Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 262046
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
446 PM EDT TUE JUL 26 2016

.SYNOPSIS...
High pressure will bring dry but continued hot conditions through
Thursday. A cold front will drop southward across southern New
England late Thursday and stall near the south coast Friday.
Low pressure will move from the Mid-Atlantic northeastward toward
southeast MA by Fri night, then exiting the coast Saturday.
This has the potential to bring some rain to much of the area.
A few showers are possible over the weekend. Then dry high
pressure builds over the northeast states early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
High pressure builds into New England resulting in diminishing
winds out of the W/NW becoming light as conditions remain mostly
clear. Considering the overall dry soils across the region and
observed dewpoints during max-heating of the day falling into and
around the mid-50s, leaning lowest forecast guidance for overnight
lows with the expectation of radiational cooling.

Looking at lows around the upper-50s to low-60s, warmer along the
coast and within urban centers. Would not be surprised to hear a
few isolated locations falling into the mid-50s for lows by
Wednesday morning. A low risk of patchy fog, mainly in sheltered
low lying locations with bodies of water (i.e., CT River Valley).

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Wednesday...

High pressure remains in control. With a H85 airmass aloft around
+16-18C and abundant sunshine, in addition to dry-air subsidence,
expect temperatures to warm easily back into the 90s. With light
and variable winds, expect sea-breezes to develop along the shores
around late morning into midday. Likely mix-down of drier air,
another day of 50 degree dewpoints and the absence of muggy air.

Wednesday Night...

Continued high pressure, light winds, mostly clear conditions.
Expect another opportunity of radiational cooling to push
temperatures lower overnight. Leaning once again with lowest
guidance advertising upper-50s to low-60s. Focus on dewpoints
during max-heating of the day which will indicate the depth at
which temperatures can drop. Perhaps a fly in the ointment is
some mid-level clouds drifting into W New England late which could
put a lid on radiational cooling. Winds perhaps begin to turn S
towards morning resulting in rising dewpoints. This in addition to
some patchy fog issues but thinking a low risk.

&&

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

* Will a storm system come close enough to give substantial rain
  to parts of the area Friday and Friday night?

Overview and model preferences...

At upper levels, zonal flow Thursday becomes west-southwest as a
Great Lakes short-wave trough approaches and then crosses the area
Friday night and early Saturday. Another short-wave trough over
the Great Lakes Saturday exits New England late Sunday and Monday.
Drier and increasingly warm upper northwest flow then develops
over New England early next week as a strong high pressure ridge
develops over the Midwest.

At the surface, a weak frontal boundary will move southward into
southern New England late Thursday into Friday and stall along the
south coast. 12Z models are in much better agreement that a low
pressure storm system will develop in the Ohio Valley...move to
the Mid-Atlantic, then head northeast toward our area. GFS is now
the farthest south solution. GEFS low track is farther north,
though, closer to the GGEM, ECMWF, and NAM. While it is way too
early to gets hopes up about substantial rain, this is our best
chance in a while. Good model agreement on high pressure building
in from the north by Monday and Tuesday of next week.

Details...

Thursday...Main weather word will be HOT. With nearly full
sunshine in the morning and all models showing 925 mb temperatures
of +26-27C, expect highs getting up to the mid and perhaps upper
90s away from the south coast. Am expecting mixing to reduce
surface dewpoints to the upper 50s to mid 60s in the afternoon,
which will mean that Heat Index values will be close to the
ambient temperatures and may be just shy of Heat Advisory
criteria.

A weak cool front will sag southward during the afternoon and
there could be a wind shift to the north as far south as the Route
2 corridor by evening. However, 700-500 mb lapse rates of less
than 5C/km and warm temps. at 500 mb will reduce precipitation
chances. However, have 20-30 percent chance of a thunderstorm in
northwest and north central MA in the late afternoon. Expect
highs in the lower-mid 90s away from the coast, warmest across the
CT valley, ranging to the upper 70s-mid 80s near the coast
possibly touching 90 in Boston and on the north shore.

Thursday night...Increasingly muggy. Can`t rule out a chance of a
shower or isolated thunderstorm. Lows in the upper 60s to near 70.

Friday and Friday night... All models are coming into more
agreement...giving us more confidence...that a low pressure storm
system will move from the Mid-Atlantic northeastward toward
southeastern MA. All models give some rain to our region. Some are
much more prolific than others. Of course, we are in a drought and
even missed out on yesterday`s convection, so it will be important
to see consecutive model runs over the next couple of days. For
this model cycle, the NAM has an intense low moving into SE MA
Friday. afternoon and evening, with heavy rains in parts of RI
and SE MA. The ECMWF is very similar with track and heavy rains
even a little farther north, but not until Friday night. The GGEM
is also on board with a low, albeit weaker, passing southeast of
Nantucket with light amounts. The GFS is farthest south, with just
a few hundredths of rain. However, the GEFS ensembles are farther
north than the operational GFS, more in line with the other
models.

