Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 222310
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
710 PM EDT Thu Jun 22 2017

.SYNOPSIS...
Warm frontal passage tonight will result in warm and humid air
on Friday along with the threat of heavy rain associated with
the remnants of Cindy. The cold front will stall across New
England Saturday before moving offshore Saturday night.
Seasonably warm and less humid conditions Sunday will be
followed by cooler and somewhat unsettled weather for early next
week.

&&

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

710 pm update...

Warm front was draped across the eastern Great Lakes Region and
southeastward into eastern PA/northern NJ. The front will
continue to move northward tonight. Mid level cloud deck is
advancing into our area, with a continuation of increasing
clouds forecast for this evening. One thing to continue to watch
is the scattered-isolated convection across central PA and
upstate NY along and ahead of the warm front. These storms will
continue to develop and move from towards the southeast this
evening per mid- level flow. Most of this precip should remain
south of the area, however cannot rule out a few isolated
showers entering southern New England.

Previous discussion for Tonight follows...

Cloud cover will increase as a warm front will push through the
region tonight. 850 mb WAA will take hold as temps warm overnight
from 13C to 18C. This combined with the overcast skies will keep
temps more mild then previous nights with lows in the mid 60s. This
frontal system will turn the winds to a more southwesterly direction
resulting in an increasing low level moisture and strengthening LLJ.
Increasing K values combined with showalters dropping to below 0 may
result in a few sct showers. Highest confidence is north of the
Pike, which will be on the nose of the LLJ. The only caveat is that
the upper level ridge will remain over the region which will limit
anything becoming widespread as southern shortwave won`t approach
until Friday.

Aside from warm frontal passage and showery activity, the other
focus is on the increasing low level moisture. Dewpoints overnight
will also be on the rise, reaching the upper 60s by daybreak Friday.
This may result in a round of fog and stratus especially across the
south coast as ocean temperatures are still in the low 60s.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Friday into Friday night...

Active weather pattern for tomorrow as southern New England remains
in the warm sector for this period. Warm and muggy to start the day
as temperatures will quickly rise into the mid to upper 80s. If
breaks of sun can occur, then a few spots may be in the low 90s,
especially across the CT and Merrimack Valleys. Continuous
southwesterly flow will keep both clouds and tropical moisture
around Friday night. Overnight lows will remain mild, dropping into
the upper 60s to low 70s. This may result in another round of fog
and stratus with the highest confidence across the south coast once
again. May need to watch for a possible dense fog advisory as
surface dewpoints will be in the 70s.

Biggest focus is on precipitation potential for this time period.
Increasing moisture will begin to pool into the area with PWAT
values increasing to above 2 inches by Friday evening/overnight.
This Gulf moisture will eventually be tapped into the tropical
moisture from Cindy which will push PWAT near 3 STD above normal. In
fact, moisture flux values at 850 mb during this timeframe is
nearing 4 STD above normal. Thus within any heavy shower, the
potential for flooding rains is possible.

Through this period, an upper level trough over the Great Lakes will
begin to approach from the west. A few weak waves will move along
the flow as the ridge begins to push eastward. Southwesterly flow
aloft will remain overhead as a few isolated showers move into
southern New England from the Mid-Atlantic. Believe these showers
will maintain themselves as they ride along a theta-e boundary and
increasing LLJ. Best timing will be during the morning hours. Models
continue to indicate a dry slot moving aloft as 700 mb RH values dry
up and K values decrease. Thus the remainder of the day could be on
the dry side, however, cannot rule out a few hit or miss showers
developing since we are in the warm sector. The risk for thunder
continues to be a possibility as surface CAPE will be near 1000
J/kg. Not expecting anything severe as lapse rates are quiet poor,
less than 5.5 C/km.

A merger between the upper level system and leftovers from Cindy
will approach the area late Friday night. Slow moving cold front
will be the focus on heavy rainfall development as higher PWATs and
moisture transport moves into southern New England. Concerned that
models are underdoing the potential rain set-up for Friday night
into Saturday morning as mass fields would indicate widespread heavy
rainfall. One possibility is that our moisture could get robbed by
the surface low associated with Cindy`s remnants. Something to watch
in the upcoming forecasts. Right now have trended the forecast
towards the EC and Canadian which highlights the heavy rainfall
potential across southern New England.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Highlights...

* Scattered showers and isolated t-storms Sat, especially in the
  morning
* Seasonably warm and less humid on Sunday
* Unsettled pattern for early next week, cooler with showers possible

Overview...

Longwave trough evolving over the Great Lakes Region continues to be
the main feature for the extended forecast. A series of weak
shortwaves move through the flow as the trough gradually moves
towards New England early next week. This will bring a somewhat
unsettled pattern into the middle of next week with cooler temps
trending near or below normal.

Details...

Saturday...

Cold front stalled out across southern New England for at least a
portion of the day, while remnant low and shortwave from Cindy
trek near or south of our area. 12Z NAM/12Z ECMWF indicate drier
air pushing into our area during the afternoon while front
makes an eastward push towards the southern New England
coastline. Meanwhile the 09Z SREF and 12Z GFS/GFS ensemble mean
are more pessimistic, keeping some of the deeper moisture and
associated precip chances lingering over southern New England
into the afternoon.

