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FXUS61 KBOX 171041
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
641 AM EDT Wed Aug 17 2022

.SYNOPSIS...

Low pressure brings periods of mainly light showers to the
region today. Gusty north-northeast winds will also impact
coastal MA. Low will lift north into Maine by early Thursday
bringing a mostly dry, seasonable day to the region, as winds
shift to the west. Very warm weather with above normal temps
returns Friday and Saturday, followed by increasing humidity for
the first half of next week. Generally dry weather is expected
through the weekend with the best chance for scattered showers
and a few thunderstorms mainly sometime Tuesday into Wednesday.

&&

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

640 AM Update...

Offshore low pressure continues to spin east of the Benchmark
and it will lift north today. It was resulting in bands of
mainly light showers rotating into southern New England at
times. We think that the bulk of the showers and rainfall
amounts will be rather light today. This a result of pockets of
mid level dry air across the region; which is quite evident by
looking at current cloud bases. The radar structure also
indicated a lot of dry pockets within the shower shield. There
was an area of steadier rain just east of Cape Cod that will
need to watch over the next several hours.

In a nutshell...thinking most locations will just see periods of
light rain showers with rather light rainfall. However, there
are signs of an inverted trough setup which may allow for a
mesoscale narrow band or two of heavier rain. The best chance
for this would be across parts of northern and eastern MA.

We will continue the Wind Advisory for Cape Cod and Nantucket
given fully leafed trees. However, given that both the
baroclinicity and pressure falls will be limited thinking is
speeds will generally remain below criteria. Later shifts may
consider dropping those headlines depending on what conditions
look like later this morning.

The High Surf Advisory also continues along the eastern MA coast
as rough seas develop across the eastern MA waters.

Previous Discussion Below:

Unfortunately, it seems like both the CAMs and Global models
are struggling to resolve this mid and low level dry air,
suggesting that widespread heavy rain may impact portions of our
region. Both the GFS and HRRR try to bring a substantial swath
of 1.5" to 2" QPF to the islands and outer Cape, likely because
of convective feedback driven by convection over the ocean to
our southeast. A more realistic solution, given the dry air and
patchy nature of showers this morning, may lie with the 00Z run
of the ECMWF, which estimates QPF around 0.75" over the islands
and Cape Cod, and extending a beneficial swath of 0.25-0.5"
precipitation to the I-95 corridor.

Some models, like the NAM 3k, are trying to resolve a secondary
surge in precipitation extending from approximately Norfolk
county west towards Springfield along the axis of an approaching
shortwave feature. While our forecast does not currently include
significant amounts of QPF from this feature, there is potential
for this system to overperform, in say, the
Springfield/Chicopee/Worcester areas. Unfortunately for those in
Connecticut, model guidance agrees that the western extent of
the precipitation shield will leave the region mostly dry, with
just a few hundredths to maybe a tenth of an inch of QPF
possible; primarily this morning before the low begins to lift
north.

In addition to the ongoing and expected wetting rain, a wind
advisory is in place across Cape Cod and Nantucket due to strong
winds between 950 and 900mb. The GFS suggests that 50 kt winds
will be present around 900mb, and while 50 kt gusts are not
anticipated to reach the surface, given the lack of pressure
falls and significant temperatures gradients that come with late
Summer, some significant gusts to 40 kt could reach the
surface, primarily at ACK.

Given the scattered showers and northeasterly flow on Wednesday,
temperatures are expected to be quite cool for mid August.
Several locations across eastern MA may have actually achieved
their high temps already, cooling modestly into the low and mid
60s for the remainder of the day. Locations in the CT River
Valley that remain mostly dry should be the warmest locations
today, with temperatures in the low and mid 70s.

&&

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

Highlights...

Low pressure begins to lift into the gulf of Maine, and
eventually in to Maine, this evening, which will cause winds to
shift from the N/NE to the W/NW. Scattered showers will likely
linger into the early morning hours of Thursday, but Thursday is
expected to be mainly dry. A cold pool at 500mb should generate
some cumulus clouds during the day Thursday, but overall, a
clearing trend is expected.

Winds will be breezy during the day Thursday, but are expected
to be much weaker than Wednesday; generally gusting less than 15
kt. Thursday is shaping up to be a relatively nice day, with
highs in the 70s to near 80, warmest in the CT River Valley,
southeast MA, and Rhode Island.

