Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 101958
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
358 PM EDT Wed Aug 10 2022

.SYNOPSIS...

Fog and low stratus develops after sunset this evening; fog may be
dense at times across the Cape and Islands through Thursday morning.
Low pressure tracks to our south during the day Thursday bringing
shower chances to southeast MA and RI, primarily south and east of I-
95. Temps will average a bit below normal Friday and Saturday with
mainly dry weather outside a few brief showers. Sunday will be the
pick of the weekend with lots of sunshine and dry weather. A period
or two of much needed widespread rainfall may finally impact
the region sometime later Monday into Wednesday.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...

Periods of scattered clouds and sun will continue through this
evening before low stratus redevelops across our eastern zones.
Persistent ENE flow that has been keeping much of eastern MA in the
upper 60s and low 70s will go calm overnight, which combined with
dewpoint depressions near 1F and the warm SSTs of August will allow
patchy fog to form across much of the CWA; the exception possibly
being across the CT River Valley, where greater dewpoint
depressions, driven by dewpoints in the upper 50s, will remain above
4 degrees. Confidence in fog formation is particularly high across
the Cape and Islands, where it is anticipated to be dense overnight;
visibilities may be reduced to 1/4 mile or less at times in this
region.

Overnight low temperatures will be limited by cloud cover and
dewpoints as lows drop into the 60s region wide; slightly cooler
across our northwest zones.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...

Weak low pressure will begin to track to our south during the day on
Thursday. Confidence is relatively low regarding the extent of the
precipitation shield, and how much QPF will fall across our area,
given we are less than 24 hours out from the event. Even at this
time, guidance is widely varied regarding how far north
precipitation gets, with some guidance, namely shorter term guidance
like the NAM, keeping most precipitation offshore and to our
southwest along Long Island. Other guidance, like the GFS, brings
much more generous precipitation event to the region, with
widespread showers impacting southeast Massachusetts and Rhode
Island. Total QPF will be widely dependent on which solution
verifies, with local maximums anywhere between 0.25" and 0.75" of
rain on the table; higher amounts seeming decreasingly likely as
only the GFS presents a generous soaking. In general, all guidance
keeps the bullseye of precipitation south and east of the I-95
corridor. In addition to the main precipitation event, both the
ECMWF and NAM, hint at the development of a secondary band of weak
showers along the I-95 corridor along a weak surface boundary, which
may bring less than 0.05-0.10" of rain a bit further north and west
into Norfolk County MA.

It will be a tale of two forecasts tomorrow, however, as central CT
and NW MA experience mostly dry conditions, partly cloudy skies, and
much more temperate dewpoints compared to the rest of the region.
Dewpoints will fall into the upper 50s in these regions and daytime
heating mixes things out; cloud cover across E. MA and RI will
prohibit mixing much above 900mb, keeping dews in the upper 60s to
near 70 across those areas. Similar to Wednesday, there will also be
a significant temperature gradient across the region; with sunshine
warming things into the mid-80s away from precipitation affecting
the south coast. Additionally, there will be low chance for a shower
or rumble of thunder across our northwest zones Thursday evening
ahead of an approaching cold front.

With low pressure just to our south, winds will be light and rather
variable again on Thursday. Winds will be primarily from the E/SE
along our coastlines, but from the N/NW across NW MA. Additionally,
southerly winds will be felt across portions of CT! Regardless of
wind direction, winds will generally be below 5kt.

Fog will redevelop again on Thursday night, although it will likely
be contained to the south coast, Cape, and Islands where dewpoints,
SSTs, and temperatures all converge within a degree or two.
Dewpoints begin to crash into the low and mid 50s across central and
NW MA late Friday night, which will keep fog at bay across much of
the interior. Overnight lows will again be in the 60s region wide,
with a chance for a few readings in the upper 50s across the highest
elevations of Franklin and Worcester counties.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...

Highlights...

* Temps will be a bit below normal Fri/Sat with dry weather
  dominating, but a few brief showers are possible

* Dry and beautiful weather expected on Sun

* A period of two of much needed widespread rainfall may impact
  the region sometime later Mon into Wed, but not set in stone

Details...

Friday and Saturday...

A potent upper trough will approach from the west Fri into Sat
coupled with distant offshore wave of low pressure. This is
somewhat similar to an inverted trough setup we often see in the
winter. However, baroclinicity is much weaker this time of year
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 Fri into Sat. Greatest risk for this
will be across eastern MA/RI. And even if there are a few
showers; any precipitation will be rather light with dry weather
dominating the majority of the time.

