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Area forecast discussion 
National Weather Service Taunton Massachusetts
314 PM EDT Friday Jul 29 2016

Synopsis...

* updates to near and short term forecast portions only...

Low pressure will sweep south of New England into the overnight
period. A brief period of drier conditions follow for Saturday
with the slight chance of showers over southwestern New England.
Another area of low pressure approaches New England towards
Sunday, passing south of New England into Monday bringing with it
a better chance of showers and thunderstorms. High pressure
returns with dry and seasonable conditions for the middle and
latter portion of next week.

&&

Near term /through tonight/...

315 PM update...

Heavy rain and embedded thunderstorms push out to sea. You win a
few and you lose a lot and in this case as all the ingredients came
together along a SW to NE axis offshore of New England. While over-
shooting around 5-10 kft agl, dual-pol radar estimates have rough
storm-total estimates of 2 to 3 inches over the waters S/east of the
S-coastline of New England. If only displaced by about 50 to 100
miles north/west over S New England, there would've likely been a bigger
impact. Live and learn, gaining experience and perspective for the
next event.

Otherwise, clearing continues across S New England allowing
boundary layer destabilization beneath a conditionally unstable
environment. Scattered heavy showers developing though low-topped,
limited on development with likely warmer and sinking air aloft
with slightly rising heights around 500 mb and in wake of the main
mid-level vortex parent with the surface low sweeping out to sea.
Slow moving through the rather weak 10 mph mean flow out of the
NW, monitoring for possible localized flooding impacts. Development
along fine-line convergence boundaries it would seem per observational
mesoanalysis. Diurnally driven, should see activity diminish with
sunset.

Tonight...

Clearing out with high pressure and drier air building in. With light
winds, a favorable setup for radiational cooling. Noting a somewhat
soupy airmass remaining in place with dewpoints hovering around
the low to mid 60s, and considering antecedent rains,
anticipating fog to develop. Confident within the CT River Valley,
east CT, interior southeast Massachusetts of some visibility restrictions.
Perhaps some issues along the coasts though may see more clouds
than fog with the NE onshore flow turning north through the overnight
period.

&&

Short term /Saturday through Saturday night/...

Saturday...

High pressure and drier air linger lending to mostly clear conditions
and light winds. Likely sea-breezes to develop around mid to late
morning. Model forecast indications of showers developing along sea-
breezes per a measure of lift of available surface based instability
and decent low level moisture availability, that or upstream convection
from PA becomes an influence. Precipitable waters forecast up to 2
inches. But considering an unfavorable environment given confluent
mid to upper level flow and mid level height rises lending to some
measure of sinking air, feel there is a low risk of showery weather
and mainly late in the day. Thus leaning with slight chance pops
mainly for short wave New England encompassing much of the north-half of CT
into the Springfield Massachusetts Metro.

Forecast +14-16c 850 mb temperatures warrant mid to upper 80s for
highs. Already temperatures were underdone earlier today after
clouds started to break, so am going to up the forecast highs a
degree or two warmer nudging the Hartford-Metro to near 90.

Saturday night...

Approaching low to mid level warm frontal boundary parent with
the surface low over the S Great Lakes region. Continued moistening
of the low to mid levels per isentropic upslope over-running flow
out ahead of the system. Leaning that high pressure and drier air
lingers long enough to buffer the onset of wet weather into the
east-half of New England much as the 29.09z sref would suggest. There
is as well continued mid to upper level height rises.

So will go with chance pops for the W, lesser to the east. Overnight
lows slightly more mild with anticipated cloud cover and winds at
the surface slightly more ashore, though beginning to see surface
low pressure take shape short wave of New England towards Sunday morning.

&&

Long term /Sunday through Friday/...

Highlights...

* high pressure and mainly dry conditions Saturday
* showers and a few thunderstorms possible Saturday night - Monday
* drier and seasonable weather Tuesday through Thursday

Overview and model preferences...

Fast mid and upper level flow across central and southern Canada
has left weaker steering currents across the northern tier of the
U.S. Into early next week. Noting a slow moving 500 mb short wave out
of the Great Lakes which will cause upper level winds to shift to
west-SW across New England. Weak surface low will move slowly along a
stalled front south of the region, keeping the chance for showers/
thunderstorms. Models and ensembles continue to signal that the
short wave will finally move east Monday night into Tuesday, so
should see improving conditions as mid level winds shift to northwest.
Also noting building heights by late next week, so will see temps
run near or slightly above seasonal normals.

