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Area forecast discussion 
National Weather Service Taunton Massachusetts
1047 am EST Monday Feb 8 2016

Synopsis...
a powerful ocean storm off the North Carolina coast early this
morning will move northeast and bring heavy snow...strong to
damaging winds and coastal flooding to eastern Massachusetts into
early this evening. Additional shortwaves move past New England
Tuesday through Thursday maintaining clouds and a chance of snow
showers. An Arctic cold front will cross the region Thursday...followed
by dry air and colder than normal temperatures for the weekend.

&&

Near term /until 6 PM this evening/...

1045 am update...

Headline changes ...

Only change to the forecast is to downgrade Hartford County from a
warning to an advisory. Shallow cold/dry Arctic airmass advecting
southward into the CT River Valley is eroding much of the snow before
reaching the ground across northern and central Hartford County
northward into western Massachusetts. This is courtsey of below zero dew points.
Unfortunately none of the hi res guidance has dew points this low. Thus
their quantitative precipitation forecast fields are slightly overdone. So doing a 12z model
blend of 12km NAM/4km NAM-WRF and rgem will forecast 2-5" for
Hartford County...highest totals south and east. Otherwise no
headline changes although may have to trim snow totals across
northern Worcester County and northwest Middlesex for the same
reason.

Key synoptic and mesoscale features/details ...

Otherwise forecast more or less on track with heavy snow and
blizzard conditions at times across southern Plymouth County/Cape
Cod and the islands. Mesoscale aspects in play today with sharp
subsidence line in between snow bands...main band over southeast
Massachusetts and the other band over eastern CT/western Rhode Island into the
Worcester Hills. In between mesoscale subsidence across eastern Rhode Island
into pvd and the I-95 corridor of eastern Massachusetts. This northwest snow band
should pivot eastward this afternoon as warm conveyor belt slides
eastward. Thus where snow intensity as diminished late this
morning snow will pickup midday into early afternoon.

Heaviest snowfall rates of 1-2" now through 18z. The exception will
be Plymouth County and Cape Cod where oes and coastal front will
enhance snow totals through 00z. Still confident in 12-18" here. Also
some oes enhancement likely for the Cape Ann area.

Snow growth not ideal thus not seeing large dendrite snow flakes.
This will limit snowfall rates away from southeast Massachusetts.

Have updated snow map for CT River Valley. Will send shortly.

Previous discussion...

***major winter storm to affect eastern New England today with heavy
snow and strong winds***

***greatest concern continues for extreme southeast Massachusetts onto the
cape/islands where blizzard warnings are posted for white-out
conditions along with damaging wind gusts/power outages with 45 to
65 miles per hour gusts***

1) overview...

Impressive low pressure spinning east of North Carolina early this
morning with lightning showing up near the storm/S center. The
models are in very good agreement in low pressure deepening near 975
mb as it passes southeast of the benchmark this afternoon. While
its unusual for our area to see heavy snowfall with a storm tracking
this far southeast...this system has a large circulation with a
potent east northeast low level jet. There is also a 1030 mb high
over eastern Canada...which will generate powerful/damaging winds
along the coast. We will break it down over the next several
paragraphs on our expectations and uncertainty.

2) timing and ptype...

The large precipitation shield associated with the storm will quickly
overspread the region trough the early to middle morning hours. Snow
should reach a Taunton to Providence line between 5 and 7 am...then
a Boston...to Hartford...to Worcester line between by 7 or 8
am...and finally into our distant interior zones of western Massachusetts by
middle to late morning. Ptype should be all snow other than perhaps a
brief period of rain across portions of the cape/islands....which
should quickly change to snow by 6 or 7 am. Heaviest snow will fall
from this morning into middle/late afternoon across the region. Should
see snow diminish in intensity by early evening...except for
localized areas along the immediate eastern Massachusetts coast.

3) quantitative precipitation forecast and snow accumulations...

As is typically the case...there is uncertainty on exact snow
accumulations and especially how far northwest the heaviest snow
reaches across our County Warning Area. The main issue is although
this storm is quite powerful...its passing southeast of the
benchmark...which is further southeast than most of our major winter
storms. In this case though...its such a large storm with a potent
northeast low level jet at 925 mb into southern New England. So
that is allowing heavier snow to spread further northwest. At the
same time...the strong forcing is significantly lower in the
atmosphere than usual and more subject to mesoscale
features/nuances. In this case...those will be ocean
effect/enhancement along with interactions near the coastal front.
Also...expect some subtle upslope along the east slopes of the
Worcester Hills.

