Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 260319

Area Forecast Discussion
National Weather Service Taunton MA
1119 PM EDT Tue Oct 25 2016

Some cold unstable air will bring areas of clouds and unseasonably
cool temperatures through Wednesday. A strong storm system impacts
the region Thursday into Friday which will bring a period of
wintry weather with onset, prior to moderate to heavy rain along
with gusty winds with passage. An active, cooler than average
weather pattern is advertised over the weekend into next week.


7 pm major changes in the forecast.


 * Freeze warning remains in effect for most of interior RI away
   from the immediate coast into interior E Mass

1055 PM Update...

Temps have been running up to 2-3 degrees above previous forecast
through 02Z, while the dewpts have run up to 3 degrees below
forecast. NW surface winds continue at 5-10 kt though noting calm
winds in a few inland valley spots at 03Z. Could see some
radiational cooling, though some spotty clouds could move across
as well. For now, clouds look to be confined across the E slopes
of the Berkshires as well as outer Cape Cod as seen on latest IR
satellite imagery.

Low pressure remains across the Canadian Maritimes, which does not
look like it is making any eastward movement at this point, so the
progression of the high pres ridge across central and western NY
state/PA appears to have slowed as well. N-NW flow aloft remains
across the region. Noting mainly NW flow up to about 475 mb on 00Z
KCHH sounding, while up to 300 mb or higher with strong upper
level jet /up to 70 kt at 33 mb/ on 00Z KALB sounding.

Have updated forecast to bring near term conditions current. With
lower dewpt trends, as well as somewhat milder temps, incorporate
into the overnight forecast but think the temps will drop close to
forecasted lows. So, have left freeze warning intact for now, but
will monitor temps closely.

Previous Discussion...

The northwest flow has been transporting colder air into the
region. With this cold air in place, expect temperatures to fall
below freezing away from the coast and the mid 30s to around 40
near the coast. With these values, we expect freezing conditions
in the interior including several areas that have not yet
experienced a killing freeze.

The freeze warning continues where previously issued, but added
SE Providence Co. and Eastern Kent Co. in RI where places outside
the urban centers will be at risk. We have also added Southern
Bristol Co. and Southern Plymouth Co. in MA for areas away from
the immediate shoreline.

Temps aloft around -5C to -6C with ocean temps 14-15C. This
20-degree differential with sustained winds 12 knots or higher
will favor bands of ocean effect clouds, possibly a shower. But
the direction will favor an offshore fetch that may clip
Provincetown and parts of the Outer Cape.



High pressure builds over the region. This should bring subsidence
and mainly clear skies. Winds over the ocean will continue at
10-14 knots sustained, turning more from the north. This may keep
some ocean clouds over Cape Cod, especially Hyannis and points

Sunshine will work on -6C temps aloft to bring max temps in the
mid 40s to around 50.

Wednesday night...

High pressure ridge will be in place surface and aloft through the
night. This should provide mainly clear skies and light winds.
Depending on specifics of the ridge axis, the north wind over Cape
Cod could back around from the northeast, drawing ocean clouds
farther west to the Cape Cod Canal.

Great Lakes shortwave and associated surface low over the Midwest
will approach overnight. Moisture fields show increasing potential
for mid and high clouds during the night, but the lower thicker
clouds hold off until near sunrise.

Based on the light wind prevailing fair skies, we have stayed
close to the existing min temp forecast. The coldest temps may
actually be reached a couple of hours earlier than normal, with
steady or slowly rising temps late at night as the clouds build

With the dry low level air expected, the lack of any source of
lift, and no forecast of measurable pcpn by this system east of
the NY border... we will show nil pops through 12z Thursday.


*/ Highlights...

 - Winter weather possible with storm onset Thursday
 - Moderate to heavy rain with flooding concerns Thursday night
 - An active weather pattern with near- to below-seasonable
   temperatures through next week

*/ Overview...

An active weather pattern is in the cards with temperatures near- to
below-seasonable throughout the remainder of October getting into
November as signaled per consensus of atmospheric teleconnections
and accompanying features within the N Hemispheric pattern. In short
colder air is being allowed to spill S and wrap into individual
systems round the base of a H5 low over the N Canadian maritimes.
Subsequently a series of weather disturbances are forecast of which
will likely bring a period of snow to areas of the NE CONUS. Further
details below.

*/ Discussion...

Thursday into Friday...

Potent storm taking aim on the NE CONUS. With onset, an over-running
setup of frontogenetical/isentropic lift ahead of a H85 low to which
there is the likelihood of wintry precipitation types. Agree with
the prior forecaster of the stronger, deeper, colder solution as it
would appear a consensus of the forecast guidance agrees upon. That
being said and taking in regard near-surface ageostrophic flow, N
winds are likely to prevail ahead of the system and keep colder air
in place. But the challenge is drier air. How quickly does top-down
moistening occur to saturate the column. It would appear that storm
onset may be delayed till midday. Then how quickly does warmer air
push in, especially at H925. By the time precipitation gets going
some areas are likely to be well above freezing.

