Area Forecast Discussion
National Weather Service Boston/Norton MA
709 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/...

710 AM Update...

Previous forecast is on track. Plenty of sunshine this morning
will give way to a bit more clouds as the day wears along
particularly towards the coast. This in association with a 
developing low pressure system south of the Benchmark. The
increasing pressure gradient will allow for a bit of a northeast
breeze along the coast later this morning and afternoon.
Previous discussion follows below.

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/...

Highlights...

* 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 /12Z TUESDAY THROUGH SATURDAY/...

Forecaster Confidence Levels:

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

12z TAF Update...

Today...High confidence. 

Mainly VFR despite increasing mid level cloudiness. However,
some marginal MVFR ceilings may develop across the Cape and
Islands toward evening. North wind becomes northeast 10 to 15 
knots, gust 20 to 25 knots for terminals on the Cape and 
Islands. Perhaps even a few gusts around 30 knots developing across
Nantucket.

Tonight...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
and up to 30 knots across Nantucket. Terminals away from the 
coast have northeast wind 5 to 10 knot.

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 in TAF.

KBDL...High confidence in TAF.

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 PM this evening to 8 AM EDT 
     Thursday for ANZ231-250-251.
     Small Craft Advisory until 8 AM EDT Thursday for ANZ232>235-
     237-254>256.

&&