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Area forecast discussion 
National Weather Service Taunton Massachusetts
411 PM EDT Fri Oct 21 2016

sub-tropical low pressure lifting north toward southern New
England will bring numerous showers and isolated T-storms with
locally heavy rainfall tonight. Additional showers are likely
Saturday as the storm moves into northern New England along with
strong winds developing late Saturday into Saturday night. Dry but
cool and blustery conditions Sunday into early next week.


Near term /until 6 am Saturday morning/...
active pattern in near and short term as high amplitude and
negatively tilted upper trof swings through. Subtropical moisture
becomes entrained this evening as reflected in a period of
precipitable waters to 2 inches across southeast New England. The
moisture plume is focused on the nose of a low level 40 knot east-southeast
jet. High resolution models focusing heavy rain across eastern Massachusetts
from south to north early to mid evening. This could result in
urban street and poor drainage flooding. Isolated thunder this
evening is not out of the question. Breaks in the clouds have
allowed temperatures to rise into 70s across much of the area this
afternoon. The temperatures will drop into the 60s toward evening
but then likely hold given the high dewpoints.


Short term /6 am Saturday morning through 6 PM Saturday/...
notable diffluence aloft Saturday morning into early afternoon is
anticipated just ahead of rigorous negative tilt 500 mb trof axis
along with support of approaching left exit region of 110 to 120 kt
upper jet. Have gone with likely pops for a time Saturday in
anticipation of a band or two of heavy showers that will probably
rotate across CT, RI, and at least central/east central Massachusetts. Cold
pool aloft will also introduce an element of instability in the
afternoon in addition to a probably comma head wrap around. This is
inducement to keep pops elevated across western and central sections.

Expect warmest temperatures to be in the early morning hours with a
significant drop west to east during Saturday afternoon. This should
be especially noticeable over the higher terrain of western Massachusetts.

A surge of strong west to northwest winds is anticipated toward evening. It
will be first noted across the east slopes of the Berkshires. A Wind
Advisory will likely be needed with a start time possibly as early
as late Saturday afternoon. Per earlier coordination with
surrounding offices, this will probably be considered with a
subsequent shift after timing, extend, and magnitude become clearer.


Long term /Saturday night through Friday/...
* gusty winds expected Saturday night and Sunday
* temperatures drop below normal Sunday and continue dropping
through Tuesday/Wednesday time frame
* mainly dry weather through this time with a few areas of showers
possible on several days

Models are in good agreement through much of the long term,
particularly on the synoptic scale pattern. There are some
discrepancies, but these are largely on the smaller scale details as
well as timing. The pattern over the next week will be largely
dominated by upper level troughing in the northeastern U.S. This
will keep unsettled weather in the region for much of the time,
along with below normal temperatures.

Saturday night and Sunday...the main concern will be strong pressure
rises combined with a tight pressure gradient and decent cold air
advection that will be moving over southern New England. This will
result in breezy conditions beginning sometime Saturday afternoon
and continuing into Sunday. While winds will likely diminish a bit
during the overnight period due to the loss of sunshine and a
decline in mixing, the pressure rises and cold air advection will
act to continue mixing and gusty winds will continue. Wind Advisory
criteria may be reached Saturday evening and again on Sunday morning
but confidence is low in which areas and how frequently gusts may
exceed criteria, so have opted to hold off on a Wind Advisory at
this time. Temperatures will be seasonable through this period,
though The Drop in temperature from today added to the winds will
make it feel much cooler.

Monday through Wednesday...the upper level trough slowly moves
offshore and low pressure moves into the Maritimes. Temperatures
continue to fall with Tuesday and Wednesday likely the coldest of
this fall so far. A shortwave moves through the upper level flow on
Monday, possibly bringing a few showers to the region. High
pressure starts building into southern New England Tuesday and
Wednesday. Temperatures will be cool enough these days to possibly
induce some ocean effect clouds and showers on the cape and islands.

Thursday and Friday...a bit more uncertain with the timing here. The
GFS is a bit slower with the progression of the upper level pattern
than the European model (ecmwf). Shortwave ridging will move over southern New
England either Wednesday or Thursday before another shortwave trough
moves through. This trough may bring another chance for some
showers either late Thursday or Friday. Temperatures rebound a bit,
climbing back to normal or even a few degrees above normal.