Thinking precipitation moves into the forecast area towards midday
starting off as snow W and central, rain elsewhere. Delay W to E by
drier air. N winds holding across the interior throughout into the
evening hours. Snow accumulation possible over the high terrain,
maybe an inch or two on grassy surfaces as supported by the EPS,
concluding with influx of warm air quickly at H925, so not expecting
much snow accumulation. Concern as to interior valleys and whether a
wintry mix occurs with shallow cold air. But given onset delay in
precipitation, valleys are likely to warm around freezing with
diurnal heating. Thinking a marginal event given the time of the
year, synoptic setup, timing of system. Not thinking the need for
winter weather headlines.

As the storm sweeps the area, will transition to a strongly dynamic,
QG-forced event. Strong forcing of deep layer moisture with omega
values up to 50 microbars per second, moderate to heavy rain is more
than likely with isolated issues of urban to poor drainage flooding
given the progressive nature of the storm. Thunder likely along with
gusty S winds of 30 to 40 mph mostly over S/SE coastal New England,
as supported by CIPS analogs. As the storm exits, strengthening and
invoking dynamical cooling, can not rule out a return of snow for
the high terrain in regions of trowaling moisture behind the system,
but drier air moving in may rob moisture in better snow growth
regions making any outcomes brief with little accumulation for N/W

Will continue mention of hazards with respect to moderate to heavy
rain and leaf-clogged drains in the hazardous weather outlook. This
along with gusty S winds which could result in isolated to scattered
wind damage for a brief period of time. Bulk of impacts Thursday


Storm lifts out behind which moisture trowals and colder air works
in. May see snow linger across the high terrain per cyclonic flow
and favorable environment to invoke lift upon residual moisture.
Blustery NW flow, scattered to broken low cloud decks, will see both
dissipate into the overnight period as a weak ridge of high pressure
builds into the region allowing conditions to dry out.

Saturday into Sunday...

Clipper-like system undergoing decent forcing per low to mid level
frontogenesis along a warm front parent to the surface low beneath
the left front quadrant of the upper level jet. Signals within the
consensus of forecast guidance, but not very good agreement on
timing nor on outcomes. An indication of a W to E moderate band of
rain where lift and forcing becomes focused. Could potentially turn
more seasonable for the area if the system stays N and we get more
of a S flow. But at this point a low confidence forecast.

Next week...

An undulating period of temperatures with an active weather pattern
expected. As to details, not a good amount of agreement in the
forecast to prevail with. A low confidence forecast.


Forecaster Confidence Levels.

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

Short Term /through Wednesday Night/...High confidence.

VFR. NW winds diminish as ocean effect CIGS / isold -SHRA linger
across the outer Cape overnight. Winds veer to N while remaining
breezy into Wednesday into Wednesday night, ocean effect CIGS /
isold -SHRA linger.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday into Friday...Moderate confidence.

Cigs lowering to IFR-LIFR into Thursday. Initial brief period of
a wintry mix is possible, transitioning to -RA/RA with embedded
+RA, TSRA over S/SE coastal terminals along with gusty S winds up
to 35 kts through around midnight Friday. Winds back out of the W
towards Friday morning, becoming VFR.

Saturday and Sunday...Low confidence.

Mostly VFR. Perhaps a mix of MVFR-IFR to places N of the Mass Pike
Saturday Night into Sunday Morning. W/SW winds throughout. Gusts up
to 20 kts.


Forecaster Confidence Levels.

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

Short Term /through Wednesday Night/...High confidence.

11 pm update...

Overnight...NW winds continue to gust up to 25-30 kt. Seas remain
in the 5-8 foot range, highest across the eastern outer waters to
S and E of Nantucket. These are running 1-2 feet higher than
forecast. Have extended the small crafts into Wednesday morning
/at least/ for most of the waters.

Wednesday...High pressure builds over the waters. Winds and seas
will slowly diminish, but timing is in question. Seas remain
around 5 feet on the outer waters through Wednesday. Have kept
small crafts going on most open waters, but may need to extend
further on the southern near shore waters on the 4 am update.

Wednesday night...North winds diminish. Widely scattered ocean
effect rain showers east of Cape Cod.

Outlook /Thursday through Sunday/...Moderate confidence.

Thursday into Friday...

Rain beginning late Thursday and continuing through Friday morning,
moderate to heavy at times with the expectation of thunderstorms.
Majority of impacts overnight. S/SE winds strengthen ahead of a
deepening area of low pressure across the region with a brief period
of gale force gusts. Seas building 8 to 10 feet, dropping off towards
Friday morning and through the day as winds turn out of the W behind
a cold front but remain breezy with gusts up to 30 kts. Gale headlines
may be needed.

Saturday into Sunday...

W/SW winds with gusts up to 25 kts, dissipating with time. Will see
seas dampen as well.


CT...Freeze Warning from 2 AM to 9 AM EDT Wednesday for CTZ003.
MA...Freeze Warning from 2 AM to 9 AM EDT Wednesday for MAZ006-007-
RI...Freeze Warning from 2 AM to 9 AM EDT Wednesday for RIZ001>004-
MARINE...Small Craft Advisory until 11 AM EDT Wednesday for ANZ231>234-
     Small Craft Advisory until 7 AM EDT Wednesday for ANZ235-237.
     Small Craft Advisory until 2 AM EDT Thursday for ANZ250-254-
     Small Craft Advisory until 2 PM EDT Wednesday for ANZ256.


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