Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
130
FXUS61 KBOX 211727
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
127 PM EDT THU JUL 21 2016

.SYNOPSIS...

Heat and humidity return Friday along with the risk for scattered
showers and thunderstorms during the afternoon and evening, some
of which may be severe. Hot weather is expected to continue this
weekend. An approaching cold front may bring us some relief from
the heat and another round of scattered showers and thunderstorms
sometime Monday and/or Tuesday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

1 pm update...no major changes to the forecast.

Just some mid to high level clouds filtering across the region
within the overall anticyclonic flow, otherwise mostly clear.
Abundant sunshine with a boundary layer becoming well-mixed up to
H85 where temperatures will warm to +18C, looking at highs today
around the mid to upper 80s with likely a few locations coming in
at or above 90 degrees (looking at the lower CT River and Merrimack
River Valleys given low-lying downsloping wind locations). Light
S/SW flow with the possibility of a sea- breeze along the immediate
E-coast. Dewpoints begin to rise back into the 60s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...

Tonight...
Another quiet night wx wise thanks to last minute influence of
high pres to the E. However in this case, in spite of the clear
skies and weak pres gradient, rising low-lvl moisture suggests a
more mild night across the region. Expect temps mainly in the low
to mid 60s. Some patchy fog possible too thanks to this increase
in moisture, but likely only in the typically prone spots.

Fri...
The primary issue for Fri remains the risk for late-day severe
wx. Although heat/humidity will be a factor. H85 temps will be
approaching +18C while sfc dwpts increase into the mid 60s to near
70, which given enough sunshine is enough for highs reaching the
upper 80s to low 90s and a low risk for heat advisory criteria.

Note that most of the following discussion will actually be moot
for the Friday (daylight) time frame if the the continued slow-
down in the guidance continues, suggesting the pre-frontal trof
doesn`t arrive until late evening, potential limiting sfc based
instability as we experience diurnal heat loss. Also, early Fri
may be marred by upstream convective cloud debris limiting the
destabilization.

Still plenty of factors pointing in the right direction, remnant
EML (peaks overnight Fri) with 6.0-7.0C/km lapse rates arrives in
time for the return flow and moistening low levels. Yielding ML
CAPE values in the afternoon near 1500j/kg (per ensemble probs).
Profiles are relatively wide, with hail-CAPE values +300j/kg.
Shear reaches 30kt at 0-3 and 0-6km with a nearly 40 kt H9 LLJ.
Therefore, should be enough for organization of any storms that
form, with hail an issue and some rotation in updrafts. Winds
still look to be the primary issue, thanks to inverted-V profiles
and LLJ, and as such will be upgrading wording to strong winds
with this morning`s wx update.

While winds/hail remain the primary risks, especially since
shear/CAPE profiles support MCS organization which would peak
overnight (at the point of EML peaking), there is a low end
tornado risk given the lowest lvl shear values and EHI between
1.0-2.0. However, not a pure S New England tornado break case per
internal study and the very dry mixed layer (high LCLs).

For now given the combination of timing uncertainty and mitigating
factors mentioned above, will be slowing timing and upgrading
gusty winds to strong winds, especially with the recent slow-down
and factors suggesting an MCS could be the primary convective
mode. Will also be adding T+ (severe type) wording given continued
agreement with SPC SWOs, which continues to highlight most of S
New England away from the ocean.

Stay tuned to updates as timing/mesoscale issues remain somewhat
uncertain.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...

Highlights..

* Heat and humidity return through this weekend
* Another cold front may bring showers and storms sometime Monday
  into Tuesday

Overview...Confidence in the details of potential thunderstorms
has slipped a bit from previous forecasts. 21/00z guidance has
presented a variety of timing issues. GFS was considerably slower
than the ECMWF and the NAM. Both the 20/21Z and 21/03Z SREF were
more of a middle ground timing-wise. Given the spread in the
solutions, preferred the SREF timing.

Expecting plenty of heat and humidity to continue into early next
week.

Details...

Friday Night...With a slower arrival timing of convection, the
issue of climatology becomes more of a factor. It is tougher to
get widespread severe weather in southern New England with
nighttime thunderstorms. There is still potential for strong to
severe thunderstorms. The details will still need to be refined
over the next day.

