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Area forecast discussion 
National Weather Service Taunton Massachusetts
1022 PM EST Mon Dec 5 2016

Synopsis...
low pressure off the mid Atlantic coast may bring some mixed light
rain and/or snow into southern New England Tuesday night into early
Wednesday. A cold front crosses the region late Thursday or Thursday
evening with another cold front Friday. This will be followed by
blustery and unseasonably cold conditions Friday night into
Saturday. Low pressure may bring some snow or rain Sunday night into
Monday.

&&

Near term /until 6 am Tuesday morning/...

1015 PM update...
some lake effect clouds have been spilling over the Berkshires
this evening and are expected to continue to do so until early am
when surface high pressure and shift to more of a northwest or even north-northwest
flow cuts off the moisture feed. Made some modifications to sky
grids and only very minor tweaks to temperatures as forecast
remains generally on track for the overnight.

Will freshen up the black ice Special Weather Statement shortly.

630 PM update...
lake moisture extending into western new eng has resulted in some
lower clouds across western Massachusetts and northern CT. Otherwise, mostly
clear skies prevailed. Expect lake effect clouds to persist into
the early morning hours across western MA, then clouds should
erode as high pres builds in and flow weakens. Adjusted short
term sky grids, otherwise forecast on track.

Previous discussion...
expect less radiational cooling tonight as pres gradient
increases with the approaching high and weak low pres development
associated with the trof. Most of this will be felt offshore, but
winds may remain 5-10 mph and mitigate temperature drop through
the early portion of the overnight.

Still temps will fall back into the 20s by the early am hours
thanks to weak cold air advection. Will be issuing a special statement for black
ice, mainly for the interior as area roadways are unlikely to dry
completely before temps cool once again below freezing. This may
need to be expanded for areas that received less snow or all rain
should the roads be observed as remaining wet through the evening
hours.

&&

Short term /6 am Tuesday morning through Tuesday night/...
tomorrow...
mainly clear day to start although some cold air advection induced SC is
possible, lingering from the overnight hours. Temps should
moderate given the sunshine, thanks mainly to h92 temps still
between 0c and -2c. Expecting highs then to rebound into the low-
mid 40s. Winds will be light as they begin to veer from the northwest to
the east by evening, in advance of another 2-wave system approaching
from the west and SW.

Tomorrow night...
similar setup to last night as double-barreled system approaches
with dominant shortwave remaining in the north stream and to the northwest of
S New England. Meanwhile, S stream wave initiates strong
cyclogenesis offshore, such that coastal low pres strengthens and
gradually shifts E, well S of the area by Wed morning. Therefore,
most of the impact comes from an inverted trof and modest
convergence between these two systems, rather than either one
themselves. Pwats increase to about 130-150 percent of normal and
modest lift is noted within the snow growth region as the column
moistens from the top down. Therefore we are monitoring for the
development of light snowfall late Tue night and continuing into
Wed am, similar to this past event. More detail to follow.

Temps...
went lower than most guidance with temps as even with increased
upper lvl, then lower lvl clouds, some modest radiational cooling
during the evening could allow mins to drop into the upper 20s and
low 30s before precipitation onset. Afternoon dwpts are lower,
suggesting some wetbulb effect cooling is likely as the precip
shield approaches from SW to NE.

Snowfall/rainfall...
with this combination of cool temps and wetbulb, combined with
modest moisture and some lift within the snow-growth regime, could
see the development of another round of light accumulating
snowfall across the region particularly during the am hours Wed
morning. Lift/temps suggest snow ratios between 10-12 per inch
liquid, but rates will once again be light enough that only a
widespread coating to an inch can be expected by sunrise. This may
once again impact commuting traffic as some un-treated roads could
become slippery.

Areas across west MA and the higher terrain may relieve more along
the line of 1-3 inches, mainly due to better moisture convergence
under east flow. This flow also will keep areas near shore, likely
all rain thanks to warm SSTs. More information will come, but stay
tuned due to the possible impact this may have on the Wed morning
commute.

&&

Long term /Wednesday through Monday/...
highlights...

* mixed snow/rain lingering into Wed morning
* blustery and unseasonably cold Fri night into Sat
* some snow/rain possible Sun night into Mon

Wednesday...
southern stream shortwave and attending coastal Low Pass well south
of new eng. However, inverted trof extending to the north combined
with deep moisture axis will result in some light snow/rain
lingering into the morning. Much of any accum will occur before 12z
Wed. Then good mid level drying moves in from the west during the
afternoon resulting in dry conditions with partial clearing possible
toward evening.

