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Area forecast discussion 
National Weather Service Taunton Massachusetts
1115 PM EST Monday Mar 2 2015

Synopsis...
high pressure will build across the region overnight...then will
begin to move offshore ahead Tuesday. A storm system across
southern Canada with a trailing cold front will be the focus for
wintry weather late Tuesday into Wednesday. This front will stall
south of the region Wednesday night into Thursday resulting in
renewed winter weather outcomes. From Thursday night Onward...
continued colder than normal conditions with additional weather
disturbances.

&&

Near term /until 6 am Tuesday morning/...

1050 PM update...
thin bands of light snow continue to cross central and eastern
areas as seen on latest kbox 88d radar. Moving rather quickly in
the northwest flow though...so not expecting much if any accumulations
except maybe on the Outer Cape where the bands hold together.
Should push offshore as winds diminish.

Northwest winds have been diminishing over the last couple of hours...but
did note a brief increase around 02z across the CT valley. Still
see gusty winds up to 25-30 knots on the Outer Cape and Nantucket at
03z. However...at 04z...noting winds inland winds down to 5 to
around 10 knots except for a few spots holding at 10-15 knots across north
Massachusetts around Route 2 region. Winds will continue to diminish
overnight as high pressure ridge builds east out of New York state.

Temperatures were running a few degrees above forecasted levels at 03z...but
should begin to drop as skies become generally mostly clear and
winds continue to drop. Should see radiational cooling in place
after midnight across the normally colder valley locations across
interior east Massachusetts and into the CT valley and north central/NE CT.

Have updated near term forecast to bring conditions current.

Previous discussion...

Best chance for radiational cooling once winds decouple...will be
across the western half of the region. Across the east...if winds
go light quickly enough during the later half of the night then
radiational cooling will occur. Otherwise expect temperatures to remain
in the low teens overnight.

&&

Short term /6 am Tuesday morning through 6 PM Tuesday/...
Tuesday...

High pressure will begin to push eastward during the day tomorrow
ahead of the next system. Expect dry weather and mostly clear skies
into the early afternoon hours. As low pressure system approaches
Hudson Bay...expect precipitation to being to overspread the region from SW
to NE during the later afternoon hours. Temperatures both aloft and at the
surface will remain cold enough for precipitation to start in the form of
snow and quickly accumulate on surfaces. This could make the evening
commute across Hartford/Springfield a bit messy tomorrow.

&&

Long term /Tuesday night through Monday/...
*/ late Tuesday into Wednesday morning...

1) highlights...

- precipitation transition from snow to rain with a wintry mix between
- Winter Weather Advisory in effect
- impacts especially to the Tuesday afternoon / evening commute

2) overview...

Inside-runner event with an area of low pressure across SW Canada
and a trailing cold front towards the SW-Continental U.S. Ahead of which S-flow
of warm-moist air isentropically ascends across S New England. An
over-running event with a push of warmer air north along with increasing
thicknesses...anticipating an initial snow event Tuesday evening to
transition SW-NE to a wintry mix before changing to rain /though
perhaps not for all locations/.

Tricky forecast in nailing down transition timing with respect to
thermal fields. This is not a perfect forecast by any means. Likely
to see some slight shifts in outcomes. Details along with forecast
thinking highlighted in the discussion below...

3) precipitation outline...

Variability with respect to h925-85 thermal fields and h85-7/h100-85
thicknesses. Preference to the 02.12z GFS and regional Canadian with
the European model (ecmwf) not far behind. The 3 will serve as the forecast consensus
for the remainder of this discussion. Believe the NAM is a tad bit
too warm and aggressive. H925-85 winds are the strongest. Even with
the previous snow event...NAM was the warmer/aggressive outlier. A
forecast consensus averages around a 0.3-0.5 total-precipitation event.

So looking at an advisory-level event. Snows beginning late Tuesday
afternoon into the evening hours will transition to a wintry mix light snow shower
NE towards midnight. While indications of the rain-line creeping north
with enhanced onshore S-flow...the deep snowpack and sub-freezing
ground will likely result rain freezing on the surface. Thinking a
good threshold in where warm-rain would overcome the colder ground
is around 36-degrees. Should see most of the area transition over to
rain as we go towards Wednesday morning...but it is perhaps that north
Massachusetts locales will still experiencing icing with near-freezing temperatures
and remnant deep snowpack.

4) snowfall...

