National Weather Service Forecast Discussion

Forecast Discussion for BOX NWS Office
FXUS61 KBOX 110528

Area Forecast Discussion
National Weather Service Taunton MA
1228 AM EST Mon Dec 11 2017

Mainly dry and cool conditions are expected through Monday. Low
pressure will approach from the west late Monday night into
Tuesday. This will likely bring a period of accumulating snow,
mainly across interior northern Massachusetts, while any snow
will quickly change to rain in the coastal plain. A shot of
arctic air follows Wednesday and Thursday. Another low pressure
system may bring more snow to the region sometime in the
Thursday night to Friday night timeframe.


10pm update...
For the most part, forecast remains on track. However, will add
an overnight risk for flurries inland as light echos are already
showing up in advance of the approaching shortwave as clouds
move over signaling column moistening. Also, will bump up POPs
along and offshore of S coastal areas per latest mesoscale
guidance beefing up chances for near shower SHRA/SHSN. Will
continue to monitor this overnight.

Previous discussion...

Lake-effect clouds were spilling over
the Berkshires into western and central MA. Expecting a mid
level shortwave to arrive tonight, which will only spread more
clouds from west to east across southern New England, especially
after midnight. As such, not expecting good radiational cooling
conditions. That said, min temperatures tonight should be below

Fairly dry air below 800 mb, so dry weather will prevail for
much of the interior. A little different story towards the
coast, and coastal waters. The arrival of colder air over the
still relatively warm ocean will kickstart the ocean-effect
process. This will be mainly in the form of clouds, but cannot
dismiss the possibility for some showers around the Cape and
islands, including Block Island. A west wind direction would
place the greatest risk for any showers across the southern
coastal waters.


Mid level shortwave departs during Monday morning, followed by a
brief period of higher pressure. A nearly stationary front may
sag far enough south to reach portions of southern New England
late Monday into Monday night. Mainly dry with clearing sky once
any lingering morning showers move offshore. High temperatures
remaining below normal.

A low pressure over the Great Lakes starts to exert more
influence on our weather late Monday Night. Another case of
increasing clouds after midnight, with a risk for some
precipitation late. Given low temperatures below freezing
across pretty much all of southern New England, light snow would
be expected over land, with the possibility of some rain over
the ocean waters.

Thinking around one inch or less across southern New England
through Monday night. It will all come down to timing. A faster
arrival would give more time for snow to accumulate before
daybreak. Slower timing would mean even less snow. At this
point, the majority of any precipitation from this low pressure
would occur after daybreak Tuesday. Some impact on the Tuesday
morning commute is expected, especially from Worcester county



* Accumulating snow Tue across interior N MA with any snow quickly
  changing to rain in the coastal plain
* Arctic air and bitter cold wind chills follow Wed/Thu
* More snow possible sometime Thu night to Fri night


Accumulating snow is the main forecast issue, but latest guidance
suggests focus for appreciable snow accum will be confined to
interior northern MA west of I495 and especially the Berkshires.
Amplifying northern stream trough across the Great Lakes will
eventually become negatively tilted over the northeast. Primary low
moves into the eastern Lakes while a secondary low is forecast to
develop across SNE, but not in time to stop southerly low jet from
advecting milder air north across SNE. Models all indicate rapid
warming below 850 mb. Any snow early Tue will quickly change to rain
across northern CT, RI and E MA as low level warming advances north.
However, there could be an issue with a brief period of freezing
rain south of the Mass Pike in the interior during the transition
from snow to rain.

Further into the interior, especially north of the Pike and west of
I495, the snow will last through the morning but even here we expect
an eventual changeover to rain in the afternoon. The exception may
be across the east slopes of the Berkshires which may remain mostly
snow. Preliminary snowfall forecast is for 2-5 inches across
northern Worcester county to the Berkshires and possibly into the
higher terrain in western Hartford county, but a few locations could
reach 6 or 7 inches in the Berkshires, where decent omega in the
snow growth region persists the longest. Any accum across RI and
eastern MA will likely be limited to less than an inch. Winter
weather advisories will likely be needed for interior northern MA,
with a low probability for marginal warnings for the Berkshires.