Thursday evening is shaping up to be the coolest night for the
foreseeable future. Dewpoints in the 50s, light winds, and
clearing skies should allow for radiational cooling. Widespread
50s are expected, with urban heat islands being the exception;
metropolitan areas such as Hartford and Boston will remain in
the 60s. The Cape will also fall back into the 60s given the
warm SSTs and slightly higher dewpoints.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...

Highlights...

* Dry with Summer-Like Warmth Fri & Sat, but humidity will remain
  comfortable for August standards

* Increasing humidity during the first half of next week with the
  best chance for scattered showers and a few t-storms Tue into Wed

Details...

Friday and Saturday...

Upper trough over the Northeast pulls away from the region as
Bermuda High pressure strengthens. This will result in summer-like
warmth with above normal temperatures Fri & Sat. High should be well
up into the 80s to near 90. Humidity levels will remain comfortable
for August standards despite the very warm weather. Upper level
ridging should also result in dry weather along with plenty of
sunshine.

Sunday through Wednesday...

The focus will be on shortwave energy across the Great Lakes
and how fast or slow it moves east. We are leaning towards the
movement of the shortwave trough being on the slower side. This
a result of Upper level ridging over the Atlantic coupled with
confluent flow across Northern New England. This may keep our
weather mainly dry Sun and perhaps Mon too. While a surface warm
front may trigger a few brief showers sometime Sun into Mon,
the lack of deeper synoptic forcing may result in generally dry
weather. A better chance for some showers and a few t-storms
will be sometime Tue into Wed as better shortwave energy
approaches from the west.

High temps will mainly be in the 80s over this time with the warmest
day expected to be Sunday when a few spots may approach 90 across
the interior. The bigger story will be the increasing humidity; so
it will certainly feel summer-like over this timeframe.

&&

.AVIATION /10Z WEDNESDAY THROUGH SUNDAY/...

Forecaster Confidence Levels:

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

12z TAF Update...

Today... Moderate Confidence.

Mainly dealing with VFR conditions today despite periods of
light showers. However, some lower clouds /MVFR conditions/ will
impact mainly eastern MA at times later this morning and
afternoon. N wind gusts of 20-25 knots develop along the coast
and between 30-35 knots across the Cape/Nantucket.

Tonight... Moderate Confidence.

VFR to marginal VFR ceilings this evening with the lower
conditions most likely towards the eastern MA coast. Improvement
to VFR occurs at most terminals by 12z. Winds becomes NW 5 to
10 kt.

Thursday... High Confidence.

Mainly VFR with conditions improving through the day. Low chance
for a shower across interior southern New England Thursday
morning. NW winds, gusting to 15 kt, become westerly in the
afternoon. Winds will be more from the W/SW on Cape Cod and
Nantucket, but still generally less than 15 kt.

KBOS...Moderate confidence in TAF.

KBDL...High confidence in TAF.

Outlook /Friday through Sunday/...

Friday: VFR. Breezy.

Friday Night through Saturday: VFR.

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

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

&&

.MARINE...

Forecaster Confidence Levels:

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

Gale Warning for eastern waters and Nantucket Sound through
Wednesday afternoon, Small Craft Advisories continues for all
other waters through Wednesday night.

Wednesday night into Wednesday Night... Moderate Confidence

Low pressure will track into the gulf of Maine into Wednesday,
which will really kick up the seas; with waves up to 11 feet
possible. Given these conditions, a high surf advisory has been
issued for our eastern facing coastlines for Wednesday. Eastern
and southeast waters experience north/northeast gales overnight
into Wednesday.

Thursday and Thursday night... High confidence

Winds will gradually shift from the W/NW to W/SW during the day
on Thursday as they die back; gusting to about 15 kts. Waves
will take some time to calm after low pressure departs, so small
craft advisories may need to be extended on the premise of wave
heights for our outer waters through the day Thursday.

Outlook /Friday through Sunday/...

Friday through Saturday: Winds less than 25 kt.

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 8 PM EDT this evening for MAZ007-015-
     016-019-022-024.
     Wind Advisory until 3 PM EDT this afternoon for MAZ022-024.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Thursday for ANZ230-
     233>237-251-256.
     Gale Warning until 5 PM EDT this afternoon for ANZ231-232-250-
     254-255.

&&

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