The main idea here is that given the storm passing well southeast of
our region...mesoscale processes will play a greater role than a
typical noreaster. This makes the snowfall forecast quite difficult
as exact amounts may vary considerably over small distances.

Overall...feel that 8 to 12 inches of snow is quite reasonable for
much of southeast Massachusetts/Cape Cod and the islands. Localized 12+ inch
amounts are certainly possible especially across eastern Plymouth
County and onto the upper cape...where coastal front/ocean
enhancement lineup. Further northwest into the Boston to Providence
corridor feel 5 to 10 inches is reasonable. We also opted to
expand Winter Storm Warning/S into northern Worcester/northwest
Middlesex County as mesoscale models are showing some higher
quantitative precipitation forecast...likely a result of subtle upslope flow. Finally...we also
did expand warning/S into the rest of northern CT as models are
showing some decent Omega in the snow growth region...so a general
4 to 8 inches expected in this region. Across the rest of western
Massachusetts will keep the advisory for a general 3 to 6 inches of snow.

4) blizzard conditions/wind damage and scattered power outages
across far southeast New England...

The greatest impact from this storm will not be specific snow
amounts...but blizzard conditions across Plymouth County and onto
the cape/islands. Powerful low level jet will result in very strong
northeast wind gusts of 45 to 65 miles per hour across this region. This will
result in whiteout conditions at times along with wind
damage/scattered power outages. Another concern is that initially
the snow will be wet...which will also add to the risk of tree
damage/power outages. Blizzard conditions along with damaging wind
gusts will make this a very dangerous storm and travel is not
recommended in this region.

While winds will not be quite as strong further northwest along
the Boston to Providence corridor...still expecting a period of
northeast wind gusts of 35 to 45 miles per hour into early this afternoon.
This will promote blowing and drifting snow along with very poor
visibility at times.

As for temperatures...they will fall into the 20s along and
northwest of a Boston to Providence line by afternoon...as strong
north-northeast winds push much colder air into much of the region. Meanwhile
across southeast Plymouth County and onto the cape/islands...temperatures
will hold into the upper 20s to the lower 30s as coastal front will
be held up in this region for a time.

&&

Short term /6 PM this evening through 6 am Tuesday/...
tonight...

Heaviest snow will come to an end by early evening as storm pulls
away and low level jet weakens. However...expect areas of light
snow to persist well into the overnight hours with moist north to
northeast flow just off the deck. While most of the snow will
be light tonight...very localized bands of moderate to heavy snow
will remain possible along the eastern Massachusetts coast as a result of ocean
enhancement/land sea interface.

&&

Long term /Tuesday through Sunday/...
big Picture...

Ridge west/trough east continues through the week. Long range models
show a similar series of shortwaves moving through New England
midweek...the last moving through on Thursday. The final shortwave
originitated over Arctic Canada and it is no surprise that temperatures
over US cool significantly after it passes.

Closed low from baffin island then slips south and maintains the
cyclonic flow over eastern Canada and the northeast USA. The European model (ecmwf)
forms an outlier solution that draws this closed low into the
northeast USA Saturday while the GFS and ggem hold it over Quebec.
The consequence is that the European model (ecmwf) forms a significant weekend
snowstorm while the others form a weak wave well offshore.

The forecast favors a model consensus through Friday...then favors a
consensus without the European model (ecmwf) over next weekend.

The dailies...

Tuesday...position of upper trough continues to favor formation of
another coastal low off the middle Atlantic coast. Said coastal low
then moves northeast toward the 40n/70w benchmark. This would
maintain at least weak lift over southern New England. Fgen fields
are marginal but favor south coastal sections and especially Cape
Cod and the islands. Not confident on snow showers vs a stratiform
snow. We will maintain chance probability of precipitation for snow showers with highest
probability of precipitation in the midday/afternoon. Moisture fields suggest potential for
a few inches...technically a moderate snow accumulate...across
Rhode Island/southeast mass.

