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Area forecast discussion 
National Weather Service Taunton Massachusetts
803 am EDT Monday Sep 1 2014

Synopsis...
a warm humid flow will continue across New England through
Tuesday with scattered showers and thunderstorms each day. A
cold front will push across the region Tuesday night. Warm but
less humid weather will follow for Wednesday through Friday.
Another cold front may bring a chance of showers and
thunderstorms Saturday.

&&

Near term /until 6 PM this evening/...
750 am update...
band of rain confined S of the islands at 1130z. Noting areas of
low clouds and fog with the highest dewpoints /around 70 degrees/
generally across north CT/RI/se Massachusetts. Clouds appear to be breaking
across S New Hampshire/NE Massachusetts with improving visibilities. Infrared satellite showing those
cloud breaks as well.

Should see improving conditions for a time through middle to late
morning before more diurnal clouds develop by midday.

Have updated grids to bring conditions current.

Previous discussion...
warm humid air with dewpoints in the upper 60s and 70s. A front
is stalled along the Canadian border. Meanwhile a Lee trough will
be positioned near the middle Atlantic coast. Both of these will
serve as foci for thunderstorm development.

Somewhat drier air moves into northern New England with precipitation
water values near 1 inch. Meanwhile...2 inch values linger along
the South Coast. This moisture will be the potential fuel for any
daytime convection. Stability parameters look favorable for thunderstorms
but likely not at severe levels. Totals start low and climb to
46-47 in the afternoon with highest values across CT-RI-se mass.
The GFS shows shows SBCAPE reaching 1000-1500 j/kg especially in
CT. Low level helicity is much lower than Sunday...20-30 m2/s2.
Probability of precipitation will favor afternoon/evening thunderstorms with highest values at the
South Coast. With precipitation water values at 1.5-2.0 inches south of
the Mass Pike...any storms in this area will have potential for
heavy downpours and possible urban/poor drainage flooding. Maximum surface
temperatures will again be in the middle 80s.

&&

Short term /6 PM this evening through 6 PM Tuesday/...
tonight...
lingering convection in the evening but diminishing. High humidity
and light wind will again favor development of fog overnight.
Min surface temperatures will be near the dew points...mainly upper 60s and
lower 70s.

Tuesday...
upper shortwave digs over the Great Lakes while high pressure
remains to our east. This will maintain the warm moist southwest
flow across New England. A cold front associated with the upper
shortwave will move east through the eastern Great Lakes to
eastern New York by evening. A pre-frontal trough will remain over
the Hudson and Delaware valleys. Favorable jet dynamics remain
well to our west much of the day...but approach western
mass/southern New Hampshire late. Totals on the GFS are 50-51 while the
European model (ecmwf) and ggem are 47-48. Middle level lapse rates are around 6c/km.
Sbcapes are 500-1000 j/kg by the GFS hints at 1000-1500 j/kg.
Overall we will favor chance probability of precipitation for showers/thunderstorms in the
afternoon with the best chance in western mass/southern New Hampshire and
diminishing values farther east. Precipitable water values start
around 1.5 inches and climb to near 2 inches...so locally heavy
downpours will again be a concern.

&&

Long term /Tuesday night through Sunday/...
overview and model preferences...
medium range models continue to show good continuity early in the
forecast cycle...as 500 mb trough lifts into southern Quebec and
Ontario as it flattens out. The upper pattern then becomes more
typical of middle Summer rather than early fall...with broad ridging
dominating for the middle and latter portions of the week. Beyond
this...models start to diverge in breaking down this ridge...with
the 12z/00z European model (ecmwf) op runs as well as ecens and GFS means showing a
slower breakdown of the upper pattern while the GFS op runs
tending to signal a quicker breakdown. Also noting upper level
energy crossing central and northern Canada around the middle and
latter portions of this forecast...though looks like this will
remain well north of the U.S./Canadian border...for now.

Have leaned this forecast toward a blend of available guidance
through late this week...as this blend has shown very good
consistency over the last several days...then pushed closer to the
ec/ecens means for next weekend which tend to be slower than most
of the other guidance. Experience shows that...with a strong
dominant pattern in place such as what will be developing...this
tends to take more time to break down unless some major system
shows up in the overall flow.

Daily details...

Tuesday night...cold front continues to move offshore overnight.
Leftover energy will lift NE into northern New England and the
Maritimes overnight as 500 mb short wave lifts into southern Quebec.
Expect drier air to start filtering in...mainly across S New Hampshire/north
central and west Massachusetts. Will take some time for SW winds to shift across
southern and eastern areas overnight...so more humid conditions
will hold in. Overnight lows will range from the Lower-Middle 60s of
the higher inland terrain of SW New Hampshire/west Massachusetts to around 70 along the
immediate coast.

