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Area forecast discussion 
National Weather Service Taunton Massachusetts
110 am EST Sat Feb 13 2016

Synopsis...

An Arctic front will deliver dangerously cold wind chills of 20 to
35 below zero later today into Sunday morning. A period of
accumulating snow and ice is then likely for much of region
especially away from the coast Monday afternoon and evening. A
powerful storm system will likely track west of New England Tuesday/Tuesday
night bringing heavy rain...strong winds and warm temperatures to
the region. A trend toward drier and colder weather follows next Wednesday
and Thursday.

&&

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

110 am update...

***bulk of accumulating snow across cape/islands ends by 5 am***

Distant ocean storm and its associated inverted trough was resulting
in accumulating snow across the cape and islands very early this
morning. Still expecting a general snow accumulation of between 1
and 3 inches across this region with highest of those amounts across
the Outer-Cape near Chatham and Nantucket. There also was snow
falling across the South Coast of Rhode Island where minor accums up
to 1 inch will be possible. Bulk of this snow should come to an end
by 5 am or so as low level convergence zone pushes east of the
region.

Across the rest of the region...mainly dry weather overnight. May
see a few brief flurries/snow showers develop across the interior
toward daybreak. However...moisture is rather limited so not
expecting much of an impact and areal coverage of any activity will
be quite limited. Temperatures mainly in the teens through daybreak...but
some single digits in the outlying locations.

&&

Short term /6 am this morning through 6 PM Sunday/...

*** dangerously cold wind chills Saturday afternoon and especially
Saturday night with strong wind gusts ***

Arctic front will sweep across southern New England from west to east 12-18z. The
front may be accompanied by a few snow showers...but limited
moisture and rapidly falling dewpoints will limit areal coverage
and intensity. The main story during this period will be the
dangerously cold airmass which will invade the region on strong northwest
wind gusts. During the afternoon temperatures will be falling through the
single numbers interior and through then teens coastal plain. By
00z sun...temperatures will likely be below zero in the interior and
single numbers coastal plain.

Core of the coldest air aloft settles over the region late Sat
night as Arctic shortwave swings across region with 925 mb temperatures
down to -29c. Widespread min temperatures below zero with 10 to 15 below
interior and zero to 10 below elsewhere. Our forecast has record
lows Sunday morning broken or tied at bos/bdl/orh and within 2
degrees of the record at pvd. Only locations escaping subzero
temperatures will be Outer Cape and islands. Strong northwest winds will yield
wind chills bottoming out 25 to 35 below across much of the
region with 10 to 25 below cape/islands. We will have wind chill
warnings for all southern New England...except wind chill advisories for
cape/islands.

Regarding wind...strong cold advection and excellent mixing Sat
afternoon and evening will result in wind gusts to 40 to 50 miles per hour
across the region. Wind advisories were not issued as this
information will be contained in the wind chill products.

Interesting set up for Sat night as potent middle level trough and
Arctic shortwave moves south across the region. Models show
deepening moisture axis rotating across NE Massachusetts to Cape Cod. Very
extreme instability develops over the ocean with Delta T from SST
to top of mixed layer 30-31c and ocean induced convective available potential energy up to 1400
j/kg. Trajectory is 300-310 degrees which is normally too much of
a westerly component for ocean effect snow due to limited fetch
but instability is so extreme that ocean effect machine may crank
up over Cape Cod Bay and mass Bay with bands affecting the Outer
Cape. Most of the guidance has up to 0.10" quantitative precipitation forecast for Outer Cape with
rgem up to 0.20". WRF-nmm has up to 0.25" while WRF-arw keeps most
of the snow showers offshore. Close call but given model consensus
and extreme instability we expect ocean effect snow to affect
Outer Cape. May also have seeder feeder processes with deepening
middle level moisture and synoptic forcing from middle level shortwave.
Potential for 1-3 inches snow accumulate for Outer Cape Sat night and
may see some snow shower activity across NE Massachusetts associated with large
scale forcing and deeper moisture with the middle level shortwave.

&&

Long term /Sunday night through Friday/...
*** dangerously cold wind chills Sunday morning ***

Highlights...

* near record lows and bitterly cold wind chills Sun morning
* some accumulating snow and ice likely Monday afternoon/evening
* temperatures in the 50s Tuesday-Tuesday night west/heavy rain and strong winds

Overview and model preferences...

