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Area forecast discussion
National Weather Service Taunton Massachusetts
541 PM EST sun Jan 22 2017

Synopsis...
moist onshore winds will result in spotty light rain/drizzle
tonight. Subfreezing temperatures are expected across the high
terrain of Massachusetts. This will result in the risk for spotty
light freezing rain/drizzle across this area. A significant storm
will reach the East Coast late Monday and move up the coast Monday
night and Tuesday. This will bring a mix of rain and/or snow along
with a period of icing well inland. The storm may also bring
damaging winds to the coast and the coastal waters. High pressure
then brings dry and mild weather Wednesday into Thursday. A cold
front will cross New England late this week, followed by
seasonably cold temperatures and blustery winds next weekend.

&&

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

440 PM update...

Backdoor cold front with associated wind shift to the northeast
along with low clouds and cooler temps thru much of eastern-central
Massachusetts and Rhode Island. However still not thru wst/ijd and hfd where temps
remain in the low to mid 50s!

Behind the front cooler airmass along with low clouds and increasing
northeast winds. Area of light rain over greater Boston area will
continue to advect southward but expecting light spotty rain/drizzle
to develop with increasing onshore flow...especially east slopes of
Worcester Hills and the Berkshires.

This is area of greatest concern. Hi res guid has temps across the
high terrain of Massachusetts falling to below freezing tonight. Thus risk of
icing from light freezing rain/drizzle. All guidance has light
measurable precip so confident that at least a few locations in the
high terrain will see at least some icing. Although less confident
how widespread precip will be tonight. Thus instead of issuing a
Freezing Rain Advisory opted for a Special Weather Statement to
increase public awareness.

Otherwise lower elevations including the valleys and coastal plain
including the urban areas will remain above freezing. Thus no
concerns here. Cooler tonight with lows in the 30s but still above
normal. However increasing NE winds with gusts up to 30 mph by
morning will provide cooler wind chills.

&&

Short term /6 am Monday morning through Monday night/...

Updated 440 PM...

Monday...

Models have slowed down onset of steady/heavier precip until late in
the day Monday and possibly not until early Mon evening. This is due
to northern stream short wave moving across Quebec into New
Brunswick. This keeps deep layer ridge over Massachusetts/Rhode Island and CT much of the
day. This will result in dry air in the mid and upper levels of the
atmosphere overspreading the area. This includes the snow growth
region. This combined with increasing moist onshore flow will result
in an abundance of low level moisture and will likely yield spotty
light rain/drizzle much of the day. Therefore not expecting much if
any snow and/or sleet until possibly late in the day.

Much cooler day tomorrow with highs only in the 30s (seasonably
cold) to around 40 along the immediate coast. Concern again is
across the high terrain where temps may not get much above freezing.
Thus low risk for spotty light freezing drizzle across the high
terrain of Massachusetts.

Winds will be on the increase as low level jet approaches. By sunset
should see NE winds gusting up to 40 to 50 mph along the South Coast
including Cape Cod and islands.

Monday night...

Deep layer moisture and lift overspread the area Mon night as
southern stream closed low comes rolling up the eastern Seaboard.
70+kt low level easterly jet off the Atlantic acts as a firehose
into the region Mon night. This combined with the likelihood of a
coastal front developing over eastern Massachusetts will result in a period of
very heavy rainfall. Good model agreement on a period of very heavy
rain over Rhode Island and eastern Massachusetts 06z-12z Tue with global guidance
offering qpf up to 1.5 inches over this region. As you expect the
high res guid is even heavier. Thus risk of significant
street/Highway/urban flooding along with small rivers and streams
across Rhode Island and eastern Massachusetts. This supports our current Flood Watch area
and reasoning.

