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Area forecast discussion 
National Weather Service Taunton Massachusetts
453 PM EST Thursday Feb 11 2016

Synopsis...
much colder airmass moves into the region tonight om gusty
northwest winds. An ocean storm will track well offshore Friday
night but will bring a period of accumulating snow to the cape
and islands. An Arctic front will deliver bitterly cold weather
this weekend with dangerously cold wind chills. Temperatures
moderate Monday. For Tuesday and Tuesday night...a storm will
likely bring snow quickly changing to rain along the coast and to
freezing rain and then rain inland as much milder air moves into
New England.

&&

Near term /until 6 am Friday morning/...
***wind chills dropping to between 0 and 10 below zero late
tonight into early Friday morning***

Scattered flurries and snow showers moving across southern New England this afternoon
will dissipate by evening followed by clearing skies tonight as
good middle level drying moves in. Strong cold advection on gusty northwest
winds with 850 mb temperatures dropping to -20c tonight...then winds
gradually diminish overnight. Min temperatures will be mostly in the
single numbers...except teens cape/islands. Wind chills will drop
to zero to 10 below overnight.

&&

Short term /6 am Friday morning through Friday night/...
Friday...
high pressure moves off middle Atlantic coast with sunshine giving way to
increasing afternoon clouds as next potent shortwave moves into
the Great Lakes. With deeper moisture remaining south and west of
the region it should remain dry through the day. There is a low
probability of a few ocean effect flurries/snow showers over cape/islands
toward evening with SW flow and cold air aloft yielding ocean
induced convective available potential energy around 500 j/kg...but moisture is very shallow
which will limit activity. Maximum temperatures will be mostly in the low
and middle 20s...with upper teens higher terrain. Winds will be
light.

Friday night...
*** accumulating snow likely across cape/islands ***

Interesting set up as ocean storm tracks well offshore but potent
middle level trough/shortwave approaching from the west will induce an
inverted trough which extends across southeast new eng. Models are in
fairly good agreement on deepening moisture and area of good low
level convergence and modest Omega in the snow growth
region...focused across cape/islands Friday night which should bring
a period of snow. Some ocean enhancement likely given steep low
level lapse rates and ocean induced convective available potential energy around 500 j/kg yielding
potential for brief heavier snow. Snow accumulate of 1-3 inches
expected with low risk of up to 4 inches. Advisories may be
needed.

Snow showers will likely extend across S coastal Massachusetts with minor
accumulate possible but main focus expected to be across cape/islands.
Otherwise...Arctic front will be approaching from the west late
Friday night and will likely bring a few snow showers to western new
eng.

&&

Long term /Saturday through Thursday/...
highlights...

* snow showers ending over the cape and islands Sat
* bitter cold Arctic air moves into southern New England for the
weekend
* snow changing to rain likely Tuesday and Tuesday night

Overview...

Closed upper low passes across New England Sat night above coldest
Arctic air witnessed here in quite a while. Strong surface pressure
gradient will most likely result in gales across the ocean waters
and wind chills approaching or exceeding wind chill warning criteria
over much of the forecast area. Upper low and surface high move
east. Short wave trough amplifies long wave trough position in North
America but so sharply that surface low looks to move north along
or just east of the Appalachians as an inside runner. With the
surface high being shown to move off the coast it is not the right
synoptic set up for cold air damming. Thus...any snow or freezing
rain at the outset will likely change rather quickly to rain even
far inland. The only caveat is that this event is still several
days away and could see some variations in model output as the
energy reaching North America becomes better resolved in the upper
air network.

Details...

Sat...snow on the outskirts of an ocean storm should end across Cape
Cod...Martha/S Vineyard and Nantucket during Sat morning. Ocean
effect snow showers may persist for a while longer over the Outer
Cape. Although there will be an impressive low level layer of a very
steep lapse rate...the mean flow in the lower levels has enough
westerly component to keep most of the snow showers offshore.

The main show of the Arctic blast arrives by Sat afternoon with
strong northwest winds driving wind chills dramatically lower during the
afternoon and hence beginning the wind chill watch at 1800 UTC or 1
PM EST. The temperatures themselves may rise a few degrees or so
from early morning to midday and then fall steadily throughout the
afternoon.

Sat night...main story will be the bitter cold. Wind chill watch in
effect for potential wind chills of -25 to -30 across most of the
forecast area. The wind chill watch covers all but the cape and
islands. Later shifts may need to reevaluate to see if the watch
needs to be expanded to the cape...Martha/S Vineyard...Nantucket and
Block Island. Near record low temperatures are forecast for Sun
morning at most southern New England locations including
Boston...Worcester and Hartford/Windsor Locks. Model consensus
brings 850 mb temperatures within a degree or two of -30c Sat
night. Ocean effect snow showers will likely remain just offshore.

Sun...air mass slowly begins to moderate to -20c to -22c at 850 mb
but still very cold. Anticipate most high to be in the single digits
to lower teens across southern New England. There should be plenty
of sunshine but still a brisk northwest wind into the early afternoon. The
wind chill watch expires at 1 PM.

