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Area forecast discussion 
National Weather Service Taunton Massachusetts
946 PM EST Thursday Jan 29 2015

Synopsis...
a clipper low pressure will move into the Great Lakes tonight
with a secondary low developing along the southern New England
coast and intensifying over the Gulf of Maine Friday into Friday
evening bringing with it a period of snow for the forecast area.
Blustery and very cold conditions are expected this weekend.
Watching for the potential of noreasters next week...one possible
Sunday night into Monday and another possible Wednesday night
into Thursday. Low confidence on both.

&&

Near term /until 6 am Friday morning/...
945 PM update...
00z aly sounding still very dry in low levels so despite light
refelectivity moving across southern New England...precipitation is mostly aloft. NAM
shows low levels moistening 03-06z. Expect light snow developing
03-06z western half new eng and 06-10z in the east.

Latest NAM/rap are slightly cooler in the low levels and with
generally light winds not allowing much advection of warmer surface
temperatures away from the islands...expect a mix of rain/snow to be
confined to cape/islands toward daybreak...with mostly rain on
the islands where southerly winds will be a bit stronger.

An inch or two is possible by daybreak across CT/western-central
Massachusetts to a dusting to less than an inch over Rhode Island and eastern Massachusetts.

Calm winds and radiational coolding has allowed temperatures to fall to
upper teens to lower 20s across portion of southeast coastal Massachusetts and Cape
Cod/mvy. Temperatures will rise quickly into the 30s on the islands when
S winds nicrease. Note bid is 34 with a S wind 10 kts.

&&

Short term /6 am Friday morning through Friday night/...
*** plowable snowfall likely for much of north-northeast Massachusetts ***

Forecast was based on a model blend given good clustering amongst
the models regarding their mass fields...quantitative precipitation forecast and thermal.

Amplifying northern stream trough takes on a negative tilt late Friday
and then evolves into a closed middle level over southern New England.
This strong forcing aloft results in parent low over New York state
fading/filling and giving way to cyclogenesis along or just off the
southern New England coast Friday. This robust middle/upper trough results
in secondary low pressure deepening to about 985 mb over the western
Gulf of Maine 12z Sat. In addition the middle/upper low captures the
surface cyclone and pulls it back briefly toward eastern Massachusetts
coastline late Friday night into Sat. This slows the system down and
results in a robust comma-head developing Friday night over northeast
Massachusetts possibly westward into Worcester County.

As middle level trough transitions from an open wave to a closed
circulation Friday night over eastern Massachusetts a modest snow band will likely
develop. Also uncertainty on exactly where these bands setup and
intensity. However model consensus quantitative precipitation forecast yields 0.5-0.6 inches over
northeast Massachusetts...possibly westward into Worcester County. Therefore
have upgraded to a Winter Storm Warning for Essex and Middlesex
counties. Later shifts may have to expand the warning westward into
Worcester County pending 00z model trends. Given the banding
signature and model consensus quantitative precipitation forecast expanded advisories into southern
Worcester/northeast CT/northern Rhode Island into northern Bristol County of
Massachusetts for 2-4 inches of snowfall.

Thought process was snowfall may fall just short of warning and/or
advisory criteria but realizing any additional snowfall will be
problematic regarding snow removal especially in the urban areas
that received 30+ earlier this week. Also additional snowfall may
result in snow Load/stress to roofs. Therefore our warnings and
advisories are somewhat based on impacts too.

Ptype...all snow most of the area expect South Coast of Massachusetts and Rhode Island
including Cape Cod and the islands where rain or a rain/snow changes
back to all snow Friday evening.

Fog? May need to monitor for the potential of warm/moist air over
the deeper snowpack to result in dense ground fog. Areas across
east/southeast Massachusetts which saw considerable amounts of snow would /climatologically-
speaking/ expect to be socked in conditions when a warm/humid
airmass spreads across the region. Will have to monitor closely.

In addition to the snowfall Friday night north and eventually northwest
winds will increase to 35 to 45 miles per hour as low intensifies east of Massachusetts.
Dangerously cold wind chills of 10 to 20 below zero in higher
terrain of central and west Massachusetts...with 5 to 10 below in the coastal
plain. Wind chill advisories may be needed for higher terrain in
central and west Massachusetts. Looks borderline so did not hoist any headlines
there. Later shifts will need to reevaluate.

&&

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

* snow ends across eastern areas early Saturday followed by Arctic
high pressure for the rest of the weekend
* watching for potential noreasters next week

An active weather pattern will continue across southern New England.
Ocean storm off the Maine coast on Saturday will exit to the east...
bringing an end to any snowfall across coastal locales Saturday
morning. Improving conditions will occur during the day on a
blustery northwest wind flow as a cold airmass moves into New England from
Canada. This will ensure a very cold weekend with temperatures running well
below average.

