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Area forecast discussion 
National Weather Service Taunton Massachusetts
721 am EDT Wednesday Sep 17 2014

high pressure will build into the region bringing cooler and drier
weather through the remainder of the week. Some frost is possible
early Friday morning in some areas. The high will then slip
offshore and southwest flow behind it will allow temperatures to
warm to near or above normal Sunday and Monday. A cold front moves
through on Monday...followed by cooler weather by Tuesday.


Near term /until 6 PM this evening/...
7 am update...
aside from a few remaining patches of fog across the
region...mainly sky clear conditions away from the S coast...where some
cirrus from an offshore system move through. Therefore...plenty of
sunshine to go around...which will lead to a rapid increase in
temperatures this morning even after the cool start. Current forecast
still reflects these trends no major changes needed
with this update.

Previous discussion...

Calm winds...clear skies...and a bit of leftover moisture from the
scattered rain showers yesterday has allowed patchy fog to
develop across the region. This fog is locally dense...reducing
visibilities below a mile in many locations and below a quarter of
a mile in some areas.

High pressure builds into the region today as low pressure moves
into southern Ontario. Expect mostly sunny skies and temperatures
climbing into the upper 60s to lower 70s.


Short term /6 PM this evening through 6 PM Thursday/...
tonight...light winds turn to the southwest ahead of a cold front
stemming from a weak low pressure system in southeastern Canada.
This will keep temperatures on the cool side but still in the middle
40s to middle 50s.

Thursday...the cold front will move through southern New England
during the day...shifting winds to the northwest. The front appears
to be moisture starved by the time it moves into the area so expect
nothing more than a few clouds. Main concern with the front will be
it ushering in cooler temperatures.


Long term /Thursday night through Tuesday/...
overview and model preferences...
the primary influence in the sensible weather through the long term
continues to be two reasonably deep longwave troughs. The first will
gradually lift out toward the end of the week as middle level ridge
slides west-east across the Continental U.S....yielding rising heights and more
zonal flow. However...the near Hudson Bay cutoff holds even as The
Heights rise across southern Canada and the a
second strong/cold shortwave slides out of the alaskan
region...the longwave trough redevelops early next week.
Therefore...expect...after a cool end of the work week...a period
of warming and milder weather for the weekend followed by another
return to cool conditions by the early half of next week. Given
both ensembles and operational guidance has general agreement with
these synoptic scale features...will use a blend as a baseline for
this forecast.


Thursday night into Friday night...
potential for the coolest portion of the forecast. A weak cold
front will slide through the area late Thursday...but allow for gradual
clearing with cold high pressure building over Thursday night. Dewpoints should
fall back into the assuming clearing occurs quickly
enough with radiational cooling...temperatures could fall into the middle
30s in northwest Massachusetts/SW New Hampshire valleys which may require frost advisories.
Elsewhere...still a cool morning Friday...upper 30s and low 40s
possible. This cool start and high pressure means dry weather with highs
topping out in the upper 50s to middle 60s in the warmest spots. Good
setup for radiational cooling again Friday night...but return flow
and rising dewpoints may mean mins are a bit warmer than Thursday night.

Sat and sun...
weak warm front slides through the region on Sat. At this looks like high pressure remains in control with subsidence
suppressing any weak lift associated with the front. So will keep
the forecast dry. In fact...subsidence between a low pressure moving
through southern Canada...and offshore of the middle Atlantic through the
weekend is likely to yield mainly dry conditions throughout.
Models do indicate this as an inverted ridge from high pressure in the
Maritimes. Otherwise...rising heights and 850 mb temperatures approaching
+12c on Sat...then +14c on sun suggest temperatures rise above normal by
sun. Therefore...looking at highs in the low-middle 70s are expected
Sat...reaching close to 80 by sun.

Sun night into Monday...
cold front associated with the northern system will cross there region
during this period. Still a few issues to work out regarding
timing. However...with at least modest precipitable waters /around 1.5 inches/
and some lift suspect a period of showers are possible with this
frontal passage. European model (ecmwf) GOES back and forth between a dry and
frontal passage and a wet one with secondary low pressure development.
But feel that at least some slight to chance probability of precipitation are
warranted...especially as k-values approach 30.

Tuesday and Wednesday...
longwave trough and cutoff low pressure develop in vicinity of the
Great Lakes. Models indicate that thickness values could drop to
around 540-550dm. Therefore...conditions look ripe for another
cool down early next week.


Aviation /12z Wednesday through Sunday/...
forecaster confidence levels...

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

Short-term /through Wednesday/...high confidence.

Through 12z...moderate confidence. Mainly VFR. Locally dense fog has
developed across portions of the region reducing visibilities to

Today through Thursday...high confidence. Visibilities should
improve quickly as fog dissipates. VFR conditions expected.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook...Thursday night through Sunday...high confidence.

Mainly VFR through the period. Although some overnight fog at
typically prone airports may lead to IFR conditions...particularly
Friday night into Sat night.


forecaster confidence levels...

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

Short-term /through Wednesday night/...moderate confidence.

Moderate to high confidence. Swell from Hurricane Edouard will
slowly build into the coastal waters with increasing seas.
Regular forecast guidance has been unreliable but hurricane wave
watch guidance looks much more reasonable so have used that. Expect
seas to remain below 5 feet except perhaps a few hours Thursday
morning. Winds remain below 15 kts through the period.

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

Thursday night Friday...high pressure north of the waters will bring a
stronger northeast wind with potential for 20 knots especially
around Nantucket and on the southern outer waters. Seas may increase
to 4-6 feet in this northeast flow...diminishing as the winds
diminish Friday evening. Small craft advisories may be needed for

Saturday-Sunday...high pressure moves off through the Maritimes. The
winds will shift to south Saturday and southwest Sunday. Gusts
20-25 kts both days with potential for 25 knot gusts on Sunday.
Most seas will remain below 5 feet...but the waters east of mass
Bay and Ipswich Bay may see seas rise again to around 5 feet.


Box watches/warnings/advisories...
New Hampshire...none.
Rhode Island...none.


near term...doody/rlg
short term...rlg
long term...doody

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