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Area forecast discussion 
National Weather Service Taunton Massachusetts
943 PM EDT Monday Oct 20 2014

Synopsis...
a long duration coastal storm will bring periods of rain Tuesday
through Thursday with lingering showers Friday as the storm slowly
pulls away from New England. Mainly dry weather expected this
weekend with seasonable temperatures.

&&

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

940 PM update...

No major changes from previous forecast. Chance of rain begins to
increase after 06z/2am and especially toward 12z and beyond per
latest 21z sref and latest rap13. Although may have to delay
precipitation a few more hours given 00z upstream sounding at okx which
indicates lots of dry air between 850 mb to 600 mb. Thus much of
the night may remain dry with rain holding off until after
sunrise Tuesday and beyond. Will have to evaluate satellite and
radar trends and 00z NAM upon arrival.

Regarding temperatures...increasing low level warm air advection will
result in temperatures holding nearly steady overnight along with low
temperatures running 3-6 degrees warmer than normal. Quite a difference from
last night.

&&

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

***narrow axis of heavy rain possible on Tuesday across eastern new
england***

Tuesday...

Interesting setup with a closed upper level low to our west and a
surface trough across eastern New England. The interaction of the
cold pool aloft...a southerly low level jet and axis of surface
convergence may lead to some localized heavy rainfall across
eastern New England. Interesting that the high resolution models
are showing a narrow axis of 1 to 2 inches of rain somewhere near
the I-95 corridor. Exact location remains uncertain and it could
remain offshore...but something to watch. We may be dealing with
localized nuisance poor drainage street flooding in this region if
this narrow axis of heavy rain develops.

Further to the west across interior southern New England...scattered
showers will be possible but best forcing/moisture will be across
our eastern zones...so activity should not be as widespread.

As for convective potential...500 mb temperatures will be below -20c and
result in elevated instability. Model soundings have been
indicating mu convective available potential energy on the order of 500 j/kg. Have included isolated
thunderstorms in the forecast across some of the region. While we
can/T rule out an isolated thunderstorm across much of the
region...best shot will be across eastern New England.

High temperatures will mainly be in the upper 50s and lower 60s across the
region.

Tuesday night...

Appears that the deeper moisture/lift temporarily shifts to the
north of our region and into norther New England.
Nonetheless...cyclonic flow around low pressure will still result in
scattered showers at times. The activity will probably be most
widespread across our far northern zones...closer to the better
dynamics and forcing. Low temperatures will only drop into the upper 40s
and lower 50s in most locations.

&&

Long term /Wednesday through Monday/...
big picture...

Closed upper low over the middle Atlantic coast Wednesday migrates
across New England Thursday and into the Maritimes Friday. Shortwave
from the Pacific northwest races across the northern tier of states
this week and crosses New England Saturday. High pressure ridge then
builds over the northeast USA Sunday and Monday. Height contours are
below normal much of the week under the influence of the upper
low...then recover to normal levels by Sunday as the ridge builds.

This pattern favors a cool wet middle and late week...then dry and
seasonable by Sunday and Monday. Moderate confidence in the types
of weather...but low confidence in exact timing.

The dailies...

Wednesday-Thursday...coastal low surface and aloft will dominate our
weather as it moves up the coast. Low pressure to our south and an
east 50-60 knot low level jet across coastal Maine and wrapping into
NH/VT. This may bring enhanced isentropic lift across southern New Hampshire
and northern mass...with weaker lift farther south. By Thursday the
cold core is directly overhead. So Wednesday is a transition from
stratiform to convective...Thursday mainly convective. Sufficient
instability both days to indicate a chance of thunder.

Friday...low pressure surface and aloft will move off to the east.
Cold core still close enough to provide clouds and some instability.
Should continue to be a diminishing chance of showers.

Saturday...cold front associated with upper shortwave moves through
later Saturday or Saturday night. The approach of this front may
actually be the nudge that gets the last of the cold pool clouds out
of our area. The front will bring a period of clouds. The
potential for showers is less defined and so we feature just slight
chance probability of precipitation in southern New Hampshire and northern mass. Temperatures aloft support daytime
maximum temperatures in the 60s.