Farther inland very impressive warm nose above 850 mb with temps in
this layer warming to +5c or so depending on model of choice. This
will limit snowfall potential and have lowered snowfall forecast
after collaborating with wpc. However below 850 mb there is a cold
layer with temps as cold as -6c to -8c across northwest Massachusetts depending
on model of choice. This will likely result in a period of freezing
rain across the high terrain of Massachusetts especially western Massachusetts. Somewhat
concerned that there is a low risk of ice accretion reaching or
exceeding 0.50 inch. However surrounding offices including wpc were
not as confident and thus have opted to go with a Winter Weather
Advisory for Monday night into Tue morning. Although will have to
watch this area for potential upgrade to a warning if forecast
confidence increases with time. Until then expect a winter mix of
snow and sleet Monday evening changing to freezing rain across the
high terrain with greatest risk of significant icing over northwest
Massachusetts.

Very strong winds remain in the forecast for Cape Cod and the
islands where sustained winds of 40+ mph and gusts near 60 mph are
likely. This is in response to a powerful 70+ kt low level easterly
jet moving across this region. More marginal for these high wind
speeds along the eastern Massachusetts coastline thus have continued the high
wind watch for those areas. May eventually need a Wind Advisory for
slightly lower wind speeds all areas including the high terrain as
model soundings show wind gust potential up to 50 mph.

Mild along the coastal plain as low level jet floods this region
with maritime airmass and temps in the 40s. Low level cold air will
remain entrenched northwest of i95 given cad signature with high
pressure over Quebec and pressure falls to our south and east.

&&

Long term /Tuesday through Sunday/...

Overview...
cutoff 500 mb low pressure and its nearby surface low will slowly
work up the eastern Seaboard during Tuesday. The low will shift
east-NE during Tue, with high pressure ridge building across Wed with
dry and mild conditions as winds back to SW.

12z models have some differences with approaching cold front,
along with NE-SW oriented long wave 500 mb trough that will slowly
cross the region late Thu or Fri. Noting differences in how
individual models handle any possibility of light precip moving
across as the front approaches. Cutoff 500 mb low sits across Hudson
Bay into northern Quebec, which will help drive the upper system
through late this week as 500 mb heights lower while another short
wave begins to shift southeast out of Manitoba late week.

Once the upper system moves offshore, seasonably cold air pushes
in, but it will be blustery late Fri through next weekend as
another reinforcing shot of colder air works in on the northwest flow at
the surface and aloft.

Details...

Tuesday...
strong east winds will continue through midday Tuesday, highest
across coastal areas. The strongest winds will occur Tue morning.
Then, the low level jet associated with the strong winds will
shift east during the day, so the surface winds will diminish.

With the surface system trapped in the upper level cutoff flow,
will see more steady rainfall across eastern mass, with another
0.50" or so of rainfall across Cape Ann likely during Tue. Will
also see mixed rn, ice pellets and patchy freezing rain across the higher inland
terrain linger early Tue, but should change over to rn by around
midday. May see a mix back to freezing rain/ice pellets Tue evening as the precip
tapers off Tue evening over the higher terrain. The steady rain
and patchy fog should exit east coastal areas after 07z Wed or so.

The low should cross Nantucket and the Outer Cape Tue evening,
while the cutoff upper system moves in tandem, passing near or
just S of the 40n/70w benchmark. Winds will back around to north by
Tue evening, with gusty winds across Cape Ann lingering.

Quite a wide range in temps forecast for Tue. Highs from 35-40
across the north central and west mass and the higher inland terrain to
around 50 on the S coast. Readings then will fall back Tue night
as colder air starts to work in. Temps bottom out in the mid 20s
to around 30 across central and western areas, ranging to the mid
and upper 30s along east coastal mass.

Wednesday-Thursday...
high pressure ridge at the surface and aloft crosses the region
Wed. As the ridge shifts east Wed night and Thu, may see scattered
rain and/or snow showers move in across the east slopes of the
Berkshires ahead of approaching weak cold front. Some timing
differences on both the frontal passage as well as how far S any
precip reaches Wed night or Thu. Temps will top off in the 40s
both days, though they will start to fall to more seasonal levels
Thu night as colder air starts to work in from Canada.

