Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 272303

Area Forecast Discussion
National Weather Service Taunton MA
703 PM EDT Sat May 27 2017

A weak ridge of high pressure will bring pleasant temperatures
and result in mainly dry weather on Sunday, other than perhaps
a brief spot shower or two. Low pressure in the Great Lakes
generates a coastal low late Monday that passes off Nantucket
on Tuesday. This will bring wet weather on Memorial Day. Upper
low and cold pool linger most of the week while surface high
pressure builds in. Expect daytime clouds and scattered showers
will pop up each day Tuesday through Friday. Otherwise fair
weather with near seasonable temperatures.



7 PM update...

No significant changes to the forecast.  Weak high pressure
bringing dry weather. Lots of mid-level clouds trapped under the
high will stay with us through the night. Could be patchy
drizzle toward daybreak if cloud bases can get low enough, but
again no real impact. Dew points in the upper 40s and lower 50s
along with clouds point to min temps in the upper 40s to mid



An abundance of clouds is one again expected with model cross
sections indicating a fair amount of low level moisture.
Nonetheless, do expect to see some peeks of sun at times with
temporary upper level ridging building into the region. This
should allow for temps to be a bit milder than today. Highs
are expected to top out between 70 and 75 in most locations,
but weak gradient will once again allow for sea breezes on the
immediate coast holding high temps in these locations in the

While the vast majority of Sunday will be dry, enough moisture
combined with diurnal heating may result in a few brief spot
showers. The best chance for this will be in western and
northern MA, but even in these locations the vast majority of
the day will be dry.

Sunday night...

Dry weather should prevail the majority of the night. While
models differ on specific timing, an approaching shortwave/warm
advection aloft will allow for the potential of showers to
increase toward daybreak Monday across the interior. Low temps
will once again be mainly in the upper 40s to the lower 50s.


Big Picture...

Longwave scale maintains a ridge west/trough east pattern for much
of the long term period.  Shortwave scale shows a closed low slowly
moving from the Great Lakes into Eastern Canada, maintaining a
cyclonic flow over the Northeast USA and especially New England
through Saturday.  Phasing northern and southern jets Monday-Tuesday
generate a coastal low that passes southeast of Nantucket Tuesday.

Mass fields are similar among the long-range models through
Wednesday, with the GFS and ECMWF similar over New England until
Friday and possibly Saturday. Thermal fields are similar through
Thursday. Moisture fields are noisier, but show a general similarity
through Thursday with some divergence late week. This brings
increased confidence in the overall synoptic pattern through much of
next week, although lingering uncertainty regarding timing of
individual shortwaves in the flow.


Monday-Monday night...

Wet weather moves through Southern New England Monday and Monday
night.  Surface low north of the Great Lakes swings an occluding
front through Upstate NY and PA during the day. Phasing upper jet
moves across this front and generates a triple point low over the
Mid Atlantic states. This low then moves offshore and passes
south/east of Nantucket on Tuesday.

The developing coastal low forms a weak low-level southeast jet that
feeds into Southern New England Monday afternoon and evening, then
shifts up the Maine coast later Monday night. This brings
precipitable water values of at least 1.2 inches into the region
Monday. This value is above average for late May in our area, but
short of the 90% threshold. These moisture values diminish Monday
night as the low level jet moves off to the northeast.

Model consensus shows measurable rain arriving in the
Worcester/Central Hills 6 to 8 am and reaching the I-95 corridor in
MA and RI between 7 and 9 am.

Convective parameters show a destabilizing airmass at most layers.
However the easterly low level flow may bring a stable layer near
the surface. Even so, the potential remains for an elevated unstable
layer sufficient to generate isolated thunderstorms.

Rain/showers taper off Monday night as the low level jet moves off.
Continued low clouds/fog/drizzle possible in the lingering
east-northeast flow overnight.

Tuesday through Friday...