Wednesday-Thursday... additional shortwaves move through and the
upper cold pool approaches. The final shortwave in this group moves
through Thursday and is associated with an Arctic cold front. This
suggests a continued potential for scattered snow showers. Only
limited mixing Wednesday...to 950 mb...with temperatures supporting maximum surface
temperatures in the 30s. Deeper mixing Thursday as cold advection starts.
Mixing reaches above 900 mb Thursday with temperatures supporting upper 20s-
lower 30s. Winds in the Thursday mixed layer are forecast at 25-30
miles per hour...should be available as northwest gusts.

Friday-Saturday-Sunday... Arctic air pours into New England and is
with US through the weekend. Mixing will bring 25 knot winds to the
surface in gusts. Temperatures at 850 mb will fall into the -20s and
suggest maximum surface temperatures in the 20s Friday and 15-25 Sat-sun. Given the
source region of the airmass...model suggestions of min temperatures in the
single numbers either side of zero look reasonable. Such cold air
aloft and winds over 10 knots will generate ocean effect snow
showers...but the wind direction should keep the showers offshore.

As noted above...we will need to monitor future model suites to see
if the 00z European model (ecmwf) weekend low is a blip or an actual problem.

&&

Aviation /16z Monday through Friday/...
forecaster confidence levels...

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

16z update ...

Not much change from 12z tafs. Heaviest snowfall rates through 18z or
so except heavy snow continues until about 00z for pym city...Cape
Cod and the islands. Much less snowfall along and northwest of a
line from kbdl-korh-klwm. Strongest winds through about 18z across
pym County/Cape Cod and the islands.

Short term /through tonight/...

Today...moderate to high confidence. Snow overspreads the I-95
corridor 13-14z and reaches back into western Massachusetts by 15z or 16z.
The snow will fall heavy at times along and especially southeast
of the I-95 corridor...where 1 to 2 inch per hour rates are
possible at times into the afternoon. Other localized bands of
heavy snow are also possible...especially in the Worcester Hills.
As for cigs/vsbys...widespread IFR to LIFR conditions expected
with blizzard conditions at times across far southeast Massachusetts/Cape Cod
and the islands as visibilities drop to one quarter of a mile or less at
times. Northeast wind gusts of 45 to 55 knots expected across the
cape and islands...with the strongest of those winds at Nantucket.
Further northwest...a period of northeast wind gusts of 35 to 40
knots will affect the Boston to Providence corridor through early
afternoon...so blowing and drifting snow also expected in these
locations.

Tonight...moderate to high confidence. While the heaviest snow will
come to an end early this evening...areas of light to moderate snow
persist overnight especially along the coast. Strong northeast wind
gusts will diminish as storm pulls away and low level jet weakens.
Nonetheless...widespread MVFR to IFR conditions will persist.

Kbos terminal...high confidence in IFR to LIFR conditions after 14 or
15z this morning. Snow may fall heavy at times with 1 to 2 inch
per hour snowfall rates possible at times through the afternoon.
Northeast wind gusts of 40 knots persist through middle afternoon.
Blowing and drifting snow is also expected.

Kbdl terminal...high confidence in IFR conditions with periods of
LIFR conditions also possible after 14 or 15z as snow works into
the region.

Outlook /Tuesday through Friday/...moderate confidence.

Tuesday...moderate confidence. Light snow or snow showers with
highest chance in Rhode Island and southeast mass. IFR ceilings/visibilities in snow
showers.

Wednesday...low-moderate confidence. MVFR ceilings/visibilities in scattered
snow showers.

Friday...moderate confidence. Mostly VFR. Northwest winds gusting
25-30 knots. Ocean effect snow showers just off the coast with
lower cigs/vsbys.

&&

Marine...
forecaster confidence levels...

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

Short term /through tonight/...high confidence.

***Strong gale to storm force wind gusts of 45 to 60 knots and seas
exceeding 20 feet expected across our eastern outer-waters later
this morning and afternoon***

Powerful 975 mb low pressure system passing southeast of the
benchmark will combined with a 1030 mb high pressure system over
eastern Canada. The result will be strong northeast wind gusts of
45 to 60 knots...the strongest of those winds across our waters
southeast of Nantucket. Gale and storm warnings posted for all
waters with seas expected to build to over 20 feet across our
eastern waters by afternoon. Heavy snow will also result in
visibilities one quarter mile or less at times this afternoon. This
is a very dangerous storm for the marine community.

Winds and seas will slowly diminish tonight as powerful low pressure
moves northeast and away from the waters. Nonetheless...seas will
be slow to diminish though with left over swell and persistent
northeast fetch.

Outlook /Tuesday through Friday/...moderate confidence.

