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Area forecast discussion 
National Weather Service Taunton Massachusetts
1046 am EDT Friday Sep 19 2014

cool temperatures will prevail today as high pressure moves in.
There is the possibility of some early morning frost Saturday
morning. A cold front crosses New England Sunday night night while
a low pressure center rapidly passes southeast of Nantucket on its
way to Nova Scotia. After the cold front passes offshore Monday
morning...high pressure dominates the region through all of next


Near term /until 6 PM this evening/...
1025 am update...
bands of ocean clouds have moved into east Rhode Island/east coastal and southeast Massachusetts
this morning on north-NE winds that remain rather gusty as colder air
moves across. Noting the clouds starting to dissipate further
inland as drier air works in from high pressure building S out of
southern Quebec and northern New England. Expect these clouds to
continue to dissipate as the ocean winds diminishes this

Temperatures at 14z have recovered to the middle 40s to middle 50s after
overnight lows ranging from the Lower-Middle 30s well inland /mainly
across S New Hampshire/ to the lower 50s along the southeast coast of Massachusetts to coastal
Rhode Island.

850 mb temperatures remain cool through most of the day across the region...
ranging from around 0c across S New Hampshire to +3-4c across S coastal areas
around midday. As winds shift to east and diminish as the high builds
across northern New England...should see 850 mb temperatures increase by
evening. This should allow daytime temperatures to rise to the middle 50s to
lower 60s at most locations...though could reach the middle 60s
across the lower CT valley this afternoon.

Have updated grids to bring conditions current and incorporated
into the afternoon forecast trends.


Short term /6 PM this evening through 6 PM Saturday/...
high pressure will crest early in the evening then begin to slide
offshore. Dry weather prevails although weak inverted trough may lead to
some building cloud cover just west of the box County Warning Area during the early
morning hours...more on the impacts of that in a bit.

The key tonight will be potential for cool temperatures and another round
of potential frost. Overall...conditions are more ripe for
radiational cooling than Thursday night thanks to a much weakened pressure
gradient under the high pressure and another start of mainly sky clear
skies. However there are some mitigating factors to
being the cloud cover just mentioned...should that build far
enough inland of the Hudson Valley region...its not out of the
question this could limit the falling temperatures. Models do indicate
the typical dewpt rise under the return flow as high exits to the
east...but feel that this is likely much too fast given the very dry
start and continued influence of the high itself. While each of
these may limit frost notice that bias corrected
temperatures support some middle 30s particularly in northwest Massachusetts and SW New Hampshire and
even a few of the typically cooler east Massachusetts suburbs. Therefore...may
need to monitor for another round of frost advisories today. Will
hold off on issuance this morning given current frost advisory in
place...but those with sensitive vegetation may wish to take
action today nonetheless.

high pressure continues slow slide to the east but remains in control as
inverted ridging. This is enhanced by subsidence between
approaching ocean system and cold front to the west.
Therefore...although upper level cloud cover is likely to increase
across the west through the day...feel much of the day will remain
dry. Middle level temperatures moderate under S-SW flow to about +8c to +10c
which with full mixing suggests temperatures may rise above seasonal
normals...however the cool start to the day and slow rise in these
middle level temperatures suggests that actual highs may be closer to normal.
Mainly upper 60s and low 70s.


Long term /Saturday night through Thursday/...
* chance of showers Sunday night with cold front passage
* then probably dry all next week


Fairly sharp short wave trough and associated front expected to cross
New England Sunday night. A potentially significant complication in
the forecast is the likely passage of a surface low just southeast of
Nantucket ahead of the cold front. Since this low pressure system
may contain tropical processes...confidence in how this system will
interact with the middle latitude short wave and cold front is low. We
note a dramatic development of an associated upper jet with the
coastal low from 80 to 100+ knots in less than 12 hours Sunday night.
The model consensus continues to keep this system distinctly
separate from the frontal system until well past New England. And
there is a strong hint that much of southern New England could be
caught in a subsidence zone between the front and coastal surface
low with resulting minimal rainfall. However...if the coastal low
pressure should have a more distinct identity as a tropical or
subtropical system...then one might expect a somewhat slower speed
and back building of the upper jet to at least bring a higher threat
of significant rainfall to southeast New England. For now plan to take a
conservative approach with probability of precipitation and quantitative precipitation forecast but keep in mind there is
above average uncertainty for the late Sunday through Sunday night
time frame. Once the low off the coast passes by and the cold front
sweeps offshore Monday morning...medium range models are in fairly
close agreement on a high amplitude upper ridge building over
eastern North America with very little chance of rain for the
foreseeable future in our area. We would anticipate relatively mild
daytime temperatures and cool overnight temperatures in this pattern
with relatively high diurnal ranges...near to above normal afternoon
temperatures and near to below normal late night/early morning

More specifically...

