Area Forecast Discussion
Issued by NWS Boston, MA

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859
FXUS61 KBOX 252045
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
445 PM EDT Sun Jun 25 2017

.SYNOPSIS...
Scattered showers and isolated thunderstorms will diminish early
tonight. Additional upper level disturbances move across New
England on Monday and Tuesday, bringing a few showers or
isolated thunderstorm. Then a warming trend begins for the
latter half of the week with a return to summer heat and
humidity by Friday. A warm front may bring some showers Thursday
with more showers and thunderstorms possible Friday and
Saturday. A backdoor front may drop south into the region
Saturday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Lingering instability along with the right entrance region of
the upper jet...this may support a few showers/tstms through the
first hours of the night. Upper shortweave moving along the
Canadian border moves off to the northeast tonight. The
instability will diminish and the upper jet will shift southeast
during the night, so expect any showers to end and skies clear.

Clearing skies and light wind will allow some radiational
cooling. With dew points in the 50s, expect min temps mainly in
the 50s...except low 60s in some urban centers.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
Upper flow remains cyclonic. A weak shortwave moves through the
flow and across New England on Monday. Temps aloft will be a
couple of degrees cooler, with solar heating working on the
surface temperatures. The resulting lapse rates should be
favorable for a few showers/tstms.

Mixing will again reach high, up to 800 mb or a little higher.
Temps at that level, equivalent to 11C at 850 mb, will support
max temps in the upper 70s and the low 80s.

Convection will again diminish after sunset with clearing skies
and light wind. With dew points in the 50s, expect min temps in
the 50s and low 60s.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Highlights...

* A few showers/isold t-storm possible Tue/Wed
* Warming trend toward end of the week with return to summer
  heat/humidity by Fri
* Thunderstorm chances increase Thursday night through Saturday
* Low confidence - Backdoor front possible far northeast MA Sat.

Overview...

Mid level trough exits New England Wed., followed by building
heights as subtropical ridge builds over the western Atlantic.
Polar jet will be in the vicinity of New Eng next weekend which
will leave us susceptible to weak shortwave passages. A warm
front will meander back and forth near the MA/NH border Friday
through Sunday with a series of weak low pressure systems moving
along the boundary. Thus the chance of showers and
thunderstorms will increase as we head into the weekend.

Details...

Tuesday and Wednesday...

Strong mid-level shortwave trough lifts northeast from the Great
Lakes Tue with axis of the trough moving into New England by
Tue. evening before exiting on Wed. With 500 mb temps cooling
to -18 to -20C, will see scattered showers and isolated
thunderstorms. The best chances, where K Indices reach 25-30
along with Total Totals greater than 50, will be in the
northwest half of the region, west of a line from northern CT to
the Merrimack Valley.

For the second run in a row, the ECWMF shows a surface trough
south of New England, which creates an area of rain showers for
south coastal RI and southeast MA Tue. night into early Wed.
morning. Will forecast a chance of showers there.

On Wed, mid level trough exits the region. There will still be a
cold pool aloft, hence Total Totals Indices in the lower 50s.
However, the column will be drying out with westerly winds and
K Indices struggling to surpass 20-25. Cannot rule out a slight
chance of a few showers. But not expecting thunder.

Highs both Tue. and Wed. from 77 to 80 in the interior.

Thursday...

Increasing warm advection pattern as warm front approaches from
the SW will lead to increasing clouds. Southwesterly low level
jet is forecast to increase to 40-50 kt at 850 mb by late in the
day. Despite some cloud cover temperatures will rise to the mid
80s and this will allow for mixing to create wind gusts to 20-30
mph, especially in the coastal plain.

GFS and ECMWF now in agreement that the warm front will move to
near the MA/NH/VT border by Thu. evening. There is a pronounced
increase in K Indices as high theta-e air moves in from the
west. The implication is that a cluster of thunderstorms,
possibly severe to our west, will travel eastward along the warm
front, aided by swift 55-70 kt west winds at 500 mb. There is a
good chance of thunderstorms in northern and western MA late
Thu. afternoon and Thu. night as a result, with scattered
storms possible elsewhere Thu. night.