Good agreement among both gefs and ecens ensembles this period
featuring a true Arctic airmass over the region sun then moderating
Monday as warm air advection pattern sets up over the northeast. This is in response
to a long wave trough developing over the Great Lakes and MS valley.
Although it will be a warmer storm track than previous events with
ridging across the northwest Atlantic yielding an inside runner with
low pressure tracking west of New England across eastern New York state Tuesday-
Wednesday per all guidance including gefs and ecens. Colder weather returns
later next Thursday as both gefs and ecens indicate 850 temperatures lowering to
about -12c /ensemble mean/ over southern New England /sne/. These
values are about -1 Standard colder than normal but not nearly as cold as
this weekend when 850 temperatures lower to -30c Sat night /-3 Standard colder
than climatology/!

As for model preferences...good model agreement through the period with
the exception of the 12z GFS for next week Tuesday system. The GFS
tracks the surface circulation over southern New England while all
other guidance including the gefs and ecens ensembles including the
UKMET track the surface low west of New England. This system
reasonable given high amplitude northwest Atlantic ridge developing. Thus will
lean away from the GFS solution here. As for temperatures leaned toward the
colder raw 2 meter temperatures sun given the anomalous cold airmass. Then
leaned toward colder MOS temperatures Sun night/early Monday given potential
ideal radiational cooling.

Details...

Sunday ...

Arctic short wave over Gulf of ME and pulling seaward. This results
in rising height aloft and strong subsidence on the backside across
the region. As result expecting plenty of sunshine but ineffective
as cold air advection still maintaining -20c to -22c at 850 mb over the
area. This yields daytime highs only in the single digits...
including Boston/Providence and Hartford! Northwest winds of 15 to
25mph will yield wind chills in the afternoon not warning or
advisory criteria but very cold at 5 below to 10 below zero! Still
very dangerous to be outdoors for any extended period of time Sunday.

Could still have some leftover snow showers over the Outer Cape
Sunday morning but intensity likely slackening as middle level low
ejects offshore. In addition subsidence inversion will be lowering
through the day and put a cap on snow shower potential. In addition
with fetch of 300 degrees only the Outer Cape will be impacted during
the Morning.

Sun night ...

Cold/dry airmass remains over the region and combined with high pressure
and light winds ideal radiational cooling conditions...provide
middle/high clouds hold off until after 12z Monday. Given this leaned
toward the colder MOS guidance for mins.

Monday/Monday night ...

Warm advection precipitation approaches the region during the afternoon per
12z deterministic and ens guidance. Initially dry air will erode leading
edge of precipitation but strong 850 SW jet will bring a risk for light
snow to overspread the area during the afternoon and then likely Monday
evening. Column cold enough initially to support snow and a blend of
deterministic and ensemble guidance suggest a risk of up to 2 inches of
snowfall along the coast before a changeover to rain Monday night.
Farther inland /NW of I-95/ there is a risk of 2-5" before a
changeover a brief period of ice and then rain Monday night. Can/T
emphasize enough this is just a preliminary first cut at potential
snowfall and wanted to get this out there given the number of
residents likely returning from the long Holiday weekend. Thus
travel will likely be impacted Monday afternoon and evening.

Tuesday/Tuesday night ...

Good model agreement on a high amplitude East Coast trough with very
impressive jet dynamics as wind anomalies at 925/850/250 mb all
achieve +3 Standard across the area! This combined with a subtropical
plume of moisture advecting up the eastern Seaboard will yield
multiple threats of hazardous weather across southern New England
including heavy rain and strong to damaging winds. In fact the 12z
European model (ecmwf) and GFS have 80-90 knots at 925 mb over CT/Rhode Island and eastern Massachusetts 00z
Wed! While soundings are inverted a good estimate at this time range
is 50% to 60% of this wind will translate to the surface...45 to 60
mph! In addition elevated convection will be possible on the nose of
the dry slot which always increases the risk of flooding and
stronger winds. Furthermore a second wind threat will exist Tuesday
night as the occluded front sweeps across the area and winds shift
to the SW with steepening low level lapse rates.

Strong thermal/warm advection will result in surface temperatures climbing
into the 50s in the coastal plain and at least 40s inland. In fact
the coastal plain /pvd-bos/ may see record highs as 925 mb temperatures
surge briefly up to +8c to +12c!

Wednesday into Friday ...

Drying trend Wednesday but windy as well with a sub 980 mb low over
southern Quebec at 12z Wednesday. Trending colder by Thursday and possibly a
bit colder than normal with ensemble 925 mb and 850 mb temperatures -1 Standard
from climatology. Cold then possibly easing by Friday.

