Area Forecast Discussion
Issued by NWS Boston, MA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KBOX 250319

Area Forecast Discussion
National Weather Service Taunton MA
1119 PM EDT Mon Oct 24 2016

Blustery west to northwest winds beneath a cool, dry airmass
will continue 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.



1050 PM Update...

large low pressure across the Canadian Maritimes continues to spin
cold air across the region at 02Z, as well as bands of low and mid
level clouds across northern and central Mass. Dewpts have lowered
to the upper 20s to mid 30s across the region, a bit lower than
previously forecast. Downsloping winds have caused the clouds to
dissipate for the most part across central and southern areas
this evening.

Will still see some bands of mid clouds cross the region in the
W-NW flow at the surface and aloft, otherwise expect partly cloudy
skies on average overnight. With continued W-NW winds, even as
temps fall back through the 30s across most areas, except 40-45
across outer Cape Cod and the islands. Frost will be limited as
winds will continue to stir though not quite as strong as this
afternoon. Will see gusts up to around 20 kt mainly across the
higher terrain and along the immediate coast, though should
diminish somewhat overnight.

Have updated near term forecast to bring conditions current.




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.


*/ 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 H5
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: H5 lows over the Bering Straight, NE Pacific,
and the N Canadian Maritimes. Round these more stable features over
the N Hemisphere, energy is promoting both an amplified and somewhat
buckled pattern. In particular with respect to the NE CONUS 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. H85 temperatures around -8C by Wednesday morning. Very steep
lapse rates, looking at temperatures well-below average with breezy
NW 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 H5 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 N. 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 N/W 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 N
across the region (per GFS). Continued low confidence but err to a
cooler than average, active pattern given teleconnections.


Forecaster Confidence Levels.

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

Short Term /through Tuesday Night/...

11 PM update...

VFR. Mainly FEW clouds at 5-7kft, except SCT-BKN at times across
NE Mass and outer Cape Cod. W-NW winds gusting up to 25 kts across
higher terrain and coastal terminals, gradually diminishing
overnight through Wednesday morning.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Wednesday through Saturday/...Moderate confidence.


VFR. Breezy NW winds diminishing and becoming N 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 SN/IP possible with potential accompanying
LLWS threats transitioning to -RA/RA with embedded +RA, possible
TSRA mostly S/SE. Blustery S/SE winds. Gusts up to 30 kts along the
immediate shoreline terminals. Improving late Friday with winds
turning out of the W.


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.

11 PM update...

Noted S-SE swells up to 6-8 ft across the outer waters, highest
from E of Cape Cod to the southern waters. Gusts up to around 30
kt at buoys 44017 and 44018 at 02Z.

NW winds will continue to gust up to 25-30 kt through Tuesday,
then gradually diminish Tuesday night. Seas will remain up to 5-7
ft, occasionally up to 8 ft on the outer waters. Small craft
advisories remain in effect.

Outlook /Wednesday through Saturday/...Moderate confidence.


Seas remaining rough with persistent NW winds becoming N 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/SE 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 W behind a cold
front but remain breezy.


Breezy W 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.


CT...Freeze Watch from late Tuesday night through Wednesday morning
     for CTZ003.
MA...Freeze Watch from late Tuesday night through Wednesday morning
     for MAZ006-007-013-014-018.
RI...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-


LONG TERM...Sipprell
MARINE...Belk/Sipprell/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.