Friday and Saturday...

Somewhat tricky forecast due to placement of active frontal
boundary. Very unstable air mass in place both Fri. and Sat.
High temperatures will reach well into the 80s with near 90
possible. Depwoint temperatures are forecast to hover between
the upper 60s and lower 70s. The frontal boundary is forecast to
become quasi- stationary near the MA/VT/NH border by
Saturday...and it may even shift southward a tad as a backdoor
cold front into the Cape Ann region on Saturday.

Several thousand Joules of CAPE are possible on either day.
Scattered thunderstorms are expected both days and there is the
potential for severe weather, with wet microbursts a possibility.
Helicity values could be higher near the MA/NH/VT border, close
to the front, which may add to severe potential.

Sunday...

Tricky forecast continues...with models suggesting a slow moving
surface trough and a continued chance of scattered showers and
thunderstorms. Highs mainly in the mid 80s due to cloud cover,
but subject to change...could be higher if more sunshine.

&&

.AVIATION /20Z SUNDAY 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/...High confidence.

Tonight...

VFR. Evening showers and scattered thunderstorms, especially in
Western and Central Mass, will diminish. Brief MVFR vsbys in any
showers. Clearing skies overnight with light winds.

Monday into Monday night...

VFR. Daytime heating will develop cumulus clouds with bases
4000-5000 feet. These will lead to scattered showers and a few
thunderstorms. Brief vsbys below 5 miles in any showers.

Clouds and showers dissipate after sunset.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday and Wednesday...High confidence.
Mainly VFR. A few showers and isold t-storms possible Tue and
still can`t rule out a shower on Wed.

Thursday...Moderate confidence.
Mainly VFR with cigs lowering from NW to SE. Afternoon showers
possible in the interior with showers/t-storms possible all SNE Thu
night. Gusty SW winds to 25-30 kt developing, especially
coastal plain.

Friday...Moderate confidence.
Patchy early morning fog, with local MVFR. Then VFR, except
local IFR in possible strong thunderstorms, mainly during the
afternoon and evening hours. MVFR in patchy fog late Friday
night, especially south coast.

&&

.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.

High pressure offshore with west to southwest winds. Speeds
should remain 20 knots or less. Seas have diminished, and should
remain at 4 feet or less through the period.

Outlook /Tuesday through Friday/...

Tuesday and Wednesday...High confidence. Quiet boating weather with
winds and seas below SCA. Gusts to 20 kt possible nearshore waters.

Thursday...Moderate confidence. Small craft advisories will
likely be needed. Increasing SW winds with gusts to 25+ kt
likely, especially over nearshore waters. Building seas may
reach 6 to 8 ft over southern waters Thu night. Chance of
showers and thunderstorms Thursday night.

Friday...Moderate confidence. SW winds continue, mainly 20-25 kt
with seas 4-8 ft over the southern waters and 3 to 6 ft over the
eastern waters. Scattered thunderstorms, some with reduced
visibilities and strong gusty winds.

&&

.TIDES/COASTAL FLOODING...
High astronomical tides have peaked at most spots, but still at
high levels for at least one more cycle. The overnight tide
cycle will be the one of concern, with Boston reaching 12.2 feet
after midnight tonight. Tidal departures will be around 0.3 to
0.4 feet along the Massachusetts East Coast. This means
conditions will be high enough along the Mass East coast for at
least some minor splashover at high tide.

Subsequent high tides will be trending lower, and thus less of a
risk for splashover concerns.

&&

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

&&

$$
SYNOPSIS...WTB/GAF
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...GAF
AVIATION...WTB/GAF
MARINE...WTB/GAF
TIDES/COASTAL FLOODING...WTB



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