&&

Aviation /06z Saturday through Wednesday/...
forecaster confidence levels...

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

Short term /today through Sunday/...

Today...moderate to high confidence. Snow and associated IFR
conditions across cape/islands should come to an end by 10z.
Otherwise...mainly VFR conditions in most locales today...but some
MVFR ceilings possible at times especially cape/islands. Mainly dry
weather after 10z other than a passing flurry/snow shower. Big
story will be Arctic front which will allow northwest wind gusts of
35 to 40 knots to develop by afternoon.

Tonight...high confidence. Northwest wind gusts of 30 to 40
knots...strongest of which will occur during the first part of the
night. Mainly VFR except cape/Nantucket where MVFR conditions are
expected in ocean effect clouds/scattered snow showers. Bulk of the
scattered snow showers will be found across the Outer-Cape. Low risk
that brief MVFR ceilings work into eastern Massachusetts for a time late tonight.

Sunday...high confidence. VFR with northwest wind gusts of 20 to 25
knots. The exception will be portions of cape/Nantucket where MVFR
ceilings may persist into the afternoon. Ocean effect snow showers
mainly across Outer-Cape should wind down Sunday afternoon.

Kbos terminal...moderate to high confidence in taf.

Kbdl terminal...moderate to high confidence in taf.

Outlook /Sunday night through Wednesday/...

Sun ... high confidence.
Mainly VFR inland...with some MVFR conditions in ocean effect
ceilings/snows early sun. Gusts 20-30 knots sun then easing toward and
after sunset.

Monday ... high confidence for VFR early but possibly lowering to MVFR
in light snow late.

Monday night through Tuesday ... low to moderate confidence. Becoming IFR
with snow changing to rain with areas of fog Monday night into Tuesday.
Strong southerly winds aloft may result in significant low level
wind shear Tuesday afternoon. Low risk of isolated T-storm Tuesday/Tuesday
evening.

Wednesday ... drying trend with VFR/MVFR likely but windy with northwest winds.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday/...high confidence.

*** Gale force winds and heavy freezing spray expected Sat
afternoon and night sun ***

Tonight...winds/seas remain below small craft thresholds with
increasing northwest winds toward daybreak. Visibilities reduced in developing
snow over S coastal waters...especially around ack.

Saturday into Saturday night...Arctic front moves through and
will be followed by extreme cold advection which will lead to
gale force gusts to 40 knots on all waters Sat afternoon through Sat
night. Heavy freezing spray almost a certainty over nearshore
waters Sat night and will upgrade to a heavy freezing spray
warning. Moderate freezing spray outer southern waters where we
will have freezing spray advisories. Snow showers and reduced
visibilities may affect east Massachusetts coastal waters and especially waters east of
Cape Cod Sat night.

Outlook /Sunday night through Wednesday/...

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

Sunday ... high confidence.
Strong and bitterly cold northwest winds will gust to gale force
into early Sunday. This will be accompanied by a risk for heavy
freezing spray. 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 night ... moderate confidence.
Winds shift to the SW as low pressure approaches from the SW. Southerly
gales likely Tuesday/Tuesday evening. Snow Monday night to rain Tuesday/Tuesday night
may lead to lower visibilities.

Wednesday ... moderate confidence.

Improving trend with low pressure exiting into southern Quebec. Gusty northwest
winds likely but dry weather and improving visibility.

&&

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 this afternoon to noon EST Sunday
for ctz002>004.
Massachusetts...Wind Chill Advisory from 6 PM this evening to noon EST Sunday
for maz022>024.
Wind chill warning from 4 PM this afternoon to noon EST Sunday
for maz002>019-026.
Wind chill warning from 1 PM this afternoon to noon EST Sunday
for maz020-021.
Winter Weather Advisory until 9 am EST this morning for maz024.
Rhode Island...Wind Chill Advisory from 6 PM this evening to noon EST Sunday
for riz008.
Wind chill warning from 4 PM this afternoon to noon EST Sunday
for riz001>004.
Wind chill warning from 1 PM this afternoon to noon EST Sunday
for riz005>007.
Marine...heavy freezing spray warning from 4 PM this afternoon to 9 am
EST Sunday for anz231>235-237-250-251.
Gale Warning from 11 am this morning to 7 am EST Sunday for
anz230>237-250-251-254>256.
Freezing spray advisory from 4 PM this afternoon to 1 PM EST
Sunday for anz254>256.

&&

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

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