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Area forecast discussion 
National Weather Service Taunton Massachusetts
106 PM EST Friday Feb 12 2016

Synopsis...
dry but very cold weather is on tap for today. An ocean storm will
track well offshore tonight but will bring a period of accumulating
snow to the cape and islands. An Arctic front will deliver
dangerously cold wind chills of 20 to 35 below zero late Saturday
into Sunday morning! 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 /through tonight/...
930 am update...
updated T/dew point grids for current obs/trends...otherwise forecast on
track.

Strong cold advection will come to an end later this
morning/afternoon as flow turns southwesterly ahead of another and
even more intense Arctic cold front. Not too much moderation
occurs this afternoon as 850 mb temperatures remain below -15c.
Therefore...expect high temperatures to only recover into the 20 to 25
degree range this afternoon with upper teens higher terrain but
winds will become relatively light. Sunny skies this morning
should give way to an increase in middle level cloudiness from west
to east during the late afternoon. Ocean effect clouds will also
develop along the South Coast with cold southwest flow across our
southern waters.

&&

Short term /Saturday/...
*** accumulating snow tonight across Cape Cod and the islands ***

*** bitterly cold air invades the region Saturday afternoon with
strong wind gusts and rapidly falling temperatures ***



Tonight...

An interesting setup for tonight as an ocean storm will intensify as
it passes well southeast of the benchmark. At the same
time...potent shortwave energy will be approaching from the west
with an Arctic cold front. This will setup an inverted trough
extending back into far southeast New England. The result will be a
period of low level convergence focused across the cape/islands.
Model soundings show modest Omega on the order of 10 to 20 microbars
per second. Will also likely have some ocean enhancement with low
level southwest flow resulting in ocean induced convective available potential energy between 400
and 500 j/kg. Overall think 1 to 3 inches of snow is a good bet for
most of the cape/Vineyard with a low risk of 4 inches. Will issue a
Special Weather Statement for these locations...but later shifts may
have to consider a Winter Weather Advisory. Lift/forcing persists a
bit longer across Nantucket and with a period of modest
snowgrowth...feel 2 to 4 inches is reasonable and will hoist a
Winter Weather Advisory for them. Bulk of the snow looks to fall
between 9 PM and 5 am...but some snow showers may persist into middle
morning Sat.

Across the rest of the region...dry weather will dominate tonight.
Some snow showers may briefly extend back into Rhode Island/eastern
Massachusetts with minor accums possible closer to the South Coast. A few snow
showers/flurries also possible across the interior mainly toward
daybreak as the Arctic cold front approaches. Low temperatures will mainly
be in the 10 to 15 degree range with upper teens and lower 20s
across cape/Nantucket.

Saturday...

Arctic cold front sweeps across the region Saturday morning. It may
be accompanied by a few snow showers/flurries...but the main story
will be the dangerously cold airmass that will invade the region.
Midday high temperatures in the middle teens to lower 20s will rapidly fall
by late afternoon/early evening. In fact...by 00z Sunday 850mb
temperatures will be down to rare values of -26 to -30c for southern New
England standards. The result will be early Sat evening temperatures
already below zero across the interior and single digits across the
coastal plain. Given the extremely cold air working into the region
expect excellent mixing. Northwest wind gusts of 35 to 45 miles per hour with
a few gusts near 50 miles per hour are expected to develop Saturday afternoon
and continue into Sat night. We already issued a Wind Advisory for
Cape Cod/Nantucket given very steep lapse rates as Arctic air
streams in over the relatively mild ocean. Wind Advisory may be
needed for a time across the rest of the region...but appeared to
marginal to issue this far out.

&&

Long term /Saturday night through Thursday/...
*** dangerously cold wind chills Saturday night ***

Highlights...

* bitter cold Arctic air moves into southern New England for the
weekend
* snow changing to rain likely Tuesday and Tuesday night

Overview and model preferences...

Models continue agree well into early next week. The deep
amplified flow which will allow for the coldest airmass of the
season to arrive by late Sat...will then transition to more zonal
flow as the southern stream looks to regain control.
However...with some link to a vortex hovering around the Queen
Elizabeth Islands...the warming trend will not last...and give way
to another round of cooler conditions toward the end of the week.
Given there is good agreement...a general blend of operational
guidance will be used as a baseline for all but the southern stream
dominant system Mon-Tue. A blend of ensembles will be used for
this feature due to track discrepancies.

Details...

Sat night into sun...
reinforcing Arctic shortwave will be moving through the longwave
trough across the region. This shortwave will have several
consequences. It will allow the deepest of the cold air to spill
across the region...nearing -30c at 850 mb. At the same time the
strong middle level cold advection and increased isallobaric response
will lead to increased wind across the region...exacerbating an
already very cold situation. Temperatures are likely to already be near
or below 0f in the interior by evening and only dropping into the
single digits to teens below 0f through the overnight hours. The
increased northwest flow at the surface...with gusts 20-30 miles per hour at
times...will lead to dangerously cold wind chills between -20f and
-30f or even -35f in spots. Will be upgrading interior Massachusetts/CT and
Rhode Island to wind chill warnings with this update...but leave watches
near the South Coast where more uncertainty lie. Will expand the
watch to include Cape Cod...as current numbers suggest it could be
close there as well. The highs will only reach into the single
digits and teens above 0f on sun...so the cold wind chills are
likely to linger well into the day in spite of mainly sunny
conditions.

