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Area forecast discussion 
National Weather Service Taunton Massachusetts
433 PM EST sun Jan 25 2015

Synopsis...
chilly and blustery conditions expected through Monday. A major
and potentially historic winter storm will affect the region
Monday night into Tuesday night...travel may become impossible and
life threatening. Drier weather follows Wednesday into early
Thursday...but will have to watch for another chance of snow by
the end of the work week.

&&

Near term /through Monday/...
4 PM update...blustery conditions continue across much of
southern New England with westerly winds gusting up to 30 miles per hour at
times. Temperatures in the 30s combined with these winds are
resulting in wind chills in the teens and 20s.

Tonight...high pressure in Quebec will build southward into southern
New England allowing winds to calm and clear skies continue. This
will allow for decent radiational cooling. However...increasing
clouds from the south in advance of low pressure moving off the
coast may put a stop to radiational cooling early. Therefore...not
dropping temperatures as low as they could be if skies remained
clear. Forecasting lows in the single digits to teens for most
locations.

Monday...high pressure moves northeastward into the Maritimes as low
pressure moves offshore the Delaware-Maryland-Virginia peninsula before approaching
southern New England Monday night. Mostly dry/quiet weather
expected for much of Monday but definitely a deteriorating trend.
Increasing clouds through the day with mostly cloudy to overcast
skies through the day. The GFS is the quickest moving snow over
southern New England around midday. However...the NAM/European model (ecmwf) are the
preferred solutions for the noreaster/blizzard. These solutions
keep the area dry through much of the day with snow moving in from
the south late Monday afternoon. Because of this...only expect a
few inches of snow at most prior to 00z Tuesday /7 PM Monday/.
Temperatures are expected to be in the 20s to middle 30s across southeast
Massachusetts.

&&

Short term /Monday night through Wednesday/...
* historic and potentially crippling blizzard Monday night into Tuesday
night
* up to 2 feet of snow for many areas with higher amounts possible
* damaging winds likely coast especially cape/islands...gusts 60 to 75 miles per hour
* pockets of major coastal flooding possible along the eastern Massachusetts
coast

Overview...

Overall multi-model agreement on surface and upper air pattern leads US
to high confidence of a historic winter storm and potentially
crippling blizzard for southern New England. Potent negative tilt shortwave diving to southeast
US coast will result in surface redevelopment off the middle Atlantic coast and
explosive cyclogenesis south of New England Monday night as middle level
low closes off. High pressure will set up across eastern Canada
providing a source of cold air and enhancing baroclinic zone along
the coast. The storm eventually gets captured which will allow for
very slow movement northward from near the benchmark and long duration
storm.

There are some differences in the track of the 850/700 mb lows and
how quickly it exits the area which will impact exactly where best
banding sets up...potential dry slot eastern new eng as well as
ptype for cape/islands. We think GFS is too progressive and a bit
too far north and west with middle level low and we are leaning toward
European model (ecmwf)/NAM blend which are reasonably close.

Despite differences in middle level low track...quantitative precipitation forecast is pretty similar
with 1.5 to 2.5 inches across southern New England with locally up to 3 inches.
Probably looking at near climatology snow liquid ratios which are close to
10:1 in the coastal plain and no more than 12-15:1 interior as middle
level temperatures in the snow production zone are near climatology.

High confidence on blizzard in eastern new eng so we are upgrading
watches to blizzard warnings. We are also expanding the blizzard
warnings to north CT...portions of central Massachusetts and Cape Cod and mvy.
Winter storm warnings for western Massachusetts as we are not confident wind
criteria will be met. And finally for ack...we kept the Winter
Storm Watch as we are not confident in 6 inches of snow due to ptype
issues and we also upgraded to a High Wind Warning.

1) precipitation type...

Thermal profile cold enough for all snow for most of the area...but
we are still concerned about enough warming for a possible change to
rain over ack late Monday night into Tuesday...with this warming possibly
reaching the Outer Cape for a time during Tuesday. European model (ecmwf) is pretty
bullish on this warming and NAM also shows it but to a lesser
extent.

