Area Forecast Discussion
Issued by NWS Boston, MA

Home | Current Version | Previous Version | Text Only | 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
000
FXUS61 KBOX 271243
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
843 AM EDT WED JUL 27 2016

.SYNOPSIS...
High pressure will bring dry but continued hot conditions through
Thursday. A cold front will slowly drop south across southern New
England Thursday night, then stall across the region Friday. Low
pressure will push off the south coast Friday into Friday evening,
bringing the chance for showers and thunderstorms. Showers may
linger this weekend, with a few thunderstorms possible Sunday.
Conditions will improve early next week as high pressure slowly
moves in from the northwest.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
845 am Update...

Main concern through afternoon is sea breeze development along
both coasts as gradient remains weak. High res models indicate
these will develop later this morning, which is in line with
current forecast.

It will be close as to whether or not BOS reaches 90 before sea
breeze kicks in, which would end latest heat wave at 6 days. BDL
should easily make it to 7 consecutive days of 90+ heat.

Dewpoints will stay in low to mid 60s so heat index is forecast to
peak in lower 90s this afternoon.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Tonight...

High pressure moves offshore but maintains fair skies and light
wind. Light south winds possible by morning, but advection of
higher dew points limited. Expect similar min temps, mainly in
the upper 50s and 60s. The light flow may also allow some patchy
fog in the valleys.

Thursday...

High pressure offshore with south to southwest winds over New
England. Fair skies will again allow deep mixing. RH fields below
850 mb remain dry while some moisture increase at 800 mb would
allow increasing clouds during the afternoon.

Temperatures in the mixed layer are equiv to 19C at 850 mb, so low
to mid 90s again looks reasonable. Depending on the strength of
surface winds, there may be another buffering sea breeze along
the eastern MA shore for part of the afternoon. But confidence in
a persistent sea breeze is low at this time.

This leaves the question of precip. Moisture and instability is
initially focused on Northern New England but could slip south
into Northern/Western MA late afternoon/evening. Models do show a
surface front moving south into our area, but also show moisture
and favorable jet dynamics remaining in Northern New England.
Plenty of dry air below 850 mb to interfere with showers. We will
show chance pops moving into Northern/Western MA starting 21Z,
with slight chance into Northern CT.

&&

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

* Temperatures near seasonal levels into early next week, then
  warming again by Tuesday
* Low pressure wave looks to pass near or south of the region
  Friday and Friday night, which may bring steady rainfall along
  with scattered thunderstorms
* Spotty showers/thunderstorms through the weekend as front lingers
* High pressure builds slowly south out of Quebec early next week

Overview and model preferences...

Medium range models continue to show digging H5 trough across the
Great Lakes region while a surface front slowly works S out of
northern New England Thu night/Friday. As the H5 flow backs to SW,
the front will tend to stall across the region. Looks like best
shot for steady rainfall as well as convection during
Friday/Friday night.

The H5 trough will slowly shift E during this weekend. The cold
front will slip S of the region Saturday with mainly dry
conditions. However, may see another wave move off the south coast
during Sunday with the chance for scattered showers, with some
thunderstorms possible near and S of the Mass Pike as well as the
E slopes of the Berkshires. Lower confidence with this feature as
models showing wide solution spread with this feature. Models also
showing the H5 trough flattening out as it shifts E while high
amplitude ridge builds toward Hudson Bay.

Expect the NW upper flow that develops with this H5 ridge to
bring high pressure into the region early next week. Can not rule
out isolated diurnal convection during Monday, but should be
mainly dry with seasonal temperatures early next week.

Details...

Thursday night...Will be a muggy and warm night as clouds
increase from the NW. Looks like there will be fair chance for
sct showers/thunderstorms, mainly after midnight. PWATs increase
to 1.6 to 1.8 inches, so might see a few downpours with any
convection. Temps will only fall back to the upper 60s to lower
70s, possibly warmer in the urban centers.

Friday and Friday night...Model suite remains in pretty good
agreement with stalled front across the region. Will see rather
potent H5 short wave move along the front. Noting PWATs on order
of 1.6 to 1.9 inches, highest along the S coast, with this
feature. So, could see some heavy downpours especially in any
convection. This signal has been increasing over the last few
model runs, so have fair confidence that we may actually see some
pretty good rainfall from this system. 00Z QPF suggests 0.5 to 0.8
inches of precip during this timeframe, highest amounts along the
S coast. Big question will be whether this will be widespread or
spotty, depending upon organization of the short wave as it comes
across.