During at least the morning hours, a plume of tropical moisture is
in place with precipitable water values of 1.5 to 2+ inches, highest
east of the stalled front. The shortwave will likely bring showers
with the chance for thunderstorms, especially eastern MA and south
of the Mass Pike. Brief locally heavy rainfall is possible.

For this forecast package will include likely pops Saturday morning
except chance north central/western MA, then chance pops continuing
into Saturday afternoon due to uncertainty of arrival time of drier
airmass. Could still see developing sunshine at Saturday afternoon,
especially over the interior.

Forecast highs continue to be a challenge, especially south of the
Pike where showers may hold temps down. Will go with continuity
here, highs mostly in the 70s to near 80 but low to mid 80s
northeast MA.  However if we clear out in the afternoon the highs
could be several degrees higher.

Saturday night drier air moves into southern New England in earnest,
with PWATs plummeting to 0.75 inch. A dry night is forecast.
Shortwave energy mainly crossing thru northern New England, may
brush our area but only anticipating some clouds at best with this
feature.

Sunday...

Quite dry airmass in place. Mid level shortwave moving into our area
should mainly bring diurnal clouds, can`t rule out a brief shower or
two across the interior. Seasonable temps in the upper 70s and lower
80s with low humidity as dewpoints will be in the 50s.

Monday into Wednesday...

Unsettled weather pattern anticipated for the first half of the next
workweek, as trough over the Great Lakes Region gradually shifts
eastward towards southern New England. Series of short waves
rotating thru the base of the trough will bring chances for showers
and some afternoon/evening thunderstorms at times. Monday looks to
have low moisture, so will limit pops to slight chance/low chance
pops. Otherwise, being several days out, still have low confidence
on timing. Temps averaging near or a bit below seasonable normals.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday Night/...

Before 00z... High confidence. VFR.

Tonight...Moderate confidence. BKN CIGs lowering towards 4-6
kft, with scattered SHRA moving in, the better chance of which
will be north of the Pike with a low risk TSRA. Increasing S
winds with the threat of MVFR/IFR VSBYs along the S coast from
stratus and fog.

Friday...Moderate confidence. IFR/MVFR stratus and fog across
the south coast should improve to VFR during the day. Much of
the region will remain VFR with hit or miss showers. Heavy
downpours possible with the potential for iso thunder. Stratus
will fill back in late afternoon esp across Cape and Islands.
Gusty southwesterly winds during the day with gusts near 25 kts.

Friday night...Moderate confidence. VFR conditions north of the
Pike through the night, with MVFR/IFR south of the Pike in
another round of stratus and fog. Better chance for showers and
iso thunder during the overnight hours. Heavy rainfall could
limit vsbys.

KBOS Terminal...High confidence. VFR, except MVFR CIGS possible
Fri evening. Gusty SW winds near 25kts Friday afternoon.

KBDL Terminal...High confidence. VFR, except MVFR CIGS possible
late Fri afternoon/Fri evening. Gusty SW winds near 25kts
during Friday afternoon.


Outlook /Saturday through Tuesday/...

Saturday...Moderate confidence.
MVFR and localized IFR in sct showers and isold t-storms, especially
south of the Pike. During the afternoon improvement to mainly VFR
north of the Pike.

Saturday night and Sunday...High confidence. Mainly VFR.

Monday...High confidence.
Mainly VFR cigs with a few showers possible in the interior.

Tuesday...Moderate confidence.
Mainly VFR cigs with some scattered showers/isolated t-storms
possible.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Friday Night/...

Southerly winds overnight as warm front passes. Wind will
increase into Friday with sustained winds 10 to 15 kts and
gusts up to 25 kts. This will push seas 5 to 6 feet and will
continue with the SCA. With a cold front sweeping down from the
N as the remnants of TS Cindy advect N from the S, will likely
see the return of mist / fog conditions resulting in low
visibility down to a quarter mile or less at times.

Outlook /Saturday through Tuesday/...

Saturday...Moderate confidence.
Some gusty W/SW winds early Sat, possibly near SCA thresholds in the
morning, should be diminishing in the afternoon. Seas up to 5-6 ft
over the south coastal waters.

Sunday and Monday...High confidence.
Winds should generally remain below small craft advisory thresholds
through the period. Lingering 5 ft seas over the south coastal
waters will subside Sun night.

Tuesday...Moderate confidence. There is a chance that winds and seas
may increase to small craft advisory thresholds.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides are rather high this weekend during the night time
cycles. Boston has a 12.4 ft high tide around midnight Sat night and
12.2 ft just after midnight Sun night. Fortunately, offshore winds
are forecast with minimal or no surge so do not anticipate any
issues.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 PM Friday to 8 AM EDT Saturday for
     ANZ231>235-237.
     Small Craft Advisory from 2 PM Friday to 8 AM EDT Saturday for
     ANZ250-254>256.

&&

$$
SYNOPSIS...Dunten/NMB
NEAR TERM...Dunten/NMB
SHORT TERM...Dunten
LONG TERM...NMB
AVIATION...Dunten/NMB
MARINE...Dunten/NMB
TIDES/COASTAL FLOODING...


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