Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 230752

Area Forecast Discussion
National Weather Service Taunton MA
352 AM EDT Fri Jun 23 2017


Mild, humid air builds across the region today into tonight out
ahead of the remnants of Cindy which will bring the threat of
heavy rain and possible flooding Saturday morning. A cold front
will sweep the remnants of Cindy out to sea through late Saturday,
improving overnight. Seasonably warm and less humid conditions
Sunday will be followed by cooler and somewhat unsettled weather
for early next week. Warmer conditions return for the latter half
of next week.



4 am update...

Showers and thunderstorms for the early half of the day, potential
for heavy rain. Consensus of forecast guidance has an initial wave
of tropical energy associated with Cindy sweeping the region during
the early half of the day. Collocated low-level convergence of high
theta-E air per nose of H925-85 jet beneath a psuedo H925-7 warm
frontal boundary with parent mid-level ascent. Especially if there
is partial clearing in the morning presenting the opportunity for
the boundary layer to destabilize, can see an opportunity where the
present wave out of the Mid-Atlantic to maintain longevity, perhaps
becoming stronger. Thinking mainly across the interior N/W away from
S flow off the cooler ocean waters which would keep the surface more
capped. However forecast guidance not so robust. Increasing moisture
with precipitable waters rising towards 2 inches, 0-6 km bulk shear
around 30 kts out of the SW, and CAPE around 1-2k j/kg. Am going to
lean with high chance PoPs N/W across the interior. Think the high-
res 3 km NAM and both WRF have the right idea. S/E becoming socked
in with low clouds, possible fog, the region cooler at the surface
is capped. May see some showers, perhaps heavy, but greater concern
is N/W. Looking at the late morning into early afternoon period. Not
so confident on severe weather outcomes but agree with the marginal
risk advertised by SPC. Believe the main threat to be heavy rain and
frequent lightning, some localized nuisance flooding concerns, with
gusty winds and hail secondary threats.

The later half of the day looks to be dry. Behind the morning wave,
a combination of subsidence and mid-level warming around H6-8 puts
the squash on any additional wet-weather activity, stabilizing. If
throughout the day places remain partially clear, some locations
could see highs into the low 90s such as the Merrimack River Valley.
Continued cool S/E under lower clouds, possible fog. Otherwise, main
theme for today is warm and muggy. Dewpoints well into the 60s, some
places near 70.



Tonight into Saturday...

Possibility of heavy rain, flooding associated with Cindy leftovers.
An anomalous tropical airmass surging NE out ahead of a cold front /
baroclinic zone. The tropical-moist plume converging with higher
theta-E ahead of a mean long-wave trough axis at the mid-levels and
beneath decent diffluence within the upper levels, there is support
for deep layer forcing yielding efficient warm-rain processes with
freezing level heights at least above 10 kft, in this case around 14
kft. However outcomes are challenging to nail down and determine as
they can often be underestimated or misplaced by forecast guidance.
In the last several forecast runs, model solutions have waffled with
the remnants of Cindy. It makes for subsequent challenges as to the
possibility of flash flooding, if any one area is under particular
threat of seeing an excessive amount of rain in a short period of

But with this forecast there is continued preference to the high-res
3 km NAM and WRF forecast model solutions. Suspect a possibility of
maintenance of shower, thunderstorm activity out of Upstate NY and
PA across S New England during the evening hours. Convergent low-
level forcing of high theta-E air beneath continued energy streaming
NE with the tropical-moist plume. Given the lack of diurnal heating,
main concern is the potential for heavy rainers, nuisance flooding.
Then around morning, crux of heavy rain is expected as the remnants
of Cindy clash with a cool front dropping S, clearing out through
the afternoon. The 3 km NAM and WRF-ARW fit the forecast thinking,
that the broad tropical-moist plume though focused with remnants of
Cindy would also converge along the low to mid level cool front that
sweeps across the region through afternoon.

Low confidence at this point concerning exactly where the greatest
threat will be. Will continue to highlight possible flooding hazards
in the HAZARDOUS WEATHER OUTLOOK. Can`t rule out potential for rain-
fall rates of around an inch per hour and excessive rainfall amounts
greater than 2 inches storm-total. Low confidence with respect to
forecast grid rainfall amounts that add up around 0.50-0.75 inches
given the difficulty in determining exactly where the heaviest rainfall
will occur.

The cool front sliding through late in the day, will see potential
blustery SW winds depending on the ability to mix down, perhaps
brought down mechanically via heavy rain given a saturated profile
that is moist adiabatic. Prior to and throughout, low clouds and fog
will likely remain an issue for the S-coast with the possibility of
visibility down to a quarter mile or less requiring headlines. Will
monitor for now.

Behind the front winds back W and we begin to see partial clearing.
Temperatures difficult to forecast given some uncertainty on the
timing of the front and how quickly we clear out. Could warm into
the mid 80s but will keep it conservative with seasonable highs
around the upper 70s to low 80s. With the warm up may see some brief
breezy westerlies behind the front with boundary layer mixing.




