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Office: BOX

FXUS61 KBOX 160718
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
318 AM EDT Tue Aug 16 2022

.SYNOPSIS...
Mainly dry and seasonably conditions on Tuesday with a low
chance for showers across southeast MA ahead of an approaching
low pressure system late Tuesday into Wednesday. Current
guidance brings a much wetter solution to the table, with
ensembles indicating the potential for 0.5" QPF east of the I-95
corridor. Shower chances continue into Wednesday evening.
As the low lifts north into Maine, dry and seasonable weather is on
tap for Thursday. Very warm weather with above normal temps returns
Friday and Saturday, followed by increasing humidity early next
week. Dry weather is expected Friday and Saturday, but the threat
for some showers and a few thunderstorms will arrive early next week
with the best chances sometime Monday and/or Tuesday.

&&

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

Temperatures will begin the day a bit brisk as clear skies overnight
allowed for healthy radiational cooling; with several of our
radiators dropping into the low and mid 50s. Given that cloud cover
was leaner than originally forecast overnight, Tuesday will begin on
a sunny note before two mechanisms bring clouds to the region. A
closed 500mb cuts off in the mid level trough axis above southern
New England today resulting in cold pool cumulus development as
daytime heating begins across our western zones. In addition to cold
pool cumulus, a significant increase in moisture at the mid
levels, thanks to onshore flow, across eastern MA, will generate
mid level cloudiness, especially across Cape Cod and the
Islands. ENE flow that brings the aforementioned mid level
moisture to the eastern half of our region will also bring much
cooler temperatures as the cooler maritime air is advected over
the region. A combination of cloudiness and onshore flow will
create another significant temperature gradient across the CWA,
with portions of the eastern MA coast and Cape struggling to
make it into the low 70s, while parts of the Connecticut River
Valley, where more sunshine will be present, reach into the low-
mid 80s. With 925mb temps in the low 20s across our western
zones, there is the potential for temperatures to overachieve
and reach well into the 80s should we mix to 825mb as indicated
by model soundings. Temperatures on Tuesday will be wildly
dependent on cloud cover, but the overall gist is that clearer
skies will yield warmer temperatures.

Guidance is split on shower development across the Cape and Eastern
MA coast today as a the parade of weak low pressure systems
continues to move just offshore of our area. Should the column
saturate by early afternoon, there is a low chance for some pop up
showers across the aforementioned areas. Shower chances will
increase should low pressure track slightly closer to our
coastline.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...

The more interesting half of the near-short term forecast will be
late Tuesday into Wednesday. The strongest low pressure of the bunch
will track off the coast of Cape Hatteras to the benchmark by
late Tuesday evening and early Wednesday morning. If this were a
winter storm, we would likely be talking about an expansive
precipitation shield, but given the late-summer lack of
baroclinicity, the exact track of the low will be extremely
important in determining who will see precipitation and how much
rain will fall.

While the previous AFD mentioned that convective feedback may
be driving the wetter solution of the ECMWF, OOZ guidance has
shifted westward, and wetter across the board, with the ECMWF
actually coming in as some of the drier guidance at this hour.
The driving factor in the increase in precipitation with the 00Z
runs stems from the position of the low in these deterministic
runs. The WRF-ARW actually has the low pressure nestling into
the MA/NH coastline by Wednesday, which would be an optimal
solution for those cheering for rain. While we must take every
piece of deterministic guidance with a grain of salt, the
ensembles are starting to settle on similar solutions; both the
GEFS and EPS indicating upwards of 0.5" of QPF east of the
I-495/I-95 corridor in eastern MA and Rhode Island. This is a
significant change from even the previous 24 hours, when most
guidance was coming in very dry. When diving deeper into things,
this change in guidance is consistent with the position of the
closed low over southern New England, which has the potential to
pull the rain shield in closer to the coast, expanding the
westward extent that beneficial precipitation. Model guidance
over the next 12-24 hours will be crucial in determining the
total precipitation potential from this event. At this junction,
confidence is growing that eastern MA and RI will see modest
QPF from this system. Unfortunately for western MA and CT,
current guidance keeps these areas mostly dry.

Temperatures on Wednesday will be dependent on the track of the low.
Should the low track further west, bringing much needed precip
to our drought stricken eastern zones, temperatures will be
tamped down into the low 70s; except across the CT River Valley
where breaks in the clouds will allow for warming into the upper
70s.