Used a consensus blend of available model and ensemble guidance
for this portion of the forecast.

Details...

Sunday through Monday...

With relative weak steering currents between the active northern
stream flow across southern and central Canada and the normal
Summer ridging across the southern tier states, expect low
pressure to move slowly along a stalled front south of New England
keeping low and mid level moisture in place along with marginal
instability during this timeframe. Pwats of 1.8 to 2 inches will
also linger mainly near and south of the Mass Pike, which could
lead to some locally brief, heavy precip mainly Sunday into Sunday
night. With the low passing S of the region, winds will generally
be east-southeast off the cooler ocean, which tend to stabilize any surface
based convection but could see some spotty elevated activity.

As the 500 mb short wave slowly pushes across the region on Monday,
any showers should push east. However, some may linger across inland
areas mainly during the afternoon, though there is individual
model solution spread so not a lot of confidence with this.

Expect temps to run close to or slightly below seasonal normals
especially on Sunday with the steadiest precip.

Tuesday through Thursday...

500 mb high amplitude ridge moving east across Hudson Bay on Tuesday
will help push the trough offshore. This will bring generally dry
conditions as northwest winds aloft take over, albeit on the light side.
Noting the 00z European model (ecmwf) is trying to keep some troughing lingering
across interior central and southern New England for Wed-Thu,
which could mean some isold diurnal convection. With somewhat
higher 500 mb heights, temps should return to near or slightly above
normal levels by late next week.

&&

Aviation /19z Friday through Wednesday/...

Forecaster confidence levels.

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

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

19z update...

Rest of today...

Improving west to southeast. Light north/NE winds. Lingering MVFR for ack with
-ra/rain but only for a few more hours. Scattered +shra over north/west interior
terminals down through the CT River Valley. Tempo MVFR-IFR
possible.

Tonight...

All terminals VFR, improving to sky clear. Overnight, monitoring for
likely MVFR-IFR fog development. Especially focused across the CT
River Valley, as well as interior east CT and southeast Massachusetts. Could Bee some
issues along the east/southeast coast of Massachusetts but lesser confidence with
respect to the dense fog.

Saturday...

Scattered-broken cigs especially towards late in the day. Light winds.
Sea-breezes developing along the shores late morning into
afternoon. Scattered rain showers/thunderstorms and rain possible across short wave New England late but
believe it to be a low risk.

Saturday night...

Broken-overcast cigs with MVFR-IFR developing along the S-coast of New
England towards Sunday morning. Increasing chance of rain from the
short wave along with visibility restrictions.

Kbos taf...high confidence. Conditions remain VFR into this
evening. Though watching closely into this evening for tempo MVFR
with NE onshore winds. Maybe even a rain showers. Believe it to be a low
risk.

Kbdl taf...high confidence. Low risk +shra towards the late
afternoon period with tempo MVFR-IFR impacts. A moderate risk.

Outlook /Sunday through Wednesday/...

Sunday through Monday...moderate confidence.

Scattered rain showers with a few thunderstorms and rain the best chance of which will be Sunday
into Sunday night. Tempo MVFR-IFR but likely VFR dominates. Could
see some visibility issues during the overnight into early morning
periods with patchy fog.

Monday night and Tuesday...high confidence.

Mainly VFR. May see brief IFR ceilings/visibilities in patchy fog after 06z
through 12z-13z in the normally prone areas as well as along the
coast.

&&

Marine...

Forecaster confidence levels.

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

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

315 PM update...

While heavy rain and thunderstorms dissipate over the southeast waters
into early this evening, and there is the possibility of visibility
restrictions with fog during the overnight into early morning
hours, the majority of the forecast is comprised of winds below
25 knots and seas below 5 feet, with increasing chances of showers
mainly Saturday night into Sunday morning.

Outlook /Sunday through Wednesday/...high confidence.

Saturday night through Monday...expect winds and seas below small
craft criteria. Seas 4 ft or less. Locally reduced visibilities in
scattered showers through the period, with patchy late night/early
morning fog. A few thunderstorms possible.

Monday night and Tuesday...NE winds gusting up to 20 kt mainly
across the eastern outer waters. Seas may brief build up to 5 ft
Tuesday.

&&

Box watches/warnings/advisories...

CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$

Synopsis...sipprell/evt
near term...sipprell
short term...sipprell
long term...evt
aviation...sipprell/evt
marine...sipprell/evt

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