Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 221436
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1036 AM EDT Tue Aug 22 2017

.SYNOPSIS...
A hot and humid day is in store for the region today with
afternoon heat index values climbing into the middle 90s away
from the south coast. A cold front will bring the potential for
scattered showers and thunderstorms late tonight which may
persist into Wednesday morning along the coastal plain.  High
]pressure brings dry weather Thursday through Sunday with very
comfortable humidity levels.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

Brought the forecast back in line with observed trends. Latest
satellite data showing breaks developing rapidly in the
stratus. It should only be a couple more hours before it
completely breaks over land. Will need to monitor the Cape and
islands to be certain stratus doesn`t redevelop.

Minor tweaks to temperatures based on expected cloud cover.
Still going to be quite hot and humid.

*/ Headlines...

 - Hot and humid away from the south coast this afternoon with
   heat index values reaching into the middle 90s

 - A few strong thunderstorms possible late tonight, mainly
   across N/W areas of MA and CT with potential threats of gusty
   winds, locally heavy downpours which could contribute to
   flooding, and frequent lightning

*/ Previous Discussion...

Mainly dry weather today but it will be hot and humid. Partly
sunny skies and 850T between +16C and +18C should result in
highs mainly in the upper 80s to near 90 away from the marine
influence of the south coast. Dewpoints well up into the 60s to
around 70 will result in heat index values in the middle 90s.
Deep mixing should also result in a rather breezy afternoon with
southwest wind gusts between 20 and 30 mph.

While modest instability will develop this afternoon, forcing
will remain well to our west and there will not be much of a
trigger for convection. While an isolated shower/t-storm can not
be ruled out through early this evening, dry weather is generally
expected.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tonight into Wednesday...

Will be watching a cluster of showers and thunderstorms across
NY State early this evening. Forcing for this convection will
probably not arrive into western MA/northern CT until after 02
or 03z. Given poor mid level lapse rates it will be difficult to
maintain severe convection into our region given the late
arrival. Nonetheless, increasing jet dynamics a strong
thunderstorm or two with gusty winds and brief torrential
rainfall can not be ruled out. Overall though the greatest
threat for severe weather will be to the west of our region.

Meanwhile, across eastern MA and RI it probably will remain dry
through at least midnight. Strong low level jet of 35 to 45
knots coupled with MUCapes increasing between 1000 and 1500
J/KG may allow scattered showers and thunderstorms to develop in
this region toward daybreak Wed, particularly along the
southeast New England coast. It is interesting because other
than the ECMWF, most models do not show much QPF in this region
so confidence is low. However, pattern recognition would
indicate the risk for scattered thunderstorms with locally heavy
rainfall. In fact, a few strong thunderstorms can not be ruled
out given decent instability and the low level jet across
southeast New England. Something will have to watch, but again
confidence is low.

The threat for scattered showers and thunderstorms may persist
into Wednesday morning across the coastal plain and perhaps even
into early Wed afternoon across the Cape/Islands. Otherwise,
much drier air will work in behind a cold front with lowering
humidity. High temps will mainly be in the lower 80s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
A long break from Summer heat. The return of the ridge-trough dipole
stretched from Siberia into the Gulf of Alaska, ridge amplification
across the N-Central CONUS into Central Canada shears energy equator-
ward downstream promoting trough persistence across the NE CONUS.

Several waves through the broader trough reinforcing cooler, drier
air across the region. With available moisture and diurnal heating,
collocated cold pool and steep lapse rates, can`t rule out isolated
to scattered shower activity in the vicinity of S New England ahead
of favorable mid-level ascent. Higher confidence over Upstate NY and
N New England. Lot of dry air and low theta-E behind early week
low pressure persisting over SE Canada. The influence of a 1025
surface high throughout the forecast period, the quasi-
stationary tropical frontal boundary remains well S/E off-shore.

Overall, looking like a prolonged period of dry weather with low
humidity, low dewpoints, making for comfortable conditions. Highs
around the mid to low 70s with lows down into the 50s. Scattered
cloud decks at times. Dewpoints ranging in the upper 40s to low
50s.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...

Today...High confidence.
Mainly VFR. Fog has largely dissipated, but still dealing with
MVFR-IFR CIGs, lingering the longest over the Cape and Islands.
SW winds increasing through the day, up to 30 kts across the
S/SE coastal terminals. Risk towards evening of MVFR-IFR
filling back in across SE terminals. An isolated SHRA/TSRA
possible across N/W MA and CT towards early evening but mainly
dry weather is expected.

Tonight...Moderate confidence.
Cluster of SCT SHRA/TSRA may enter N/W MA and CT closer to 2-3z
sweeping E tot he coastal plain after 6z, closer to 12z
Wednesday. VFR with some marginal MVFR conditions will
probably dominate tonight, but some IFR CIGS/VSBYS may impact
the SE New England coast along with some LLWS from the
increasing low level jet.

Wednesday...High confidence in trends but lower confidence in
overall timing. SCT SHRA/TSRA may persist near and especially
southeast of the I-95 corridor into early Wednesday afternoon.
Improvement to VFR conditions expected from west to east on
Wednesday, but timing somewhat uncertain.

KBOS Terminal...High confidence in VFR into this evening.

KBDL Terminal...High confidence in VFR today. A cluster of
scattered showers and thunderstorms may approach the terminal
after 2 or 3z this evening.

Outlook /Wednesday Night through Saturday/...

VFR. Daytime SCT low-end VFR CIGs 4-5 kft agl. N/W winds
throughout, light at times to allow onshore E sea-breezes.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Wednesday/...High confidence.

Today and Tonight...Southwest wind gusts of 20 to 30 knots
expected to develop this afternoon and persist into the evening.
Strongest winds this afternoon should be near shore given
excellent mixing over the land. Small craft headlines posted for
all waters. Will also have to watch for a few strong
thunderstorms that may develop across southeast New England
toward daybreak Wednesday.

Wednesday...While pressure gradient weakens, seas will remain
above small craft levels into early Wednesday afternoon across
the open waters. Therefore, have extended small craft headlines
for the open waters into early Wed afternoon. A few strong
thunderstorms may also remain possible into early Wednesday
afternoon across the southeast New England waters.

Outlook /Wednesday Night through Saturday/...

Good boating weather throughout. N winds persisting. Reinforcing
shots of cool, dry weather as high pressure builds into the region.
Subsequent slight enhancement in winds, gusts remaining below 20 kts
with seas 4 feet or less.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Wednesday for ANZ231>234-
     251.
     Small Craft Advisory until 2 AM EDT Wednesday for ANZ230-236.
     Small Craft Advisory until 2 PM EDT Wednesday for ANZ235-237.
     Small Craft Advisory until 4 PM EDT Wednesday for ANZ250-
     254>256.

&&

$$
SYNOPSIS...Frank/Sipprell
NEAR TERM...Belk/Frank/Sipprell
SHORT TERM...Frank
LONG TERM...Sipprell
AVIATION...Belk/Frank/Sipprell
MARINE...Frank/Sipprell


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