Friday through Sunday...
northwest winds at the surface and aloft will usher in seasonable
temperatures for late January. Should remain mainly dry, but may
see some widely scattered snow showers over the east slopes of the
Berkshires. Otherwise, should see mainly dry but blustery
conditions during this timeframe. Some question about whether
there may be a quick passing weak low and trough late in the
weekend that might bring some light precip, but held off on this
feature for now.

&&

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

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

Short term /through Monday night/...moderate confidence thru this
period.

Thru 00z...

Trend will be toward MVFR/IFR from northeast to southwest as
backdoor front moves into the region. Any precip will be light
and spotty along with above freezing temps. Light northeast winds.

After 00z...

Mainly MVFR with marginal IFR around 00z. Light spotty
rain/drizzle. Concern is across the high terrain including korh
where temps drop to near freezing yielding potential for light
spotty freezing rain/drizzle. Elsewhere in the lower elevations
temps remain above freezing. NE winds increase overnight up to 35
kt along the South Coast of Massachusetts and Rhode Island.

Monday...

MVFR with spotty light rain/drizzle...possibly freezing
rain/drizzle high terrain. Steady precip holds off until 21z-24z
from south to north. Strong northeast winds with gusts up to 50 kt
by late in the day across Cape Cod and islands.

Monday night...

MVFR/IFR in periods of heavy rain and strong winds across much of
the region with snow/sleet and freezing rain likely high terrain
especially northwest Massachusetts.

Kbos taf...moderate confidence in taf. Greatest uncertainty
concerns areal coverage of light precip.

Kbdl taf...moderate confidence in taf. Greatest uncertainty
concerns areal coverage of light precip.

Outlook /Tuesday through Friday/...moderate confidence.

Tuesday...

MVFR-IFR ceilings/vsbys, with lowest conditions across central and east
mass into Rhode Island. Expect mainly -ra across the coastal plain and lower
CT valley, with mixed -ra/-ip across north central and west mass into far
northwest CT early Tue, then should change over to all -ra from S-north as
temps increase to above freezing. Areas of fog. May see a mix with
freezing rain across highest terrain of North Worcester County and the east slopes
of the Berkshires toward Tue evening as temps fall below freezing
again. Expect ceilings/visibilities to improve to VFR across central and
western areas from 06z-09z.

Precip should taper off across S and west areas by around midnight,
though spotty rain/fzra/fog may linger briefly after midnight.
Remainder of the -ra across eastern areas should end by 07z-09z.

East-NE winds gusting up to 25-30 kt inland, then up to 45-50 kt
across Cape Ann and Outer Cape cod Tue morning which will slowly
diminish by around midday. Gusts linger at around 25 kt through
the afternoon around Cape Ann and moving across Cape Cod Tuesday
night as winds back to north.

Wednesday...
VFR. An approaching cold front may bring a period of MVFR
ceilings/visibilities in -shra/-shsn late Wed/Wed night across the east slopes
of the Berkshires. Low chance for isold -shra and patchy fog
across the Route 2 corridor of north mass. Northwest winds gusting up to 25
kt on Outer Cape cod and the islands early Wed, then diminishing.

Thursday-Friday...
mainly VFR. Patchy MVFR ceilings linger across north central and west mass
Thu, along with sct rain showers/shsn with local MVFR visibilities Thu. SW winds
gusting up to 20 kt on Outer Cape cod and the islands Thu, then up
to 25 kt Thu night into Friday.

&&

Marine...
forecaster confidence levels...

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

*** Storm force wind gusts Monday night into early Tue ***

440 PM update...

Tonight...

Increasing NE winds overnight with speeds reaching 25-30 kt by
morning except up to 35 kt along the South Coast. Vsby reduced at
times in areas of fog and drizzle.

Monday...

