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Area forecast discussion 
National Weather Service Taunton Massachusetts
410 PM EDT Wednesday Oct 1 2014

Synopsis...
the cool...wet weather continues into early Thursday. High
pressure begins to bring dry air back in late tomorrow into
Friday. A frontal system will bring a period of rain Saturday
into Saturday evening...followed by cooler weather Sunday.
Temperatures moderate early next week with a chance of showers
Tuesday as another front approaches.

&&

Near term /until 6 am Thursday morning/...
slow development of a hanging trowal formation across the region
late this afternoon. This combined with upper level cutoff
meandering along the S coastal region continues to combine with
moist column /pwats locally exceed 1.5 inches/ continues to yield
bands of rainfall stretching across the whole box County Warning Area. The NE flow
continues too...streaming in plenty of marine moisture from the
Gulf of Maine. This trowal/surface inverted trough feature will be
defining the overnight weather.

Already we are seeing the development of convection in the
vicinity of ack where a modest axis of upper level instability
defined by a dry slot along the Upper Cutoff exists. Although
soundings suggest most of this is elevated it is enough to
initiate locally heavy convective elements. This is also along a
slowly increasing Ely low level jet...which is expected to increase to
around 40-45 knots at h92 between 00z and 06z this evening. The
combination of this moisture /pwats nearly 2 Standard deviations above
normal/ the robust low level jet and modest elevated instability under the
slowly erd moving cutoff all suggest that pockets of heavy
rainfall are likely somewhere in around southeast Massachusetts. 12z guidance all
now generally agree on a locally high quantitative precipitation forecast bullseye although with
some disagreement and convective feedback apparent. The
possibility that some mesoscale-scale guidance shows these convective
elements continuing/increasing overnight has led to the issuance
of a Flood Watch for southeast Massachusetts...where pockets of total
rainfall could quickly exceed 3 inches in spots /see Hydro section
below/. In fact...reports already indicate over an inch has fallen
in the watch area. The flux in the location of the inverted trough
does suggest that the axis could lie offshore...but with the
potential so close and convection already occurring late this
afternoon...feel the watch is warranted for primarily the urban
flood threat.

Otherwise...elsewhere across the region...periodic rainfall is
likely to continue as moisture continues to stream in from the east.
Although do note the increase in dry air from the west as high pressure
attempts to regain control. Therefore...by 12z the focus mainly
may be away from northwest Massachusetts and SW New Hampshire.

Mins remain mostly in the 50s tonight.

&&

Short term /6 am Thursday morning through 6 PM Thursday/...
tomorrow...
early morning rains continue especially across the east half of the
region as surface inverted trough and upper level cutoff begin slow shift
offshore. Drier air will be attempting to work in from the west
through the day...however gradient flow remains mainly N-NE.
Therefore...even though rainfall potential will be decreasing
through the day...the low clouds/fog may remain at least into the
early afternoon with some clearing possible...slowly...from west to east
during the afternoon such that some actually may see a sunset. The
east shores may remain socked in with clouds most of the day
however...as it will take until high pressure builds over and a modest
subsidence inversion arrives to scour out some of the low-middle level
moisture. Highs remain on the cool side...mainly upper 50s and low
60s due to this cloud cover.

Tomorrow night...
continued improvement as high pressure begins to nose in from the north.
Noting enough drying through the column across southern New England
that some may see some cirrus filtered Star-light and even some
clearing skies. With the drier air moving in dewpoints are likely to
fall back into the 40s and temperatures are likely to head this way as
well. Therefore...with some leftover ground moisture...fog is
likely in some spots...and may even be locally dense.

&&

Long term /Thursday night through Wednesday/...
highlights...

* a period of rain likely Sat into Sat evening
* dry and cooler Sunday
* moderating temperatures early next week with next chance of showers Tuesday

Overview...
models are in good agreement with negative tilt shortwave rotating
around Great Lakes low this weekend and timing of a strong cold front
late Sat and Sat evening which will bring a period of rain...most of
which looks to fall Sat afternoon and evening. Middle level low lifts north
into Canada through early next week with trough setting up across the
Great Lakes and broad cyclonic SW flow into new eng. Models differ on
the amplitude of next shortwave rotating around the mean trough but
but it appears some unsettled weather is possible Tuesday.

Dailies...

Friday...
southern New England will be in between systems with high pressure ridge across the
region. The column is mostly dry which supports mosunny skies...but
models indicate low level moisture backing in from the east which
may bring some low clouds to cape/islands and into east Massachusetts during the
afternoon. These low clouds are expected to expand west across much
of the region Friday night and models indicate potential for some
drizzle developing in eastern new eng with abundant low level
moisture and NE flow below drier air aloft. Temperatures Friday will be in the
60s...coolest east Massachusetts coast and mildest in the CT valley.

