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Area forecast discussion 
National Weather Service Taunton Massachusetts
1241 am EST sun Feb 1 2015

Synopsis...
blustery and very cold conditions tonight and into tomorrow. A
major winter storm will affect the region very late Sunday night
into Monday evening with heavy snow for many locations. Bitterly
cold wind chills follow later Monday night into Tuesday morning.
Moderating temperatures Wednesday then very cold conditions will return
toward the end of the week. A coastal storm will pass well south
of New England late in the week but will have to be monitored.

&&

Near term /through today/...
1240 am update...
sky clear across the region but noting some lower clouds moving into
the Berkshires which may spill into west zones overnight. Adjusted
T/dew point grids...otherwise forecast on track.

Previous discussion...
surface ridge across New York state collapses toward the middle Atlantic
coast overnight as Arctic front approaches Canadian border. Skies
are clear but some lower clouds in eastern New York may drift into
western new eng overnight. Still gusty winds along the coast but
trend will be for diminishing wind overnight. Where winds have
decoupled temperatures have already fallen to near zero. Currently 1 at
Oregon. Expect subzero temperatures northwest Massachusetts with single numbers elsewhere away
from the coast. There will be enough wind along the coast to keep
overnight lows in the low/middle teens.

Tomorrow...

850mb Arctic front will push through the region tomorrow. However
temperatures will be warmer than today as 925 mb temperatures jump from -13c to
-8c. Expect temperatures to warm into the middle 20s to perhaps the low 30s
along the coastal plain. Middle to high level moisture will be
increasing throughout the day which will increase cloud cover.
Otherwise winds will be calmer and dry weather will prevail
through most of the day.

&&

Short term /tonight through Tuesday/...
highlights...

* major winter storm very late Sun night into Monday evening
* heavy snowfall expected for much of the region
* biggest uncertainty snowfall amts near South Coast - ptype issues
* bitterly cold air late Monday night - wind chills 15 to 25 below zero

Details...

A major winter storm will affect southern New England very late Sun
night into Monday evening. Arctic high pressure across eastern
Canada will combined with low pressure approaching from the west.
The result will be strong southwest flow aloft over running the
Arctic Dome at the surface. Then as the low deepens...much of the
region will see snow on the backside of the system. Biggest
uncertainty is how much of the region transitions to a period of
mixed ptype during the middle of the event...cutting down on
possible snow accums.

1) timing and uncertainty

Snow will likely arrive from southwest to northeast very late sun
evening in our western zones and after midnight across the rest of
the region. Extremely tight middle level thermal packing will allow
snow to quickly become heavy. Snow will fall heavy Monday morning
at 1 to 2 inches per hour and significantly impact the am rush hour.

Things then become more uncertain later in the morning and
afternoon. The GFS is most aggressive in surging warm middle level air
to the Massachusetts Pike...resulting in a change to a period of sleet/freezing
rain and even plain rain along the far southeast New England coast.
The NAM/ECMWF/ggem appear the coldest keeping most areas heavy
snow...except for the cape and islands. The UKMET appears to be in
between the other solutions. Given the uncertainty will blend the
models. Right now were thinking transition area may get briefly
near or perhaps just north of the the Taunton to Providence
corridor...before collapsing southeast.

Regardless how far north the transition line gets...most areas will
change back to snow Monday evening. Given closed middle level centers and
very cold northeast flow...could be some ocean enhancement across
eastern New England for a time before snow ends. Bulk of snow
should wind down after midnight although the ggem is a bit slower.

2) snowfall accumulations and headlines

We are pretty confident in a heavy snowfall for much of the
region...except for areas near the South Coast where ptype issues
maybe more problematic. 8 to 14 inches expected for much of the
region. Have upgraded all areas from Providence to Taunton
northward to Winter Storm Warning/S with high confidence on criteria
being met. Areas southeast of that line...there is some more
uncertainty especially cape/islands. If a lot of mixing occurs these areas
may struggle to reach warning criteria...but its still certainly
possible depending on model trends. Therefore...we have held the
Winter Storm Watch for the South Coast and the islands.