Saturday night...dry and milder as return flow about surface high
pressure east of area and approaching cold front over the
Great Lakes becomes better established.

Sunday...thinking that much of area will remain dry with two notable
exceptions. One exception could be across northwest Massachusetts and SW New Hampshire where air
mass becomes marginally unstable and more moist ahead of an
approaching cold front. Intend to indicate chance
showers/thunderstorms roughly northwest of a mht-orh-bdl line. There will
be increasing vertical shear and cannot rule out an isolated strong
or even severe thunderstorm northwest Massachusetts and SW New Hampshire late Sunday afternoon or
evening. The exception is the southeast portion of the forecast area. Will
raise probability of precipitation to chance in southeast ahead of coastal low by Sunday afternoon
as moisture may stream rapidly northward from coastal low pressure
system to the south...which is expected to trigger a strengthening
of an upper level jet along/just off the coast.

Sunday per overview section we have above average
uncertainty for this forecast period as rain chances will depend
upon interaction between cold front and low pressure passing just
offshore. For now plan on chance probability of precipitation with highest values far northwest and
far southeast. Vertical shear increases to 40 to 50 knots 0 to 6 km Sunday
evening and any thunderstorms...most likely northwest sections...could
contain strong winds.

Monday...lingering chance of showers far southeast and otherwise dry as
surface high pressure builds into the region. May be breezy from the
northwest due to combination of moderately tight surface pressure gradient
and moderate cold air advection.

Tuesday through Thursday...relatively high confidence of dry
conditions through the period with mild days and cool nights. It is
possible that radiational cooling during Tuesday night and/or
Wednesday night could be robust enough for some patchy frost SW New Hampshire
and northwest Massachusetts...but confidence on this is quite low this far out.
Otherwise...expect the main story is that we will be increasing a
precipitation deficit for much of area next week. Do not see any
credible rain threat in the foreseeable future after Sunday night.


Aviation /14z Friday through Tuesday/...
forecaster confidence levels...

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

Short term /through Saturday/...high confidence.

Mainly VFR through the period...except some early morning fog is
possible at the typical terminals late tonight/early Sat.

Winds sustained around 10 knots continue through the early half of
the day with a few gusts to 20 knots...especially southeast coastal areas.
The winds diminish tonight. Winds out of the S-SW on Sat...with
afternoon gusts to 20 knots possible once again.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook...Saturday night through Tuesday...

High confidence through the period except moderate confidence Sunday
afternoon and night.

Saturday night...VFR expected except for possibly patchy valley fog.

Sunday...VFR expected except MVFR ceilings/visibilities in vicinity of
scattered showers/thunderstorms northwest of a mht-orh-bdl line Sunday
afternoon. A second area of MVFR ceilings/visibilities may develop Sunday
afternoon along and S of a bid-hya-cqx line in areas of showers.

Sunday night...MVFR ceilings/visibilities possible in showers across the region.

Monday through Tuesday...VFR conditions expected.


forecaster confidence levels...

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

Short term /through Saturday/...high confidence.

This afternoon and tonight...cold air advection continues across
the waters through continued with north-NE winds gusting
up to 25 knots. Winds should diminish from north-S this afternoon as high
pressure builds toward the waters. Lingering wind waves at 5-6 feet will
continue on the outer waters...though starting to see them subside
east of Cape Ann /buoy 44029/. Have continued small crafts for now.
Will monitor for decreasing trends on the near shore waters and
possibility of lowering small crafts during the afternoon.

Will likely need to continue small crafts into the evening on the
outer waters. Expect conditions to improve overnight as winds
shift to the S and...along with seas...diminish.

S-SW winds dominate...with a few gusts to around 20 knots in the
afternoon...but should generally remain below Small Craft Advisory
thresholds. Seas too will remain generally 3-4 feet on the ocean
waters and lower near shore.

Outlook...Saturday night through Tuesday...moderate confidence.

Saturday night through Sunday...high confidence of winds and seas
below Small Craft Advisory levels except possible building swell
over the southern coastal waters late Sunday.

Sunday night into Monday...moderate confidence. May see seas
building to Small Craft Advisory levels across at least the outer
waters Sunday night and persisting into Monday. In addition...may
have a period of Small Craft Advisory gusts from the northwest during the
day Monday. Low pressure center passing southeast of Nantucket may have
very significant winds and seas on its east side...but probably
well offshore of our coastal waters.

Tuesday...moderate to high confidence of winds and seas below Small
Craft Advisory levels.


Box watches/warnings/advisories...
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory until 2 PM EDT this afternoon for
Small Craft Advisory until 5 PM EDT this afternoon for anz231-
Small Craft Advisory until 8 PM EDT this evening for anz250.
Small Craft Advisory until midnight EDT tonight for anz254-255.
Small Craft Advisory until 10 PM EDT this evening for anz256.


near term...evt
short term...doody
long term...Thompson

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