2) heavy snow/blizzard conditions/wind

Snow will be ramping up quickly Monday evening...with very heavy snow
likely developing after midnight into Tuesday morning from south to
north as very impressive banding signature develops and lifts north
across the region. This occurs as the middle level low closes off to
the south with tightening thermal gradient enhancing frontogenetical
forcing. Very strong Omega through the favorable dendritic growth
zone combined with -epv suggests potential for 2-3"/hour snowfall
rates and pockets of thunder snow 06-15z as the band lifts to the north.

Models show banding signature moving into the interior west of I-95
corridor during Tuesday and pivoting from east-west to NE-SW
configuration...while possible dry slot moves into portions of east Massachusetts.
Forecasting the exact location of the banding...where it pivots and
location of the dry slot Tuesday is very challenging and will
determine where axis of heaviest snow sets up. This will depend on
the track of the middle level low. European model (ecmwf) pushes this band all the way
into western new eng while NAM is closer to the I-95 corridor. We
think it will set up a little west of I-95 on the cold side of the
coastal front and this is where we think heaviest snow accumulate will
be.

Potential for 2-3 feet of snow in this zone near and west of I-95...
up to 2 feet far west Massachusetts and also southeast Massachusetts where dry slot may cut back on
snow accumulate a tad despite heavier quantitative precipitation forecast here. It is not uncommon to
find the heaviest snow a bit northwest of maximum quantitative precipitation forecast axis because of where the
banding sets up. For the cape and mvy we are looking at 10-18" with
heaviest near the canal. Low confidence forecast for ack and we
have up to 6 inches here but will depend on timing of changeover.

Highest probability of heavy wet snow will be across southeast Massachusetts and Cape
Cod where there is enhanced potential for down trees and power
outages...especially given the strong winds. Drier snow in the
interior.

Very strong winds are likely along the coast as impressive low level
jet develops north of the deepening low pressure. NAM soundings show
potential for hurricane force wind gusts 70-80 miles per hour for the Outer
Cape and islands...especially late Monday night into Tuesday morning when
strongest winds will occur. Gusts to 50-60 miles per hour possible across rest
of southeast Massachusetts east of the i95 corridor...and 30-40 miles per hour across the
interior.

Combination of heavy snow and very strong winds will result in
blizzard conditions with blowing and drifting snow and near zero
visibility later tonight into Tuesday...especially eastern new eng. This
is a serious and life threatening storm and travel is highly
discouraged tonight into Tuesday.

It looks like the worst of the storm will begin to wind down late
Tuesday and especially Tuesday night as the low becomes vertically stacked
and banding becomes fractured...but light snow will persist most of
the night given proximity of middle level low near the coast...with
snow finally ending Wednesday morning.

&&

Long term /Wednesday through Sunday/...

While the focus of the forecast remains on the blizzard...we will
update this portion of the forecast as time permits.

Snow comes to an end Wednesday morning as high pressure starts
building over southern New England. Then another winter storm is
possible sometime Thursday into Friday /ECMWF is slower than GFS/
as low pressure moves eastward from the Great Lakes over southern
New England. High pressure expected to build in next weekend.

&&

Aviation /21z Sunday through Friday/...
forecaster confidence levels...

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

Through 00z...high confidence. VFR. Scattered-bkn040 possible through
the day. West winds gust to 30 kts.

Tonight...high confidence. VFR.

Monday...high confidence in trends. Moderate confidence in timing.
Start off VFR with deteriorating conditions throughout the day.
IFR conditions and snow will not occur until late in the
day...likely after 21z. However...they could occur as early as
18z.

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Monday night through Friday/...

Monday night through Tuesday night...widespread LIFR in heavy
snow and blowing snow. Strong NE winds developing near the coast
with gusts 50-65 kts expected.

Wednesday...improving conditions expected as high pressure builds
in.

Thursday and Friday...deteriorating conditions with another
potential winter storm.