3) strong winds and blowing and drifting snow

Northeast wind gusts of 35 to 50 miles per hour expected along the coast Monday
into Monday night as storm intensifies and pressure gradient
increases. This will likely result in poor visibility along with
blowing and drifting snow. Its possible that a few locations along
the coast could see near blizzard conditions for a very short
time...but storm doesn/T seem to warrant those type of headlines.

4) bitterly cold air Monday night into early Tuesday morning.

Temperatures will likely plunge below zero to 5 above zero in many
locations by early Tuesday morning. This will result in wind chills
values between 15 and 25 below zero. Wind chill advisories will
likely be needed.

&&

Long term /Tuesday night through Saturday/...
highlights...

* cold pattern continues through next weekend
* clipper low appearing more likely than coastal low Wednesday/Thursday

Good agreement among 12z deterministic...12z gefs and 00z ecens
ensembles that the polar jet will dominate the northern tier states
including New England this period. This combined with streams
expected to remain unphased will support mainly dry weather this
period. One caveat will be clipper low entering the northeast
Wednesday/Wednesday night. Earlier model runs suggested secondary development
along the trailing cold front southwest of New England...with
possible coastal-ocean storm impacting our region around Thursday.
However latest guidance including ensembles suggest middle level trough
will lack sufficient amplitude to back the flow for a secondary low
to impact the region. Therefore leaning toward a more offshore track
and just a period of light snow possible Wednesday/Wednesday night. However at
this time range can/T be too deterministic. Thus won't totally
discount closer secondary development.

As for temperatures...bitterly cold Tuesday behind departing Monday night coastal
low. Then cold eases Wednesday ahead of approaching clipper low followed
but yet another Arctic blast late in the week behind the clipper. As
for into next weekend ensemble trends suggest temperatures colder than
normal.

&&

Aviation /06z Sunday through Thursday/...
forecaster confidence levels...

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

Short term.../through Monday/...

Today...high confidence. Mainly VFR...but low probability for areas of
MVFR ceilings developing by afternoon.

Tonight into Monday...high confidence in trends but lower
confidence in timing.

VFR this evening deteriorates to IFR-LIFR ceilings/visibilities in moderate
to heavy snow after midnight to daybreak from west to east.
IFR/LIFR in moderate/heavy snow continues through the day Monday. Ptype
may transition to a period of sleet/freezing rain around midday
from pvd-tan-pym south and changing to rain over the Outer
Cape/islands. NE wind gusts to 30-35 knots developing across east
coastal Massachusetts Monday...with 25 knots across Rhode Island and remainder of east Massachusetts.

Kbos taf...high confidence. Lower confidence in exact timing of
IFR conditions in snow.

Kbdl taf...high confidence. Lower confidence in exact timing of
IFR conditions in snow.

Outlook /Monday night through Thursday/...

Tuesday into Wednesday...moderate confidence. Mainly VFR on
Tuesday. Could see some MVFR ceilings in scattered snow showers on
Wednesday.

Thursday...moderate confidence. Mainly VFR. Low risk of MVFR
along southeast mass depending on track of clipper low.

&&

Marine...
forecaster confidence levels...

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

Short term /through Monday night/...

High confidence through Sunday afternoon.

Tonight...strong low pressure pulls farther away with winds
diminishing below gale after 06z...but gusts 25-30 knots will
continue overnight. Moderate freezing spray likely
continuing...especially east Massachusetts coastal waters.

Sunday...winds and seas gradually diminish through the day. Winds
and seas will slowly diminish throughout the day but expect Small Craft Advisory
waves to remains through the period. Light freezing spray will
persist.

Sunday night into Monday...moderate to high confidence.

***Strong gale force wind gusts/high seas and the risk of heavy
freezing spray Monday into Monday night***

Winds/seas quickly ramp up very late Sun night into Monday as low
pressure intensifies near the South Coast. Gale watches issued for
expected 40+ knot northeast wind gusts by Monday morning.
Seas build to 15+ feet across our eastern waters by late Monday
afternoon/evening. In addition...bitterly cold air moving over the
waters Monday night will result in the potential for heavy
freezing spray. Have also issued a freezing spray watch.

Outlook /Tuesday through Thursday/...moderate to high forecast
confidence.

