Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 150820
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
420 AM EDT Tue Aug 15 2017

.SYNOPSIS...
Showers lingers today, with a stray thunderstorm possible
before improvement arrives again tomorrow night. High pressure
brings fair weather Wednesday and Thursday. A weather system
from the Plains will bring showers and scattered thunder Friday
and Saturday. High pressure returns with fair weather Sunday and
Monday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Today...High confidence.

A soupy morning is shaping up across the region as southerly flow
continues to increase the low level moisture. Several locations
across the Cape and the Islands are reporting fog less than a mile,
which is also shown in webcams. Have contemplated about spreading
the dense fog adv, but because rain is moving into the region, it
may keep sites from falling below a half of a mile. Thus will hold
off for now.

Showers continue across southern CT and into portions of New England
early this morning. This is in conjunction with stalled stationary
boundary south of the region, weak WAA and upper level jet streak.
As the jet streak continues to move across the region, expect
showers to become more widespread resulting in precip lingering
into the morning commute. This is suggested by the latest few
runs of the HRRR which seems to be on the right track per current
conditions. An increase in mid-level moisture while a weak
shortwave rides along the front will also aid in the shower
development.

Showers will become more scattered in nature by mid-morning but
still lingering thanks to the near by boundary and increasing low
level moisture. Another shortwave will ride along the front during
the afternoon hours. Guidance is hinting that these will be more
widespread and clip the south coast resulting in likely precip
across the Cape and the Islands. Def not turning into a nice beach
day today. Because of the focus on precip across the south, the
potential for a few strong thunderstorms seems to be unlikely at
this time.

Potent shortwave across the Great Lakes will bring a few strong
storms across northern New England. Because of the precip potential
across the south coast, cloud cover will be dense today. This will
limit heating and thus anticipate highs only in the upper 70s and
keep Cape values low. Mid-level moisture as indicated by the K
values will also drop this afternoon away from the south coast. Thus
limiting any strong thunderstorm potential. Can`t rule out one
across NW MA closer to the northern shortwave and steeper lapse
rates, but overall threat is low.

Lastly, QPF amounts will generally be light today, but with PWAT
values reaching above 1.5 to 2 inches south of the Pike, may need to
watch for nuisance flooding.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Tonight into Tomorrow... High confidence.

Upper level trough will swing through the region tonight as High
pressure to the west begins to build. Still plenty of low level
moisture around so another night of stratus and fog will be on deck.
This is shown in BUFKIT cross sections, especially across the south
coast and CT valley. Conditions will improve once surface cold front
swings through the area and winds switch to a more westerly
direction bringing in drier air.

High pressure will build on Wednesday resulting in mostly sunny
skies and temperatures warming back into the 80s.

Beach Forecast:
One thing to watch is the high surf and rip current threat from
Hurricane GERT. Swells up to 7 feet are expected to approach
the region late tonight into tomorrow morning. This combined
with a period of 14 sec and waves above 5-8 feet will result in
a life- threatening conditions for all people who enter the surf
from dangerous rip currents and high surf. Because of this,
went ahead and issued a high surf adv for Wednesday. Use caution
if heading to the beach.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Big Picture...

Subtropical high remains in control across the Southern USA while a
general zonal flow continues across Canada and the Northern USA. A
series of shortwave ridges and troughs will move through this flow.
A closed low over Quebec and cyclonic flow over New England all
shift east Wednesday night. Multiple shortwaves move through
New England Friday through Sunday.

Model mass and thermal fields from the 00Z suite are in general
agreement through Friday. They are then similar in general through
the weekend but show differences in details. Run-to-run consistancy
has had problems the past few days, which tempers confidence
especially for the end of week system.

Details...

Wednesday night and Thursday... High confidence.

Shortwave ridge moves over the region with dry air through most of
the column. Light gradiant means light surface wind Wednesday night,
which should allow a period of radiational cooling. Mid and high
level moisture increases Thursday, especially afternoon/evening.
Overall, a fair weather period.