Saturday into Saturday night...
models in decent agreement on timing of the cold front late Sat and
Sat evening across southern New England...reaching CT valley by 00z and off the coast
by 06z. Modest low level jet and low level convergence along with
precipitable water plume 1.5"+ will bring a period of widespread showers to southern New England.
Timing looks to be mostly in the afternoon into the evening from
west to east...although areas of drizzle possible through the
morning and it/S possible bulk of rain could hold off until late Sat
for east coastal Massachusetts and cape/islands. There is some marginal
instability noted in the models so cant rule out a brief rumble of
thunder or heavy convective shower at the nose of the low level jet...but
system is progressive which will limit duration of rainfall with
rain exiting the region 00-06z from west to east.

Sunday and Monday...
dry and somewhat cooler weather Sunday with modest westerly winds
and mosunny skies...then breezy and milder Monday as warm air
advection begins with developing SW flow. A bit more clouds possible
Monday...especially west zones as middle level moisture moves in from
the west in warm air advection pattern.

Tuesday and Wednesday...
despite differences in amplitude of next shortwave...GFS and European model (ecmwf)
indicate potential for showers Tuesday as some sort of boundary
approaches from the west. Then some drying on Wednesday although
this is low confidence this far out. Seasonably mild temperatures expected.

&&

Aviation /19z Wednesday through Monday/...
forecaster confidence levels...

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

Short term...today through Thursday...moderate confidence.

Through tonight...
mainly mix of IFR/MVFR in periods of rain and low ceilings through
the rest of the day. The periods of rain continue
tonight...especially in the eastern half of the region. Between
rainfall...conditions could briefly dip to LIFR at some terminals.
Also...there is the threat for heavy rainfall and even a brief
thundershower for Rhode Island and southeast Massachusetts late this evening and early
tomorrow morning. Winds increase out of the north-NE with gusts 25-30
knots possible at near coastal terminals overnight.

Tomorrow into tomorrow night...
rainfall gradually comes to an end with a slow lift from IFR/MVFR
to VFR from west to east. Some east locations may remain IFR/MVFR for much
of the day and may wait until tomorrow night before fully breaking
out. However...the overall trend is expected to be for
improvement.

Kbos...high confidence in trends...lower confidence in timing.

Kbdl...high confidence in trends...lower confidence in timing.

Outlook...Friday through Monday...

Friday...moderate confidence. Mostly VFR...but MVFR ceilings may back in
from the ocean into east coastal Massachusetts and cape/islands Friday afternoon.
Expect ceilings lowering to IFR Friday night and expanding west across the
region with patchy fog and drizzle possible.

Saturday...moderate confidence. Widespread MVFR/IFR ceilings expected.
Patchy drizzle in the morning...then showers will move west to east
across southern New England Sat afternoon and evening ahead of a cold front. South
winds Sat shifting to west Sat night.

Sunday and Monday...high confidence. VFR.

&&

Marine...
forecaster confidence levels...

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

Short term...tonight through tomorrow night ... confidence

Increasing NE winds are expected through tonight into
tomorrow...such that some wind gusts around 30 knots are possible.
Not even out of the question a brief wind gust approaches gale
force in some of the heavier rainfall expected especially along
the southeastern waters of southern New England. Small craft
advisories continue...and have been extended into tomorrow night.
Even though winds will begin to drop off by then...swells
approaching 9 feet are possible on the ocean waters and these will
take some time to fall.

Outlook...Thursday night through Sunday...moderate confidence.

Friday...expect diminishing NE winds during the day with speeds
remaining below Small Craft Advisory thresholds. But hazardous seas will continue
over outer waters.

Saturday...southerly winds may gust up to 25 knots...especially
nearshore waters as low level jet moves across the waters. Current
forecast winds may eventually need to be increased. Visibilities will be
reduced in areas of drizzle and fog in the morning and showers
during the afternoon and evening. Winds shift to west Sat night with
improving visibilities.

Sunday...west wind gusts could reach Small Craft Advisory levels and hazardous seas
will persist.

Monday...SW winds mostly below Small Craft Advisory with seas subsiding below 5 feet.

&&

Hydrology...
Flood Watch has been issued for southeastern Massachusetts. The
issue at hand is the possibility of locally heavy rainfall this
evening and overnight. Rainfall rates of 1-2 inches are possible
along with final storm totals of 3-6 inches. This may lead to
urban/street and even possibly some basement flooding in the watch
area. There is some uncertainty in exactly where the heaviest axis
of rainfall sets up...as it may remain offshore. However...given
the possibility of it being further west...and that heavy rain is
currently falling in this area...feel the watch is warranted. May
also need to monitor for possible expansion further west...for the
urban areas of Rhode Island given that some slight westward progression is
evident in some guidance.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...Flood Watch through Thursday morning for maz017>024.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory until 2 am EDT Friday for anz232-235-237.
Small Craft Advisory until 8 PM EDT Thursday for anz231-233-
234.
Small Craft Advisory until 8 PM EDT Thursday for anz230.
Small Craft Advisory until 8 am EDT Friday for anz250-251-
254>256.

&&

$$
Synopsis...kjc/doody
near term...doody
short term...doody
long term...kjc
aviation...kjc/doody
marine...kjc/doody
hydrology...staff

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