Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
726 am EST Friday Jan 30 2015

Synopsis...
low pressure will weaken over southern Quebec as a secondary low
develops along the southern New England coast this afternoon. This
low will intensify over the Gulf of Maine by tonight bringing
periods of snow. Blustery and very cold conditions are expected
this weekend. Low pressure will pass south of New England Sunday
night and Monday...possibly bringing another accumulating
snowfall. Cold conditions will continue through most of next
week. Yet another low may develop around next Wednesday or Thursday with
a threat for snow...though low confidence.

&&

Near term /until 6 PM this evening/...
705 am update...
brief break in the precipitation shield noting on NE regional 88d
radar...but more light precipitation down the coast will work NE this
morning. Will see precipitation become better organized as secondary low
deepens during the day. Will still see a mix of rain and/or snow
across southeast Massachusetts with onshore winds prior to the low moving
by...probably around midday or early this afternoon.

Have updated near term forecast to bring conditions current.

Previous discussion...
amplifying middle level trough across the Great Lakes becomes negative
tilted as it reaches the coast late today. Associated height fall
center and shortwave energy will result in parent low filling
across central new eng with cyclogenesis increasing south of Cape
Cod later this afternoon. Expect a period of mainly light snow
today ahead of the open middle level wave which should taper off this
afternoon across the CT valley to the Rhode Island coast. Warming boundary
layer along the immediate southeast new eng coast will result in rain or
mixed rain/snow for the cape and islands.

Used a blend of model quantitative precipitation forecast which results in snow accumulate through
today of 1-2 inches away from the coast...with up to 3 inches
north central and northwest Massachusetts. Along the S coast...expect less than an
inch.

&&

Short term /6 PM this evening through 6 PM Saturday/...
tonight into Saturday...

Negative tilt trough evolves into a closed middle level over southern New
England this evening then it jumps to the Gulf of Maine later
tonight. The surface low deepens rapidly tonight in the Gulf of Maine
but likely remains a bit too far offshore to rotate heavy snow
back across southern New England as the heavier precipitation will remain to the north
over Maine. However...a robust comma head will develop to the
west of the middle level low tonight and extend across eastern new
eng which will likely bring bands of snow to the region.

The westward extent of the snow tonight will likely be across
central Massachusetts and Rhode Island with the main focus across east Massachusetts including the
cape/islands. Mainly dry weather expected in the CT valley.
Models backed off a bit on the quantitative precipitation forecast so we have lowered snow accumulate a
tad...but have to watch NE Massachusetts and Cape Cod which will be closest
to the best forcing.

Snow lingers across east Massachusetts into Sat morning...before gradually
moving out. The Outer Cape will be last to dry out around midday.
Otherwise...clearing skies will develop from west to east late
morning through the afternoon but windy and very Cold Saturday
with highs mostly in the teens.

We kept the Winter Storm Warning for Essex County but downgraded
Middlesex County to an advisory. Expanded the advisory to Cape
Cod which should get into a decent band of snow tonight.
Otherwise...dropped the advisory for NE CT...north Rhode Island and adjacent southeast
Massachusetts where snow amounts should fall shy of advisory criteria.

Total snow accumulate of 4-7 expected across NE Massachusetts with the maximum
amounts in Essex County...with 2-4 inches central Massachusetts to east coastal
Massachusetts including Cape Cod. An inch or 2 possible near the S coast.

In addition to the snowfall tonight...northwest winds will
increase late tonight into Sat with gusts to 40 to 45 miles per hour as low
intensifies east of Massachusetts. Low probability wind gusts could reach 50 miles per hour
near the S coast and wind advisories may eventually be needed.

Very cold air moves in tonight into Saturday combined with gusty
northwest winds will result in dangerously cold wind chills of 10 to 20
below zero in central and western Massachusetts and portions of north CT where
wind chill advisories have been issued. Wind chills 5 to 10 below
in the coastal plain.

&&

Long term /Saturday night through Thursday/...
headlines...

* cold conditions through Sunday as winds diminish
* low pressure looks to pass S of New England Sunday night and
Monday with accumulating snow possible
* cold conditions continue through most of next week
* another low is possible around Wednesday or Thursday...low confidence

Overview...
overall...noting a rather progressive upper level pattern across
the lower 48 which will keep weather systems moving...but there is
also the potential for a couple more snow events on the horizon.

Details...

Saturday night-Sunday...high pressure moves off the middle Atlantic coast as
a ridge pokes north into the region. Northwest winds will remain blustery
early Sat night...then will diminish. A dry cold front will push
across the region Sunday morning...bringing large high pressure out of
south central Canada into the northern Great Lakes. Noting a
digging 500 mb short wave working east out of the middle Mississippi Valley
as surface low develops. Will likely see clouds pushing in during
Sunday.