Tuesday...northwest gales likely along with freezing spray...possibly
moderate to heavy. Mainly dry with good visibility except far offshore
where snow showers will be common.

Wednesday...winds ease and become southwest as clipper low enters the
Great Lakes and New York state. Not as cold so freezing spray unlikely.
Visibility may briefly lower in a period of light snow.

Thursday...Arctic front with northwest gales behind frontal passage. Moderate to
heavy freezing spray possible.

&&

Tides/coastal flooding...
*** minor to perhaps isolated areas of moderate coastal flooding
possible Monday/Monday night eastern Massachusetts coastline ***

Good model agreement on surface low tracking somewhere between
Nantucket and the 40n/70w benchmark with NAM the fastest and GFS
farthest northwest. European model (ecmwf) splits the difference. Model consensus
brings strongest onshore winds between 18z and 00z...close to low
tide. If this timing holds up worst case scenario would be minor
coastal flooding.

The first tide cycle of concern is the Monday middle morning. However
all wave guidance suggest seas less than 10 feet at high tide given
arrival of strongest winds later during the afternoon. This also
yields surge values of a foot or less.

As for the Monday evening high tide cycle...astro tides are about a
1 feet lower. However a storm surge of 1.5 to 2.5 feet is possible.
Estofs and etss are lower...so I blended the two guidance sources and
added 50 percent to come up with surge values of 1.5 to 2.5 feet. In
addition...seas will likely build to 15 to 20 feet during the evening
high tide. All of these factors yield a moderate risk of minor
coastal flooding with a low risk of isolated moderate flooding.

While winds...seas and storm surge will be less than the previous
coastal storm there could still be some modest impact especially for
those communities such as Marshfield Massachusetts that were hit hard earlier
this week where coastal structures such as seawalls were damaged.
Given the low track is close to Nantucket the greatest risk of
coastal flooding will be farther northward from Cape Cod to Cape Ann
with perhaps the highest risk from Hull/Cohasset/Scituate/
Marshfield/Plymouth to Sandwich Harbor.
/Duxbury

Given it appears marginal for significant coastal flooding and still
48-60 hours out in time will hold off on a coastal Flood Watch.

&&

Climate...
with extremely cold air moving in behind the departing low Monday
night...temperatures may fall back close to or surpassing record
levels early Tuesday morning. And that is not taking into account
the strong winds.

Here are the record lows for Tuesday 2/3...

Boston -5 set in 1881
Providence -6 set in 1961
Worcester -7 set in 1931, 1955 and 1971
Windsor Locks -3 set in 1955
Blue Hill observation -7 set in 1955

&&

Box watches/warnings/advisories...
CT...Winter Storm Warning from 9 PM this evening to 1 am EST
Tuesday for ctz002>004.
Massachusetts...Winter Storm Watch from this evening through late Monday night
for maz020>024.
Winter Storm Warning from 9 PM this evening to 1 am EST
Tuesday for maz002>019-026.
Rhode Island...Winter Storm Watch from this evening through late Monday night
for riz005>008.
Winter Storm Warning from 9 PM this evening to 1 am EST
Tuesday for riz001>004.
Marine...gale watch from Monday morning through Tuesday morning for
anz231>235-237.
Heavy freezing spray watch from Monday evening through Tuesday
morning for anz231>235-237-250-251-254>256.
Freezing spray advisory until 8 am EST this morning for anz231-
232-250-251-254-255.
Gale Warning until 1 am EST early this morning for anz231-232-
250-251-254-255.
Small Craft Advisory until 7 am EST this morning for
anz233>235-237-256.
Freezing spray advisory until 1 am EST early this morning for
anz233>235-237.
Gale watch from Monday morning through late Monday night for
anz230-236.
Small Craft Advisory until 1 am EST early this morning for
anz230-236.
Gale watch from late tonight through Tuesday morning for
anz250-251-254>256.

&&

$$
Synopsis...Frank/nocera/dunten
near term...Frank
short term...Frank
long term...nocera
aviation...kjc/Frank
marine...kjc/Frank/nocera/dunten
tides/coastal flooding...
climate...

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