Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 140202
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1002 PM EDT Sun Aug 13 2017

.SYNOPSIS...
High pressure brings dry weather into Monday. Moisture well
ahead of an approaching cold front will allow for the chance for
showers and thunderstorms Tuesday afternoon. Dry conditions
follow for Wednesday. A warm front approaches Thursday and
Friday, bringing increasing clouds, and scattered showers along
with a few thunderstorms. Showers may linger into Saturday as
low pressure approaches.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

Only minor tweaks to bring the forecast back in line with
observed trends. Just some cirrus to waft overhead over the next
few hours. It`s still early in the evening, so the impact on
radiational cooling should be muted.

Previous Discussion...

Tonight...High confidence.

Diurnal cumulus have dissipated, with some patchy cirrus passing
thru the area. Mostly clear skies will prevail for tonight as
surface high pressure moves across the region.

The nearly clear skies coupled with light winds will allow for
good radiational cooling. Many locales will have overnight lows
in the mid and upper 50s. Locations near the waters and metro
regions will stay slightly warmer. Anticipate another round of
patchy fog to develop across the low lying regions and in the
vicinity of Nantucket. BUFKIT profiles suggest it will be
rather shallow and should burn off with sunrise Monday. One
thing to note is that with skies remain clear, should be a good
night to view the Perseid meteor shower.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Monday and Monday night...High confidence.

Despite longwave trough pattern over the region, a mid-level ridge
will move across southern New England on Monday. This will lead to
dry weather and light winds. Surface high pressure will begin to
move offshore during the later half of the day resulting in light
winds/sea breezes for the coastlines. Otherwise, another pleasant
day will be on tap as temperatures will be similar to todays as
850mb temps remain around 13-14C. Humidity will be low during the
first half of the day, but return southerly flow will begin to inch
dewpoints back into the 60s by the evening hours. Cloud cover will
also be on the increase by the later afternoon/evening as
approaching shortwave moves through the upper level flow.

Return southerly flow will continue to increase the low level
moisture across the region. Stalled boundary well south of Long
Island will turn into a warm front and begin to move northward
towards the region. This will increase the fog and stratus potential
once again in the WAA pattern. Overnight lows will remain mild
leading to lows in the mid 60s.

Lower confidence on the shower potential for Monday night/Tuesday
morning across the Cape and Islands. As this front gets closer,
combined with the approaching surface trough from the west, there
could be enough to bring some showers to the region if the front
lifts north enough. The GFS/RGEM keep the front farther south
compared to the EC/NAM. Thus went down the middle until models can
sort out there differences.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Details...

Tuesday...Moderate confidence.

Early in the day should be dry, however models show a sharp moisture
gradient to the south of Long Island and Nantucket. Precipitable
water increases to 2 inches offshore with moisture pooling along a
front well to the north of what as of today is TD8. If this gradient
were to nudge further north there could be some rain over the
Islands and possibly Cape Cod. Otherwise, dry across the area
Tuesday morning.

Continue to anticipate a potent short wave moving thru the area
later in the day. Timing of the short wave, preceded by diurnal
heating, should allow for scattered showers and thunderstorms.
Precipitable water ranges from 1 to 1.5 inches, not very high.
However continue to note LIs around 0 to -1 ,along with steep low
level lapse rates. SPC places interior southern New England in a
marginal risk for severe weather. Will go with chance pops within
the area denoted by a marginal risk for severe. Tuesday afternoon
should remain dry closer to the shoreline. Convection subsides
around sunset.

Wednesday...Moderate confidence.

Cold front sinking out of Canada pushes southward thru southern New
England during Wednesday, bringing a dry airmass into the region.
Moisture is quite limited even to start off the day, so anticipating
this frontal passage to be dry. High pressure prevails Wednesday
night, may see increasing clouds late.

There is also a chance for rip currents Wed-Thu along south
coastal MA/RI as well due to swell from TD8 and its projected
forecast.

Thursday thru Friday...Low to moderate confidence.

Expect increasing clouds Thursday as low pressure approaches.
However there is considerable model differences with respect to the
timing of this system`s approach and subsequent timing on chances
for rainfall. 12Z ECWMF is quicker with the surface low, tracking it
over New England during Thu. Hence the ECWMF brings a soaking
rainfall to our area Thu-Thu night. 12Z GFS and the 12Z GFS ensemble
mean are much slower with the low`s approach, with high pressure to
the east delaying deeper moisture and precip arrival until Thu
night/Fri.

Plan to go with chance pops for Thu into Fri with this forecast
package, with highest pops Thu night. As low pressure nears, PWATs
increase to near 2 inches and low instability brings the potential
for isolated thunderstorms.

Saturday-Sunday...Low confidence.

Much uncertainty for next weekend regarding timing of possible
showers, but do not anticipate the weekend will be a washout. Model
consensus brings the better chance for showers on Saturday, drier
for Sunday.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight...High confidence. VFR. Patchy MVFR fog possible in low
lying terminals and in the vicinity of ACK.

Monday...High confidence. VFR. Seabreeze along the coasts from mid
morning through the afternoon.

Monday night...Moderate confidence. Mainly VFR with some MVFR/IFR
cigs developing across the southern terminals as low level moisture
streams in from the south.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...Moderate confidence.

Tue-Thu...Moderate confidence.
Mainly VFR conditions Tue-Thu. May see areas of MVFR-IFR CIGS/VSBYS
in late night/early morning fog each night. Brief MVFR CIGS/VSBYS
across the interior Tuesday afternoon/evening. Scattered showers
with local MVFR conditions from W-E during Thursday.

Thu night-Fri...Low confidence.
A period of rain/showers is possible within this timeframe. East
winds could produce a period of MVFR/IFR clouds/vsbys with patchy
fog.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...High confidence.

Seas continue to subside across the southern coastal waters.
Roughest seas confined to areas south and east of Nantucket.
Cancelled the Small Craft Advisory for the waters east of Cape
Cod. May be able to cancel the remaining advisory south of
Nantucket before the 1 AM update. Will continue to monitor.

Previous discussion...

As of 7 pm this evening, seas had fallen below 5 feet with the
exception of the waters southeast of Nantucket. In this area,
Small Craft Advisory continues until 2 am. Building high
pressure across the waters tonight and tomorrow will relax seas.
Thus good boating weather is expected for Monday. Patchy fog is
possible tonight in the vicinity of Nantucket. Then increasing
low level moisture may lower vsbys across the southern waters
late Monday night in fog.

Outlook /Tuesday through Friday/...Moderate confidence.

Winds expected to remain below small craft criteria through
Thursday. Seas 4 ft or less Tuesday, and probably remain at 4 ft or
less Wed-Thu. However, there is a chance for increasing swells along
south coastal MA/RI Wed-Thu, with TD8 forecast to become a Tropical
Storm and remain well south of the area. There is also a chance for
rip currents Wed-Thu along south coastal MA/RI as well.

Return of patchy late night/early morning fog across most waters Tue
and Wed nights. Scattered showers are possible Thu-Thu night.

During Fri an approaching low pressure system may allow for seas and
E/NE winds to increase to SCA thresholds. Reduced visibility
possible in scattered showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ255.

&&

$$
SYNOPSIS...Dunten/NMB
NEAR TERM...Belk/Dunten/NMB
SHORT TERM...Dunten
LONG TERM...NMB
AVIATION...Dunten/NMB
MARINE...Belk/Dunten/NMB



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