Wednesday and Thursday...

Behind the departing low pres, a surge of arctic air will invade the
region with blustery NW winds as deep upper trough moves through.
Temps well below normal with highs mostly in the 20s and lower 30s
near the south coast. The gusty winds will make it feel much colder.
Mainly dry weather during this period, but can`t rule out a few
flurries Wed as the upper low moves across New Eng.

Thursday night into Friday night...

Another amplifying northern stream trough approaches from the
west with multiple shortwaves leading to the potential for some
accumulating snow sometime during this period. However, low
confidence on timing as models are struggling with resolving
what will become the dominant shortwave. May have to watch the
late Fri/Fri night period per ECWMF and EPS ensembles.

Saturday and Sunday...

Mainly cold and dry Sat then moderating temps Sun ahead of next
upper trough approaching from the west as SW flow develops.
Milder air may be accompanied by a few rain or snow showers.


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

Short Term /through Tuesday/...

Through today...High confidence.
Mainly VFR except brief MVFR CIGS mainly across Cape/Island
terminals this morning. Occasional very light SHSN/SHRA through
mid day.  W winds gradually shift to the SW.

Tonight...Moderate confidence.
VFR to start, will give way to MVFR then IFR early AM Tue as
CIGS lower and light SN/FZRA moves in mainly after 06Z from W-E.
SN accums would be light. Winds shift around to the E-NE.

Tomorrow...Moderate confidence.
Mixed MVFR and occasional IFR conditions in a mix of SN/FZRA
giving way to all RA through sunrise into mid day Tue. Risk for
NW MA to remain SN long enough for accums to exceed reach 3-6
inches with generally less further SE. Low risk also for a
period of FZRA before the change to RA. Conditions improve after
20Z from S-N.

KBOS Terminal...High confidence in TAF, lower categories don`t
move in until after 06Z tonight.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday: MVFR/IFR conditions with snow changing to rain.
Windy along the coast with areas gusts to 30 kt.

Tuesday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHSN.

Wednesday: Mainly VFR, with local MVFR possible. Windy with
gusts to 35 kt.

Wednesday Night: VFR. Windy with gusts 25-35 kt.

Thursday: VFR. Windy with local gusts to 30 kt.

Thursday Night and Friday: MVFR/IFR conditions possible. Chance


Forecaster Confidence Levels...

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

Short Term /through Tuesday/...High confidence.

Gusty west winds gradually diminish Monday afternoon. However,
rough seas will take longer to subside, especially across the
southern coastal waters, where the fetch will be longer. Therefore,
most Small Craft Advisories will continue into tomorrow.

Chance for showers, especially across the southern coastal
waters tonight into Monday morning, then again late Monday

Outlook /Tuesday Night through Friday/...

Tuesday: Low risk for gale force winds eastern waters with
gusts up to 35 kt. Local rough seas. Rain likely.

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 9 ft. Local visibility
1 to 3 nm.

Wednesday: Strong winds with gusts up to 40 kt. Rough seas up
to 14 ft. Slight chance of snow showers. Visibility 1 to 3 nm.

Wednesday Night: Moderate risk for gale force winds with gusts
up to 40 kt. Rough seas up to 15 ft. Local visibility 1 to
3 nm.

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas.

Thursday Night and Friday: Winds less than 25 kt. Local rough
seas. Chance of snow and rain. Visibility 1 to 3 nm.


MARINE...Small Craft Advisory until 1 PM EST this afternoon for
     Small Craft Advisory until 6 PM EST this evening for ANZ235-
     Small Craft Advisory until 7 AM EST this morning for ANZ251.
     Small Craft Advisory until midnight EST tonight for ANZ254>256.


NEAR TERM...Belk/Doody

NWS BOX Office Area Forecast Discussion