NE winds continue to increase to near 50 kt by sunset along the
southern waters...35 to 40 kt elsewhere. Vsby reduced at times by
drizzle and fog. Steady rain holds off until sunset across southern
waters...later elsewhere.

Monday night...

The brunt of the storm is Mon night with east-northeast winds up to 55 kt.
Strongest winds over eastern Massachusetts waters including Cape Cod and
Nantucket waters. Very heavy rain with isolated thunder possible.
Vsby reduced to less than a mile at times in fog and heavy rain.

Outlook /Tuesday through Friday/...moderate confidence.

Tuesday...
low pressure moves across Cape Cod Tuesday morning. East wind gusts
up to 50-55 kt on the eastern open waters early Tue, diminishing
Tue afternoon as winds back to north. Seas up to 25 to 30 ft early,
subsiding to 12-18 kt Tue evening. Rough seas will continue Tue
night as northwest winds continue to diminish. Visibility restrictions
in rain and patchy fog into Tue night, then improving from S-N.

Storm warnings continue from Monday afternoon through Tuesday
morning. This covers all waters except Boston Harbor and
Narragansett Bay, where gale warnings remain in effect.

Wednesday through Friday...
northwest winds on Wed shift to west-SW Thu and continue on Fri. Gusts up
to 25-30 kt continue across most of the waters with seas remaining
at or above 5 ft. Seas may linger around 5 ft during Wed at the
outer entrance to Boston Harbor, otherwise winds and seas diminish
below small craft criteria on Boston Harbor and Narragansett Bay.

&&

Tides/coastal flooding...

440 PM update...

Still looking at potential minor with pockets of moderate coastal
flooding along east Massachusetts coast during high tide Tue morning.

Despite low astronomical tides (8.2 ft at Boston Mon evening and
9.4 ft Tue morning), combination of persistent and very strong east
winds and high seas up to 20-30 ft offshore may lead to minor to
perhaps pockets of moderate coastal flooding with Tue morning high
tide. Surge guidance has values around 2.5 ft at the time of high
tide along with very strong wave action with seas 20-30 ft across
the eastern Massachusetts waters. This wave action ontop of the elevated storm
tide will likely be sufficient for a risk of minor coastal flooding
with a lower risk of moderate flooding. Still 36-48 hrs away and a
difference in 6 hrs of timing the strongest winds can have a big
impact on flood potential. Thus most likely scenario is a coastal
flood advisory event. Thus will hold off on any watches at the
moment.

&&

Box watches/warnings/advisories...
CT...Winter Weather Advisory from 4 PM Monday to 7 am EST Tuesday
for ctz002.
Massachusetts...High Wind Warning from 9 am Monday to 6 am EST Tuesday for
maz022>024.
Flood Watch from Monday afternoon through Tuesday morning for
maz005>007-013>021.
High wind watch from Monday afternoon through late Monday
night for maz007-018-019-021.
Winter Weather Advisory from 4 PM Monday to 7 am EST Tuesday
for maz002>004-008-009.
Rhode Island...High Wind Warning from 9 am Monday to 6 am EST Tuesday for
riz008.
Flood Watch from Monday afternoon through Tuesday morning for
riz001>007.
Marine...Storm Warning from 1 PM Monday to 4 am EST Tuesday for anz231-
232.
Storm Warning from 1 PM Monday to 3 am EST Tuesday for anz233-
234.
Gale Warning from 7 am Monday to 7 am EST Tuesday for anz230.
Gale Warning from 3 am Monday to 4 am EST Tuesday for anz236.
Storm Warning from 7 am Monday to 2 am EST Tuesday for anz235-
237.
Storm Warning from 11 am Monday to 7 am EST Tuesday for anz250-
254.
Storm Warning from 2 PM Monday to 6 am EST Tuesday for anz251.
Storm Warning from 4 am Monday to 4 am EST Tuesday for anz255-
256.

&&

$$
Synopsis...nocera/evt
near term...nocera

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