The final issue of note...is that it will turn middle level winds
toward the north. In spite of the flow remaining more northwest at the surface.
This may allow a long enough fetch across anomalously warm Gulf of
Maine waters to yield a higher risk for ocean effect snows
especially across Cape Cod. With SST-850 mb Delta-T values nearing
30c and normalized cape values around 0.3 will need to watch if
any bands setup...especially as an inverted trough from the Maine
coast shifts north. Accumulating snow is certainly possible given the
very destabilized low levels.

Sun night into Monday...
high pressure will be moving in and crossing the region...yielding
mainly dry conditions and some warming. H92 temperatures rebound back
closer to -10c...or at least closer to seasonal normals. After a
cold start with several sites still below 0f /thanks to some
radiational cooling/ highs reach into the middle 20s to low 30s.

Monday night into Tuesday night...
ensemble means are starting to lean closer to an inside runner
low pressure system with ties to Gulf of Mexico moisture thanks to its
stronger southern stream influence. Therefore...will continue the trend
set forth by the previous forecaster...and lean the forecast in
this direction. This is better news as it does not promote good
cold air damming. Therefore...thermal profiles on BUFKIT suggests
an initial snowy start late Monday night...transitioning to an all
rain event by Tuesday. 40-50 knots low level jet and precipitable waters nearly 2 Standard deviations
above normal support the high quantitative precipitation forecast models currently project...so it
could be that liquid totals of an inch or even more are possible
by the time this system moves out Tuesday night. Certainly something
to watch given it will be a mixed precipitation event with the potential
for heavy rain.

Wednesday into Friday...
second round of Arctic air moves in associated with a cold
frontal passage on Wednesday. This airmass is not nearly as deeply cold
as this weekend/S airmass. 850 mb temperatures drop to around -22c on
average...supported by ensemble means. This means temperatures will
certainly remain below normal...but not as dangerous as this
weekend/S. Will still need to watch for wind chill values reaching
advisory levels for some mainly Wednesday night into Thursday...when winds
are at their strongest. Slight moderation expected by Friday.

&&

Aviation /18z Friday through Wednesday/...
forecaster confidence levels...

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

Short term /through Saturday night/...

Tonight...moderate confidence. Expect widespread MVFR/IFR in snow
across cape/islands...mostly from 02-09z. Snow showers and MVFR
will likely extend across portions of S coastal MA/RI.
Otherwise...a mix of VFR/MVFR ceilings across rest of southern New England.

Saturday...high confidence. VFR/MVFR ceilings expected with a few
brief snow showers as Arctic front crosses region 12-18z.
Increasing northwest winds behind the front with gusts to 35-40 knots
developing in the afternoon.

Saturday night...moderate confidence. Mostly VFR...but a period of
MVFR ceilings and scattered snow showers possible across Outer Cape. Low
probability that snow showers and lower ceilings extending across NE Massachusetts. Northwest
gusts to 35-40 knots in the evening diminishing to 25 knots overnight.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Saturday night through Tuesday/...

Sat night through sun...high confidence.
Mainly VFR inland...with some MVFR conditions in ocean effect
ceilings/snows Sat night into early sun. Bitterly cold conditions with
wind gusts 20-30 knots possible until middle day sun.

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 Saturday/...high confidence.

Today...northwest wind gusts still gusting over 30 knots early this
morning as bitterly cold air moves over the relatively mild ocean.
Winds should continue to diminish this morning and drop below Small
Craft Advisory thresholds by noon...as cold advection comes to an
end and winds become southwest. Freezing spray advisories continue
through 8 am...but should be allowed to expire on time as winds
diminish.

Tonight...winds/seas remain below small craft thresholds for most of
the night...but northwest winds wind gusts of 25 knots will develop
by daybreak.

Saturday...Arctic front blasts through with extreme cold advection
over the waters. Pretty much a slam dunk on northwest wind gusts of
35 to 40 knots across all waters. Have hoisted gale headlines
Saturday afternoon through Saturday night. The airmass is so cold
that moderate freezing spray will have already developed by early
Sat evening.

Outlook /Saturday night through Tuesday/...

*** gale force winds and heavy freezing spray expected Sat evening
into early sun ***

Saturday night into Sunday...high confidence.
Strong and bitterly cold northwest winds will gust to gale force
throughout the night and into early Sunday. This will be
accompanied by a risk for heavy freezing spray. Gale warnings and
freezing spray watches have been issued for this risk. Conditions
drop to small craft thresholds by late sun. Ocean effect snowfall
is likely across some of the other eastern waters.

Sun night into Monday...high confidence.
Brief ridge of high pressure moves across the waters. This will allow
any small craft advisories to drop by early Monday morning with
mainly quiet boating weather to follow for the rest of Monday.

Monday night into Tuesday...moderate confidence.
Winds shift to the SW as low pressure approaches from the SW. Winds
and seas may reach small craft thresholds as early as Tuesday morning
and then continue through the day. Some rain/fog may lead to lower
visibilities.

&&

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 warning from 4 PM Saturday to noon EST Sunday for
ctz002>004.
Massachusetts...wind chill warning from 4 PM Saturday to noon EST Sunday for
maz002>019-026.
Wind chill watch from Saturday afternoon through Sunday
afternoon for maz020>022.
Winter Weather Advisory from 7 PM this evening to 9 am EST
Saturday for maz024.
Wind Advisory from 11 am Saturday to 4 am EST Sunday for
maz022-024.
Rhode Island...wind chill warning from 4 PM Saturday to noon EST Sunday for
riz001>004.
Wind chill watch from Saturday afternoon through Sunday
afternoon for riz005>007.
Marine...heavy freezing spray watch from Saturday afternoon through
Sunday morning for anz231>235-250-251.
Gale Warning from 11 am Saturday to 7 am EST Sunday for
anz230>237-250-251-254>256.

&&

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

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