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Area forecast discussion
National Weather Service Taunton Massachusetts
227 PM EST Tue Dec 12 2017

Synopsis...
strengthening low pressure over upstate New York redevelops over
northeast Massachusetts this evening, then intensifies into a
gale center over New Brunswick Wed. A shot of Arctic air wraps
around this exiting low Wednesday and Thursday, with a period
of strong winds and bitterly cold wind chills. Another low
pressure may bring some light snow across south coastal areas
Friday night into Saturday if it tracks close enough to the
coast. Somewhat milder weather will arrive by the end of the
upcoming weekend.

&&

Near term /through tonight/...
continuing to monitor temperatures this afternoon. So far,
timing of the ongoing forecast looks good. Winter Weather
Advisory currently slated to expire at 4 PM. Will make a final
decision on whether to extend it or not after 3 PM.

Radar data showing light snow continuing across western Massachusetts.
Where surface temperatures are still at or below freezing in
north central MA, it appears the precipitation had temporarily
waned, meaning not too much ice accretion was occurring.

Potent negatively-tilted mid level shortwave crosses our region
later tonight. This feature will help to drive much colder air
into southern New England by Wednesday morning. Expecting plenty
of clouds with this shortwave. Thinking it might just a bit too
dry for widespread snow showers, but that remains a possibility.
Most of the moisture looks to be trapped below 800 mb, which
should keep any showers mainly on the western side of the
Berkshires with a west wind.

Below normal temperatures, well below freezing, tonight. Any
standing water and/or slush will freeze. Thus this afternoon is
your chance to remove any leftover snow/ice.

&&

Short term /Wednesday through Wednesday night/...

Strong low pressure will spin across the Maritimes into
Labrador through Wednesday night, continuing a strong surge of
Arctic air into our region. While the core of this Arctic air
remains north of our region, will see increasing west-northwest winds
with the sharp pressure gradient. 0-3 km lapse rates are near
dry adiabatic, meaning excellent mixing and momentum Transfer.
Will probably need a Wind Advisory for portions of southern New
England, especially across the higher terrain and towards the
coasts. Still trying to refine the area and timing a bit more.

Some leftover snow showers may linger across the east slopes of the
Berkshires through midday Wednesday, with a few lingering along
the S coast early. Otherwise, mainly dry across much of southern
New England. Below normal temperatures with highs below
freezing. Wind chill values later in the day remaining in the
single digits and teens above zero. A few locations towards the
Berkshires could see subzero wind chills Wednesday afternoon.

Winds diminish some Wednesday night as better mixing moves
offshore. Another mid level shortwave should pass by to our
south. While this should mean some clouds for our region,
temperatures will still fall into the teens away from the
immediate coast. Lows in the 20s for there. Still very low wind
chills in the single digits and teens for much of the region,
with readings as low as -5 toward daybreak across the east slopes
of the Berkshires.

Any snow showers would be closer to the South Coast of New
England. Limited moisture would also limit any accumulations,
which should be less than 1 inch, where it snows at all.

&&

Long term /Thursday through Monday/...
overview...

Deep 500 mb long wave trough sets up by mid week from the Arctic
Circle southward to the mid Atlantic coast, while high amplitude
ridge continues from the northwest territories through the
Pacific coast. This will bring the coldest air so far this
season to the region along with strong west-northwest winds through
Thursday.

As the cold pool retreats into eastern Canada late this week,
appears that the western ridge may break down as a short wave
moves into the Pacific northwest late Fri or Sat. Also noting a weak
mid level short wave that may wrap around base of the eastern
Canadian cutoff low and cross the region. May also see a
strengthening southern stream system try to ride up across the
western Atlantic. Rather wide model solution spread at this
point, so track is in question along with the possibility of the
northern fringe of the precip shield approaching portions of
the South Coast late in the week or into the weekend. 00z GFS is
farthest west with this system, while the Canadian ggem is further
offshore. Something to keep an eye on.

With rather wide solution spreads amongst the model suite from
about Friday into early next week, lower forecast confidence for
this portion of the forecast.

Will use a blend of available model guidance into Friday, then
transition over the model ensembles for the latter portion of
this period.

Details...

Thursday...

Expect the gusty west-northwest winds to continue through midday Thursday,
but will start to weaken as the eastern Canadian low slowly
exits.

