Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

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

Synopsis...
high pressure will bring dry weather with mild temperatures into
this evening. A powerful ocean storm developing off the Carolina
coast will bring heavy snow...strong winds and coastal flooding to
eastern Massachusetts and Rhode Island Monday and Monday night.
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/...
1025 PM update...

No changes will be made to the current forecast until we thoroughly
review the entire 00z suite of model data along with the latest
radar/satellite trends. Impressive storm with lightning showing up
east of the Carolinas. Snow reaches the South Coast between 2 and
4am...Providence to Taunton line between 3 and 5 am...then into the
Boston/Worcester metropolitan areas between 5 and 7 am. Portions of the
cape/islands and immediate South Coast may begin briefly as
rain...but will quickly flip to snow by 6 am or so.

The biggest uncertainty is how far northwest does the heavy snow
shield reach given the powerful storm tracking so far southeast of
the benchmark. As previous forecast noted...strong east to northeast
low level jet well north of the storm will allow precipitation
shield to reach further northwest than one would normally expect
from this track. There also will likely be ocean enhancement from
cold low level northeast flow developing...as well as the land/sea
and coastal front which will be sagging south. Finally...may also be
some upslope enhancement along the east slopes of the Worcester
Hills with northeast low level flow. On the flip side of the
Coin...convection off the Carolina coast sometimes causes issues
with the model quantitative precipitation forecast fields and limit northwest extent of heavy snow.
Middle level centers so far southeast of the region may also be a
limitation...since we may have to rely on low level/mesoscale forces
for the heaviest snow. Overall...heaviest snow fall will be along
the coast particularly far southeast Massachusetts/cape and islands...but there
may be other banded areas for mesoscale reasons. A much broader
area of light to moderate snow will work back into the interior.

Overall...if anything snowfall amounts may be a tad high based on
some of the latest data but will hold the forecast until reviewing
the entire 00z model suite.

Regardless of snow amounts...this will be a major winter storm with
blizzard conditions along the southeast New England coast. Blowing
and drifting snow with 40 to 60 miles per hour wind gusts across the cape and
islands will result in near whiteout conditions along with scattered
power outages.

Previous discussion...

*** Blizzard Warning Plymouth County/Cape Cod and the islands ***
*** strong winds/heavy wet snow/potential power outages southeast
Massachusetts ***
*** heavy snow likely all of eastern Massachusetts/Rhode Island and northeast CT ***
*** significant coastal flooding likely south of Boston ***

12z models...

12z global guidance European model (ecmwf)/UKMET and GFS have all trended upward in
qpf/snowfall. This combined with the same trend in the 12z rgem
gives US higher confidence in the very robust 12z NAM which is
picking up on the ocean effect and land/sea enhancement over
Plymouth County into the upper cape. Thus this portion of the
forecast will be heavily based on the 12z NAM. Furthermore the NAM
highest skill is within the first 36 hours. Thus we are in the NAM
wheelhouse.

Overview ...

Impressive southern stream system off the southeast U.S. Coast
this afternoon with explosive cyclogenesis underway. Mesoanalysis
indicating pressure falls on the order of 7mb in the past 3 hours off
the Virginia coast. Water vapor satellite imagery showing a nice
subtropical plume of moisture being tapped from the Bahamas and
advancing up the eastern Seaboard. This vertically stacked low
tracks well southeast of the 40n/70w benchmark 18z Monday which
typically means too far out to sea for southern New England.
However this cyclone is very intense with surface pressure lowering to
about 975 mb 18z Monday and with a very large middle level circulation
that overspreads Rhode Island and eastern Massachusetts. Thus heavy snow will track
much farther inland than what this typical track offers. In fact a
model blend gives storm total quantitative precipitation forecast of up to 0.50 inches across
eastern CT into the Worcester Hills to northeast Massachusetts/New Hampshire border.

Onset ...

