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Area forecast discussion 
National Weather Service Taunton Massachusetts
1115 am EDT Friday Oct 9 2015

low pressure and its attending cold front will yield widespread
showers to the region this afternoon and evening...along with mild
conditions. Behind the front...dry but much cooler weather late
tonight into Saturday. High pressure provides dry weather for the
remainder of the Holiday weekend along with a warming trend Sunday
and Monday. A cold front may bring a few showers Monday night into
Tuesday before dry weather returns Wednesday and Thursday.


Near term /until 6 PM this evening/...
*** heavy showers & gusty winds likely this afternoon and evening ***

1115 am update...
with bulk of the forecast on track...updates were limited. Primary
changes with this update were to attempt to better time clouds
and rainfall. Minor tweaks to temperatures to account for observed

Previous discussion...

Low pressure exits the eastern Great Lakes and moves across northern New York
state and northern New England today. Fairly robust jet dynamics
will act on a moist airmass with precipitable waters up to +2 Standard...about 1.5
inches. Impressive low level jet associated with this trough and
will yield strong warm air advection yielding modest elevated
instability. This will enhance the response from the forcing for
ascent and result in widespread showers with locally heavy

Timing for showers is focused mainly in the afternoon and early
evening with showers affecting western Massachusetts and CT beginning later
this morning.

This synoptic setup yields a high shear/Low Cape environment with 0-
1 km shear of 20-30 knots this afternoon. Typically the case in these
events - will there be sufficient low level instability for an
isolated T-storm with strong winds. While middle level lapse rates are
not impressive...0-3km and 925mb-700 lapse rates are marginal 6-
6.5c/km with a focus across CT/Rhode Island and south of the Mass Pike in
western-central Massachusetts. This is a result of strong low level warm air
advection with surface dew points climbing into the l60s today across the
area along with surface temperatures rising into the l70s. Both anomalous
for early Oct.

What could be the wild card to potential storms is additional jet
energy diving into the base of the trough later today yielding a 100
knots upper level jet streak moving across the area. This will enhance
the forcing for ascent as well increase wind fields. The hi res guidance
such as the arw and nmm hint at this with a sharp increase in quantitative precipitation forecast
and model simulated reflectivity after 18z across the region ahead
of the cold front.

So while most of the area will just see heavy showers and gusty
winds there is a low risk of an isolated strong T-storm. If low
level lapse rates/instability is greater than models simulate there
is a very low risk that a strong storm could yield a brief isolated
tornado. However the more likely scenario is for a period of heavy
showers with gusty winds.


Short term /6 PM this evening through 6 PM Saturday/...

Any evening showers move offshore quickly with an abrupt wind shift
to the northwest with the frontal passage. Model soundings suggest northwest winds behind
the front could gusts up to 35 miles per hour in the cold air advection and
modest pressure rises. Dry air quickly invades the area so expect
rapidly clearing from northwest to southeast. Much cooler with dew points crashing
from l60s early in the evening into the 40s and 30s by sunrise Sat.


Definitely a fall-like day with highs only 55 to 60. Gusty north
winds in the morning quickly diminish by midday as 1020 mb high
crest over the region. Abundant sunshine and light winds in the
afternoon will help offset the cool temperatures.


Long term /Saturday night through Thursday/...
* dry with a warming trend for the Holiday weekend
* few showers Tuesday followed by dry and seasonable weather

Overview and model preferences...
noting better agreement with the 09.00z model guidance
particularly with the late phasing of northern/southern stream shortwaves
for early next week. Otherwise...the weak ridging over the weekend
giving way to this feature are well agreed upon.
Therefore...agree with the previous forecaster that confidence is
generally high in details through much of the long term. After
this trough passage...slow deepening of longwave trough associated
with a cutoff settling across Hudson Bay. This increased cyclonic
and influx of colder air suggest a trend toward cooler
temperatures by next week. In fact...ensemble mean thickness
values hover between 540 and 550dm.