Thursday...
decent mid level shortwave passage and attending cold front in the
afternoon and there is some indication that a weak wave may develop
just to the east. But model consensus and gefs/eps ensembles suggest
any precip will remain mostly offshore so looking at just a few
snow/rain showers with the fropa. Seasonable temps.

Friday and Saturday...
the unseasonably cold air that moves in Fri night into Sat will be
the main story as mainly dry weather expected with exception of a
few flurries for the Berkshires on Fri. Secondary fropa brings 850
mb temps down to -10 to -12c Fri with further cooling to -14/-15c
Sat. Friday will be a transition day with highs mostly in the 30s,
cooling to the mid 20s to lower 30s Sat. Gusty northwest winds both days
will add to the chill with wind chills single numbers and teens Fri
night into Sat. Sat night lows tricky and will depend on extent of
radiational cooling. There may be some clouds and leftover wind
which would limit cooling but potential exists for temps to be
several degrees colder than forecast if it ends up clear with winds
decoupling.

Sunday into Monday...
next shortwave approaches from the gt lakes and there are
significant differences in timing/amplitude between GFS and European model (ecmwf).
Low confidence on details but appears there is an increased risk of
some snow/rain, sometime Sun night into Mon. Deterministic GFS is
more threatening than European model (ecmwf) but very low confidence given it's a day
7 forecast and this will change. Most of the guidance and ensembles
keep it dry with moderating temps on sun.

&&

Aviation /03z Tuesday through Saturday/...
forecaster confidence levels...

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

Overnight into Tuesday...high confidence. Only change from prior
forecast for near term was to adjust winds a little to fit current
observations. VFR with only exception being patchy MVFR cigs near
the crest of the Berkshires until about 08z. Increasing high
clouds late Tuesday. Winds mainly west through about 08z and then
becoming northwest and then north by around 15z. Gusts 20-25 kt near shore
overnight, but these diminish during Tuesday.

Tuesday night...high confidence in trends, lower confidence in
timing. Similar setup to last night/this morning. VFR early gives
way to light snow/rain mix (mainly snow first with light
accumulations generally an inch or less). This transitions to rain
during the morning. With the arrival of precip, expect category to
drop to widespread IFR/MVFR. Winds mainly east.

Kbos taf...high confidence. VFR. Winds becoming north or north-northwest by around
daybreak.

Kbdl taf...high confidence. VFR.

Outlook /Wednesday through Saturday/...

Wednesday...moderate confidence. Areas of MVFR/IFR in lingering
snow/rain Wed morning, then gradual improvement in the afternoon.

Thursday...moderate confidence. Mainly VFR cigs but areas of MVFR
possible interior with a few snow/rain showers.

Friday and Saturday...moderate confidence. Mainly VFR cigs.
Localized MVFR in isolated snow showers far interior Massachusetts Fri.

&&

Marine...
forecaster confidence levels.

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

Short term /through Tuesday night/...

Tonight into early Tue...high confidence.
West-northwest winds increase overnight as low pres shifts east of the waters
and high pres moves in to take it's place. Gusts around 25 kt can
be expected across much of the waters as a result. Otherwise, this
will lead to a slight building of seas, reaching 5-6 ft on the
ocean waters which will linger into the early am hours. Current
scas seemed good, but will extend outer waters as seas may take a
bit longer to diminish.

Rest of tomorrow and tomorrow night...high confidence.
High pres will slowly build from west-east across the waters leading to
diminished winds and seas below Small Craft Advisory thresholds.
Some early morning rain is possible, mainly across the S and southeast
waters.

Outlook /Wednesday through Saturday/...

Wednesday...high confidence. Light winds and seas.

Thursday...high confidence. Increasing west winds in the afternoon with
gusts to 25-30 kt developing Thu night.

Friday into Saturday...high confidence. Northwest gusts to 30 kt likely
Fri/Fri night and there is a moderate risk for gale force gusts.
Winds gradually diminishing Sat.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 7 am EST Tuesday for anz231>235-237-
251.
Small Craft Advisory until 10 am EST Tuesday for anz250-
254>256.

&&

$$
Synopsis...kjc/doody
near term...kjc/doody/Thompson
short term...doody
long term...kjc
aviation...kjc/doody/Thompson
marine...kjc/doody

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