&&

Marine...
forecaster confidence levels...

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

Short term /through Monday/...high confidence.

Small craft conditions will continue through Monday. However...
focusing on the upcoming noreaster/blizzard...and associated storm
force to hurricane force winds expected with this storm...have
dropped the small craft advisories.

Outlook /Monday night through Thursday/...

***life threatening storm for mariners with seas building to 30 feet
and wind gusts to 65 knots Monday night through tuesday***

Monday night through Tuesday night...rapidly intensifying low
pressure moving across the waters will result in northeast wind
gusts increasing to 55 to 65 knots over the open waters with seas
building to 30 feet over eastern waters. Hurricane force wind warnings
have been issued for most of the open waters with Storm Warning
elsewhere. This is dangerous and life threatening storm and mariners
should return to port by Monday afternoon.

Wednesday...moderate confidence. Should see at least leftover north-northwest
wind gusts up to small craft criteria during Wednesday...then should
diminish Wednesday night.

Thursday and Friday...low confidence. Winds should remain below
small craft criteria. Seas may linger at around 5 feet.

&&

Tides/coastal flooding...
significant coastal flooding is expected during the early Tuesday
morning high tide along the Massachusetts East Coast. High tide
occurs between 4 and 6 am along most of the coastline. In Boston
high tide is at 430 am. Have upgraded to a coastal Flood Warning for
the Tuesday am high tide and have kept the watch in place for the
Tuesday late afternoon high tide.

For the Tuesday am high tide...anticipate the storm surge to be 3 to
3.5 feet and still rising to possibly 3.5 to 4 feet by the time of
the later Tuesday morning low tide. By the Tuesday early am high
tide...anticipate seas to have built to between 20 and 25 feet just
offshore...highest east of Cape Cod and Nantucket. NE surface winds
anticipated to be gusting between 50 and 60 knots by the time of the
early Tuesday am high tide. These seas will be high enough for
overwash to be an issue in those places typically prone to it.
Severe beach erosion is likely in a few spots given the elevated
water levels and strong wave action. This is a storm that could
produce one or more new inlets along exposed east and northeast
facing barrier beaches.

The Tuesday late afternoon high tide is somewhat lower
astronomically but the surge could be about the same or even a few
tenths higher than at the Tuesday am high tide. Also seas could be
still 25 to 30 feet just offshore at the time of the Tuesday late
afternoon high tide.

&&

Box watches/warnings/advisories...
CT...Blizzard Warning from 7 PM Monday to 1 am EST Wednesday for
ctz002>004.
Massachusetts...Blizzard Warning from 7 PM Monday to 1 am EST Wednesday for
maz005>007-012>021.
Coastal Flood Warning from 3 am to 7 am EST Tuesday for maz007-
015-016-019-022>024.
Coastal Flood Watch from Tuesday afternoon through Tuesday
evening for maz007-015-016-019-022-024.
Winter Storm Warning from 7 PM Monday to 1 am EST Wednesday
for maz002>004-008>011-026.
High Wind Warning from 7 PM Monday to 1 am EST Wednesday for
maz024.
Winter Storm Watch from Monday evening through Tuesday
afternoon for maz024.
Blizzard Warning from 7 PM Monday to noon EST Tuesday for
maz022-023.
Rhode Island...Blizzard Warning from 7 PM Monday to 1 am EST Wednesday for
riz001>008.
Marine...hurricane force wind warning from 7 PM Monday to 7 PM EST
Tuesday for anz231>235.
Storm Warning from 11 PM Monday to 7 PM EST Tuesday for anz230-
236.
Storm Warning from 7 PM Monday to 7 PM EST Tuesday for anz237-
251.
Hurricane force wind warning from 1 am to noon EST Tuesday for
anz250-254>256.

&&

$$
Synopsis...kjc/rlg
near term...rlg
short term...kjc
long term...rlg
aviation...kjc/rlg
marine...kjc/rlg
tides/coastal flooding...rmt

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