Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 200541
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
141 AM EDT Sat May 20 2017

.SYNOPSIS...
A cold front moving over Southern New England will move
offshore this evening. High pressure from Canada will build
south over our region tonight and remain in place for much of
the weekend. More seasonable weather is expected for the weekend
into early next week. Dry initially then turning wet Monday
ahead of a sweeping cold front. A brief reprieve Tuesday prior
to more rain expected mid to late week along with continued
near-seasonable conditions.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
1010 PM update...
Cold front has pushed south of the islands with north winds
ushering in drier air as dewpoints fall through the 50s along
the coast. This has pushed convection offshore. Some mid/high
clouds will move across SNE leading to a period of partly
to mostly cloudy skies. Gusty north winds will gradually subside
overnight. Much cooler temps tonight with lows falling back into
the 40s, except lower 50s along the coast.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/...
Saturday...

Fair weather day with high pressure build in. Some high clouds
may linger to the south and southwest, but otherwise a sunny
day. Mixing should again reach at least 850 mb, where
temperatures will be 4-6C. That would support max temps in the
mid and upper 60s. If we mix higher, which is very possible in
the interior, temps would reach the lower 70s. Winds will turn
northeast in eastern Mass and RI in response to the position of
the high center. There could also be a sea breeze component
along the immediate coast. Either way, temps in eastern Mass
should be cooler than farther west. We will go with a range of
60s east to lower 70s west.

Saturday night...

Fair skies and light wind. Dew points in the mid 30s to low 40s.
Expect min temps in the upper 30s to mid 40s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
*/ Highlights...

 - Seasonable and dry for Sunday
 - Rain with embedded heavier showers for Monday
 - Dry on Tuesday
 - Wet for the mid to late week period, remaining near-seasonable

Overview and model preferences...
The ridging Rex-like block allowing for the nice weekend will
be shifting to the E by Mon as the upstream cutoff moving out of
the Plains to the Great Lakes interacts with deep trof near
Hudson Bay. This forces the cutoff further E and digs/deepens it
toward the SE through the end of the week. This provides a
conduit for several shortwaves within the cyclonic flow on the E
side of the cutoff. Therefore, as previous forecaster noted, an
active pattern sets up with periods of showers/storms possible,
but not a washout as each individual wave will be followed by
weak ridging yielding breaks. Noting fair agreement here between
models such that a blend of guidance can be used as a baseline
for this long-term forecast update.

Details...

Sun...
The pleasant weekend continues. Plenty of sunshine under high
pres which remains in control. May be a few late day clouds
building over from the W, but this should not limit the pleasant
conditions. H85 temps warm through the period starting around
+4C at 12Z but reaching +8C by late afternoon. This should allow
temps to inch back into the low-mid 70s away from coastal areas
which will be cooled by sea breezes.

Sun night into Mon night...
Occluding low pres sliding into Ontario and Quebec will be
pushing its occluding fronts through the region by daytime Mon.
In fact, noting the possibility of triple point low pres
formation, slowing the system down by Mon evening. This should
be enough lift to interact with modest moisture (PWATs reach
about 1.5-1.8 inches) and allow for a period of wet wx with
embedded heavier downpours through the period, starting from W-E
Mon morning. The risk for downpours amplifies by the potential
triple point low. Modest convective risk also adds to the risk
for heavier downpours as SLIs are noted to dip to near 0 with
some conditionally unstable lapse rates. Therefore, could see
widespread rainfall totals of 1.00-1.50 inches with the
possibility of a few higher amounts where heavier rains are
observed. Flooding risk is very low given the progressive nature
leading up to the triple point development. Typical nuisance
and poor drainage flooding are the potential impacts here. Did
undercut guidance somewhat for highs especially Mon, with the
warm front likely never making it through New England
(especially given the triple point risk) leaned more heavily on
raw model 2m temps which were much cooler.

