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Area forecast discussion 
National Weather Service Taunton Massachusetts
350 am EDT sun Aug 31 2014

Synopsis...
warm humid flow over the northeast USA. A upper shortwave from the
Great Lakes drives east through New England late afternoon/evening
bringing potential thunderstorms with heavy downpours and strong
winds. Showers and thunderstorms will linger into Monday...with
the best chance across CT/Rhode Island and south of the Mass Pike. Another
cold front approaches later Tuesday. Warm but less humid weather
will then follow for middle week.

&&

Near term /until 6 PM this evening/...
through 8 am...
warmer more humid air continues to flow into southern New England.
As of 2 am dewpoints had climbed into the low to middle 60s. Expect
these values to slowly increase through morning. Clouds are
filling in over the northeast...so we expect mostly cloudy skies
through sunrise.

Today...
back edge of the cloud area is southwest of Philadelphia. This is
about where dewpoints are around 70. This means a cloudy start to
the day...but potential for the sun to break through later in the
morning or early afternoon. A southwest upper flow and surface
cold front in the Great Lakes suggests no frontal passage today. The upper
shortwave passes across northern New England...but close enough to
affect southern New England. A pre-frontal trough supported by an
upper shortwave is a reasonable scenario...with best chance
closest to the shortwave in western/northern mass and in southern
New Hampshire.

At the least this should be a warm very humid day. The airmass
will contain deep tropical moisture with precipitable water values
forecast at 2.0 to 2.30 inches...above 2 Standard deviations and so
quite significant. Questions of the day are potential for
convection and potential for damaging convection. Stability
parameters are favorable for thunderstorms...Li around -2 to -4/totals
into the middle 40s. Upper wind fields suggest severe wind potential
with 30 knots at 850 mb and 40-50 knots at 500 mb.
Afternoon/evening shear values look sufficient to provide
organization to some thunderstorms.

Putting it all together: potential for afternoon/evening strong
thunderstorms with wind and heavy downpours...and a lower but real
potential for damaging wind gusts. Flash flood indices are above
3.5 inches... so flooding problems will be along the lines of
urban and poor drainage flooding.

&&

Short term /6 PM this evening through 6 PM Monday/...
tonight...
convection lingers into at least the start of the night. Signs in
the model data that the surface boundary may linger over southeast
mass/RI/CT later at night. This may provide a focus for at least
scattered convection continuing overnight in this area. No
airmass change so it should be a warm and humid night with
dewpoints around 70...and so min temperatures should be around 70 or in
the lower 70s.

Monday...
warm humid airmass lingers over the region. Precipitation water values
continue above 2 inches south of the Mass Pike and 1.5 to 2.0
inches north. Dynamics will be diminishing...but southern New
England will continue under the right entrance region of the
departing upper jet for at least part of the day. We will continue
with chance probability of precipitation for showers/tstms...and with locally heavy
downpours.

&&

Long term /Monday night through Saturday/...
headlines...

* heavy showers/T-storms possible Monday...Tuesday evening into early
Wednesday
* brief break/dry weather Tuesday
* drying high pressure Wednesday through Friday

Overview...the overall pattern has the states containing a ridge in
the east and a trough in the west. The boundary in bewteen should
then bring in moisture along a cold front. After the rain-causing
trough moves through Wednesday...a ridge builds over the region for
the rest of the work week as a cold front approaches from the west
for Saturday. A negative nao forms blocking up the pattern late
while a negative pna stays over the United States keeping the ridge
over the East Coast.

Models have a good agreement on the first part of the period...however
the magnitude of the ridge over the Midwest comes into question
early Wednesday as the European model (ecmwf) has a digging trough on the West
Coast whereas the 6z GFS has more of a zonal flow pattern during
this period. With the quicker zonal flow pattern...the 6z GFS
brings the cold front through quicker than the European model (ecmwf)...which is
its normal bias...so have leaned against the 6z GFS for that
period. The 6z GFS is later than the European model (ecmwf) bringing that trough
down into the states as well so extra instability is into the
region Thursday night via the 6z GFS. Have leaned against that as
well and more towards the European model (ecmwf)...12z GFS and ensembles that have
a high still over the East Coast.