Sun night...clear skies and lighter winds over the snow cover should
be a good set up for efficient radiational cooling. Temperatures
will likely drop to near or several degrees below zero most interior
locations and not too much above zero across the southeast urban centers.

Monday...temperatures moderate considerably although maximum temperatures
will likely top off below freezing outside of the cape and islands.
High clouds ahead of a vigorous short wave dropping into the mean
long wave position will increase during the afternoon.

Monday night through Tuesday night...model consensus is for a sharpening
trough over the east central Continental U.S. With associated surface low that
runs near or just east of the Appalachians. There is currently good
model consensus for an inside runner...although the event is still
several days away. Current model consensus would favor snow changing
rather quickly to freezing rain and then rain inland and to just
rain along the coast. A strong low level jet at 925 mb in excess of
80 knots may present a wind issue if enough of that momentum can mix to
the surface...a question mark as an inversion is likely to exist.
Significant enough rafl for local street flooding is possible...but
confidence on quantitative precipitation forecast this far out is quite low.

Wednesday through Thursday...for now this period looks to be dry with short
wave energy not sharp enough to produce a significant surface
reflection. However...some prior model runs have shown a clipper
during this time period and so confidence is not all that high. If
nothing else...the short wave trough should help usher in another shot
of Arctic air but not nearly to the extent of what is expected this
weekend.

&&

Aviation /22z Thursday through Tuesday/...
forecaster confidence levels...

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

Short term /through Friday night/...

Through 00z...scattered snow showers and MVFR conditions confined to east
Massachusetts this afternoon...otherwise mainly VFR with scattered flurries and
brief MVFR. Partial clearing toward evening. West/northwest gusts to
25-30kt.

Tonight...high confidence. VFR ceilings evening...then clearing. West/northwest
gusts to 20-30 knots in the evening...diminishing overnight but
remaining gusty along the coast.

Friday...high confidence. Mainly VFR...but some MVFR ceilings may
develop in the afternoon north of the Mass Pike.

Friday night...moderate confidence. Conditions lowering to MVFR/IFR
cape/islands as snow overspreads the region with some accumulate
likely. Scattered snow showers may extend into southeast Massachusetts...otherwise a mix
of VFR/MVFR ceilings.

Kbos terminal...high confidence.

Kbdl terminal...high confidence.

Outlook /Saturday through Tuesday/...

Sat through sun...moderate to high confidence. MVFR ceilings/visibilities in
snow showers over the cape and island...improving during Sat afternoon.
Otherwise...VFR for the period but gusty northwest surface winds.

Monday...high confidence. VFR.

Monday night through Tuesday...low to moderate confidence. Becoming IFR
with snow changing to rain with areas of fog late Monday night into
Tuesday. Strong southerly winds aloft may result in significant low
level wind shear Tuesday afternoon.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday night/...high confidence.

Tonight and Friday...a period of west/northwest gales around 35 knots through
this evening in strong cold advection. Winds slowly diminish
overnight and drop below Small Craft Advisory Friday morning with light SW winds
developing Friday afternoon. Areas of moderate freezing spray over east
Massachusetts waters and Cape Cod Bay tonight so freezing spray advisory will
continue.

Friday night...winds and seas below Small Craft Advisory. SW winds becoming northwest after
midnight...increasing toward daybreak. Visibilities reduced in areas of
snow.

Outlook /Saturday through Tuesday/...

Moderate to high confidence.

Strong surface pressure gradient and cold air advection is expected
to result in gale force northwest winds across all waters Sat afternoon
into sun. In addition...there is a risk for heavy freezing spray Sat
night into Sun morning.

Winds and seas subside Sun night and Monday. A developing low moving
along or just east of the Appalachians may produce southerly winds
of gale force across at least some of the waters Tuesday along with
building seas.

&&

Climate...
bitterly cold temperatures are expected this weekend. Record cold
high and low temperatures may be tied or broken. Here are the
current records for the weekend.

Record cold highs for Feb 13th - 14th...

Boston.......15/1979 - 14/1916
Hartford.....11/1979 - 11/1979
Providence...10/1979 - 10/1979
Worcester.... 8/1899 - 7/1979
Blue Hill.... 9/1899 - 10/1979

Record cold lows for Feb 13th - 14th - 15th...

Boston...... -3/1967 - -3/1934 - -14/1943
Hartford.... -7/1967 - -9/1979 - -18/1943
Providence.. -5/1967 - -7/1979 - -14/1943
Worcester...-12/1967 - -11/1979 - -19/1943
Blue Hill...-10/1967 - -9/1979 - -18/1943

&&

Box watches/warnings/advisories...
CT...wind chill watch from Saturday afternoon through Sunday
afternoon for ctz002>004.
Massachusetts...wind chill watch from Saturday afternoon through Sunday
afternoon for maz002>021-026.
Rhode Island...wind chill watch from Saturday afternoon through Sunday
afternoon for riz001>007.
Marine...Gale Warning until 4 am EST Friday for anz231>235-237-250-251-
254>256.
Small Craft Advisory until 4 am EST Friday for anz230-236.
Freezing spray advisory until 7 am EST Friday for anz231-250-
251.

&&

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

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