Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 250818
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
418 AM EDT MON JUL 25 2016

.SYNOPSIS...
Summer heat will continue into much of the upcoming week. A weak
front will bring an increased risk of showers and thunderstorms
this afternoon and evening and again late next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
***Hot and humid, Late Day Severe Weather Possible***

Tricky balance to the forecast today regarding both the heat and
convective potential for this afternoon and evening. Regarding the
heat, have quite a bit of upstream convective cloud debris to
contend to the SW combined with short-term guidance a bit cooler
at H85, mainly between +18C and +20C, rather than the +20C
previously progged. However, it will not take too much sun to
allow mixing to reach H85 or higher, and with dwpts in sliding
into the upper 60s to around 70, heat indices will approach 100.
Currently, however, dwpts are starting lower than most guidance
suggests, mainly in the 50s and low 60s. Therefore, given slight
downslope flow, it still appears the lower CT valley has the best
chance of reaching heat advisory criteria while others may fall
just short, influenced by cloud cover and/or marine layer.
Therefore, do not have the confidence to expand current heat
advisories although several locations will see heat between 95F
and 100F.

Approaching shortwave is a bit faster than previously forecast.
The impact here is that it`s too fast for upper lvl cold pool (and
core of remnant EML) to lag the lift. Still, even with clouds,
CAPE values between 1000-1500j/kg are likely. Shear values start
mainly at or below 30 kt at both 0-3 and 0-6km, but do increase
with the approaching shortwave toward the afternoon to around 35
kt. Although mid lvl lapse rates are not expected to be as robust
given the lagging EML, this is still enough for typical diurnal
convection to fire as the upper lvl shortwave approaches. The
highest instability/shear overlap moreso across W MA/CT (after
moving through NY), this correlates to current SPC SWODY1 Marginal
Risk, down from a Slight Risk. This suggests SPC shares concern
for the mitigating factors.

Expect convection to begin firing mainly around 2PM or after
across NY. The primary issue will be strong-damaging winds, as
inverted-V profiles and high D-CAPE values support this once
again. Hail a risk as well thanks to about 300j/kg CAPE between
-10C and -30C, but WBZ heights are rather high. High PWATs near
2.0 inches by late afternoon and low magnitude Corfidi vectors all
support a heavy rain with localized urban flooding threat. The
shear values and high LCLs typically do not support much of a
tornado risk, but given stronger stability or a localized
boundary, will still need to monitor.

Stay tuned to later updates through the day as timing and any
warnings ultimately are issued.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Tonight...
With increasing mid lvl lapse as the core of the upper shortwave
moves across the region, it may lead to lingering convection into
the earlier overnight hours. This correlates to ML CAPEs near
1000j/kg lingering along with an increase in shear, closer to 35
kt. Timing of shortwave will be key, but eastern areas could see
the remnant of this convection linger through 02-04Z (10-midnight
local).

Otherwise, dwpts will be slow to decrease even as winds shift
toward the W-NW. Expect some localized ground fog especially where
rainfall is observed. Indications suggest Cape/Islands see a mix
of marine fog/stratus.  Min temps mainly in the 60s.

Tomorrow...
Even with nose of high pres, NW flow and some cooling aloft. Temps
will still approach the low to mid 90s thanks to some downsloping
and H85 temps starting near +18C. Clearing skies after any stratus
and or remnant high clouds dissipate.

&&

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

* Hot temperatures continue through the middle of this week, away
  from the coast
* Should be a little less humid Tuesday and Wednesday
* Showers and thunderstorms are possible again late this week

Overview...

25/00z guidance is in decent overall agreement through mid week,
then more significant differences in the details start to emerge.
This is a bit of change from previous runs.  Will favor a consensus
approach for this forecast.  That should smooth over the more minor
differences through mid week, as well as account for the greater
uncertainty late this week into next weekend.

Details...

Tuesday Night and Wednesday...Drier weather with high pressure in
control.  Still hot, especially away from the coasts.  Sea breezes
are more likely

Thursday and Friday...Uncertainty increases with this portion of the
forecast. Temperatures will cool a few degrees Thursday as clouds
increase and a cold front starts to move through southern New
England. This front is expected to stall somewhere near our region
on Friday. The presence of this front, and likely increase in
clouds, should lower max temperatures Friday.

Scattered showers and thunderstorms will be possible with this
frontal passage, particularly on Thursday when more instability is
expected.  They may linger into Friday, but as mentioned above, that
will largely depend on how far off the south coast the front pushes.
Regardless, Friday is likely to be cloudy and cooler, though more
humid than previous days.

Saturday and Sunday...Lots of uncertainty remains with this portion
of the forecast, leading to a low confidence forecast. Latest runs
of the models now keep a frontal boundary nearby. Will mention a
chance of showers, for now.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels.

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

Short Term /through Tuesday/...

Through today...Moderate confidence.
Mainly VFR through the afternoon. Between 20Z and 02Z, a risk for
TSRA and SHRA is expected with some strong winds and heavy
rainfall.  Localized IFR conditions likely in any TSRA.

Tonight...moderate confidence.
Most thunderstorms/showers end between 02Z and 04Z with VFR
developing initially then late night fog especially at typically
prone airports. Stratus also possible along the Cape/Islands
especially. Mix of IFR/MVFR conditions.

Tomorrow...high confidence.
Mainly VFR after early morning fog/stratus dissipates. Winds
mainly NW with gusts 15-20 kt.

KBOS TAF...Moderate confidence in TAF. Timing of afternoon
shra/TSRA may be off.

KBDL TAF...Moderate confidence in TAF. Timing of afternoon
shra/TSRA may be off.

Outlook /Tuesday Night through Friday/...Moderate to high confidence.

Quiet boating weather is expected through this time.  The exception
will be Thursday into Friday. While winds and seas will remain below
small craft advisory criteria, low clouds, fog, and periodic showers
and thunderstorms should limit visibilities.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Tuesday/...High confidence.

Seas remain below SCA. Winds from the W-SW, then shift to the NW
tomorrow with some gusts 15-20 kt. There is a risk for late day
and evening thunderstorms today which will need to be watched.

Outlook /Tuesday Night through Friday/...Moderate to high confidence.

Quiet boating weather is expected through this time.  The exception
will be Thursday and Friday when winds and seas will remain below
SCA criteria, but low clouds, fog, and periodic showers and
thunderstorms will limit visibilities.

&&

.CLIMATE...
Here are the record high max and min temperatures for July 25:

Boston - 96 (1882)/78 (2001)
Hartford - 98 (2001)/75 (2001)
Providence - 96 (2001)/75 (2001)
Worcester - 93 (1941)/73 (2001)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory from 11 AM this morning to 6 PM EDT this evening
     for CTZ002.
MA...Heat Advisory from 11 AM this morning to 6 PM EDT this evening
     for MAZ010-011.
RI...None.
MARINE...None.

&&

$$
SYNOPSIS...Belk/Doody
NEAR TERM...Doody
SHORT TERM...Doody
LONG TERM...Belk
AVIATION...Belk/Doody
MARINE...Belk/Doody
CLIMATE...staff


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