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FXUS61 KBOX 111348 PZB
AFDBOX


Outlook /Friday Night through Monday/...

Friday through Friday Night: Winds less than 25 kt. Slight
chance of rain showers.

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers.

Saturday Night through Sunday Night: Winds less than 25 kt.

Monday: Winds less than 25 kt. Slight chance of rain showers.

&&

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

&&

$$
SYNOPSIS...Loconto/Chai
NEAR TERM...Loconto/Chai/KS
SHORT TERM...Chai
LONG TERM...Loconto
AVIATION...Loconto/Chai
MARINE...Loconto/Chai

FXUS61 KBOX 111348 PAA
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
948 AM EDT Thu Aug 11 2022

.SYNOPSIS...
Low pressure tracks to our south during the day today bringing
shower chances to southeast MA and RI, primarily south of the
Mass Pike. Friday will feature below normal temperatures with
mainly dry weather outside of a few brief showers. Low pressure may
brush southeast New England with rains Saturday but most of the
weekend is dry and tranquil for the interior, with low humidity
levels. Unsettled weather pattern evolves early to mid next
week. While not set in stone, the potential exists for a much
needed multi-day rain event around later Monday into Wednesday.
Cooler than normal temps are likely this weekend into midweek.

&&

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

9:45 AM Update:

Showers have continued to overspread southern Connecticut this
morning, with light rain reported in Bridgeport. These showers
will continue to expand north and east into Rhode Island and
southeast MA over the next few hours. Cloud tops have begun to
cool which may generate some more substantial showers over
coastal Rhode Island. Additionally, some heavier showers have
developed off of the eastern tip of long island and may move
over Martha's Vineyard and Nantucket; where we are expecting the
bullseye for rainfall today; perhaps up to 0.25". Guidance is
still settled on keeping most, if not all, precipitation south
and east of the I-95 corridor today, with just an outside chance
of a shower across the Boston metro area.

While a surge in moisture across northwest MA initially
increased cloud cover this morning, it is anticipated that
clouds will begin to clear out in this region as drier air
pushes in. Some of the more aggressive guidance this afternoon,
namely the HRRR drops dewpoints into the mid and upper 40s this
afternoon in our western zones; where daytime heating will allow
for better boundary layer mixing. While the HRRR appears to be
overly assertive in it's mixing potential, most guidance shows
dews falling into the 50s across the CT River Valley and west of
Worcester. At this time, temperatures remain on track to reach
into the mid 80s across the CT River Valley, but, much like
yesterday, temperatures may overachieve across CT and western
MA if clouds clear earlier than forecast. Low stratus and
showers will limit mixing across eastern MA and RI which will
keep dewpoints much more sticky through this afternoon. Even so,
patches of sunshine will develop across our eastern areas this
afternoon and evening as the weak low to our south begins to
push off the coast.



710 AM Update:

Still anticipating rains around mid morning across RI and SE MA
from ongoing heavy showers and embedded t-storms pulling ENE off
the NJ coast. Much lighter (if any) rains north of I-95, with
the heavier rains mainly along the southern coastline and the
Cape and Islands. An early look at day cloud phase RGB shows
some deepening convective towers ahead of the main area of
heavier showers where there's about 1000 J/kg of CAPE south of
Long Island; a rumble or two of thunder appears possible for
the southern waters and MVY/ACK but the risk probably won't
make it much further north than that. Chance for rains look
fairly short north of I-95, with better chances for rains
through the afternoon across the Cape and Islands.

Most areas under an overcast, but expect improvement from west
to east from late-AM to early-PM; will take till mid to late in
the day for SE MA and central/southern RI before skies begin to
scatter out there. No changes to highs attm, with upper 70s to
near 80 across eastern and southeast New England with low-mid
80s in the interior where skies project to be mostly clear the
soonest.

Previous discussion:

* A period of showers today with best chance for appreciable
  rainfall south of the Mass Pike, and especially along the MA/RI
  south coast into Cape and the Islands.