Sat night into Monday...
cool fact with high pressure center in place Sat
night...radiational cooling should allow several locations to dip
down into the middle to upper 30s /low 40s elsewhere/. May need to
monitor for some patchy frost Sun morning. However...gradual
warming with weakening ridge moving in will allow temperatures to rebound
near normal for sun...but then above normal on Monday. In fact...with
850 mb temperatures near +12c and h92 near +16c. This will allow highs to
once again reach low-middle 70s. Dry weather prevails under continued
influence of the high pressure through the period.

Monday night through Tuesday...
cold front associated with northern stream shortwave will approach
around the same time as a coastal low pressure associated with southern
stream low pressure. More guidance /including ensembles/ suggest that
phasing of these systems if it occurs at all...will be beyond
impact for southern New England. Precipitable waters approach 1 Standard deviation above
normal...or near 1.5 inches. Therefore...some rainfall is
possible...along the east from the coastal flow...and from the west
associated with the cold front. Still given the risk for
subsidence between these two systems could limit the rainfall
potential. Quantitative precipitation forecast values on models reflect this risk...mainly below
0.25 inches. Otherwise...temperatures still warm...but not as warm as Monday
due to increased cloud cover.

Wednesday into Friday...
slow digging longwave trough suggests another round of fall like
temperatures. As mentioned above...thickness values dip below 550
in spots. H92 temperatures then dip back to around +6 and +10c and 850 mb
closer to +5c. Strong cyclonic flow aloft could yield a risk for
diurnal rain showers but noting that the airmass is quite dry.
Therefore...will limit any probability of precipitation to slight chance.
expect diurnal cloud cover. Mins could dip below normals if some
radiational cooling is allowed...but mass fields suggest some
uncertainty in the pressure gradient/isallobaric flow through the


Aviation /15z Friday through Tuesday/...
forecaster confidence levels...

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

Today...moderate confidence...mainly due to timing issues.
Isolated MVFR but mostly VFR lowers to MVFR this afternoon as
showers move across CT/Rhode Island and Massachusetts from west to east. Few heavy
embedded showers along with an isolated T-storm possible. Strong
low level SW jet up to 45 knots moves across the area 18z-00z. Most
of this wind mixes to the surface.

Tonight...MVFR improves to VFR as cold front sweeps across the
area. Showers with embedded heavy downpours along with an isolated
T-storm moves offshore 00z-03z along with gusty SW winds shifting
to northwest.

Saturday...VFR with gusty north winds in the am diminishing in the

Kbos terminal...high confidence in taf trends but lower on
exact details.

Kbdl terminal...high confidence in taf trends but lower on exact

Outlook /Saturday night through Tuesday/...

Sat night through Monday...high confidence.

Tuesday...moderate confidence.
Some MVFR possible in showers/low clouds through the day.


forecaster confidence levels...

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


South-southwest winds increase to 20 to 30 knots with strongest winds later this
afternoon. Low risk of a few gale force gusts. Showers become more
numerous late today from west to east ahead of an approaching cold
front. Low risk of an isolated T-storm.


South-southwest winds 20 to 30 knots shifting to northwest during the evening with the
passage of the cold front. Heavy showers early move offshore later
this evening. Low risk of an isolated T-storm early.


Gusty north winds early diminish by midday as 1020 mb high builds over
the area. Seas subside as well. Dry weather and good visibility.

Outlook /Saturday night through Tuesday/...

Through Monday...high confidence.
High pressure will gradually settle over the waters allowing the seas
from Friday night and Sat to relax. This will also lead to winds
below small craft thresholds. headlines

Tuesday...moderate confidence.
The combination of an approaching cold front and weakening coastal
low will lead to a risk for showers/fog across the waters. At this
point it appears that winds/seas should stay below Small Craft Advisory criteria
through the day...but this may need to be monitored.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 6 am EDT Saturday for anz230>237-


near term...nocera/doody
short term...nocera
long term...doody

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