Dailies...

Tuesday...possibility of fog in valleys and other fog prone areas.
Otherwise areas of isentropic descension...rising heights and rising
700 mb temperatures to close to 10c allude to the possibility of a
lull in the precipitation during this period. Believe that occurs
from early morning to early afternoon. Dew points will again reach
the 70s during the day. Then...a cold front pushes through overnight
into Wednesday with a gerater possibility of showers and
thunderstorms ahead of it especially over northwestern Massachusetts. This is
where negative showalter values and better shear exists.

Wednesday...as the cold front pushes through in the morning...
expect to see any showers come to an end and drier air push in. A
high pressure system begins to take control with northwest winds.

Thursday and Friday...high pressure continues. Clearing skies and
drier air with dew points into the upper 50s.

Saturday...have to watch for an approaching cold front for this time
period.

&&

Aviation /08z Sunday through Thursday/...
forecaster confidence levels...

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

Short term /thru Sunday night/...high confidence in trends but
lower confidence in precise details and timing.

Today...VFR sky cover with areas of MVFR ceilings around 2000 feet.
The lower ceilings should improve to VFR late morning and afternoon.
Developing thunderstorms after noon with best chance after 3 PM. Best
chance will be western/northern mass and southern New Hampshire. MVFR/IFR
conditions in any storms with potential for heavy downpours and
strong wind gusts...possibly a few damaging wind gusts.

Tonight...convection continues into the early night but should
diminish after sunset. MVFR/IFR ceilings and visibilities in any
thunderstorms. MVFR/IFR ceilings and visibilities in fog overnight.

Monday...MVFR ceilings/visibilities in showers and scattered thunderstorms. IFR
ceilings/visibilities in morning fog. Locally heavy downpours still possible.

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...Monday night through Wednesday...

Tuesday...moderate confidence.

May see patchy fog after midnight in normally prone valley areas in
the morning. A window of precipitation-free weather expected
sometime during this period. Otherwise another front pushes across
the region Tuesday night. MVFR conditions in showers and storms. SW
winds continue.

Wednesday and Thursday...moderate confidence.

Mainly VFR. Local MVFR-IFR visibilities from departing showers Wednesday
will improve by middle morning with cold frontal passage. Eventual
change from SW winds to northwest winds Wednesday. VFR conditions Thursday
with high pressure overhead.

&&

Marine...
forecaster confidence levels...

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

Moderate confidence today through Monday.

Today...
dry weather for much of the day. Potential for showers/thunderstorms after
4 PM...except after 2 PM north of Cape Ann. Any storms will have
strong wind gusts as well as poor visibility in heavy downpours.
Southwest wind will gust to 20-22 knots which is close to small
craft levels. The persistance of the wind will build seas a tad
with 5 foot heights moving into the outer waters late in the day.
A Small Craft Advisory has been put in effect on the outer waters
starting this evening. It is mainly for the 5 foot seas...but
winds will be close to threshold and so we will keep the headline
non-specific.

Tonight...
the potential for 5 foot seas will extend into Rhode Island Sound on the
southwest wind. Gave some thought about similar potentials for
Block Island Sound and Buzzards Bay...but prefered the better
fetch into Rhode Island Sound where a Small Craft Advisory will be in
effect.

Showers and thunderstorms may move across the waters. Best chance
on timing of the storms would be the first part of tonight...but
conditions will remain favorable through the night. Any storms
would have strong wind gusts early tonight and poor visibility in
heavy downpours at any time.

Monday...
winds and seas diminish below small craft levels. Small crafts
will linger over the outer waters during the morning.

Outlook...Monday night through Wednesday...

Tuesday through Thursday...moderate confidence.

Expect winds and seas below small craft criteria. SW winds will veer
to northwest late Tuesday night into Wednesday.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory from 6 PM this evening to 5 am EDT Monday
for anz250.
Small Craft Advisory from 6 PM this evening to 11 am EDT
Monday for anz254>256.
Small Craft Advisory from 10 PM this evening to 6 am EDT
Monday for anz235.

&&

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

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