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

Synopsis...
cool...damp conditions remain in place into Thursday morning...with
more widespread rainfall expected today. Dry weather returns later
Thursday into Friday as high pressure builds back across the region.
A cold front will move across New England later Saturday afternoon
and early Saturday night...followed by cooler and drier conditions
for Sunday and Monday.

&&

Near term /until 6 PM this evening/...
130 PM update...
period of rain beneath Upper Cutoff continues to pinwheel across
the region. Thankfully...rainfall rates have generally been
moderate at best...just a good soaking. Of concern for the rest of
the afternoon is the potential convective and sharpening of
inverted trough and moderate 40+ knots low level jet late this evening which
could increase the threat for heavy rainfall somewhere in the southeast
Massachusetts and Rhode Island region. This could lead to locally very heavy rainfall
amounts should they set up. However...nailing this down exactly is
difficult thanks to convective feedback issues.

Previous discussion...
an upper level low over Pennsylvania moves eastward over southern
New England today. Combined with the low pressure system well
southeast of Nantucket...an inverted trough should develop just
west of southern New England. This will create a deep layer of
lift that will allow rain to become widespread across the region
today. Persistent northeasterly flow brings in plenty of cool
moist air in off the ocean and precipitable waters are 125 to 175 percent of
normal for early October. This will allow for a much needed steady
rainfall across most of the area with roughly half an inch to an
inch of rain expected in most locations. Higher amounts are
possible where bands of heavier rain set up. While we can/T
determine exactly where these bands will develop...the best chance
for higher rainfall amounts looks to be across southeast mass
where rain will last the longest before the low pulls away to the
east.

Used locally produced bias corrected MOS for temperatures today
which will remain cool around 60 degrees for most locations.

&&

Short term /6 PM this evening through 6 PM Thursday/...
tonight...steady rain will come to an end slowly from west to east
as low pressure pulls farther away from the region. Rain is likely
to continue across eastern Massachusetts and Rhode Island through much of the night.
Continued easterly flow will keep low level moisture in place
allowing for low clouds...drizzle...and fog to remain across the
region. Low temperatures should be in the 50s.

Thursday...will start to see some drying...particularly in the west
as high pressure starts to build in. Cape and islands will be last
to lose the moisture but clouds should begin breaking up by the end
of the day. Below normal temperatures remain with highs around
60...except for the Connecticut valley where they may climb into the
middle 60s.

&&

Long term /Thursday night through Tuesday/...
big picture... Alaska shortwave digs over the western USA/Canada and
kicks the established upper trough east to the Great Lakes. This
brings a broad cyclonic flow over the eastern USA with below
normal heights while an upper ridge builds over the western USA.

Embedded in this flow...a closed low over New England moves off
through the Maritimes Thursday and Friday.

The dailies...

Thursday night-Friday... high pressure builds south over New
England. Cross sections of relative humidity show drying in most layers Thursday
night but then an increasing layer of moisture below 800 mb by
Friday afternoon. This suggests clearing...but followed by
increasing low clouds again during Friday. Relative humidity charts from the GFS
and European model (ecmwf) show cloud moisture being pushed west across the Gulf of
Maine from the departing coastal low...and into southeast New Hampshire/eastern
mass Friday afternoon. By Friday night the same models show light
precipitation over this area...suggesting sprinkles or drizzle.

We will have a dry forecast during Thursday night and Friday...but
with increasing clouds from the east Friday night along with
fog/drizzle and in east coastal areas a chance for measurable precipitation.

Light east winds will limit mixing...and temperatures in this shallow layer
will support maximum temperatures in the 60s...coolest near the east mass coast
and warmest in the CT valley.

Saturday... the upper trough moving across the Great Lakes deepens
as it moves it. The trough uses a 110 knot jet to push a cold front
east toward New England. Temperature profiles show a strong thermal
gradient across the front. The deepening of the trough also turns
the upper flow over New England more from the south-southwest
drawing moisture north...precipitable water values are forecast to
reach 1.5 to 1.6 inches. Stability parameters are less than
marginal...middle level lapse rates are 5c/km or less and totals are
less than 44.

Forecast will continue to feature likely probability of precipitation but slightly slower
than previously. This slower timing aligns with similar trends in
the GFS and European model (ecmwf) with windshift in the CT valley 2 PM to 8 PM and
in the coastal plain 8 PM to midnight.

Sunday-Monday-Tuesday...shortwave moves north of our area
Sunday...but the main trough axis remains over the Great Lakes.
Contour heights at 500 mb are below normal over the weekend but then
moderate to near normal during the first part of next week. Sunday
and Monday look dry with seasonably cool temperatures. The trough axis
ejects northeast by Tuesday and may support a chance of showers at
that time.

&&

Aviation /17z Wednesday through Sunday/...
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...Thursday night through Sunday...moderate confidence.

Thursday night-Friday...VFR. Areas of IFR ceilings/visibilities in patchy fog
early Friday morning. Areas of IFR ceilings move west off the ocean
into east coastal Massachusetts including the cape and islands late
Friday and more likely Friday night.

Saturday...IFR ceilings from the Worcester Hills east during the
morning. VFR farther west to start the day but lowering to MVFR and
scattered IFR as a cold front approaches late in the day and brings
showers. Wind shifts from south during the day to west behind the
cold front late in the day and early at night.

Sunday...VFR with gusty west winds. High pressure builds over the
region with fair weather.

&&

Marine...
forecaster confidence levels...

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

Short term...today through Thursday...high confidence

Persistent northeasterly winds increase through the day gusting
to around 25 kts by about midday today. Seas continue to
increase...particularly on the northeastern waters and into Boston
Harbor and Cape Cod Bay. Added all the waters except for
Narragansett Bay to the Small Craft Advisory for both winds and
seas and all small craft advisories have been extended through
Thursday.

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

Thursday night-Friday...northeast winds gusting 20 to 25 knots will
maintain 5 to 9 foot seas on the outer waters and exposed eastern
waters such as Massachusetts Bay. Small Craft Advisory will be
needed. Fog and low clouds moving in from the Gulf of Maine may
create poor visibilities Friday night.

Saturday... lingering poor visibilities Saturday morning in fog and low
clouds. These conditions will improve later in the day as a cold
front approaches with showers. South winds will gust 25 to 30 knots
during the day and evening...shifting to west after the cold front
moves through Saturday night. Seas will continue at 5 to 8 feet on
the outer waters and other exposed waters. Small Craft Advisory is
likely.

Sunday...winds and seas diminish a little but still rough. Seas will
linger at 5 to 7 feet on the outer waters. West to southwest winds
will gust to 25 knots.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory until 8 PM EDT Thursday for anz232.
Small Craft Advisory until 5 PM EDT Thursday for anz233-234.
Small Craft Advisory from 5 PM this afternoon to 8 PM EDT
Thursday for anz230.
Small Craft Advisory until 8 PM EDT Thursday for anz231-235-
237-250-251-254>256.

&&

$$
Synopsis...wtb/rlg
near term...doody/rlg
short term...rlg
long term...wtb
aviation...wtb/doody
marine...wtb/rlg

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