Models continue to signal an 500 mb short wave passes S of New
England. The northern fringe of the precip shield may clip the S
coast Thursday morning through midday as the weak low passes
close to or just S of the 40n/70w benchmark. Have carried chance
pops across Nantucket and Martha's Vineyard. Will see snow
showers or a period of light snow for a few hours as the low
passes. Little if any snow accumulations are expected.

The Arctic air will continue across the region, with high temps
only in the upper teens and 20s across the higher inland
terrain, ranging to the lower-mid 30s at the shore. As winds
drop off during the day, wind chills will not be quite as harsh
as on Wed. However, with mainly clear skies Thu night, temps
will fall back to the single digits well inland, ranging to
20-25 across the Outer Cape and islands.

Friday through Saturday...

Another weak short wave develops across the Great Lakes Fri,
while stronger low pressure forms off the southeast U.S. Coast. The
weak low will push east while the coastal low moves NE off the
eastern Seaboard. Models showing some spread with their
development and track of the coastal low, with the GFS closest
to the coast but still passing S and east of the 40n/70w
benchmark.

Could still see some light snow or snow showers push into southeast
mass/east RI, but this is still up in the air for exact track and
impacts later Friday into early Saturday. Should see improving
conditions with slowly moderating temps Sat.

Sunday and Monday...

High pressure ridge builds across the region Sunday. Winds back
from west-northwest to SW, which will bring milder temps, actually near or
just a few degrees below seasonal normals. May see another short
wave bring some light precip by Sun night and continuing into
Monday, but timing and track of this system is in question.

&&

Aviation /19z Tuesday through Sunday/...
forecaster confidence levels...
low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Short term /through Wednesday night/...

Through 00z...high confidence on trends but lower on exact
details, particularly timing of precipitation type changes.

MVFR ceilings across central and western areas will push E, with
local IFR-LIFR at times across north central and western areas.

Tonight...high confidence on trends, lower on details.



MVFR ceilings/MVFR-IFR visibilities improve to VFR by around 05z-07z,
except lingering lower ceilings across higher terrain. Gusty west-northwest
winds develop.

Tomorrow...mainly VFR, with local MVFR possible in scattered
shsn. Strong winds with gusts to 40 kt.

Tomorrow night...VFR. Strong winds with gusts to 40 kt.

Kbos terminal...moderate confidence in taf.

Kbdl terminal...moderate confidence in taf.

Outlook /Thursday through Saturday/...
thursday: VFR. Windy with local gusts to 30 kt.

Thursday night: VFR. Breezy.

Friday: VFR.

Friday night: mainly VFR, with local IFR possible. Breezy.
Slight chance snow.

Saturday: VFR. Breezy.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday night/...

Tonight...Arctic cold front sweeps across the area with southeast
winds shifting to west-SW up to 20-30 kt. Vsby improves after
evening rain/snow showers.

Wednesday and Wednesday night...gale force winds with gusts up
to 45 kt. Rough seas up to 15 ft. Slight chance of snow showers
Wednesday.

Outlook /Thursday through Saturday/...

Thursday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Chance of snow showers.

Thursday night: low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas.

Friday: winds less than 25 kt. Seas locally approaching 5 ft.
Chance of snow. Areas of visibility 1 to 3 nm.

Friday night: low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
snow. Visibility 1 to 3 nm.

Saturday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Slight chance of snow.
Areas of visibility 1 to 3 nm.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...Winter Weather Advisory until 4 PM EST this afternoon for
maz002>004-008-009-026.
Rhode Island...none.
Marine...Gale Warning from 9 am Wednesday to 6 am EST Thursday for
anz232.
Gale Warning from 9 am Wednesday to 4 am EST Thursday for
anz233-234.
Gale Warning from 1 PM Wednesday to 1 am EST Thursday for
anz230-236.
Gale Warning from 10 am Wednesday to 6 am EST Thursday for
anz231.
Gale Warning from 8 am Wednesday to 6 am EST Thursday for
anz235-237-251.
Gale Warning from 6 am Wednesday to 6 am EST Thursday for
anz250-254.
Gale Warning from 5 am Wednesday to 6 am EST Thursday for
anz255-256.

&&

$$
Synopsis...Belk/evt
near term...Belk

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