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Area forecast discussion 
National Weather Service Taunton Massachusetts
717 PM EDT Mon Oct 24 2016


Winds become blustery out of the west/northwest beneath a cool, dry airmass
which continues through midweek. Some of the coldest air of the
season impacts the region Wednesday into Thursday. Quite cold
Thursday morning, this prior to a strong storm system into Friday
which may bring a period of wintry weather prior to moderate to
heavy rain along with gusty winds. Another shot of wet weather
late Saturday into Saturday night, then possibly again early the
following week. Overall an active, cooler than average weather
pattern is advertised.


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

7 PM update...

Cyclonic flow persisting round which the boundary layer remains
well mixed contributing to the mix down of gusty northwest winds to the
surface and drier air. While mixing will become limited, gusts
upwards of 30 mph remain possible overnight acorss the high terrain
as well as over the warmer ocean waters and immediate coastline.
Such winds will limit frost development. Dewpoints down into the
20s contributing to low relative humidity, lows should easily drop
down into the 30s with the cold air advection. Down into the 20s
over the high terrain. Overall roughly 5 to 10 degrees colder when
you factor in the wind.

Also seeing fetch off the lakes yielding a scattered to broken
cloud deck into the west zones, dissipating with downsloping into the
CT River Valley. This too should dissipate with limited mixing


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


Expecting another day of gusty west to northwest winds to develop
by mid morning. Some diurnal clouds develop, too. More clouds
should be along the coast, and over the ocean, where the humidity
is more favorable.

High temperatures should be about 10 degrees below normal.

Tuesday night...

Anticipating the start of a rather cool, if not cold, period.
Northwest winds should be still be blowing, so not thinking frost
will be the real concern. Instead, looking more at freezing to
subfreezing temperatures across portions of southern New England.
Will hoist a freeze watch where there is moderate confidence for a
potential freeze, and the growing season has not already ended.
Farther inland, we would expected those same conditions, even
though no watch will be issued.


Long term /Wednesday through Monday/...

*/ highlights...

- coldest temperatures of the season Thursday morning possible
- winter-weather threats possible with onset of storm Thursday
- transitioning to flooding threats with heavy rain into Friday
- another shot of wet weather into the weekend, maybe early week
- overall pattern of cooler-than-average temperatures

*/ overview...

Looking at the bigger picture. Last week saw impressive warmth as a
fair number of teleconnections were in a near-neutral state. The 500 mb
pattern relatively flat with some slight ridging gave US a period of
above-average temperatures and record warmth. That has all changed.

A cooler than average, active weather pattern lies ahead. Roughly 3
features Worth noting: 500 mb lows over the Bering straight, NE Pacific,
and the north Canadian Maritimes. Round these more stable features over
the north hemisphere, energy is promoting both an amplified and somewhat
buckled pattern. In particular with respect to the NE Continental U.S. Cyclonic
flow prevails round the base of which individual impulses undergoing
amplification are promoting deepening areas of surface low pressure
over the forecast area. With the Madden-Julian oscillation forecast
into phase 8 as the ao/nao/epo phases have shifted negative, there
are several signals indicating that the Arctic door is open for
business allowing colder air to spill S and overall temperatures
into early November to be below-average. As the previous forecaster
mentioned, the Labrador trough downstream of which there is a
combination of favorable ridging and weak blocking.

*/ Discussion...

Bringing it home. Initially a shot of some of the coldest air of the
season. 850 mb temperatures around -8c by Wednesday morning. Very steep
lapse rates, looking at temperatures well-below average with breezy
northwest flow. Luckily abundant sunshine but still it is going to feel
cold. Clouds on the increase into Thursday morning, it becomes a
question as to whether radiational cooling proceeds which could
knock out a fair number of forecast areas still observing a growing
season. A majority of the overnight period Wednesday night into
Thursday morning with light winds and clear conditions, will go with
lows down into the 20s for many locations, but again, on the cusp of
that all changing is if mid to high clouds move in faster.

Thereafter, looking at 3 shots of disturbed weather: Thursday into
Friday, late Saturday into Saturday night, and possibly again early
next week. Focusing on the first two:

Thursday into Friday...

Storm characteristics similar to a Miller-b undergoing rapid cyclo-
genesis beneath a deepening 500 mb closed low. Strong frontogenetical /
isentropic lift ahead of the low with accompanying strong mid to
upper level forcing and favorable venting, along with a measure of
instability. Looking at a good forward-thump of rain exacerbated by
strong low to mid level moisture convergence in response to the deep-
layer forcing. Thunder possible given instability with higher thetae
slipping in aloft within a moist-adiabatic / conditionally unstable
atmospheric profile.