Sunday-Monday...high pressure builds over the northeast with temperatures
aloft warmer from Sunday to Monday. Temperatures aloft support 60s both
days.

&&

Aviation /02z 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/...

940 PM update...

No major changes from 00z tafs. Earlier discussion below.

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

Tonight...high confidence. VFR. Scattered showers after midnight
but should not bring lower conditions.

Tuesday...moderate confidence. Conditions deteriorate to mainly
MVFR thresholds in morning near coast...but brief IFR ceilings/visibilities
are possible. Scattered showers expected with an isolated
thunderstorm or two possible. Bulk of the focus should be across
eastern New England.

Tuesday night...moderate confidence. Low end MVFR to perhaps IFR
conditions dominate in low clouds...scattered showers and fog
patches. The bulk of the activity will likely be found across our
northern zones.

Kbos...high confidence in taf tonight with moderate confidence on
Tuesday. Low probability of an isolated thunderstorm on Tuesday.

Kbdl...high confidence in taf tonight with moderate confidence on
Tuesday.

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

Wednesday-Thursday...prolonged period of mixed MVFR/IFR...with more
IFR in rain Wednesday and more MVFR in showers Thursday. Chance of
thunder both days. Chance of 30 knot east-northeast wind gusts
Wednesday morning along the Outer Cape and Massachusetts North Shore
areas.

Friday-Saturday...VFR. Areas of MVFR ceilings/visibilities in showers on
Friday...with the best chance in southern New Hampshire and eastern mass.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Tuesday night/...

940 PM update...

Only change to previous forecast is to increase wind speeds a bit
overnight to 10-15 knots with gusts up to 20 knots. Earlier discussion
below.

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

Tonight...high confidence. High pressure will continue to move
further east of the region. This will result in south to southwest
winds of 10 to 15 knots. However...winds/seas should remain below
Small Craft Advisory thresholds.

Tuesday and Tuesday night...moderate to high confidence. Developing
low pressure south of the waters will combined with a 1030 mb high
over eastern Canada. Easterly winds on Tuesday will begin to shift
to the northeast Tuesday night as pressure gradient strengthens.
Pretty much a lock that Small Craft Advisory seas will develop across our eastern and
particularly our northern outer-waters Tuesday afternoon into Tuesday night.
In fact...by daybreak Wednesday seas may be approaching 10 feet
across our far northern waters along with gusts up to 30 knots. Small Craft Advisory
headlines posted for this region.

We may also see some 5 foot seas develop across the southern waters
towards 12z Wednesday...but its too marginal for late 3rd period Small Craft Advisory
headlines in this region.

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

Wednesday-Thursday...low level east-northeast jet will be feeding
into the Maine middle-coast Wednesday. The potential for strong surface
winds should remain north of our waters. Winds of 25-30 knots may
extend as far south as the Merrimack River and possibly Cape Ann.
Winds diminish and become variable Thursday as the coastal low moves
across the waters. Seas Wednesday reach 5 feet on the outer waters
with 8 to 10 feet possible from Cape Ann to Merrimack River. By
Thursday the persistent northeast flow will expand the area of 8
to 10 foot seas across the eastern waters. Small Craft Advisory
will be needed for the eastern waters and southern outer waters.

Friday... as the coastal low pressure moves off toward the
Maritimes...winds will become northwest with gusts around 20 knots.
With the shifting of the wind direction to offshore...we expect seas
to diminish. But 5 foot seas may linger on the outer waters through
the day.

Saturday...winds and seas should remain below small craft levels.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory from noon Tuesday to 8 am EDT Wednesday
for anz250-254.
Small Craft Advisory from 3 PM Tuesday to 8 am EDT Wednesday
for anz251.

&&

$$
Synopsis...wtb/Frank
near term...wtb/nocera
short term...Frank
long term...Frank
aviation...wtb/Frank/jwd
marine...wtb/Frank

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