With radiational cooling expected, we nudged min temps down a couple
of degrees Wednesday night.  With temps aloft 12-14C, expect
Thursday max temps in the upper 70s to mid 80s.

Thursday night to Saturday... Moderate confidence.

Next group of shortwaves moves through late in the week. First will
be with the approaching warm front, second with the cold front, and
a third trailing the second. Moisture builds in the column with PW
values building to 2 inches Friday, then diminishing late Saturday
as the cold front moves through. Stability parameters are mixed,
with the Totals marginal, but the LI unstable. Looks like showers
with some potential for thunder especially on Saturday.  High dew
points will contribute to areas of fog each overnight/morning.

Sunday-Monday...

Lingering instability Sunday as the third shortwave moves through.
But moisture fields dry out Saturday night, which makes it hard to
support any forecast of showers.  High pressure builds later Sunday
into Monday. Overall, a dry forecast with near seasonal
temperatures.

&&

.AVIATION /08Z 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/...

Before 12z...Moderate confidence.
VFR away from the Cape and Islands, but many eastern terminals
will drop to MVFR cigs by sunrise. LIFR conditions will continue
across the Cape and Islands as IFR occurs along the south
coast. Widespread showers across the region.

Today...Moderate confidence.
Lingering fog burns off after sunrise. Sct showers will
continue until late this morning. Otherwise, VFR with a few
showers and isolated T-storms mainly W MA during the afternoon.
Weak sea breezes along the east coastline.

Tonight...Moderate confidence. VFR gives way to another mix of
IFR/MVFR mainly CT/RI and SE MA while the remainder stays mostly
VFR, then as winds shift around to the W, transition back to
VFR everywhere toward the morning.

Wednesday...High confidence. VFR with dry weather.

KBOS Terminal...Moderate confidence in TAF. Low probability for
a few hours of MVFR conditions after 09z.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Saturday/... Moderate confidence.

Wednesday night-Thursday... High confidence.

VFR with light wind. Patches of fog are possible overnight and
Thursday morning, especially in the usual fog spots.

Thursday night through Saturday... Moderate confidence.

VFR with areas of MVFR cigs/vsbys in showers and scattered
thunderstorms. Lowest conditions are expected Friday night in areas
of fog.

&&

.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...
S winds develop with gusts to around 20 kts on the E waters
during the day, but brief. Otherwise seas will begin to build
as swells from GERT begin to approach the waters. Should remain
below SCA until this evening. Otherwise widespread showers will
impact the southern waters today.

This evening and into tomorrow...
A few showers will lingering but conditions will be improving.
Still anticipate another round of fog tonight. Waves begin to
reach above 5 feet across the southern waters as swells from
GERT increase. SCA has been issued for tonight and lasts into
tomorrow as waves will reach between 5-8 feet with a southerly
swell near 7 feet.

Outlook /Wednesday Night through Saturday/... Moderate confidence.

Winds less than 20 knots through the period, although gusty at times
especially on Narragansett Bay Friday and Saturday.  Lingering 5-6
foot seas on the southern waters Wednesday night, subsiding to less
than 4 feet Thursday through Saturday. Areas of fog will bring
reduced visibility most mornings. Showers and scattered thunder
Friday and Saturday will also bring reduced visibility.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory from 9 AM to 8 PM EDT Wednesday for MAZ020-
     022>024.
     Dense Fog Advisory until 10 AM EDT this morning for MAZ022>024.
RI...High Surf Advisory from 9 AM to 8 PM EDT Wednesday for
     RIZ006>008.
MARINE...Small Craft Advisory for hazardous seas from 11 PM this
     evening to 8 PM EDT Wednesday for ANZ235-237.
     Small Craft Advisory for hazardous seas from 7 PM this evening
     to 8 PM EDT Wednesday for ANZ255-256.

&&

$$
SYNOPSIS...WTB/Dunten
NEAR TERM...Dunten
SHORT TERM...Dunten
LONG TERM...WTB
AVIATION...WTB/Dunten
MARINE...WTB/Dunten



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