With onset, cold air damming, even drier air, may not only delay the
storm but also invite some initial mixed wintry precipitation. The
details will be ironed out with time but agree with the previous
forecaster: one can get burned by the isallobaric component of the
wind when out of the north. Promoting less veering of winds within the
interior valleys results in colder air holding in longer rather than
scouring out. Warmer air proceeds above a shallow inversion of cold
air trapped in a valley, concerns grow as freezing rain is possible.
It will be very cold Wednesday and dewpoints are low. We'll have a
better idea as more high-res forecast guidance becomes available to
capture such small-scale processes. Timing difficult given fly in
the ointment of drier air. Would expect with the fast movement of
the low center that shallow cold air should scour out, especially as
the low sweeps across the interior valleys, as presently forecast.

Expect threats to transition towards moderate to heavy rain with
time and given Leaf-clogged drains and flooding that just occurred
over central portions of New England, there are underlying flooding
concerns. Potential for faster momentum to mix down to the surface
with heavy rain, gusty S winds. As the storm lifts out and occludes,
trowaling rearward and wet-bulb-zero values falling to at or below
freezing, likely contending with wet-snow again for the high terrain
mainly north/west and on Friday.

Multiple headlines may be needed but too early to say exactly what
and when just yet. Will go with a mention in the hazardous weather
outlook for the potential of urban, poor drainage flooding. A quick
shot of breezy winds and cooler air immediately behind the system
dampening with mid-level ridge building across the region Friday
night into early Saturday.

Late Saturday into Saturday night...

A lull prior to a quick follow-up clipper-like disturbance. Moderate
confidence given recent swings in forecast guidance. Another shot of
wet weather is possible along with the possibility of some wet snow
for the higher terrain given wet-bulb-zero heights. Front-end thump
with a majority of the isentropic / frontogenetic forcing collocated
ahead of the accompanying sweeping cold front to the surface low.
But so far out in the forecast, nothing yet sampled, wanting to hold
off on any further details. Behind this system it would appear given
the broader pattern that another shot of blustery winds will usher
colder and drier air S.

Early next week...

Still a lot of uncertainty. Either a Continental polar airmass with
an accompanying cold front drops S (per ec) or a warm front lifts north
across the region (per gfs). Continued low confidence but err to a
cooler than average, active pattern given teleconnections.


Aviation /00z 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 night/...

0z update...

VFR. Scattered-broken low-end cigs. Gusty west/northwest winds with gusts up to 30
kts for high terrain and coastal terminals. Roughly around 25 kts
elsewhere. A gradual diminishing trend overnight through Wednesday

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Wednesday through Saturday/...moderate confidence.


VFR. Breezy northwest winds diminishing and becoming north into evening. Gusts
up to 25 kts during the early half of Wednesday.

Thursday into Friday...

Lowering and thickening cigs down to IFR-LIFR centered around
Thursday night. Initial snow/ice pellets possible with potential accompanying
low level wind shear threats transitioning to -ra/rain with embedded +ra, possible
thunderstorms and rain mostly S/se. Blustery S/southeast winds. Gusts up to 30 kts along the
immediate shoreline terminals. Improving late Friday with winds
turning out of the west.


Brief period of VFR before conditions return low-end VFR to MVFR
with another chance of -ra/ra.



Forecaster confidence levels.

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

Short term /through Tuesday night/...high confidence.

7 PM update...

Northwest winds with gusts up to 30 kts through Tuesday subsiding as we
go into Tuesday night. By this point will also see the dampening
of wave heights. Small craft advisories in effect throughout much
of the forecast period with seas on average around 5 to 7 feet.

Outlook /Wednesday through Saturday/...moderate confidence.


Seas remaining rough with persistent northwest winds becoming north with time
and dissipating. Wave heights gradually diminishing below 5 feet
towards the later half of the day.

Thursday into Friday...

Rain on the increase through Thursday, moderate to heavy at times
with the possibility of thunderstorms. S/southeast winds strengthening
ahead of a deepening area of low pressure across the region. Seas
building 8 to 10 feet the height of which will be on Friday, slowly
dropping off thereafter as winds turn out of the west behind a cold
front but remain breezy.


Breezy west winds continue as there is a brief lull in the weather.
Seas remain above 5 feet on a good chunk of the waters as winds
increase once again along with wet-weather late Saturday into
Saturday night.


Box watches/warnings/advisories...

CT...freeze watch from late Tuesday night through Wednesday morning
for ctz003.
Massachusetts...freeze watch from late Tuesday night through Wednesday morning
for maz006-007-013-014-018.
Rhode Island...freeze watch from late Tuesday night through Wednesday morning
for riz001-003-006.
Marine...Small Craft Advisory until 2 am EDT Wednesday for anz230>232-
Small Craft Advisory until 8 PM EDT Tuesday for anz233-234-236.
Small Craft Advisory until 6 am EDT Wednesday for anz250-



near term...Belk/sipprell
short term...Belk
long term...sipprell

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