Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 251117
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
717 AM EDT THU AUG 25 2016

.SYNOPSIS...
High pressure moves farther offshore today. Warm and more humid
conditions return ahead of a cold front Friday, which may lead to
a few showers or thunderstorms. Large high pressure will crest
across New England this weekend, bringing dry and somewhat less
humid conditions. Another front will slowly move across the region
late Sunday night and Monday with a chance for showers and
thunderstorms. Conditions for Tuesday and Wednesday look dry for
now.

&&

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

705 AM Update...

Band of cirrus clouds pushed across the region early this
morning, but is now offshore. Some thin band of cirrus remain
across the region, but another area of mid and high level clouds
will work out of upstate NY through midday. Noting a line of
showers across central and western NY at 11Z. May begin to reach
the MA/NY border by early this afternoon, but may tend to become
more scattered as it moves E.

Temps at 11Z running mainly in the 60s, except a few upper 50s
across N central/NW Mass. Expect readings to recover rather
quickly as the high clouds approach. Will remain dry as showers
remain well W through midday.

Have updated forecast to bring conditions current and
incorporated into near term trends.

Previous Discussion...

High pressure will continue to move offshore. Expect a persistent
southwest flow today, with less of a risk for a sea breeze along
the east coast of MA. As the moisture increases, so will the
clouds. The loss of any sunshine is expected to be offset by the
advection of warmer air from the southwest. So, max temperatures
mostly similar to slightly higher than Wednesday.

The main issue today will be the potential for showers and
thunderstorms later today. Plenty of heat and humidity will mean
very good low level lapse rate. However, the mid level lapse
rates are still expected to be poor. Combined with a seaward-
moving high pressure, and that usually spells a slower arrival
time for precipitation. Am thinking the majority of today will
remain dry across most of southern New England. Cannot rule out a
stray shower or thunderstorm late this afternoon, especially
across far western MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Subtropical moisture plume moves into southern New England ahead
of a cold front with precipitable water values approaching 2.00".
The forcing continues to be rather weak, although mid level lapse
rates should become a bit more supporting of thunderstorms. Not
expecting an all-the-time washout everywhere. However, wherever
showers and thunderstorms develop, there will be the possibility
for a torrential downpour.

Humidity continues to increase tonight into Friday. As such,
temperatures tonight are not expected to drop much below 70 at
most places. It will likely be muggy sleeping weather. The heat
continues to build Friday. A cold front should move through or
region by late Friday, which should bring an end to the rainfall
chances. The humidity will take longer to drop off.

&&

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

* Shower and thunderstorm chances Friday evening and late
  Sunday night into Monday
* Expect a warm and somewhat less humid but dry weekend
* Lower confidence for sensible weather conditions Tue/Wed

Overview and model preferences...

Overall upper level pattern across the northern tier of North
America appears to remain essentially the same with a nearly zonal
flow aloft into this weekend. Do note a weak short wave in this
flow, with its associated frontal system that pushes through
Friday night. Large high pressure builds east out of central
Canada to the Great Lakes by Saturday, then shifts eastward
through the weekend as high amplitude H5 ridge builds but remains
progressive. With higher H5 heights, will still see temperatures
across the region running 5 to 10 degrees above seasonal normals
through the weekend, though somewhat lower humidity will make it
feel comfortable.

As the northern strong ridge builds toward the Maritimes later
Sunday, noting another H5 short wave in the flow. Big question
will be how far S the energy from this short wave will work as the
surface front moves along in the upper flow for late Sunday night
into Monday. Appears what energy and moisture will be mainly
across central and northern areas, but not much of either to be
had at this point.

Most models and their ensembles all signaling the storm track
across the northern stream appears to be retreating into southern
Canada early next week. Looks to be difficult to get any moisture
or instability to work in, as it appears the front crossing the
region during Monday tries to wash out as it shifts S. It may
linger as it stalls near or S of the region by the middle of next
week. With mid level subsidence allowing for capping, will not see
much in the way of convection. Models having their issues in the
timing and placement of any precip that may develop for into the
middle of next week. Most guidance is trying to keep any moisture
that may organize across SW New England, mainly N CT into RI, near
or just N of the stalled front.

Then there`s what could happen with the tropical wave 99L as well
as Hurricane Gaston. For now, appears only effects that will be
felt from Gaston will be mainly across the coastal waters, and
that will be dependent upon its track well E of Bermuda at this
point. As for 99L, that appears to be a southern U.S. concern, but
still needs to be monitored.

Details...

Friday night...May see isolated-sct showers/thunderstorms
lingering in the evening ahead of cold front as it crosses. The
best PWATs have already pushed offshore, so not a lot of moisture
to work with. Any leftover precip across southern areas should
end. May see patchy late night fog develop in the normally prone
inland locations. Expect lows in the 60-65 degree range well
inland, coolest in the E slopes of the Berkshires, ranging to
around 70 along the S coast.

Saturday-Sunday...Large high pressure crosses New England
Saturday, settling into Maine and the Maritimes during Sunday.
With the center of the high N of the region, will see mainly light
N-NE winds with sea breezes especially on Saturday, then winds
become more S-SE during Sunday. With the high mid level heights,
temperatures will remain warm. Expect highs both days in the
lower-mid 80s with some upper 80s across the lower CT valley.
Inland locations will see drier dewpts, mainly in the mid-upper
50s, but will be somewhat muggier along the coast with the onshore
winds.

