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Area forecast discussion 
National Weather Service Taunton Massachusetts
1003 PM EDT Wednesday Oct 22 2014

Synopsis...
a powerful early season coastal storm will bring strong to damaging
winds in heavy rain squalls and isolated thunderstorms overnight
into Thursday morning. Showers will linger Friday as the storm
slowly pulls away from New England. Showers possible again
Saturday as low pressure moves into southern Quebec. Dry...seasonable
weather returns early next week.

&&

Near term /through Thursday/...

*** a powerful early season coastal storm will bring strong to
damaging winds overnight into early Thursday morning ***

10 PM update...

Very impressive/vigorous short wave-jet streak rotating around a
middle level low south of Long Island and advecting into southeast Massachusetts
and Rhode Island. On the nose of short wave and dry slot middle level lapse
rates are on the order of 7c/km per Storm Prediction Center mesoanalysis and this has
been sufficient combined with strong forcing for ascent /lfq of
upper level jet streak/ to yield numerous convection over eastern
CT/Rhode Island and southeast Massachusetts this evening. Much of the model guidance
has additional convection firing south of New England overnight
and advecting northwest into eastern Massachusetts and eventually southern New Hampshire toward
morning.

Strong wind gusts have been observed in this convection given the
strong low level northeast jet across the eastern half of the
region. Therefore have expanded the Wind Advisory to include all
of Rhode Island/eastern CT northward into the Worcester Hills and much of
southeast Massachusetts. Farther west into CT River Valley of CT and Massachusetts wind gusts
should be not as strong given core of low level jet will remain
farther east over Rhode Island...eastern Massachusetts into southeast New Hampshire. As mentioned
above new convection south of New England should pivot northwest into
eastern Massachusetts overnight /possibly Rhode Island too/ and then into southeast New Hampshire
toward morning. Thus heaviest rain and strongest winds overnight
will be focused across this region. Earlier discussion below.

=============================================================

Potent closed upper level low will continue to amplify tonight.
This will allow surface low pressure to intensify as it slowly
lifts to the northeast passing near the benchmark on Thursday.
Given that this system has closed middle level circulations...were
expecting a break down in precipitation fields that we often see
during winter storms.

1) heavy rain potential:

In a nutshell...periods of heavy rain are expected tonight across
the entire region. The biggest uncertainty is trying to locate
where the heaviest rain bands will set up. There are a lot of
moving parts to this forecast...which makes this a difficult task.

We expect heavy rain to initially overspread southeast New England
and work northward across the rest of the region this evening.
The middle level dry slot will then approach southeast New England by
late evening. This may result in the precipitation field more
scattered at times across southeast sections overnight...but also
more convective given some elevated cape. So while we may see some
breaks in the precipitation shield across southeast
sections...isolated thunderstorms with locally heavy rainfall will
also be possible. In addition...we probably will see a subtle
coastal front set up across southeast Massachusetts late tonight into Thursday
morning so some enhancement is possible.

Will also have to watch for a second area of heavier precipitation
in association with the middle level deformation zone/back bent warm
front. Location of this is tricky but perhaps further back into
the interior across southern New Hampshire and east slopes of berkshires?

Finally in between the two bands of heaviest rain there will likely
be a minimum. So basically...a widespread 1 to 2.50 inches of rain
is expected for much of the region...but localized 4+ inch amounts
are certainly possible across a portion of the region. Will just
have to continue to monitor radar/satellite trends overnight and
fine tune our quantitative precipitation forecast forecast. The Flood Watch is in effect across
eastern New England for the potential for localized flooding if the
higher amounts are realized.

2) timing:

Heavy rain over spreads the region from southeast to northwest this
evening. Periods of heavy rain will occur tonight into Thursday
morning...which will likely impact the morning rush hour. Isolated
thunderstorms are possible tonight into Thursday morning across
southeast New England near the dry slot. The steadiest
rain should be over by Thursday afternoon...but scattered showers
will continue.

3) strong wind potential:

Northeast low level jet over 50 knots will impinge on eastern New
England through early Thursday morning. In fact...BUFKIT soundings
showing some pretty impressive wind fields below 1000 feet. The
uncertainty is that an inversion will attempt to keep the strongest
winds just off the deck. However...heavy rain bands may be able to
pull brief strong wind gusts to the ground. The Wind Advisory
continues for northeast Massachusetts into coastal Plymouth County. Problems
may be exacerbated given the many fully leafed trees...resulting in
some downed tree limbs and even isolated power outages. There
is the chance that the Wind Advisory may need to be expanded further
northwest...but again its uncertain how much wind will mix down.
The winds should diminish by middle morning on Thursday as the low
level jet weakens.



&&

Long term /Thursday night through Wednesday/...
* lingering showers possible on Friday
* showers possible again Saturday as low pressure moves into Quebec
* mainly dry and seasonable weather early next week

Overall the 12z model suite is in fairly good agreement through the
long term. There are some discrepancies in the mesoscale details but
otherwise they are in good agreement. After the coastal storm
currently affecting the region moves away from southern New
England...the weather starts to dry out and become more seasonable.
There are a couple of cold fronts expected to move through the
region and each of these may bring some showers with them.