Snow overspreads much of the area between 08z/3am and 11z/6am
with main shield approaching the South Coast from the ocean.
However there may be some lighter upslope snows during this time
across the higher terrain of the Worcester Hills northward to the
Massachusetts/New Hampshire border. This is in response to increasing moist onshore
flow. Precipitation may initially begin as rain or a mix of rain/snow but
quickly change to all snow toward 12z/7am.

Snow intensity ...

Heaviest snow with hourly rates of 1-2" will occur 12z-20z.
Travel is not recommended during this time. It will continue
snowing after 20z/3pm but at a much lesser intensity. Heavy snow
may linger until 7 PM across Cape Cod and Plymouth County. Snow
growth looks good across Rhode Island and eastern Massachusetts 09z-17zish. This
enhance the snowfall rates and lower visibility. In addition a sharp
coastal front will setup vicinity of the I-95 corridor with
shallow Arctic air on the westward side of the boundary. This
boundary will enhance snowfall along and to the east while
diminishing snowfall west of the Worcester Hills into the CT River
Valley. Furthermore this shallow Arctic air will result in ocean
effect snows to develop and enhance overall snowfall rates first
across Cape Ann and slipping south with the Arctic airmass during
the afternoon into Plymouth County and Cape Cod. Overall the
morning commute will be greatly impacted and also the late day
commute especially travel across rt-3 in Plymouth County and
across Cape Cod.

Strong winds/wet snow/power outages ...

Initially blyr layer and surface temperatures will be marginal to
support snow across southeast Massachusetts. This will result in a heavy wet
snow during the morning hours. With trees already stressed across
this region from Friday/S snowstorm there will be an increased
risk for down tree limbs and additional power outages. Adding to
this threat will be very strong northeast winds with gusts up to
50 to 60 miles per hour from Plymouth County southward to Cape Cod and the
islands. Even a low risk of a few locations here possibly gusting
up to 70 mph!

Hazards/headlines ...

Given the above reasoning we will upgrade to a Blizzard Warning
for all of Plymouth County...Cape Cod and the islands given the
likelihood of 8 to 12 inches across this area with low risk of up
to 18" across coastal Plymouth and upper Cape Cod. This combined
with strong to damaging winds will reduce visibility to 1/4 mile or less
at times Monday. Winter storm warnings for the remainder of
eastern Massachusetts to New Hampshire border...all of Rhode Island and northeast eastern CT for
5-8 inches. Winter weather advisories for remainder of northern
CT ... Massachusetts for 2-5 inches.

&&

Short term /6 PM this evening through 6 am Tuesday/...
Monday night...

Offshore low pressure moves off south of Nova Scotia Monday
night. Although upper dynamics are marginal...low level lift will
draw upon the lingering northeast flow off the Gulf of Maine to
bring snow to the region...especially areas east of the central
hills. The best chance will be in southeast mass/Cape Cod where
the exposure to the northeast flow is strongest. Snow will taper
off overnight as the offshore low gets farther away.

&&

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 /09z Monday through Friday/...
forecaster confidence levels...

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

Short term /through tonight/...



Through midnight ...

VFR/dry with light/vrb winds becoming northeast.

After midnight ...

Ceilings lowering quickly into MVFR after midnight with light snow
developing throughout the region 08z-12z. Visibilities mainly VFR/MVFR
in light snow but quickly lowering to IFR/LIFR toward 12z South
Coast of Massachusetts.

After 12z Monday ...

Heavy snow at times across Rhode Island and all of eastern Massachusetts with IFR/LIFR
12z-18z...possibly lingering to 21z-24z southeast Massachusetts. Snowfall
rates of 1-2" will be common 12z-18z over Rhode Island and eastern Massachusetts...less
into CT-western/central Massachusetts. Very strong winds along the eastern Massachusetts
coast with strongest over Plymouth County/Cape Cod and the islands
with afternoon wind gusts up to 55 knots likely with low probability up 65
kt! Snowfall totals through 00z Tuesday ...