Much of the snow occurring from the late afternoon hours Tuesday
towards midnight Wednesday. Perhaps initially fluffy...snow likely
to maintain a wetter consistency with influx of warmer air within
the low-levels. Thinking 10:1 to 12:1 snow-to-liquid ratios.

Overall did not want to be cute with the snowfall amounts. Looking
an average 2-3 inch snowfall event for most of the area. Some areas
may see higher amounts. Worth noting...this is slightly lower than
what was previously forecast. The most significant change is across
southeast New England. A front-end thump is to be anticipated of snow into
the evening period prior to transition. A combination of onshore S-
flow and thinking a wetter snow with 1:10 ratios has lessened the
amounts on the order of 2-3 inches.

5) sleet and freezing rain...

Again...the threshold for the wintry mix will be set at 36-degrees.
Feel with the lingering Arctic Tundra that surfaces will remain sub-
freezing for slightly longer even as air temperatures warm above the
freezing-mark. Looking at the wintry-mix timeframe around midnight
Wednesday into Wednesday morning during which time there will be a S-
north transition to plain rain as warmer air Ushers in and north aloft.

Per a forecast consensus...expect more sleet than freezing rain...
especially in areas of moderate precipitation where there would be
likely less time residing in the shallow warm-airmass h9-7 aloft per
GFS BUFKIT profiles during the overnight hours. Though there is some
concern towards morning as precipitation begins to become lighter
that areas across the interior at or below 34 degrees would result
in sub-freezing surfaces to freeze with the presence of rain.

So while not by definition freezing rain...icing issues look to
develop by morning once the whole column was just above the freezing-
mark keeping in mind the sub-freezing ground conditions and deep
snowpack we have been enveloped.

Expecting ice accumulations upwards of a tenth of an inch.

6) headlines and impacts...

Based on the forecast consensus...will be going with an advisory for
all areas of responsibility except the islands as it is anticipated
that areas will see at least a trace of a wintry mix comprised of
sleet and freezing rain.

Concern for the Tuesday afternoon and evening commute as snow will
be likely beginning. Slick and slippery travel conditions along with
significantly reduced visibilities. Also concerns for Wednesday morning
especially over the interior with the potential for icing.

*/ Wednesday into late Thursday...

1) highlights...

- renewed over-running event along an offshore cold front
- period of moderate snow...perhaps heavy?
- Greatest impact S of the Mass-Pike...especially S-coast

2) overview...

Cold front sweeping the region Wednesday will stall S and offshore
for the remainder of the period becoming a focus for an elongated
area of low pressure and additional middle-level impulses attendant
with low- to middle-level convergent flow. Deep-layer ascent coupled
with undercutting return S-flow /an isentropic response/ yields a
mainly snow-event especially focused across the S-tier of the
forecast region...more specifically S of Mass-Pike.

3) precipitation outline...

GFS is the colder solution over the regional Canadian / European model (ecmwf).
This far out in the forecast timeframe /d3-4/ will go with a blend
of the forecast solutions and consider this to be the forecast
consensus.

So with that being said...rain could be an issue Wednesday as the
cold front sweeps the region...yet near parallel flow and lacking
dynamics result in a lull across the region. All models indicate a
period of dry-weather for the most part.

The main show kicks off towards evening. As middle-level energy
ahead of the trough pattern aloft digs across the NE-Continental U.S.
Anticipate an enhancement to the offshore elongated low such that
another overrunning event materializes. The isallobaric response
of the wind nets a driving northwest-flow resulting in undercutting
colder air to the over- running event aloft.

Looking at a north-S transition of rain to snow likely to occur more
quickly in areas of moderate precipitation through the quickly
cooling column aloft. It may be perhaps that some locations start
off as snow.

A sharp north-S precipitation gradient with locales along the immediate
S-coast / cape / islands seeing the most with an average of
0.6-0.7 based on the forecast consensus. Along the Mass- Pike...an
average 0.1-0.2 event is advertised...so in-between a roughly
0.3-0.6 event. Sharp gradient an outcome of building ridge of high
pressure rear of the trough pattern aloft and attendant
subsidence.

4) snowfall...

Should the precipitation event remain as mostly all snow...could
be discussing warning-level snows for the immediate S-coast and
islands with advisory levels snows north from there to the Mass-Pike.
There are wobbles with the thermal fields and precipitation amounts.
Exact strength and magnitude of the over-running event are
somewhat in question. Some hint per sref of inch per hour snowfall
rates. Headlines will not be issued at this time...but will focus
on the impacts within the hazardous weather outlook.