Upper low and associated cold pool remain to our west Tuesday but
could be close enough to generate scattered showers.  A shortwave
moves through the cyclonic flow Wednesday advecting overhead with
it. This brings a better chance of daytime showers Wednesday and
possibly Thursday. More question marks and less confidence on Friday
and Saturday as additional shortwaves move through the flow. Cross
sections show adequate moisture between 600 and 850 mb Friday,
enough for minimal chance pops. Less available moisture Saturday, so
we kept it dry for now.  Temps at that level support max temps in
the mid to upper 70s inland Wednesday, with 80 possible, and low to
mid 70s Thursday to Saturday. Dew points fall to 45-50 by Thursday,
so expect min temps 45-55 during the period except a couple degrees
milder Wednesday morning.


Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...

Tonight...Moderate confidence.

Mainly VFR conditions. Patchy MVFR/IFR cigs may develop
overnight as temperatures cool, but most places will stay VFR.
Southeast winds become light south.

Sunday...Moderate confidence. MVFR to perhaps some localized IFR
conditions early should improve to mainly VFR by afternoon,
despite a scattered to broken deck of clouds persisting and perhaps
a brief spot shower or two.

Sunday night...Moderate confidence. Mainly VFR conditions for
much of the night. However, some lower conditions may arrive
toward daybreak Monday especially across the interior depending
on the timing of rain showers.

KBOS TAF...Moderate confidence in TAF. SE sea breeze should
shifts from the SSW early tonight. SE sea breezes should re-
develop by late Sunday morning or early afternoon. Mainly VFR,
but there is a potential for a period of lower clouds between
07z and 15z Sunday.

KBDL TAF...Moderate confidence in TAF. VFR but with potential
for a period of MVFR ceilings developing overnight. Improvement
to mainly VFR should occur by late Sun morning/early afternoon.

Outlook /Monday through Thursday/...Moderate confidence.

Monday... Showers move in during the day with isolated thunder. Cigs
and vsbys lower from VFR early to MVFR and areas of IFR in the
afternoon and night. Southeast winds less than 20 knots except gusts
to 25 possible late in the day on the Cape and Islands. The wet
weather diminishes Monday night, but expect lingering fog/low
clouds/drizzle during the night...especially over Eastern/Central
Mass and RI.


Lingering IFR in fog/drizzle early in RI and Eastern Mass.
Conditions trending to VFR all areas.  Potential for brief MVFR
vsbys in scattered showers in the afternoon especially over
Western/Central Mass.  South winds remain less than 20 knots.


VFR. Scattered afternoon showers with MVFR vsbys.  Westerly winds
with gusts less than 20 knots.


Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...

Tonight and Sunday...High confidence. Weak ridge of high
pressure will keep winds/seas below small craft advisory

Sunday night...Moderate to high confidence. Winds and seas will
generally remain below small craft thresholds most of the night.
However, approaching low pressure will increase the pressure
gradient toward daybreak and enough southeast fetch may develop
across our southwest outer-waters for some marginal 5 foot seas
near 12z Monday. It is still too early to hoist any marine
headlines for a potential late 3rd period event.

Outlook /Monday through Thursday/...Moderate confidence.


Southeast winds gusting to 20 knots.  Seas near 5 feet on the outer
waters, but less than 5 feet closer to shore.  Showers and isolated
thunder. Drizzle/fog linger at night.

Tuesday through Thursday...

Winds less than 25 knots and seas less than 5 feet through the
period. Scattered afternoon showers possible.


We opted to issue a coastal flood statement roughly between
midnight and 3 am Sunday along the eastern MA coast. Boston has
another very high astronomical tide of 12.3 feet just before 130
am Sunday. Storm surge values are running a bit higher than
guidance, and may still be close to a one half foot during this
coming high tide. We did have a few minor coastal flood reports very
early this morning along the eastern MA coast, so felt it was worth
a statement for some of the most vulnerable shore roads
experiencing some very minor flooding near high tide. Overall
though impact will be minimal, so just went with a statement.




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