Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 231842
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
242 PM EDT SAT JUL 23 2016

.SYNOPSIS...
Hot conditions continue this afternoon/early evening with the risk of
some strong to severe thunderstorms particularly in northern
and eastern MA. Otherwise, excessive heat and humidity is expected
at times through the middle of next week, at least away from
the immediate coast. Another risk for scattered showers
and thunderstorms is possible late next week with a cold front
dropping south.

&&

.NEAR TERM /THROUGH TONIGHT/...
2 PM update...
Scattered showers and t-storms developing to the north and west of
SNE this afternoon where deeper moisture and higher KI values are
present. MLCAPES generally around 500 J/kg, limited by lower
dewpoints which have dropped into the 50s. 0-6km shear around 40
kt, but lower shear values present to the north.

Mid level cold pool near the Canadian border will drop south
across SNE later this afternoon with increasing mid level lapse
rates. Expect sct showers/t-storms to move into SNE as shortwave
approaches with increasing synoptic forcing. MLCAPES expected to
peak around 500-1000 J/kg and not likely much higher due to lower
dewpoints while deep layer shear will decrease from the north mid
to late afternoon. This will limit organization and areal coverage
of convection but there are still some concerns. Specifically the
very dry air in the low levels with pronounced inverted V profile
supports strong gusty winds with any storms. Downdraft CAPES up to
1200 J/kg which is impressive. Seabreeze boundary moving into
eastern MA could become a focus later on.

Previous discussion...
Another hot day today with highs reaching the low to mid 90s
across eastern MA/CT/RI although a bit cooler along immediate
south coast where sw winds expected. Some of the hi-res guidance
also hinting at a weak seabreeze across the immediate coast in
eastern MA. Dewpoints to mix out this afternoon and likely drop
into the upper 50s to lower 60s away from the immediate south
coast.

Main concern for this afternoon is the potential for another
round of strong to possibly severe t-storms as rather potent
shortwave moves into New Eng later today. Very good mid level
cooling with this shortwave as 500 mb temps drop to -12 to -14C
by evening which is impressive with temps into the 90s. Mid level
lapse rates expected to increase to around 6.5 C/km associated
with the cooling temps aloft which will allow MLCAPES to increase
to around 1000 J/kg. The instability will be tempered by the
decreasing dewpoints this afternoon so do not expect MLCAPES to
get much higher. Hi-res guidance suggesting showers and t-storms
will develop in northern New Eng and spill south into the region
after 3 pm with focus across northern and eastern MA where core
of cold pool moves.

Currently, 0-6km shear is around 40 kt which is more than enough
to support organized severe convection. However, guidance is
indicating deep layer shear decreasing from the north mid to late
afternoon and may drop below 30 kt which would limit organization
of storms. However, very large T/Td spread and inverted V sounding
profile support gusty winds and cant rule out isolated wind damage
with the stronger storms. Hail is also a concern with cooling
temps aloft.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
Thunderstorms/showers should end earlier than Friday night thanks
to faster movement of the forcing shortwave. Drier air will lead
to some drying during the overnight but leftover convective debris
cloudiness will likely keep temps from dropping too far. Expect
mins mainly in the 60s. A few spots of fog possible, especially
where late day rainfall is observed.


&&

.SHORT TERM / SUNDAY THROUGH 6 AM SUNDAY/...
Thunderstorms/showers should end earlier than Friday night thanks
to faster movement of the forcing shortwave. Drier air will lead
to some drying during the overnight but leftover convective debris
cloudiness will likely keep temps from dropping too far. Expect
mins mainly in the 60s. A few spots of fog possible, especially
where late day rainfall is observed.

&&

.LONG TERM /SUNDAY THROUGH SATURDAY/...
Highlights...

* Excessive heat at times through mid week at least away from the
  immediate coast and especially Monday

* Mon/Mon night is the highest risk for scattered showers/t-storms
  with the threat for some severe weather and even very localized
  urban type flooding

* Cold front may bring another risk for scattered
  showers/thunderstorms sometime late next week but timing uncertain

Details...

Upper level ridge over the southern half of the country will
generate a westerly flow of air aloft and anomalously hot
temperatures, especially for the first half of the week.  GFS
Ensembles indicate 925T between 1 and 2 standard deviations above
normal for most of next week.  So confidence is fairly high in above
to at times much above normal temperatures.  ECMWF ensembles are
pretty much in agreement as well.

Monday...