By late Wednesday, low pressure begins to track into Maine, but
showers will linger into the early evening hours.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...

* Lingering showers possible Wed night particularly in northern MA

* Mainly Dry & Seasonable Thu

* Dry with Summer-like Warmth/Above normal temps Fri & Sat

* Increasing humidity with some showers/t-storms possible early next
  week with the main chances looking to be sometime Mon and/or Tue

Details...

Wednesday night...

Vertically stacked low pressure system slowly lifts northward into
Downeast Maine. Depending on the exact track of the system;
lingering showers may wrap around the system Wed night. This is
especially true across northern MA Wednesday evening. Low temps will
mainly be in the upper 50s to the lower 60s.

Thursday...

The vertically stacked low pressure system will slowly lift
northward across Maine. A drier WNW flow of air will work into our
region behind this departing system. This should result in partial
sunshine and seasonably high temps in the upper 70s to the lower 80s
and comfortable humidity levels. We maintained a dry forecast
although we can not rule out the low risk of a brief spot shower in
northern MA with some shortwave energy. Regardless, generally
dry/very pleasant weather with seasonable temps is in store for the
region on Thu.

Friday and Saturday...

Upper level ridging re-asserts itself off the mid-Atlantic coast Fri
and Sat. GEFS/EPS indicate above normal height fields, so a good
signal of summer-like warmth and above normal temps returning. Highs
should be well up into the 80s to around 90. A ridge of high
pressure in place should support dry weather too with the lack of
synoptic scale forcing.

Sunday through Tuesday...

Upper level trough/shortwave energy over the Great Lakes will be
working eastward early next week. This will result in humidity
levels increasing along with the potential for some unsettled
weather. Timing is still uncertain at this point...but thinking
Sunday may end up mainly dry with increasing chance for some showers
& a few thunderstorms sometime Mon and/or Tue as shortwave energy
approaches and increases the forcing for ascent. Highs on Sun may
again reach well up into the 80s to around 90. Temps may not be
quite as warm Mon/Tue with an increasing threat for some showers and
a few thunderstorms, but it will be turning more humid.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels:

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

06Z TAF Update: VFR cloud bases and NE/E flow for much of the
day on Tuesday. Some gustiness may develop at terminals along
the coast. VCSH developing, especially across eastern terminals,
late in the period.
===================================================================

Tuesday...High confidence.

Mostly VFR with MVFR conditions possible for eastern MA terminals as
early as 18z. North wind becomes northeast 10 to 15 knots, gust 20
to 25 knots for terminals on the Cape and Islands.

Tuesday Night...Moderate confidence.

VFR for western terminals. MVFR/IFR conditions with VCSH/-RA
possible for eastern MA terminals, including the Cape and
Islands. Northeast wind 10 to 15 knot with gust 20 to 25 knots.
Terminals away from the coast have northeast wind 5 to 10 knots.


Wednesday... Moderate Confidence.

Increasing chances for -RA across eastern terminals. VFR for
western terminals but MVFR and IFR conditions possible as low
ceilings develop across eastern zones. Northerly winds will be
gusty; up to 25 kt along the eastern MA Coast, including the
terminals of BOS and ACK.

KBOS...High confidence.

KBDL...High confidence.

Outlook /Wednesday Night through Saturday/...

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

Thursday through Thursday Night: VFR. Breezy.

Friday through Saturday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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


Tuesday...High confidence.

As low pressure begins to track towards our waters from Cape
Hatteras, winds and waves will build into small craft
territory. Small craft conditions will gradually spread east and
then north by Tuesday evening. Winds will gust to between 25
and 30 kt as seas build to 5+ feet.

Tuesday Night into Wednesday Night... Moderate Confidence

The low will track into the gulf of Maine overnight Tuesday
into Wednesday, which will really kick up the seas; with waves
up to 10 feet possible. Given these conditions, a high surf
advisory has been put in place for our eastern facing coastlines
for Wednesday.

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft.

Thursday Night through Saturday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory from 8 AM to 8 PM EDT Wednesday for MAZ007-
     015-016-019-022-024.
RI...None.
MARINE...Small Craft Advisory from 8 AM this morning to 8 AM EDT
     Thursday for ANZ232>235-237-254>256.
     Small Craft Advisory from 11 PM this evening to 8 AM EDT
     Thursday for ANZ250-251.

&&

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