Saturday into Sunday...Could see some showers and thunderstorms
lingering into Saturday morning. Otherwise, much of this weekend
should be dry, hot and humid.

Monday into Tuesday...A low pressure moves into Quebec, pushing
another cold front through southern New England late Monday into
early Tuesday. This will likely bring a bit of relief from the
heat and humidity of this weekend. Another round of showers and
thunderstorms is possible. Will need to keep and eye on the
strength of an thunderstorms.

Tuesday and Wednesday...High pressure builds into southern New
England. This will result in a period of quiet and dry weather.
Temperatures/dewpoints will be a bit lower than this weekend, but
still seasonable.

&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...

Forecaster Confidence Levels.

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

Short Term /through Friday/...

18z update...

Today...High Confidence.

VFR. Light W/SW flow. FEW to SCT mid-high cigs. Likelihood of
sea-breezes along the immediate E-coast.

Tonight...High Confidence.

VFR. Increasing W/SW flow. Gusts up around 15 kts for S-coast
terminals. SCT to BKN mid-high cigs dropping down from the N.

Friday into Friday Night...Moderate Confidence.

VCSH during the morning period with SCT-BKN cigs. Clearing later
half of the day ahead of SHRA/TSRA for the late afternoon into
evening period. With any TSRA, TEMPO MVFR-IFR conditions. Some
TSRA may be severe with strong to damaging W/NW winds, hail, even
an isolated tornado possible. Focus 22.20z to 23.04z. S Winds
with the likelihood of gusts up to 25 kts especially for S-coastal
terminals.

KBOS TAF...Sea-breeze may hang just off the door-step of the
terminal around 19-20z. W/SW winds prevailing.

KBDL TAF...VFR prevailing.

Outlook /Saturday through Monday/...

Saturday...Moderate confidence.

Mainly VFR conditions expected. Brief periods of MVFR/IFR
conditions possible in SCT SHRA/TSRA over SE New England. Patchy
fog possible during the early morning Saturday.

Sunday...High confidence. VFR.

Monday...Moderate confidence. Mainly VFR conditions expected.
Brief periods of MVFR conditions in SCT SHRA/TSRA possible.

&&

.MARINE...

Forecaster Confidence Levels.

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

Short Term /through Friday/...High confidence.

1 pm update...no major changes.

Today and tonight...
Winds shift mainly to W-SW. A few gusts around 20 kt possible
through the afternoon, and a very low risk of a few gusts reaching
25 kt, but these will likely be few and far between. Otherwise
quiet boating wx.  Winds drop off tonight.

Friday...
Increasing wind gusts ahead of approaching cold front. SW gusts
25-30 kt at times expected, will be issuing small craft advisory.
This will also lead to some wind driven seas near 5-6ft.

Outlook /Friday Night through Monday/...

Increasing southwest winds ahead of a cold front will continue to
generate rough seas, particularly across the southern coastal
waters into Saturday. Winds and seas briefly diminish Sunday
behind a cold front.

Showers and thunderstorms are likely possible over the waters Friday
evening and night, and again on Monday afternoon. Storms Friday
night may become strong, producing dangerous boating conditions
at times. In addition, areas of fog may develop on Friday night,
limiting visibilities.

&&

.FIRE WEATHER...

Massachusetts state fire officials have advised that given the
forecast warm temperatures into the upper 80s to low 90s, low
humidity values, and lack of rainfall as of late that there is a
heightened fire danger. Such conditions likely exist for other
parts of Southern New England, namely CT and RI.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from noon to 8 PM EDT Friday for
     ANZ231>234-236.
     Small Craft Advisory from 11 AM to 8 PM EDT Friday for ANZ235-
     237-255-256.
     Small Craft Advisory from 2 PM to 8 PM EDT Friday for ANZ250-
     254.

&&

$$

SYNOPSIS...Belk/Doody
NEAR TERM...Belk/Doody/Sipprell
SHORT TERM...Doody
LONG TERM...Belk
AVIATION...Belk/Doody/Sipprell
MARINE...Belk/Doody
FIRE WEATHER...



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.