester county and northwest Franklin. Farther
south an inch or two is possible to the MA/CT border and eastward
into the I495 corridor. Elsewhere...less than an inch of snow and
sleet across northern CT/RI into Metro-West Boston. Southeast MA
and southern RI mainly rain with a bit of sleet this evening.

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 southwest 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. This may result in isolated power outages.


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.



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


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.


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.


Forecaster Confidence Levels...

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

20z Update...

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


Conditions lowering to IFR with LIFR likely across the high
terrain. Rain changing to a period of moderate to heavy snow 00z-
03z across interior N/NE MA. Snowfall rates up to an inch per
hour. Freezing rain likely vicinity of BDL and BAF, and possibly
ORH too later tonight as warming aloft overspreads the area. ENE
winds picking up by midnight and thereafter.


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

Specific Terminals...

KBOS TAF...bulk of precip will be rain however sleet and snow may
mix in from 23z-01z. Gusty NE winds late tonight into Wed.

KBDL TAF...Initial onset of RA transitioning to a 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

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.


Forecaster Confidence Levels...

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

3 pm Update...

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


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 with some sleet possible this


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.


CT...Winter Weather Advisory until 7 AM EST Wednesday for
MA...Winter Weather Advisory until 7 AM EST Wednesday for
MARINE...Gale Warning from 8 AM to 4 PM EST Wednesday for ANZ231-232-
     Small Craft Advisory from 11 PM this evening to 7 PM EST
     Wednesday for ANZ230-233>237-250-251-256.


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