Thursday night and Friday...low pressure slowly moves into the Gulf
of Maine and then the Maritimes Friday. While the bulk of the rain
will be ending by Thursday night...could see some lingering showers.
However...winds shift to the northwest early Friday bringing
somewhat drier air into the region. Overall expect drier weather
and a gradual improvement as we move into Friday afternoon.

Saturday...another upper level trough moves over the northeast with
low pressure moving through southern Quebec and into the Maritimes.
The models Don/T show a whole lot of moisture or a big wind shift
with this front but we could see some showers. The GFS has a
stronger low level jet than the European model (ecmwf) which could enhance the amount
of rainfall but there is still much to be seen with this system.

Sunday through Tuesday...high pressure starts to build into southern
New England bringing dry and seasonable weather. Temperatures begin
to climb and may warm to well above normal by Tuesday.

Wednesday...low pressure moving through the Great Lakes and into
Quebec may bring a cold front through southern New England. Another
chance of some showers possible with this front but plenty of
uncertainty.

&&

Aviation /02z Thursday through Monday/...
forecaster confidence levels...

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

Short term /through Thu/...

Tonight...high confidence. Mainly IFR conditions in periods of
heavy rain. Isolated thunder likely across southeast New England.
Northeast wind gusts of 30 to 40 knots expected across northeast
Massachusetts...with 50 knots gusts along the immediate coast...including at
kbos. Low level wind shear will also affect some of the area for a time.

Thursday...moderate to high confidence. IFR conditions may improve
to low end MVFR thresholds in the interior...but not much
improvement is expected on the coast. Scattered showers are
expected and there will remain the threat for isolated thunderstorms
across southeast New England...especially during the first part of
the day.

Kbos...moderate to high confidence in taf. Northeast wind gusts up
to 50 knots tonight.

Kbdl...moderate to high confidence in taf.

Outlook...Thursday night through Monday...

Thursday night and Friday...high confidence. A few lingering
showers may bring MVFR/IFR conditions but overall a slow improvement
to VFR expected.

Saturday through Monday...moderate confidence. VFR. Low probability
of scattered showers Saturday.

&&

Marine...
forecaster confidence levels...

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

Short term /through Thursday/...

***20 foot seas and storm force northeast wind gusts continue
into Thursday across the eastern Massachusetts waters***

Low level jet will continue to result in northeast wind gusts of
40 to 50 knots across the northern Massachusetts waters including
Boston Harbor through Thursday morning before gradually
diminishing. Strong winds and long northeast fetch will result in
20 foot seas across portions of our northern Massachusetts waters.
Gale force northeast wind gusts will continue across the southern
waters through Thursday morning.

Outlook...Thursday night through Monday...

Thursday night and Friday...high confidence. 8 to 11 foot seas will
slowly diminish as low pressure moves into the Maritimes. Northeast
winds gusting to near 30 kts will diminish and shift to the
northwest. Visibilities may be reduced in scattered showers.

Saturday and Sunday...moderate confidence. After a brief lull...seas
and winds will increase ahead of a cold front. Small craft
advisories will likely be needed for at least a portion of the
waters.

Monday...moderate confidence. Winds and seas diminish as high
pressure builds over the waters.

&&

Tides/coastal flooding...
despite rather low astronomical high tide cycles late tonight and
again midday Thursday...opted to issue a coastal Flood Advisory
for a portion of the eastern Massachusetts coast. This is mainly for the area
north of Cape Ann and the Scituate area. A long duration of
northeast winds combined with 15 to 20 foot seas across our
northern Massachusetts waters may yield pockets of splash over and pockets of
minor coastal flooding. Certainly not expecting a significant
coastal flood event...but felt it was Worth an advisory.

In addition...there is potential for significant beach erosion along
the exposed beaches from Salisbury to Plum Island.

&&

Box watches/warnings/advisories...
CT...Wind Advisory until 8 am EDT Thursday for ctz004.
Massachusetts...High Wind Warning until 8 am EDT Thursday for maz007-014>016-
019.
Flood Watch through Thursday morning for maz005>007-013>022-
026.
Coastal Flood Advisory until 2 PM EDT Thursday for maz007-019.
Wind Advisory until 8 am EDT Thursday for maz005-006-012-013-
017-018-020-021.
New Hampshire...Flood Watch through Thursday morning for nhz012-015.
Wind Advisory until 8 am EDT Thursday for nhz012.
Rhode Island...Wind Advisory until 8 am EDT Thursday for riz001>007.
Marine...Gale Warning until 5 am EDT Thursday for anz231>237-254>256.
Storm Warning until 5 am EDT Thursday for anz230.
Storm Warning until 6 am EDT Thursday for anz250-251.

&&

$$
Synopsis...Frank/rlg
near term...Frank/rlg
short term...Frank/nocera
long term...rlg
aviation...Frank/rlg
marine...Frank/rlg
tides/coastal flooding...

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