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Area forecast discussion 
National Weather Service Taunton Massachusetts
902 am EDT Sat Sep 20 2014

milder temperatures return today and tomorrow. However a few
showers are possible late tonight and early Sunday as well. A
cold front crosses New England Sunday night...while low pressure
rapidly passes southeast of Nantucket on its way to Nova Scotia.
After this cold front passes offshore Monday morning...high pressure
dominates through all of next week. Mild temperatures linger Monday but
then become cooler than normal thereafter before moderating late
next week.


Near term /until 6 PM this evening/...

9 am update...

Skies were mostly sunny at middle morning in most locales...except for
a deck of low clouds still covering southern New Hampshire/western Massachusetts. Should
see these low clouds erode to some degree over the next few hours.
Therefore...expect partly to mostly sunny skies across all areas by

Despite the very chilly start early this morning...850 mb temperatures
warming to between +8c to +10c and increased mixing will allow for a
rapid recovery. Highs should actually top out in the upper 60s to
the lower 70s in many locations by middle to late afternoon.


Short term /6 PM this evening through 6 PM Sunday/...
tricky forecast for tonight. Guidance continues to really struggle
with a weak area of convection associated with tropical moisture
currently sitting off of the southeast coast. While the incoming and
deepening trough to the west is likely to kick this wave to the north...the
speed and exact trajectory remain in question due to an overall
lack of baroclinicity to work with. 12z guidance kept the final
upper level jet streak and surface wave mainly east of the 40/70 benchmark
while 00z runs have now brought it inside by 12z. In any
case...expect increasing moisture tonight as precipitable waters approach 1.5
inches by the early morning hours /about 1-2 Standard deviations above
normal/. While the bulk of the dynamic forcing and instability
remain to notice as an inverted trough extends into southern New
England after 06z...that a pocket of modest instability follows.
Mu cape values of about 500-1000j/kg above the near surface warm
layer. This is colocated with the higher precipitable waters and k-values near it is possible that modest convection /showers and a
possible T-storm/ spills across mainly the southern tier of southern New
England through the morning hours /particularly about 09z-15z/.
The higher precipitable waters suggest a pocket of heavy rain can/T be ruled
out. Will continue to highlight chance probability of precipitation from southern CT-RI-se Massachusetts
with slight chance probability of precipitation further north until this can be better
resolved. Thankfully shear is modest and stronger associated with
a cold front well to the northwest of New England...but this will need to
be watched. There are a couple of mitigating factors to
note...hence the chance and slight chance probability of precipitation...ongoing
convection offshore where upper level and low level jet is stronger
could usurp instability and moisture away from southern New England.
Also...suspect an area of subsidence will reside across the region
in between the northern system and this weaker offshore wave. Models do
reflect this as a dry layer from about h6 and up.

threat for modest convection lingers into to about middle day as the
offshore wave makes its closest pass. However...suspect that a
period of mainly dry conditions may prevail as the system moves
offshore and a dry slot with subsidence develops across the area
during the afternoon and early evening. This area of subsidence is
the result of the offshore storm system and a slow approaching
cold front to the west...along which is likely to be some afternoon
and evening convection. At this time...instability looks modest at
best despite the increase in surface dewpoints. Breaks of sun are
possible...which may have to be watched...but at this
least through 00z Monday...suspect the showers and thunderstorms
remain mostly to the west. High temperatures in the middle-upper 70s are
expected...although a few spots may reach around the 80f mark
especially if some breaks of sun are observed.


Long term /Sunday night through Friday/...

* low risk of showers Sun night then dry much of next week
* mild Sun night/Monday then cooler than normal midweek before
moderating late next week

Synoptic overview and guidance evaluation...

00z deterministic and ensemble guidance are in good agreement on the
large scale flow which features a high amplitude trough moving
across the northeast Sun night and Monday...then slowly lifting out
into the Maritimes the middle of next week. This will yield a low
risk of showers Sun night followed by cooler weather Monday night into
the middle of next week. Height rises look to be a good bet as
subtropical ridge builds into the region late next week. Precise
temperatures will be difficult at this time range as all model guidance
indicates some weaknesses within the northeastern periphery of the
subtropical ridge within the northeast states.

Sun night...trailing northern stream short wave and attending
surface cold front sweep across the region. Modest qg forcing and
deep layer moisture accompany the trough and surface front. Thus
expect scattered showers with highest probs northwest Massachusetts into southwest
New Hampshire. It will remain mild given frontal passage not until after daybreak Monday.

Monday...any lingering showers associated with the front will clear
Cape Cod early in the morning. Thereafter expecting a mix of sun and
clouds along with a well mixed blyr as west winds gust up to 25 miles per hour.
Highs should climb well into 70s including Cape Cod and the islands
as wind direction will be westerly.

Tuesday through Thursday...1035 mb high crest over New England this
period bringing mild days but cool nights. Leaned toward the cooler
mavmos during the nights. Dry weather prevails along with light

Friday...subtropical ridge builds northward along with moderating
temperatures. Difficult to say how warm given some guidance suggest a
weakness within the ridge.


Aviation /13z Saturday through Wednesday/...
forecaster confidence levels...

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

Short term /through Sunday/...

7 am update...

No major changes to 06z tafs. Earlier discussion below.


Through today...high confidence.
Mainly VFR outside of some localized for at typically prone
terminals this morning. Winds S-SW with a few gusts to around 20
knots today.

Tonight...moderate confidence.
VFR to start...but some terminals see MVFR ceilings and possibly IFR
visibilities in some low clouds and fog especially after 04z. Best chance
looks to be CT and west Massachusetts terminals...but some lower categories
further east not out of the question. Late night shower or possibly
even an isolated T-storm possible mainly southern CT/Rhode Island and southeast Massachusetts.

MVFR/VFR start gives way to mainly VFR during the afternoon and
early evening. Isolated -shra possible.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf through today...lower
confidence in timing of MVFR possible late tonight/early Sun

Outlook...Sunday night through Wednesday...

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

VFR through the period. The only exception will be Sunday night when
possible MVFR may accompany scattered showers. Modest west wind Monday 15-20 knots.
Otherwise fairly light winds and dry weather prevails.


forecaster confidence levels...

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

Short term /through Saturday night/...

Today...high confidence.
S-SW winds develop through the day today. Wind gusts may approach
25 knots at times along the northern tier of waters against the Gulf of
Maine...but most gusts should remain below. Seas mainly 4 feet or

Tonight...moderate confidence.
S wind continue...but diminish somewhat overnight tonight.
Conditions remain below Small Craft Advisory thresholds along with
seas. Some showers and even a possible T-storm over the southeast waters
after 04z along with the potential for fog and reduced visibilities.

Sun...moderate confidence.
Winds remain S and even shift to the southeast through the day. While
wind gusts generally remain below small craft thresholds...not out
of the question seas reach the 5 feet mark on the southern ocean waters
by late in the day. Otherwise...bulk of the showers and
thunderstorms should shift offshore through the morning hours.

Outlook...Sunday night through Wednesday...

Modest west wind Monday into Tuesday then light winds as high pressure crest over
the area Tuesday night and beyond.


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


near term...Frank
short term...doody
long term...nocera

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