Sunday night-Monday...big questions with low pressure passing S of New
England. First...more cold Arctic air works across the region...so
temperatures will be rather cold. However...most models and several
ensembles signaling low pressure will pass close to just S of 40n
latitude...possibly passing near the 40n/70w benchmark. Noting
the 00z GFS and European model (ecmwf) were more in line this morning in spreading
a swath of quantitative precipitation forecast across the region while high pressure extends into
Quebec. Looks like a set up for more accumulating snowfall.
Current forecast suggests around 0.3 to 0.5 inches quantitative precipitation forecast and...with
the cold air in place...could see snow to liquid ratios of around
15:1.

Exact timing is still in question though as the pattern remains
progressive...but will be monitoring this development very
closely.

Tuesday...another high crosses the region during Tuesday with
more cold air working in.

Wednesday-Thursday...models and ensembles continue to signal low
pressure and cold front moving out of the Great Lakes Wednesday night...then
moving offshore Thursday morning. Low pressure may develop along this
front...possibly bringing more southern stream moisture up the
coast. Way too early to tell how the northern and southern streams
will interact...low confidence.

&&

Aviation /12z Friday through Tuesday/...
forecaster confidence levels...

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

Short term.../through Saturday/...moderate confidence.

Today...a mixture of conditions early this morning...mainly
MVFR/IFR in areas of snow...with rain cape/islands. Snow tapers
off and ends CT valley to the Rhode Island coast during the afternoon with
mainly MVFR ceilings...but periods of snow continue central and east Massachusetts.
Gusty northwest winds to 25 knots developing across CT valley by late
afternoon.

Tonight...main focus for areas of snow and MVFR/IFR conditions
will be across east Massachusetts...with VFR CT valley. Gusty northwest winds develop
from west to east in the evening with gusts to 30-40 knots after
midnight.

Saturday...lingering MVFR/IFR in areas of light snow across east Massachusetts
and cape/islands early...otherwise improving to VFR with clearing
skies from west to east. Gusty northwest winds to 35-40 knots.

Kbos taf...moderate confidence.

Kbdl taf...moderate confidence.

Outlook /Saturday night through Tuesday/...

Saturday night-Sunday...high confidence. VFR. Northwest winds gusting to
25-35 knots Saturday...highest along the coast. Lighter winds
Sunday.

Sunday night-Monday...low confidence. Developing low pressure looks to
pass S of New England with accumulating snow possible. Could see
IFR conditions for a time...especially S of the Mass Pike.
Conditions may improve early Monday night

Tuesday...moderate confidence. Mainly VFR. May see gusty northwest winds
early.

&&

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...southerly winds will shift to west then northwest during Friday
afternoon...with gusts to 25 knots developing across Rhode Island coastal
waters by late afternoon.

Tonight and Saturday...as low pressure intensifies over western Gulf
of Maine...gale force northwest winds will develop. Gusts to 40-45 knots
expected late tonight into Sat. The gusty winds and rough seas
combined with Arctic air moving into the region will result in
areas of moderate freezing spray over the nearshore waters so
freezing spray advisories were issued. Snow reduces visibility over
eastern waters tonight into Sat morning.

Outlook /Saturday night through Tuesday/...moderate confidence
through Sunday...then low confidence Sun night-Tuesday.

Saturday night...northwest winds gusting to 35-40 knots early...then should
start to diminish around or after midnight. Seas up to 10-14 feet on
the outer waters early...then slowly subsiding but remaining well
above 5 feet. Light to moderate freezing spray.

Sunday...expect winds and seas remain at small craft levels.
Light freezing spray likely.

Sunday night-Tuesday...highly dependent on strength and track of
developing low pressure south of the region. Worse conditions
would be Monday with slow improvement on Tuesday.

&&

Box watches/warnings/advisories...
CT...Wind Chill Advisory from 1 am to 9 am EST Saturday for ctz002-
003.
Massachusetts...Winter Weather Advisory until 8 am EST Saturday for maz004-005-
012>016-018-019-026.
Wind Chill Advisory from 1 am to 9 am EST Saturday for maz003-
004-010-011.
Wind Chill Advisory from 11 PM this evening to 11 am EST
Saturday for maz002-008-009.
Winter Weather Advisory from 6 PM this evening to 8 am EST
Saturday for maz022.
Winter Storm Warning until 8 am EST Saturday for maz006-007.
Rhode Island...none.
Marine...freezing spray advisory from 11 PM this evening to 6 PM EST
Saturday for anz231>235-237-250-251.
Gale Warning from 11 PM this evening to 6 PM EST Saturday for
anz232-250-254-255.
Gale Warning from midnight tonight to 6 PM EST Saturday for
anz230-231-233-234-251.
Gale Warning from 1 am to 1 PM EST Saturday for anz236.
Gale Warning from 9 PM this evening to 6 PM EST Saturday for
anz235-237.
Gale Warning from 7 PM this evening to 6 PM EST Saturday for
anz256.

&&

$$
Synopsis...kjc/evt
near term...kjc/evt
short term...kjc
long term...evt
aviation...kjc/evt
marine...kjc/evt

National Weather Service Glossary of Abbreviations