Aviation /20z Friday through Wednesday/...
forecaster confidence levels.

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

Short term /through Saturday/...

Rest of this afternoon into tonight...high confidence.
Anticipate general lowering of ceilings and visibilities due to high
dewpoint air and numerous showers further saturating the lower
atmosphere. Anticipate fairly widespread IFR conditions tonight with
areas of LIFR conditions due to low clouds and fog/drizzle. Pockets
of heavy rain appear likely this evening over eastern Massachusetts.
Isolated thunder is possible as well this evening.

Saturday...moderate confidence.
More showers, some heavy, are anticipated morning into early
afternoon across central and northeast portions of the area. Still
more showers are expected to expand underneath a developing comma
head across western Massachusetts and northwest CT during the mid and late afternoon.
Increasing west to northwest winds late Saturday afternoon to the west of a fit-
orh-cef-bdl line. The strong winds will move toward eastern sections
toward evening.

Kbos taf...high confidence in trends but lower confidence in

Kbdl taf...high confidence in trends but lower confidence in

Outlook /Saturday night through Wednesday/...

Saturday night...moderate confidence. Improving conditions to VFR.
Westerly winds increase, gusting to 25 to 30 kts, possibly up to 35
to 40 kts on the South Coast, cape, and islands.

Sunday...high confidence. VFR. Gusty northwest winds continue but will
diminish slowly.

Monday through Wednesday...moderate confidence. Mainly VFR. Low
confidence in MVFR/IFR conditions developing on the cape and islands
in ocean effect clouds and rain showers Tuesday and Wednesday.


forecaster confidence levels.

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

Short term /through Saturday/...high confidence.

Near term issue will be areas of fog including pockets of dense fog.
There could also be some brief gusty winds in vicinity of showers
this evening but in general below Small Craft Advisory criteria. For
Saturday, there will be increasing SW winds during the early/mid
afternoon becoming west during late afternoon, and a Gale Warning is
posted for all waters.

Outlook /Saturday night through Wednesday/...

Saturday night and Sunday...high confidence. Westerly gale force
winds will continue through this period with a tight pressure
gradient between the departing low pressure system and building high
pressure in the Great Lakes. Westerly winds will shift to the
northwest on Sunday. Gale warnings have been extended for all waters
through Sunday.

Sunday night and Monday...high confidence. Small Craft Advisory
conditions continue though both winds and seas will diminish
gradually through the period as the pressure gradient slackens.

Tuesday and Wednesday...moderate confidence. Marginal small craft
conditions continue, particularly on the outer waters Tuesday and
Tuesday night. Winds and seas will be diminishing through this
period as high pressure builds over the waters.


Tides/coastal flooding...
a high astronomical tide and storm surge of about one foot will be
enough to cause some spotty, minor coastal flooding along the
Massachusetts East Coast. Have issued a coastal Flood Advisory for
Nantucket Harbor where the total water level is expected to reach
near or a little over the 5 foot threshold for minor coastal
flooding. Believe that the surge of .9 feet at 1:15 PM may
increase a little to 1.1 or 1.2 feet as a consequence of an
increasing easterly gradient piling some additional water into
Nantucket Sound. In addition, high tide may coincide with a period
of heavy rain that could have difficulty draining due to the high
Harbor water level. Models suggest the nose of a 40 knot low level
jet will edge close to the East Entrance to Nantucket Sound around
the time of the very late afternoon high tide. Elsewhere, believe
any minor coastal flooding will be spotty enough to be covered by
a coastal flood statement. Anticipate the usual suspects such as
Longs wharf in Boston, a Lane or two of morrissey Boulevard,
Scituate Harbor parking lot, etc. Will get briefly wet.


Box watches/warnings/advisories...
Massachusetts...coastal Flood Advisory until 7 PM EDT this evening for maz024.
Rhode Island...none.
Marine...Gale Warning from noon Saturday to 6 PM EDT Sunday for
Gale Warning from 2 PM Saturday to 6 PM EDT Sunday for anz230-


near term...Thompson
short term...Thompson
long term...rlg
tides/coastal flooding...Thompson

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