Kfmh ... 10-16 inches
kbos ... 6 to 10 inches
kpvd ... 8 to 12 inches
kbdl ... 2 to 5 inches
korh ... 4 to 7 inches

Kbos terminal ... moderate to high confidence in taf. Heavy snow
threat 12z-18z with visibility 1/4 or less at times.

Kbdl terminal...moderate to high confidence in taf. Heaviest snow
should remain east across Rhode Island and eastern Massachusetts.

Outlook /Tuesday through Friday/...

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.

Overnight...west to SW winds gusting to 20-25 knots over the eastern Massachusetts
waters...gradually diminishing toward daybreak.

Today...tranquil wind and seas along with dry weather and good
visibility.

Tonight...NE winds increase to gale force across the Rhode Island and
southern Massachusetts waters...and possibly the northern Massachusetts waters toward
daybreak. Gale warnings posted for all of the Massachusetts and Rhode Island coastal
waters. Visibility lowering in snow late along the South Coast. Seas
will build rapidly with powerful low pressure well off the North
Carolina coast combining with a 1035 mb surface high over Quebec.

Monday...gale force winds gusting to 35-45 kts over all coastal
waters along with visibilities reduced to below 1 mile in snow.
Locally near zero visibility possible in heavier snow squalls. The
only exception is over Narragansett Bay where small craft
advisories are posted for wind gusts of less than 30 kts.
Very rough seas building up to 14-18 feet off the Massachusetts coast.

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 neeeded.

Wednesday...winds become west less than 20 knots. Seas linger 5 feet
or higher on the soutehrn 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...
4 PM update ...

Have upgraded to a coastal Flood Warning 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. Low level winds
drop off from Boston northward. Thus less storm surge and coastal
flooding likely in the minor category. High tide cycle of greatest
concern is the late Monday morning to midday...basically 9 am to 1
PM is the timeline.

Expecting a storm surge of around 2 feet across the warning area
with 1-1.5 feet from Boston northward to the Massachusetts/New Hampshire border. Etss was
higher than the estofs and seems reasonable given NE winds will
gusts 50 to 60 miles per hour with low risk of 70 miles per hour across Cape Cod and
Nantucket. Thus followed the more bullish etss surge. In addition
large waves of 10-20 feet just offshore on top of these high water
levels will promote waves to runup the shoreline and up and over
seawalls and other structures. This will also result in potential
moderate beach erosion. Again greatest impacts Monday 9 am to 1 PM
along Plymouth coast to Cape Cod Bay to Nantucket...with less
impacts Boston northward to Massachusetts/New Hampshire border.

Could have some minor coastal flooding during the late Monday evening
toward midnight high tide cycle. However astro tide is
lower...less winds and pressure rises overspreading the area.

Rhode Island coastline ...

Given this ocean storm is developing so far south of New England
there may be enough southeast swells and push of water that minor coastal
flooding may occur during the Monday evening high tide cycle. Will
have to watch this closely.

&&

Box watches/warnings/advisories...
CT...Winter Storm Warning until 7 am EST Tuesday for ctz002>004.
Massachusetts...Blizzard Warning until 7 PM EST this evening for maz018-019-
021>024.
Coastal Flood Warning from 9 am this morning to 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 from 9 am this morning to 1 PM EST this
afternoon for maz007-015-016-023.
Winter Weather Advisory until 7 am EST Tuesday for maz002-003-
008>011.
Rhode Island...Blizzard Warning until 7 PM EST this evening for riz008.
Winter Storm Warning until 7 am EST Tuesday for riz001>007.
Marine...Storm Warning until 6 PM EST this evening for anz231>234-250-
254>256.
Gale Warning until 9 PM EST this evening for anz230-235-237.
Gale Warning until 7 PM EST this evening for anz236.
Gale Warning until 10 PM EST this evening for anz251.

&&

$$
Synopsis...wtb/nocera
near term...Frank/nocera
short term...nocera
long term...wtb
aviation...wtb
marine...wtb
tides/coastal flooding...

National Weather Service Glossary of Abbreviations