High temps will probably be in the 70s to the lower 80s
depending on the amount of solar insolation that is realized.
Greatest risk for more clouds and the cooler temps will be
across eastern MA/RI. Either way it looks like temps will be
a bit below normal, which is quite the change of what we have
been experiencing the last several weeks.

Sunday...

The upper level shortwave will have lifted to the northeast of
the region. This will allow Sunday to be the pick of the
weekend with more sunshine and warmer temps. Highs should be in
the lower to middle 80s except perhaps a bit cooler on the
immediate coast. Regardless...humidity levels will be quite
comfortable for this time of year. So a rather nice day to close
out the weekend.

Monday through Wednesday...

Appears that we will have our first shot in a period or two
of widespread rain sometime later Mon into Wed, but given the
timeframe it is certainly not set in stone. The ECMWF/GFS/CMC
all indicate a strong shortwave diving southeast from the Great
Lakes and closing off at 500 mb. This combines with a surface
high over eastern Canada and a wave of low pressure to our south.
In addition...Pwats may climb to over 1.5 inches given
meridional flow. Again, this is still 5-7 days in the future so
nothing is set in stone. However, for the first time in a while
there are some signals there for a period or two of widespread
rainfall. Temps will be seasonable although humidity levels
will increase; but not to the levels we saw earlier this week.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...

Forecaster Confidence Levels:

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

18z TAF Update:

Tonight...Moderate confidence.

MVFR to IFR conditions overnight across interior terminals.
Potential for LIFR conditions to develop across the Cape and
Islands as fog develops after midnight. Light to near calm SE/S
winds overnight will shift slightly towards SW near daybreak.

Thursday...Moderate confidence.

IFR conditions to begin the day across the Cape and Islands,
with MVFR to VFR conditions elsewhere. Fog will dissipate across
southeast MA however shower activity and low stratus will
develop after about 15Z south and east of the I-95 corridor, so
conditions are not expected to improve too drastically at ACK,
HYA, and FMH. BOS and interior terminals should improve to VFR
after sunrise, but showers cannot be ruled out for BOS and PVD
Thursday afternoon. Winds will be light but variable in
direction, generally 5 kt.

Thursday Night: VFR across the interior, with MVFR across the
Cape and Islands. Winds light and variable before flow becomes
northerly by sunrise. IFR conditions cannot be ruled out across
the Cape due to low ceilings.

KBOS...Moderate confidence. MVFR/VFR this evening will give way
to MVFR conditions overnight. There is an outside shot that fog
develops and moves over the terminal, which would reduce vsbys
to IFR before sunrise. Showers cannot be ruled out at BOS on
Thursday, but most precipitation will remain south and east of
the terminal. Winds will transition from the E/SE today to calm
overnight before becoming S/ESE, between 5-10 kt, again for
Thursday.


KBDL...High confidence. Generally VFR, MVFR possible overnight
but quickly becoming VFR after sunrise. Shower activity will
remain south and east of the Terminal. Winds generally light and
variable, less than 5kt on Thursday.

Outlook /Friday through Sunday/...

Thursday Night: Mainly VFR, with local MVFR possible.

Friday: Mainly VFR, with areas MVFR possible. Slight chance
SHRA.

Friday Night through Saturday: Mainly VFR, with areas MVFR
possible. Breezy. Slight chance SHRA.

Saturday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA.

Sunday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Tonight and Thursday...High Confidence. Low pressure will track
across the southern waters during the day on Thursday, but does
not look to bring much wind along with it. Winds will generally
blow below 10 kt. Direction will be variable based on the
position of the low, but will generally prevail from the east
across our southern waters, and from the south across our
eastern waters by Thursday afternoon. After days of persistent
southwest flow, a change in wind direction will allow wave
heights to subside a bit, generally at or below 3 ft across the
outer waters, with smaller waves expected in and around the
harbors and sounds.

Outlook /Friday through Sunday/...

Friday: Winds less than 25 kt. Slight chance of rain showers,
patchy fog.

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

Sunday: Winds less than 25 kt.

&&

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

&&

$$
SYNOPSIS...KS/Frank
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...Frank
AVIATION...KS/Frank
MARINE...KS/Frank


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