* Seasonably warm and less humid on Sunday
* Cooler and somewhat unsettled pattern for early next week with
  showers possible at times
* Warmer weather returns toward the end of next week


Longwave trof over the Gt Lakes region will gradually slide east to
New Eng Tue/Wed timeframe as multiple shortwaves rotate through the
flow. This will bring a somewhat unsettled pattern for the first
half of the week with cooler temps, near or a bit below normal.
Models signaling a pattern change for the end of the week as ridging
builds northward along the east coast which should bring warmer
conditions for the end of next week.


Saturday night and Sunday...

Cold front expected to be moving off the coast Sat evening followed
by drier conditions during the night. Low risk of a lingering
evening shower for the Cape/Islands, otherwise clearing skies during
the night with cooler and much less humid airmass moving in.

The dry airmass will continue into Sunday with sunshine mixing with
diurnal cu in the afternoon. Fairly robust mid level shortwave will
move NE from the Gt Lakes with a secondary cold front moving into
SNE. Brunt of shortwave energy passes to the north and west but
can`t rule out a few showers developing in the interior in the
afternoon. 850 mb temps 12-13C and soundings indicate deep mixing on
Sunday above 850 mb so temps may overachieve.  Expect highs reaching
low to mid 80s, except a bit cooler along the south coast with SW
flow. Comfortable humidity levels with dewpoints in the 50s.

Monday into Wednesday...

Mid level trof gradually moves into New Eng as series of shortwaves
rotate through the flow. Cooling temps aloft with 500 mb temps
reaching -18 to -20C will likely bring some diurnal showers at times
although certainly not a washout and expect a mix of clouds and sun.
Any showers Mon should be confined to the interior, but all areas
Tue as the trof moves into the region. Best chance for any thunder
will likely be Tue with TT into the lower 50s and 500 mb temps
approaching -20C. Upper trof begins to slide to the east on Wed.
Cold pool aloft lingers but moisture is limited so expect limited
coverage of any showers Wed. Temps slightly below normal with highs
mainly in the 70s and lows in the 50s.


As mid level trof exits, rising heights into New Eng as SE US ridge
builds north. High pres moves off Mid Atlc coast with good warm
advection. Warmer conditions expected with temps possibly reaching
well into the 80s in some locations.



Forecaster Confidence Levels...

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

Short Term /through Saturday/...Moderate confidence.

BKN-OVC IFR/LIFR stratus and fog developing along the S-coast
with SCT-BKN low-end VFR elsewhere. Brief improvement possible
at times along the S-coast up to VFR. S winds around 10 to 15
kts with gusts up to 25 kts, strongest across E/SE New England.
Best SHRA/TSRA chances over N/W CT and N/W MA, mainly afternoon
into early evening. TEMPO MVFR/IFR with RA/+RA. Gusty winds and
hail possible with strongest storms.

Tonight into Saturday...
tonight approaching from the W. RA/+RA approaching from the SW
towards morning, exiting around midday ahead of a wind shift
from the W. Prior to the wind shift will continue to see SW
winds with potential gusts 25 to 30 kts LLWS possible for SE
coastal terminals as is some embedded TSRA. Improving towards
evening to low-end VFR / SKC.

KBOS Terminal...VFR today with gusty SW winds up to 25 kts,
lower CIGs into this evening with increasing rain chances.

KBDL Terminal...May need to watch for possible SHRA/TSRA NW of
the terminals around late morning into early afternoon.
Otherwise low-end VFR CIGs today with blustery SW winds that
will lower into evening prior to onset of RA/+RA.

Outlook /Saturday night through Tuesday/...High confidence.

Sunday and Monday...Mainly VFR with sct-bkn diurnal clouds. A few
diurnal showers possible in the interior

Tuesday...Mainly VFR cigs with a few showers/isolated t-storms



Forecaster Confidence Levels...

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

Short Term /through Saturday/...

SW winds on the increase with gusts up to 25 to 30 kts through
early Saturday prior to a cool frontal passage. Waves building
around 5 to 6 feet on the waters as the remnants of Cindy are
advected NE across the waters around Saturday morning. Prior to
and during this time, likely to be either a combination of low
clouds and fog with visibility down to a quarter mile or less
possible. Improving late Saturday as winds become westerly while
beginning to diminish along with wave action.

Outlook /Saturday night through Tuesday/...High confidence.

Sunday...Increasing SW flow but speeds should remain below SCA with
a few gusts 20-22 kt nearshore waters in the afternoon.

Monday and Tuesday...Quiet boating weather with winds and seas below



Astronomical tides are rather high through this weekend during the
night time cycles. Boston has a 12.3 ft tide just before midnight
tonight, 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.



MARINE...Small Craft Advisory from 8 PM this evening to 11 AM EDT
     Saturday for ANZ231>234.
     Small Craft Advisory from 8 PM this evening to 8 PM EDT
     Saturday for ANZ235-237.
     Small Craft Advisory from 2 PM this afternoon to 11 AM EDT
     Saturday for ANZ250.
     Small Craft Advisory from 2 PM this afternoon to 8 PM EDT
     Saturday for ANZ254>256.



NEAR TERM...Sipprell
SHORT TERM...Sipprell
TIDES/COASTAL FLOODING...WFO BOX Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.