Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 200202
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1002 PM EDT TUE JUL 19 2016

.SYNOPSIS...
High pressure in control will bring dry and warm afternoons through
Thursday with comfortable humidity.  The heat and humidity will
return Friday along with the risk for scattered showers and
thunderstorms during the afternoon and evening.  Hot weather is
expected to continue this weekend and an approaching cold front may
bring us another round of scattered showers and thunderstorms
sometime next Monday and/or Tuesday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
10pm update...
Last of the diurnal CU continues to dissipate across the region.
Plenty of room for cooling thanks to dwpts still in the upper 40s
and low 50s. Adjusted mins down a bit with this update, otherwise
the forecast remains on track.

Previous discussion...

Cool and comfortable conditions forecast overnight
which have not been observed in the last week given the hot and
humid conditions.  Lows down into the low to mid 50s for most
locations, warmer in the urban centers while cooler N/W with the
likelihood for lows into the upper 40s. Dewpoints a few degrees
lower will make for considerably pleasant and dry conditions
overnight.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Wednesday...

Roughly 1024 hPa high pressure building into the region in wake of
the mid-level trough pushing E and ridging building in from the W.
Light winds overall with accompanying H85 airmass aloft around +10C.
Warming up to around the low-80s and with the weak wind field expect
sea-breezes to develop along the coast roughly around late morning.
Comfortable and dry conditions, mostly clear conditions.

Wednesday night...

Quiet and pleasant weather. Light winds continuing from the S/SW
under mostly clear conditions, another opportunity for radiational
cooling and followed with MOS guidance closely. Comfortable
conditions continue.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights..

* Very warm/dry Thursday with comfortable humidity
* Heat/humidity returns Fri with afternoon/eve severe wx potential
* Hot weather this weekend with highs mainly in the 90s
* Another round of sct showers/thunderstorms poss next Mon and/or Tue

Details...

Thursday...

High pressure will be moving off the coast, but still provide us
with a partly to mostly sunny day.  Afternoon highs should reach
into the upper 80s to near 90 away from the marine influence of the
south coast/Cape and Islands.  Dewpoints will be in the 50s, so
humidity levels will be in check and tolerable for July standards.

Thursday night...

Low level moisture will begin to increase Thu night ahead of an
approaching shortwave/cold front, but expect dry conditions to
continue.  Low temps will only drop into the 60s to around 70 in
response to increasing low level moisture.  Patchy fog may develop
late in the typically prone locations.

Friday...

Main concern is the potential for scattered severe thunderstorms
across southern New England, sometime Friday afternoon and/or
evening.  While much of the day will be dry, it will become hot and
humid. High temps should recover into the upper 80s to lower 90s
with dewpoints well into the 60s.

West to northwest flow aloft will allow a remnant EML to work into
our region.  Just how steep the mid level lapse rates get still
needs to be determined, but the potential is there for them to rise
to between 6.5 to 7C/KM. At the same time, shortwave energy will be
dropping down from the northwest as low level moisture returns.
SPCSREF indicating fairly high probs for MLcapes greater than 1000
J/kg and 0 to 6 km shear greater than 30 knots later Friday into
Friday evening.

So with all that said, there is definitely the potential for
scattered severe thunderstorms during the afternoon and/or evening,
but this is far from set in stone. Severe weather often comes down
to very subtle mesoscale details, which are hard enough to detect in
the near term let alone 3 days in the future. Timing/location of the
shortwave, area of best forcing, amount of instability still need to
be determined.  A remnant EML and west northwest flow aloft can
result in high end severe weather in the northeast, but that comes
down to timing.  For example, if the shortwave arrives too early or
late we can be spared much in the way of severe weather.
Nonetheless, this certainly has potential and will need to be
watched closely.

Saturday and Sunday...

Overall, this weekend looks hot as GFS ensembles show 925mb
temperature anomalies 2+ standard deviations above normal.  This
should allow high temps mainly in the 90s away from the immediate
coast and any risk for seas breezes. The majority of the weekend
looks dry right now, but that can sometimes change quickly this time
of year with west to northwest flow aloft.

Monday and Tuesday...

Very warm to hot temperatures likely continue with increasing
humidity ahead of an approaching cold front.  Depending on how far
south the cold front make it and timing, there will be the risk for
a round or two of scattered showers/thunderstorms Mon and/or Tue but
a washout is not expected.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels.

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

Short Term /through Wednesday Night/...High Confidence.

Tonight into Wednesday...

VFR. Variable winds becoming S/SW.

Wednesday Night...

VFR. SW winds with potential gusts up to 20 kts for the S/SE coast
terminals.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday...High confidence in VFR.

Friday...Moderate to high confidence.  Mainly VFR but scattered
showers/thunderstorms may result in brief lower CIGS/VSBYS Friday
afternoon and evening.  Southwest wind gusts of 25 to 30 knots
develop Friday afternoon along and southeast of a Boston to
Providence line.

Saturday and Sunday...Moderate to high confidence in mainly VFR
conditions.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Wednesday Night/...Moderate confidence.

Mainly quiet boating weather through Wednesday Night thanks to
high pressure building across the region from the W. NW winds
veering out of the S/SW with time. Sea-breezes anticipated along
the near-shore.

Outlook /Thursday through Sunday/...

Thursday...High confidence.  Winds/seas mainly below sca thresholds
most of the day. However, near shore southwest wind gusts of 20 to
25 knots and choppy seas are expected to develop along the south
coast during the afternoon.

Friday...Moderate to high confidence.  Increasing southwest low
level jet expected ahead of a cold front.  This should allow
southwest wind gusts of 25 to 30 knots to develop Friday afternoon.
Long southwest fetch will allow seas to build to between 4 and 7
feet, with the highest of those seas across our souther most waters.

Saturday and Sunday...Moderate to high confidence.  Left over swell
will likely require the need for small craft headlines across our
southern waters into the first part of Saturday.  Otherwise,
relatively weak pressure gradient should keep winds and seas below
small craft advisory thresholds.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

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


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