*/ Thursday night Onward...

Will prevail with a dry and below normal temperature forecast.
There are subtle hints of continued weather disturbances
prevailing through the continued cyclonic flow pattern across the
region. This along with shots of colder air. Winter does not look
like it is going to end any time soon.

&&

Aviation /04z Tuesday through Saturday/...
forecaster confidence levels...

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

Short term /through Tuesday/...

Overnight...high confidence.
VFR. Northwest gusts gusting to 20-30 knots through 05z-06z across east Massachusetts
will diminish overnight. Scattered shsn across east coastal Massachusetts will end by
07z.

Tuesday...moderate to high confidence.
VFR conditions through at least middle afternoon. MVFR-IFR develop
by late Tuesday afternoon across western Massachusetts/northern CT as light
snow develops.

Kbos taf...high confidence.

Kbdl taf...high confidence.

Outlook...Tuesday night through Friday night...

Tuesday night into Wednesday...moderate confidence.

IFR-vlifr with snow. Possible visibility improvement with transition to
rain...yet could turn soupy with milder air over remnant snowpack.
Breezy S/SW-winds with gusts up to 30 kts possible for coastal
terminals. Snow accums anticipated from 21z Tuesday - 6z
Wednesday. Low confidence on inch per hour snowfall rates.

Wednesday...moderate confidence.

Potential improvement north-S as a cold front sweeps the terminals.
Rain showers may linger. Could potentially be dealing with soupy conditions
with warmer air over the snowpack initially. Winds back west with
passage.

Wednesday night into Thursday morning...moderate confidence.

Focus along the Mass-Pike S. Deteriorating conditions. IFR-vlifr
with snow especially along the S-coast where +sn possible. Inch
per hour snowfall rates will be possible. Breezy N/NW-winds.

Thursday into Friday night...moderate confidence.

Improving conditions towards VFR. Continued west/northwest winds diminishing
under high pressure.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Tuesday/...

Overnight...high confidence.
Have ended gales on all but the eastern outer waters...which
should diminish by around 06z. Extended small crafts overnight...
but winds will diminish further as high pressure pushes east.

Widespread light to moderate freezing spray will continue into
the early morning but should end as winds drop off. Freezing spray
advisory continues.

Tuesday...high confidence. Both winds and seas will relaxed below
Small Craft Advisory thresholds by early morning as high pressure
builds across the waters. However...left over swell will keep
small craft seas going across the outer-waters until the late
morning hours.

Outlook...Tuesday night through Friday night...

Initial disturbance Tuesday night into Wednesday will result in
near gale-force S/SW-winds. Seas to build 6-8 feet on the outer
waters. Visibility will be restricted at times due to snow
initially Tuesday night and likely fog as warmer air pushes north over
the colder waters as we go into Wednesday. Not thinking gale-force
warnings at this time...feel gales will only mange an hour or two
becoming a low- risk.

Visibilities will still be rough along with seas. A cold front
sweeps into the waters Wednesday...stalling over the S-waters
Wednesday night into Thursday becoming a focus for snow. Will see
west/NW-winds increase along with the likelihood of light freezing
spray.

Improvement begins by Thursday night as weather is pushed out to
sea behind which high pressure builds into the region to allow
both winds and seas to relax.

&&

Box watches/warnings/advisories...
CT...Winter Weather Advisory from 3 PM Tuesday to 10 am EST
Wednesday for ctz002>004.
Massachusetts...Winter Weather Advisory from 3 PM Tuesday to 10 am EST
Wednesday for maz002>022-026.
Rhode Island...Winter Weather Advisory from 3 PM Tuesday to 10 am EST
Wednesday for riz001>007.
Marine...Small Craft Advisory until 6 am EST Tuesday for anz231-232.
Small Craft Advisory until 3 am EST Tuesday for anz233-234.
Freezing spray advisory until 8 am EST Tuesday for anz231-250-
251.
Small Craft Advisory until 5 am EST Tuesday for anz235-237-251.
Gale Warning until 1 am EST Tuesday for anz250-254.
Small Craft Advisory until 11 am EST Tuesday for anz255.
Small Craft Advisory until 7 am EST Tuesday for anz256.

&&

$$
Synopsis...dunten/sipprell
near term...dunten/sipprell/evt
short term...dunten
long term...sipprell
aviation...dunten/sipprell
marine...dunten/sipprell/evt

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