That said, have forecast cloudy skies with showers and isolated
thunderstorms likely...both Friday and Friday night, except high
chance PoPs in northwesternmost areas. Highs only in the lower to
mid 80s.

Saturday and Sunday... Low pressure departs the coast Saturday
morning. A weak pressure pattern exists, with some lingering
moisture around. So, basic summer weather with partly cloudy
skies, highs in the 80s, and a low chance of a scattered mainly
afternoon and evening shower or thunderstorm.

Monday and Tuesday...Expecting high pressure to build over
northern New England, providing increasing sunshine. Just a slight
chance of a shower in northwest areas Monday and dry on Tuesday.
Highs Monday 80 to 85 with mid and upper 80s possible on Tuesday.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels.

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

Short Term /through Wednesday Night/...High confidence.

Rest of Today...
VFR. W/NW winds with gusts 15-20 knots. Sea-breeze hanging along
the immediate E shore of Essex and Plymouth County MA.

Tonight...
VFR. Low risk of MVFR-IFR cigs/vsbys with fog towards Wednesday
morning, mainly focused in the CT River Valley. Sea-breeze washes
out. VRB winds developing.

Wednesday...
VFR. VRB wind becoming onshore along the coastline towards late
morning. If any fog during the morning period, it will quickly
burn off.

Wednesday night...
VFR. VRB winds becoming S but remaining light towards morning. Low
risk of MVFR-IFR patchy fog developing, mainly focused again in
the CT River Valley and possibly along the S-coast of RI and MA.

KBOS TAF...W/NW winds diminishing as a sea-breeze washes out off-
shore. With VRB winds more likely Wednesday, expect a sea-breeze
to develop close to mid-morning (15z) with potential gusts up to
15 kts out of the E into midday and afternoon.

KBDL TAF...W/NW winds diminishing. VRB into Wednesday. VFR and SKC.

Outlook /Thursday through Sunday/...

Thursday...High confidence. VFR except MVFR cigs/vsby possible in
widely scattered showers and thunderstorms mainly in northwest and
north central MA.

Thursday night...Moderate confidence. VFR except areas of IFR in
patchy fog late at night especially south coast. Also, MVFR
possible in any scattered showers/thunderstorms.

Friday into early Saturday morning...Moderate confidence.. VFR
early Friday lowering to MVFR throughout the region by afternoon.
IFR possible in showers and thunderstorms. Locally heavy downpours
possible. Areas of fog.

Rest of Saturday and Sunday...Moderate Confidence. Mainly VFR,
except MVFR CIGS/VSBYS possible in scattered showers and
thunderstorms. Potential for local MVFR-IFR in patchy fog and low
CIGS Sat night.

&&

.MARINE...
Forecaster Confidence Levels.

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

Short Term /through Wednesday Night/...High confidence.

W/NW winds diminishing overnight. High pressure settling over the
waters which will make for good boating weather. Sea-breezes
developing along the shores around mid- morning Wednesday, so
watch out for some gusts out of the S/E around 15 kts. Low risk
for patchy fog along the S-coast of RI and MA towards Thursday
morning.

Outlook /Thursday through Sunday/...Moderate to High confidence.

Thursday and Thursday night...Winds and seas below small craft
criteria. Patchy late night/early morning fog with reduced
visibilities. Isolated showers/thunderstorms possible Thursday
night.

Friday-early Saturday...Southeast winds become northeast. Speeds
generally 10-20 kt, depending on strength of possible low
pressure approaching from the mid-Atlantic. Swells will build to 4
to 5 ft on the southern outer waters by Friday night into early
Saturday. Patchy fog. Reduced visibilities in showers and
thunderstorms.

Rest of Saturday and Sunday...Seas subsiding with northeast winds
becoming southeast...generally 10-15 kt or less.

&&

.FIRE WEATHER...
Drier conditions are expected to persist through Thursday across
S New England as much of the region is in drought with significant
year-to-date rainfall deficits.

An elevated fire weather potential is forecast as minimum relative
humidity values range from 30 to 40 percent. While overall winds
are anticipated light and variable, sea-breezes are expected to
develop around mid-morning into midday behind which S/E wind gusts
up around 15 mph are possible. Some moderation in relative humidity
is expected with marine-layer air coming ashore.

&&

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

&&

$$
SYNOPSIS...Sipprell/Field
NEAR TERM...Sipprell
SHORT TERM...Sipprell
LONG TERM...Field
AVIATION...Sipprell/Field
MARINE...Sipprell/Field
FIRE WEATHER...Sipprell


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