Wednesday...surface high pressure will build east out of the Great
Lakes...allowing drier air to spill in across the region during
the day as winds shift to northwest. However...with the general offshore
flow in place and 500 mb heights rising with broad ridge building
aloft... looks like temperatures will remain on the warm side. Temperatures will
top off in the Lower-Middle 80s...except from 75 to 80 along the
immediate coast.

May see some patchy fog develop in normally prone valley areas
Wednesday night as temperatures finally fall back to the 50s...though holding
in the Lower-Middle 60s along the immediate coast. Winds become
light/variable or calm...which may help to promote the fog
development.

Thursday and Friday...high pressure will dominate...so expect dry
and warm conditions to continue across the region. Dewpoints will be
comfortable...mainly in the middle 50s to around 60 on Thursday...but
look to start creeping back up again on Friday as the high will
slip off the coast and SW winds take over. Highs Thursday will be
in the Lower-Middle 80s again...though some readings may reach the
upper 80s well inland on Friday.

Saturday and Sunday...model runs tending to diverge on the
breakdown of the upper level pattern across the eastern U.S.
During this timeframe and the approach of a cold front...so lower
forecast confidence. At this point...a cold front will approach
the region during Sat...pushing offshore Sat night or early Sunday
with high pressure returning.

&&

Aviation /12z Monday through Friday/...
forecaster confidence levels...

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

Short term /through Monday night/...high confidence in trends but
lower confidence in precise details and timing.

Today...IFR ceilings may linger along the South Coast through most of
the day. North of there conditions improve to VFR. Another
disturbance passes south of New England but may generate another
round of showers/thunderstorms across CT/RI/se mass this afternoon/evening
with locally heavy downpours possible. Brief MVFR/IFR in any
thunderstorms.

Tonight...evening showers/thunderstorms especially over the cape and
islands. Brief MVFR/IFR in any storms. Quiet weather the remainder
of the night with areas of IFR/LIFR in stratus and fog. Best chance
will again be along the South Coast and islands as well as the CT
River Valley.

Tuesday...morning fog and low conditions burn off. VFR through
much of the day. Increasing clouds from the west during the
afternoon/evening with potential for brief MVFR in scattered
thunderstorms.

Kbos terminal...high confidence in taf regarding trends but lower
confidence on precise details and timing.

Kbdl terminal...high confidence in taf regarding trends but lower
confidence on precise details and timing.

Outlook...Tuesday night through Friday...

Tuesday night...moderate confidence.
Precipitation should taper off after midnight with conditions generally
improving to VFR. Patchy fog after midnight mainly across the
normally prone inland locations as well as along the S
coast...Cape Cod and the islands where more humid conditions hold
in. Expect MVFR to local IFR cigs/vsbys.

Wednesday through Friday...moderate confidence.
Expecting mainly VFR conditions. Local MVFR-IFR visibilities and ceilings in
late night patchy fog and low clouds. Main areas of concern will
be the typically prone locations across the far interior /SW New Hampshire
and north central and western MA/. On Thursday night...with SW winds in
place...may see patchy fog along the S coast with local MVFR-IFR
conditions as well.

&&

Marine...
forecaster confidence levels...

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

Moderate confidence through Tuesday.

Today...
high pressure offshore and low pressure over the Great Lakes will
maintain a southwest wind flow across the waters through Tuesday.
Winds will remain at or below 20 knots. Seas will start around 5
feet on the outer waters but will diminish through the day. We
have maintained Small Craft Advisory on the southern outer waters
through the day due to the lingering rough seas. A few
thunderstorms will move across southern New England with the best
chance on the waters occurring south of Boston.

Tonight...
evening thunderstorms diminish early at night. Light southwest
flow will allow areas of fog overnight with poor visibility.

Tuesday...
areas of fog will start the morning...with visibility improving
during the morning. Showers and thunderstorms will move into
western New England during the afternoon and may threaten the
coastal waters toward evening. Thunderstorms could cause strong wind
gusts...otherwise expect winds and seas to remain below small
craft levels.

Outlook...Tuesday night through Friday...

Moderate confidence through the period.

Expect winds and seas to remain below small craft criteria. May
see SW wind gusts up to 20 knots Tuesday night on the southern waters
before shifting to west and diminishing by Wednesday morning. Winds back
around to SW again late Thursday night/Fri.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory until 6 PM EDT this evening for
anz254>256.

&&

$$
Synopsis...wtb/evt
near term...wtb/evt
short term...wtb
long term...evt
aviation...wtb/evt
marine...wtb/evt

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