Sunday night-Monday...Another front approaches. Best PWATs, on
order of 1.7 to 1.8 inches, cross the region Sunday night and push
offshore by 12Z Monday. So, best shot for any precip will be later
Sunday night through about midday Monday. Not a lot of QPF
expected with any precip. Looks like best shot will be near and
north of the Mass Pike but will be light. Will be another warm day
on Monday with highs mainly in the 80s, though a bit cooler along
the immediate S coast.

Tuesday-Wednesday...Lower confidence due to possible waves along
stalled front S of the region that may influence sensible weather
across N CT/RI and possibly into SE Mass. For now, kept forecast
mainly dry, but much uncertainty.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels.

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

Short Term /through Friday/...

Today...High confidence. VFR with cigs 5-10k ft moving in across
western New England during the afternoon. SW gusts to 20-25 kt,
especially along the S-SE coast this afternoon.

Tonight...Moderate confidence, mainly due to timing issues.
Mainly VFR cigs, but areas of MVFR cigs possible. A few SHRA
possible with isolated TSRA.

Friday...Moderate Confidence, mainly due to timing issues.
Scattered SHRA/TSRA, mainly across N/W portions of southern New
England. Possible TEMPO MVFR-IFR impacts with any storms. Breezy
S/SW winds with gusts up to 25 kts.

KBOS Terminal...Will hold winds out of the S/SW with the terminal
with the possibility of gusts of around 25 kts this afternoon.

KBDL Terminal...S winds increasing with gusts up to 25 kts
possible.

Outlook /Friday Night through Monday/...

Friday night...Moderate to high confidence.
May see leftover isolated SHRA/TSRA across RI/SE Mass Friday
evening with brief local MVFR conditions. Otherwise, mainly VFR.
May see areas of MVFR-IFR CIGS/VSBYS lingering along S coastal
Mass, Cape Cod and the islands. Patchy fog develops across
normally prone inland locations after midnight with MVFR-IFR
conditions. Expect light N-NW or calm winds.

Saturday and Sunday...High Confidence.
VFR. Light N-NE winds with sea breezes along the coast Saturday.
E-SE winds as high pressure moves into the Maritimes. May see
brief patchy late night/early morning fog in normally prone
inland areas both days.

Sunday night and Monday...Moderate Confidence.
May see scattered SHRA/isolated TSRA move into N Mass mainly
north of the Mass Pike after midnight Sunday night with brief
local MVFR conditions. Otherwise, mainly VFR conditions. Brief
patchy fog with local MVFR-IFR VSBYS after 05Z Sunday night,
improving 11Z-12Z.

Isolated SHRA/TSRA may linger across central and northern areas
through early-mid afternoon on Monday, then should dissipate.
W-SW winds around 10 kt or less.

&&

.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.

Increasing S/SW winds ahead of a cold front through Friday. Seas
should generally remain less than 5 feet. Cannot rule out some
higher seas across the outer coastal waters, particularly tonight
and Friday. The main issue will be the potential of 25 kt gusts at
times, particularly near shore where better mixing should occur.
Increasing risk for scattered showers and thunderstorms tonight
into Friday ahead of a cold front. Southwest winds and more humid
conditions could also lead to some fog across the southern coastal
waters with reduced visibility.

Outlook /Friday Night through Monday/...

Friday night...Moderate Confidence.
SW winds 10-15 kt Friday evening, with gusts up to 20 kt on the
southern waters, shifting to N-NW overnight. Seas 4 ft or less.
Patchy fog on the southern near shore waters with visibility
restrictions.

Saturday and Sunday...High Confidence.
Generally light N-NE winds with sea breezes along the near shore
waters Saturday, becoming S-SE around 10 kt Sunday. Seas remaining
below 5 ft, but may see SE swells increasing during Sunday.

Monday...Moderate Confidence.
W-SW winds remain light, though may see some gusts up approach 20
kt on the eastern waters Monday morning. SE swells from distant
Hurricane Gaston may build to around 5 ft on the eastern waters as
well as east and south of Cape Cod and Nantucket.

&&

.CLIMATE...
As we wind down August, we looked at the annual precipitation to
date. As dry as we have been lately, there have actually been
drier January to August periods. Here is how we rank at each of
the climate sites:

Boston:

 1. 16.30" (1965)
12. 20.26" (2016)*
13. 20.28" (1950)
14. 20.45" (1980)

Worcester:

 1. 17.16" (1907)
17. 23.40" (2016)*
18. 23.46" (1923)
19. 23.50" (1999)

Providence:

 1. 16.84" (1957)
42. 25.83" (2016)*
43. 25.95" (1945)
44. 25.99" (1912)

Hartford:

 1. 16.75" (1965)
 6. 22.34" (2016)*
 7. 22.51" (1921)
 8. 22.57" (1980)

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 10 PM EDT
     this evening for ANZ231>237-251.
     Small Craft Advisory from 2 PM this afternoon to 7 AM EDT
     Friday for ANZ250-254.
     Small Craft Advisory from midnight tonight to 7 AM EDT Friday
     for ANZ256.

&&

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


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