Currently, Monday looks like it may be the worst in terms of heat
and humidity.  850T near +20C should allow high temps to rise into
the mid to upper 90s away from any coastal sea breezes.
Surface temps may even reach 100 in a few locales if clouds do not
get in the way. In addition, low level moisture may pool ahead of a
pre frontal trough/cold.  This may push heat index value to 100+ and
decent shot will need heat advisories for portions of the region.

The heat/humidity combined with frontal boundary/pre-frontal trough
in the vicinity may lead to scattered showers and thunderstorms
developing during Monday afternoon and night.  Pretty good shot at
MLCapes reaching or exceeding 1500 J/KG.  0 to 6 KM shear initially
not impressive, but increase to between 25 and 35 knots during the
late afternoon and especially the evening with approaching
shortwave. A lot will depend on timing, but there certainly is the
risk for scattered severe thunderstorms.  If they are develop the
primary risk would be strong to damaging straight line wind gusts.
While activity may be hit and miss, will have to watch if any low
level boundary washes out or becomes stationary.  If this happens,
there may be a very localized urban type flood threat as well with
PWATS over 2 inches.  Lots of uncertainty at this point, but in
addition to the excessive heat/humidity potential is there for
some severe weather and perhaps even a very localized flood risk
later Monday into Monday night.

Tuesday and Wednesday...

Assuming cold front clears the region by early Tuesday morning, dry
weather should prevail Tue into Wed but certainly not a guarantee
this far out.  High temps should still be mainly in the 90s Tue and
Wed away from at least the immediate coast.  Should be somewhat less
humid Tue, but some more humidity may return Wed.  Either way it
will likely be hot away from any onshore flow.

Thursday through Saturday...

Above normal temps will continue over this time, but
probably not quite as hot as early in the week.  A frontal boundary
may drop down and bring the risk for a round of two of
showers/t-storms by late in the week but timing highly uncertain
and by no means a washout.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Forecaster Confidence Levels.

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

Short Term /through Sunday night/...

Through 00z...Mainly VFR, but widely sct showers/t-storms
developing will result in briefly lower conditions, mainly north
of a KBAF-KTAN line. Some strong winds possible in some of these
storms. Otherwise, mainly NW winds 10-20 kt with a few higher
gusts CT valley and higher terrain.

Tonight...High confidence. Mainly VFR. Patchy late night fog
possible in the normally fog prone locations.

Sunday and Sunday night...High confidence. VFR.

KBOS TAF...Moderate confidence. A brief t-storm is possible 4-7
pm. Some of those storms could produce strong wind gusts.
Seabreeze just east of BOS may briefly move onshore shifting
winds.

KBDL TAF...High confidence.

Outlook /Sunday through Thursday/...

Monday...Moderate confidence.  Mainly VFR outside of lower
conditions in scattered showers/thunderstorms mainly Monday
afternoon and evening.

Tuesday and Wednesday...Moderate to high confidence.  Mainly VFR
other than a few hours of early morning patchy fog in the typically
prone locations.

Thursday...Moderate confidence. Mainly VFR outside the risk for
scattered showers and thunderstorms.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Tonight/...High confidence.

Seas will continue to dissipate through the morning as winds
outside of thunderstorms have already dropped to or below 20 kt.
Seas will also gradually dissipate this morning allowing the
remaining small craft advisories to be dropped.

Otherwise, another round of showers and thunderstorms are possible
over the waters this afternoon and evening which could contain
localized strong wind gusts.

Outlook /Sunday through Thursday/...Moderate to high confidence.
Winds and seas should generally remain below small craft advisory
thresholds over this time.  A period of southwest wind gusts of 20
to perhaps up to 25 knots are possible near the south coast for a
few hours Monday afternoon.  Otherwise...main concern is the risk
for scattered thunderstorms mainly late Monday into Monday night and
perhaps again on Thursday.

&&

.EQUIPMENT...
KBOX RADAR IS BACK IN SERVICE AFTER GOING DOWN FOR
MAINTENANCE EARLIER THIS MORNING. HOWEVER...IT IS OPERATING IN A
DEGRADED STATE. RADAR RETURNS ARE RUNNING ABOUT 10 DBZ ABOVE WHAT
THEY ARE. FOR EXAMPLE...RADAR RETURNS SHOWING 70 DBZ ARE ACTUALLY
ABOUT 60DBZ. KEEP THIS IN MIND WHEN EVALUATING ANY STORMS. WE
APOLOGIZE FOR THE INCONVENIENCE.

&&

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

&&

$$
SYNOPSIS...KJC/Frank
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...Frank
AVIATION...KJC/Frank
MARINE...KJC/Frank
EQUIPMENT...


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