Tuesday...north to northeast winds will be 20 knots or less. Seas
will slowly subside through the day but remain 5 feet or higher on
the exposed waters. Small Craft Advisory will be needed.

Wednesday...winds become west less than 20 knots. Seas linger 5 feet
or higher on the southern waters as well as east of Cape Cod. A
Small Craft Advisory will be needed.

Thursday-Friday...an Arctic cold front sweeps across the waters
Thursday...followed by much colder air. Winds will shift northwest
with gusts 25 to 30 knots. Seas of 5-7 feet mainly on the outer
waters...subsiding Friday.

&&

Tides/coastal flooding...
***pockets of moderate coastal flooding expected during the late
morning and early afternoon high tide cycle south of Boston
along the eastern Massachusetts coast***

915 am update...

Prior forecast looks to be right on target with moderate coastal
flooding likely for the late morning high tide from Hull to
Plymouth...north and east facing shorelines of Cape Cod...and
Nantucket north and east facing shorelines. At the time of high
tide...projecting seas approaching 20 feet mass Bay and 20 to 25
feet east of the Outer Cape and east of Nantucket. Prior surge
forecast looks reasonable. Anticipate surge to be 1.7 to 2.2 feet
from Boston north and generally 2.1 to 2.6 feet along east and
north facing shorelines south of Boston including
Scituate...Sandwich/Dennis...Provincetown...Chatham and Nantucket.

At least some erosion is expected all along the Massachusetts coastline from
Salisbury to Nantucket...most severe along the Outer Cape and the
east side of Nantucket including Siasconset.

As of 915 PM...reports of coastal flooding have started to come
in with portions of Oceanside Road and central Avenue in Scituate
and the Brant Rock area of Marshfield already impacted. Flooding
should already be starting to occur along portions of Nantucket
Harbor including but not limited to Easy Street.

Minor coastal flooding looks likely for at least some of the Massachusetts
coastline for the late evening high tide due to residual surge and
wave action. The wind will have backed to a more north direction and
speeds considerably less by the late evening high tide...which is
a half to a little less than a foot lower astronomically along
most of the eastern Massachusetts coastline. Seas will probably still be
running 14 to 18 feet a little offshore...perhaps around 20 feet
still east of Nantucket. Thus...at least some erosion will likely
be witnessed again tonight around the high tide. A coastal Flood
Advisory may need to be issued for portions of the eastern coastline
for the late evening high tide.

Early am discussion is still relevant and follows...

Coastal Flood Warning continues south of Boston through coastal
Plymouth County to Cape Cod and Nantucket given higher confidence of
strong wind field across this region. Expecting areas of moderate
coastal flooding in this area during the late morning into midday
high tide. Low level winds not quite as strong from Boston
northward. Thus less storm surge and coastal flooding will likely be
mainly in the minor category...but can not rule out pockets of low-
end moderate coastal flooding. High tide cycle of greatest concern
is the late this morning into midday...basically 9 am to 1 PM is the
timeline.

Expecting a storm surge of between 2.5 and 3 feet across the warning
area and near 2 feet from Boston northward to the Massachusetts/New Hampshire border. Etss
was higher than the estofs and seems reasonable given NE winds will
gusts 45 to 65 miles per hour. In addition large waves in excess of 20 feet just
offshore...will promote wave runup pushing waves and over seawalls
and other structures. This will also result in potential moderate
beach erosion. Again greatest impacts from 9 am to 1 PM along
Plymouth coast to Cape Cod Bay to Nantucket...with less impacts
Boston northward to Massachusetts/New Hampshire border.

We may have some minor coastal flooding during the late evening high
tide cycle along the eastern Massachusetts coast. However astro tide is
lower...less winds and pressure rises overspreading the area...but a
coastal Flood Advisory may be needed.

&&

Box watches/warnings/advisories...
CT...Winter Storm Warning until 7 am EST Tuesday for ctz003-004.
Winter Weather Advisory until 7 am EST Tuesday for ctz002.
Massachusetts...Blizzard Warning until 7 PM EST this evening for maz018-019-
021>024.
Coastal Flood Warning until 1 PM EST this afternoon for maz019-
022-024.
Winter Storm Warning until 7 am EST Tuesday for maz004>007-
012>017-020-026.
Coastal Flood Advisory until 1 PM EST this afternoon for
maz007-015-016-023.

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