Tue into Wed...
Modest ridging is noted in the mass fields this period as the
upstream cutoff continues to slowly dig/deepen across the lower
Great Lakes. This should allow for a reprieve from precipitation
for the most part across the region as the amplifying pattern
will slow shortwave progression. Will generally highlight
another two day stretch of generally nil POPs given this ridging
and associated high pres. H85 temps remain near +10C through
the period suggesting highs in the low 70s for the most part
while lows (assuming enough clearing could dip in the upper 40s
and low 50s). In essence, near seasonal normals.

Thu into Fri...
Strong shortwave looks to rotate through the longwave
trof/cutoff forcing the whole pattern to shift E. Tapping into
Gulf of Mexico moisture and yielding good lift, we are looking
at low pres development E of the Appalachians then sliding NNE
to once again yield a prolonged period of wet wx with pockets of
embedded heavier rain. Timing somewhat uncertain given the
pattern, in fact at this point, its likely too fast pushing most
of the rain through on Thu. This is a typical long-range bias
with highly amplified flow.

&&

.AVIATION /06Z 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/...High confidence.

Through 12z...VFR cigs with mid/high clouds. N wind gusts to 25
kt Cape/Islands.

Today...VFR. N/NE winds interior with E/NE winds along the
coast.

Tonight and Sunday...VFR. Light winds tonight, then seabreezes
developing around midday Sunday.

KBOS TAF...High confidence.

KBDL TAF...High confidence.

Outlook /Sunday Night through Thursday/...

Sun night into Mon night...Moderate confidence.

MVFR-LIFR. Lowest conditions likely for the S-coast with potential
fog/rain impacts. Increasing S winds with gusts up to 25 kts.
RA/+RA at times. Low risk TSRA. Possible LLWS impacts with S/SW
winds 2 kft AGL 40-50 kts.

Tuesday into Wednesday...Moderate confidence.
Improvement expected Tuesday with mainly VFR conditions W winds
shift to S-SW. Wednesday uncertain, but mix of VFR is possible
although if rain occurs, predominant MVFR/IFR expected.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

130 AM update...
SCA was expanded to most waters overnight. Gusts to 25 kt
occurring over waters around Cape Cod and south coast and
expect winds to increase over eastern waters.

Previous discussion...
High pressure builds over the waters Saturday and Saturday
night. Winds turn from the northeast Saturday and then become
light variable Saturday night. Seas will remain less than 5
feet.

Outlook /Sunday Night through Thursday/...

Sun and Sun night...High confidence.
Quiet boating weather expected winds will shift to the S on Sun.

Mon into Mon night...High confidence.
Period of Small Craft Advisory conditions as low pres passes
along the S waters. Winds will shift out of the S to the SE late
Mon, then to the W-NW Mon night. Wind gusts 25-35 kt expected,
with a risk for low end Gales. Seas will build to 5-7 ft on the
ocean waters.

Tue and Wed...Moderate confidence.
W winds shift to the E on Wed. At this time, it appears
winds/seas should remain below Small Craft Thresholds, however
there is some uncertainty in the pattern by mid week that may
change this thinking.

&&

.CLIMATE...
High temperatures through 4 pm...

BOS 90 90 (1986)
PVD 91 New record, old record 89 (1906)
BDL 92 94 (1962)
ORH 84 92 (1962)

Lost in the talk of high temperatures... all four climate sites
broke their high minimum temperatures on Thursday.

BOS 71    Old record 63 (1896)
PVD 70    Old record 62 (1943)
BDL 67    Old record 64 (1906)
ORH 69    Old record 63 (1943)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ232.
     Small Craft Advisory until 8 AM EDT this morning for ANZ231-
     233>235-250.
     Small Craft Advisory until 1 PM EDT this afternoon for
     ANZ254>256.

&&

$$
SYNOPSIS...WTB/Doody
NEAR TERM...KJC
SHORT TERM...WTB
LONG TERM...Doody
AVIATION...WTB/Doody
MARINE...WTB/KJC/Doody
CLIMATE...



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