Mesoanalysis shows a weak 1014mb surface low centered over the
Jersey coast. The only significant area of reflectivity on the
mosaic radar is across far southeast PA into northern Delaware.
Closer to New England, there are some hints of reflectivity across
CT but nothing appreciable is making it to the ground. Winds are
light but enough to have prevented fog formation. So have
significantly trimmed the area coverage of fog but it is still
possible Cape and interior valley locations could see localized fog
towards daybreak. Did also trim PoPs through the early morning hours
as some of the 00z CAMs appear overly aggressive in bringing
widespread rainfall to a good part of our area.

Looks like best chance for appreciable rainfall will be south of the
Mass Pike, and especially near and along the MA/RI south coast into
Cape and the Islands. Timing wise, the leading edge of the
precipitation will be entering Connecticut right around daybreak,
spreading into eastern MA by early to mid morning. Forecast sounding
cross sections show deeper RH values only up to 6-7k ft, so not
expecting too much in the way of rainfall, i.e. mainly in the form
of a few sprinkles or showers. PWATs over 1.5 inches (seasonably
high, although not record territory like the past couple of days)
will overspread areas south of the Pike and into eastern MA by
daybreak. Then during the day, a swath of 0.75 to 1 inch PWATs
(roughly 25th percentile according to SPC sounding climatology for
Chatham, MA) overspreads from west to east, which should help
suppress the best shot for appreciable rainfall to areas near and
along the south coast into Cape and Islands.

While low to nil impact, there is somewhat a low to moderate
confidence forecast, especially in the precipitation department,
given limited baroclinicity this time of year. So it is somewhat
challenging to pinpoint the northward extent of a synoptic QPF
field, even inside 12 hours time frame. Nonetheless, 00z CAMs are in
fairly good consensus with the track of the low pressure giving
areas north of the Mass Pike mostly dry weather.

Then by late afternoon, as the rainfall associated with the wave of
low pressure moves off the eastern MA coastal waters, an approaching
cold front from NY state will spark a few scattered showers and even
an isolated thunderstorm across western and central MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
* Cool night tonight especially across western MA with patchy fog
  possible across southeast MA.
* Friday will feature below normal temperatures with mainly dry
  weather outside of a few brief showers.

Tonight...

Shower activity associated with the cold front that falls apart
across central MA will diminish with sunset. There will be quite a
dew point and consequently temperature spread for our area by mid
August standards. Overnight lows should fall into the upper 50s for
western and north central MA with mid to upper 60s across southeast
MA and southern RI where dew points will be higher due to proximity
to the low pressure center. In addition, there should be more
widespread fog development compared to the previous night although
the fog should mostly be confined to the Cape and Islands into
portions of the MA coastal plains.

Friday...

A potent upper trough will approach from the west on Friday. This
coupled with a distant offshore wave of low pressure, should provide
modest but adequate convergence for shower activity and perhaps even
an isolated thunderstorm. This is somewhat similar to an inverted
trough setup that we often see in winter. However, baroclinicity is
much weaker in mid August and the overall forcing is also quite
limited. Therefore, we expect dry weather to dominate but a few
showers may briefly impact parts of the region on Friday. Greatest
risk for this will be across eastern MA and RI. And even if showers
do materialize, any precipitation will be rather light with dry
weather dominating for most locations.

Temperatures wise, daytime highs should be mainly in the 70s to the
low 80s depending on the amount of solar insolation. Greatest
probability for more clouds and cooler temperatures will be across
eastern MA and RI. Regardless, temperatures will be a little below
normal, which is quite a dramatic shift from the oppressive heat and
humidity that we experienced over the past several weeks.

&&

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

* Monitoring risk for rains for southeast New England Sat, but
  weekend is overall generally dry and tranquil for the remainder of
  SNE.

* Pattern change toward unsettled weather; while not yet set in
  stone, potential exists for a multi-day rain event around Tue to
  Thurs as an upper low meanders over New England.

* Below normal temps likely through the period; comfortable humidity
  levels this weekend begin a modest increase into early-mid next
  week but not to the oppressive levels we saw last week.