The synoptic pattern next week will feature shortwaves diving into
the upper Midwest and across New England. This will allow for
potential noreasters to develop. However, much will depend on how
sharp the troughs become...whether they become negatively tilted and
phase or not with southern stream energy.

There have been model differences from both GFS/European model (ecmwf) in terms of
the strength and track of the lows so will follow a blended model
approach. The timing of these potential systems looks to be Sunday
night and Monday and again Wednesday night through Thursday. These
are the periods to monitor for potential high impacts to the area.
Whether or not we receive significant additional snowfall or these
ocean storms miss US to the east is just too tough to say with any
degree of confidence. So stay tuned.

For the Sun night-Monday low...both the operational 29.12z GFS and
European model (ecmwf) runs have the low center passing just outside the benchmark
which would mean a glancing blow to southeastern New England...but
still a plowable snowfall to eastern areas. However, a few ensemble
members are further northwest with the low track...so a more
significant impact is a possibility...as is no impact if the low
were to track even further off shore. The first runs of the
operational European model (ecmwf) for the blizzard of 2015 didn't show major impacts
to New England until 72 hour in advance of the event. We are still
outside of this window...so lots can change.

Tuesday will be a lull day if the aforementioned low impacts New
England. Then we look to yet another potential ocean storm middle
week...with models centering on the Wednesday night-Thursday timeframe. The
29.12z operational European model (ecmwf) is aggressive with this low...slamming
heavy snows over the interior with a snow to rain scenario for the
coast. However, the GFS does not phase the northern and southern
streams...so is progressive and shows minimal impacts. So used a
model blend and...once again...too early to bank on either a hit or
a miss. Certainly a lot to monitor closely in the days ahead!

&&

Aviation /03z Friday through Tuesday/...
forecaster confidence levels...

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

Short term...through Friday night...moderate confidence.

0z update...

Tonight into Friday night...

Ceilings lower MVFR / IFR with S-draw of air advecting marine stratus
onshore as -sn begins to envelop the terminals west to east mixing /
changing to rain along the immediate S/se-coast including the cape
and islands. Tailored deteriorating conditions towards the midday
into late-afternoon period. Highlighted the worst of anticipated
conditions with IFR visibilities. Going to have to watch closely the
S-draw of warm/moist air over deep snowpack. Could see conditions
become socked in with an appreciable ground fog just above the
snow.

Should see improvement into evening as winds shift out of the northwest
gusting 25-30 kts allow conditions to improve VFR.

Kbos taf...moderate confidence...but lower confidence on exact
timing of snow and lower cigs/vsbys.

Kbdl taf...moderate confidence...but lower confidence on exact
timing of snow and lower cigs/vsbys.

Outlook /Saturday through Monday/...

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

Sunday night-Monday...low confidence. Low pressure develops S of the
region...but track remains uncertain. Too early to have any
confidence on VFR or IFR this period.

Tuesday...moderate confidence. If low impacts the terminals Monday,
conditions would be improving on Tuesday.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday/...high confidence.

7 PM update...no major changes.

Tonight...increasing southerly winds expected ahead of low pressure
moving through the Great Lakes...but wind gusts should remain below
Small Craft Advisory.

Friday...southerly winds will shift to west then northwest during Friday
afternoon...with gusts to 25-30 knots developing across Rhode Island coastal
waters by late afternoon.

Friday night...low pressure intensifies over western Gulf of Maine with
widespread north-northwest gales. Snow reduces visibility as well.

Outlook /Saturday through Monday/...moderate confidence

Saturday night...winds and seas will diminish as low pressure
departs the area.

Sunday...expect winds to diminish but remain at small craft
levels...though some gale gusts may linger on the eastern outer
waters early. Seas will slowly subside...but will remain at or above 5 feet
on the outer waters.

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

&&

Box watches/warnings/advisories...
CT...Winter Weather Advisory until 6 am EST Saturday for ctz004.
Massachusetts...Winter Weather Advisory until 6 am EST Saturday for maz004-012-
013-015>019.
Winter Storm Warning until 6 am EST Saturday for maz005>007-
014-026.
Rhode Island...Winter Weather Advisory until 6 am EST Saturday for riz001.
Marine...Gale Warning from midnight Friday night to 6 PM EST Saturday
for anz230>234-251.
Gale Warning from 2 am to 1 PM EST Saturday for anz236.
Gale Warning from 9 PM Friday to 6 PM EST Saturday for anz235-
237.
Gale Warning from 11 PM Friday to 6 PM EST Saturday for anz250-
254-255.
Gale Warning from 7 PM Friday to 6 PM EST Saturday for anz256.

&&

$$
Synopsis...nocera/gregoria
near term...kjc
short term...nocera
long term...gregoria
aviation...nocera/sipprell/gregoria
marine...nocera/gregoria

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