Looks like pretty good elevated instability as TQ values up to
around 20 during the day Friday into Friday evening. Also noting
surface based LIs in the zero to -2 range and K indices in the
lower 30s. Most parameters maximize during Friday
afternoon/evening then tend to weaken Fri night.

As short wave exits after midnight, should see slowly improving
conditions across NW Mass. Will also see late night patchy fog
with dewpts lingering in the 60s.

Highs on Friday will be from 80-85 for most areas, a bit cooler
along the coast.

Saturday and Sunday...With the departing low, expect mainly dry
conditions during Saturday. May see a few showers lingering across
the region as a muggy airmass remains in place along with a light
N-NE wind. Have kept slight chance of showers going for Saturday.

May see another weak short wave move across during Sunday, but
low confidence due to wide model solution spread. Have chance POPs
going for this feature, mainly for sct showers. However, some
instability works in across the E slopes of the Berkshires as well
as S of the Mass Pike, so have mentioned possible thunderstorms
there mainly from late Sunday morning into the evening.

Monday and Tuesday...High pressure builds out of Quebec, with a
drier NW flow in place. However, it is still summer so can not
rule out a few isolated showers during Monday. Also have a slight
chance of showers across the higher inland terrain Tuesday
afternoon. Expect highs Monday in the lower-mid 80s, then in the
mid-upper 80s on Tuesday.

&&

.AVIATION /13Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels.

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

Short Term /through Thursday/...High confidence.

VFR through tonight. Sea breezes develop along both coasts 15z-
17z. Patchy valley fog possible with MVFR/IFR cigs/vsbys
overnight.

Thursday... VFR. Local MVFR cigs/vsbys in northern/western MA
during the late afternoon due to scattered showers/tstms.

KBOS TAF...High confidence. Sea breeze develops around 15Z.

KBDL TAF...High confidence.

Outlook /Thursday Night through Sunday/...

Moderate confidence through the period.

Thursday night...Mainly VFR. Areas of MVFR-IFR in patchy fog late
at night mainly along the south coast. MVFR CIGS/VSBYS possible in
any scattered showers/thunderstorms.

Friday-Friday night...VFR early Friday, lowering to MVFR
throughout the region by afternoon. Areas of IFR conditions
possible in showers and scattered thunderstorms Friday
afternoon/night. Locally heavy downpours possible. Areas of IFR
in patchy fog Friday night.

Saturday and Sunday...Mainly VFR, except MVFR CIGS/VSBYS possible
in scattered showers. Chance for thunderstorms across E slopes of
the Berkshires and S of the Mass Pike Sunday with local MVFR-IFR
conditions. Potential for local MVFR-IFR in patchy fog and low
CIGS after midnight both nights.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Thursday/...High confidence.

Winds remain below 25 knots and seas below 5 feet through the
period. Sea breezes will develop near shore late this morning and
afternoon.  Winds become south to southwest Thursday.

Outlook /Thursday Night through Sunday/...

Moderate to High confidence through the period.

Thursday night...Winds and seas below small craft criteria. South
winds 10 kt or less. Patchy late night/early morning fog with
reduced visibilities. Isolated showers/thunderstorms possible.

Friday-Friday night...Winds and seas remain below small craft,
mainly S-SE winds Fri...becoming N-NE Friday night. May see gusts
up to 15 kt Fri night. Reduced visibilities in patchy fog as well
as scattered showers and thunderstorms. Best chance for showers
from late Friday morning into Friday evening.

Saturday and Sunday...Expect N-NE winds around 10 kt with gusts
up to 15 kt Saturday morning, then becoming light/variable
Saturday afternoon/night. Mainly E-SE winds 10 kt or less Sunday.
Seas may build to around 4 ft on the southern outer waters
Saturday night. Visibility restrictions in late night/early
morning fog each day, and in scattered showers. Isolated-scattered
thunderstorms possible Sunday, mainly on the waters south of the
RI coast.

&&

.FIRE WEATHER...
Dry conditions are expected to persist Today and Thursday across
Southern New England. Minimum relative humidity values will be 30
to 40 percent inland both days, and 40 to 60 percent along the
South Coast. Less wind Today than Tuesday, becoming a sea breeze
along the coast late this morning and afternoon. Wind directions
become more southerly on Thursday but remain below 20 mph.

Concern for Thursday will be how far south showers/tstms reach.
Most support is in Northern New England, but scattered
showers/t-storms could reach Northern/Western MA late afternoon.

&&

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

&&

$$
SYNOPSIS...WTB/EVT
NEAR TERM...JWD
SHORT TERM...WTB
LONG TERM...EVT
AVIATION...WTB/EVT/JWD
MARINE...WTB/EVT
FIRE WEATHER...WTB/EVT



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