Area Forecast Discussion
Issued by NWS Boston, MA

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872
FXUS61 KBOX 232334
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
734 PM EDT Fri Jun 23 2017

.SYNOPSIS...

Mild, humid air continues into tonight out ahead of the
remnants of Cindy which will bring the threat of showers and
thunderstorms mainly very late tonight into the first part of
Saturday. 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
weather and few diurnally driven showers/isolated thunderstorms
Monday and Tuesday. A return to summerlike warmth and humidity
is expected by the end of the work week.

&&

.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...

725 pm update...

Tricky forecast this evening as a cluster of showers and
embedded thunderstorms were moving across portions of eastern PA
and NJ. Some of the model guidance brings this activity
northeastward into southern New England over the next few hours.
This a result of increasing low level jet in advance of
shortwave energy. However, the higher instability remains to our
south which is often where the majority of the showers and
thunderstorms tend to gravitate towards.

So overall, a low confidence forecast this evening but tend to
think the main complex of showers and thunderstorms may pass to
our south this evening. Still may see some showers and isolated
thunderstorms, especially across our southern zones.

A better chance of more showers and thunderstorms with heavy
rainfall very late tonight into the first part of Saturday,
which is discussed in the next paragraph.

Lastly, some patchy fog along the south coast, Cape and Islands
tonight. However, enough wind may keep it from becoming
widespread/dense overnight but still will need to monitor.

&&

.SHORT TERM /MIDNIGHT THROUGH 6 PM SATURDAY/...

After midnight into Saturday...

*** Increasing localized flood potential for southern New England ***

Active weather pattern for very late tonight and for the first
half of tomorrow as southern New England remains in the warm
sector for this period. 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. Muggy to start the day tomorrow but depending on how
quickly the front will push through, the later half of the day
will begin to improve. Highs will remain in the mid 80s.

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 2.5 inches by tonight. This tropical moisture
from Cindy will push PWAT near 3 to 4 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.

Models are struggling with the placement of the axis of heavy
precipitation as there are several features to note. Aside from the
approaching front out west, a LLJ will be across the southeast
portion of the area. However, the higher instability values will be
across the western half of the area. If both of these features
could align, then we could see widespread heavy rainfall. But
because there is some separation, believe that the threat is more
localized. Again the heavy rainfall axis amongst the guidance are
in different locations, but there is agreement that the potential
for over 1.5 to 2 inches. If this falls in just a few hours, then
flash flooding is possible. Best timing for this to occur will be
after midnight and into Saturday morning.

Cold front will begin to sweep through the region on Saturday.
The latest hi-res guidance is a lot slower than synoptic models so
have blended the forecast down the middle. More widespread showers
and embedded thunderstorms are anticipated along the frontal
passage. Convection along the front continues to be a possibility
especially across eastern MA during the late morning hours. CAPE
values will be near 1000 J/kg with 40 kts of 0-6 km shear. The
caveat is poor lapse rates and the bulk of the moisture will be
pushing offshore. One thing to watch for is the potential for a
quick spin-up thanks to the Tropical airmass with 70F dewpoints and
lower LCLs. Hodographs do show some helicity and good 0-1 km shear.
The Frontal system should push through by Saturday afternoon
resulting in clearing skies and drier air as westerly flow takes
hold.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...

Highlights...

* Seasonably warm/less humid Sun with a spot shower/t-storm possible
* A few showers/iso t-storms possible Mon/Tue but not a washout
* Below normal temps Mon/Tue return to summerlike readings Thu/Fri

Details...

Saturday night...

Dry and a much less humid airmass will work into the region behind
Saturday`s cold front.  This should allow low temps to fall into the
50s across many outlying locations, to between 60 and 65 in some of
the urban centers.

Sunday...

A pleasant end to the weekend across southern New England.  850
temps between +11C and +12C should allow highs to reach into the
lower to middle 80s in most locations, but dewpoints in the 50s will
make it feel much more comfortable outside.  Mainly dry weather
anticipated, but approaching shortwave may be enough to trigger an
isolated shower/t-storm or two by mid-late afternoon across the
interior.

Monday and Tuesday...

Anomalous upper trough/cold pool aloft overhead will result in
slightly below normal temps with comfortable humidity levels.  Highs
mainly in the 70s are expected both days.  The cold pool
aloft/shortwave energy will result in the potential for a few
diurnally driven showers/isolated thunderstorms both days.  Not
expecting a washout by any means, but the main risk for any activity
will be during the afternoon/early evening hours.

Wednesday...

Axis of upper trough will probably have shifted to the east of the
region.  This should allow temps to warm a few more degrees than
Mon/Tue and result in mainly dry weather. However, if trough ends up
slower than currently expected there would be the risk for a few
more showers/isolated thunderstorms.

Thursday and Friday...

Upper trough lifts northeast of the region with rising height
fields. This should result in a warming trend for the end of the
work week, with a return to summerlike warmth and humidity.

&&

.AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

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

Tonight into Saturday...Moderate confidence. MVFR to IFR
conditions expected into Saturday morning. Low risk of LIFR
conditions along the south coast in fog, but enough wind in the
boundary layer may prevent that from happening. Scattered
showers and thunderstorms mainly late tonight into early Sat
afternoon.

Improving conditions from west to east 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...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Saturday Night through Wednesday/...

Saturday night through Wednesday...High confidence.  Mainly VFR
conditions other than a few mainly diurnally driven showers and
perhaps isolated t-storms.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

SW winds continue to gust up to 25 to 30 kts through early
tomorrow prior to a cool frontal passage. Waves building around
5 to 7 feet on the waters as the remnants of Cindy are advected
NE across the waters around the morning hours. 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 Wednesday/...

Saturday night through Wednesday...Moderate to high confidence.
Quiet boating weather overall during this time period.  A few hours
of near shore lower 20 knot wind gusts and choppy seas are possible
on both Sun and Mon afternoons.

&&

.MARINE...

SW winds continue to gust up to 25 to 30 kts through early
tomorrow prior to a cool frontal passage. Waves building around
5 to 7 feet on the waters as the remnants of Cindy are advected
NE across the waters around the morning hours. 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 Wednesday/...

Saturday night through Wednesday...Moderate to high confidence.
Quiet boating weather overall during this time period.  A few hours
of near shore lower 20 knot wind gusts and choppy seas are possible
on both Sun and Mon afternoons.

&&

.TIDES/COASTAL FLOODING...
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. While, offshore winds are forecast
current conditions suggest a 0.4 surge which will result in
minor splashover. Thus will go ahead an issue a coastal flood
statement for tonight`s high tide.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 3 PM EDT Saturday for ANZ231>234.
     Small Craft Advisory until 9 PM EDT this evening for ANZ230-
     236.
     Small Craft Advisory until 8 PM EDT Saturday for ANZ235-237-
     250-254>256.

&&

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



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