Details:

While some amplitude differences are apparent, the overall mid-level
pattern remains generally well specified in this portion of the
forecast by the ensembles and deterministic model suite. The mid-
level pattern across northern CONUS amplifies with a prominent mid-
level ridge building into the northern Rockies/Intermountain West
which generally remains stationary. Downstream and closer to home,
it features a anomalous mid-level trough over the Northeast to mid-
Atlantic states, a trough which becomes reinforced by additional
shortwave energy in the early to mid week and evolving into a closed
upper low. In fact, indications of seasonably below-normal heights
over the Northeast may last at least a week as the pattern becomes
rather blocky and slow to evolve. Thus fairly solid confidence in
below normal temps through much of this period. Quite a change from
the last several days!

For the weekend...while most of the interior should remain dry with
low humidity levels, there is a little more uncertainty as it
pertains to rain chances for Fri night/Sat across southeast New
England. While the operational GFS/CMC keep our area dry with a more
progressive trough, the 00z ECMWF and its ensemble show an initial
closed low in vicinity of NJ by 12z Sat. This draws a field of
moisture/rain chances back NW from the baroclinic zone over the Gulf
Stream vicinity. Not too confident on that evolution but ECMWF
ensemble QPF probs of rains at/over 0.50 inches in the 30-50% range
suggested carrying at least lower-end PoP for Sat. A washout doesn't
seem too likely but could bring a round of rains Sat to areas S/E of
I-95. Will need to monitor this closely for upward/downward
adjustments. This upper low pulls into northern New England Sun,
with drier weather returning.

For early to midweek...additional shortwave energy digging SE from
the Gt Lakes helps to reinforce the longwave trough Mon. Eventually
this trough evolves into a closed upper low with strong ensemble
support for this evolution sometime later Mon into Wed. Per 00z
deterministic guidance there are amplitude differences on how deep
this closed low may get, and in most of the guidance the closed low
was found to be less deep than model forecasts 12 hrs ago indicated.
Even still, with rather solid ensemble probs for 0.50" or more of
QPF in a 24 hr period, the potential still exists for a multi-day
rain event around Tue to Wed, and potentially into Thurs as well.
This is a pretty atypical pattern for mid-August; not set in stone
yet, and timing and details still need to be shaped but odds seem
tilted toward wetter conditions moving into the early to midweek
period. Kept NBM based temps going with highs in the 70s to near 80
and lows in the 60s; may also see a rise in humidity level as PWAT
values rise toward the 1.5" range but not nearly to the level we saw
much of the past handful or so of days.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels:

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

12z TAF Update:

Today: Moderate confidence.

Mix of MVFR-IFR eastern and southeast airports due to stratus
and approaching rain. Steadier rains to mainly be focused in
areas south and east of I-95; thunder possible at ACK as soon as
15z, but too uncertain to include VCTS in the TAF. Should see
west to east improvement 17-21z for most, but ACK likely to stay
IFR for the longest period of time. Light SE winds.

Tonight...Moderate confidence.

Remaining VFR across western MA and CT despite a deck of 4-6k ft
clouds spreading in from the west ahead of a cold front. Widely
scattered showers are possible but will be hit or miss in nature.
Terminals across southeast MA and RI will continue to see MVFR to
IFR ceilings, with localized LIFR possible. Winds will overall be
light and variable but generally turn N across western and central
MA into CT but changing to the SW for eastern MA terminals by
daybreak. Localized fog could also lead to reduced vsby across the
Cape terminals.

Friday...Moderate confidence.

Mainly VFR, with areas of MVFR possible during periods of rain. Best
chance for showers south of the Mass Pike.

KBOS...Moderate confidence. Risk for showers is brief and
between 15-17z, runways likely to stay dry with steadier rains
well to the south.

KBDL...Moderate confidence.

Outlook /Friday Night through Monday/...

Friday through Saturday: VFR. Slight chance SHRA.

Saturday Night through Sunday Night: VFR.

Monday: VFR. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today into Friday...High confidence.

Winds and seas will remain below SCA criteria during this period.
Low pressure will track across the far southern waters today,
bringing light and variable winds along with periods of rain showers
during the day into the early evening hours. There is also the low
probability of an isolated thunderstorm across the southern waters.
Localized fog is also possible overnight tonight into Friday morning
especially across the southern waters into Cape Cod and the islands.