541
FXUS61 KBOX 120138
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
938 PM EDT Tue Jun 11 2024

.SYNOPSIS...
Weak high pressure will maintain dry conditions through
Wednesday, but a passing shower cannot be ruled out Wednesday
afternoon in Rhode Island and eastern Massachusetts. Warmer and
more humid weather will arrive Thursday and Friday, then an
approaching cold front will bring scattered showers and
thunderstorms Friday afternoon and evening. High pressure builds
in for the weekend bringing drier weather with cooler
temperatures and low humidity.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
10 PM Update:


Pesky upper low is still maintaining its grip on the Northeast
with plenty of cloudiness. The remaining spot showers have now
dissipated, but cloudiness should linger through midnight before
more clearing occurs. Temps across the region have already begun
to fall into the low 60s on there way down to the low to mid 50s
later tonight.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
215 PM Update:

Wednesday:

Although the upper-level low over New England is expected to pull
away from the Northeast later in the day, the forecast for Wed is
essentially similar to today. Residual cyclonic flow aloft and a
modifying cold pool should again support clouds filling back in with
a partial to mostly cloudy look, and that should also keep
temperatures from reaching into widespread low 80s as today`s NBM is
advertising. At least a lighter westerly flow could bring highs
closer to the upper 70s in western MA and much of northern CT
though, with highs in the lower to mid 70s for eastern/northeast MA
and much of RI.

Latest guidance seems a bit more bullish on isolated to scattered
shower chances Wed than today, as the east coast sea breeze
generates a mesoscale convergence zone in eastern MA/RI with the
lighter westerly flow across the interior. Dewpoints are also a
touch higher too over the coastal plain, and while the NAM`s
dewpoints still look a few degrees too high, values in the mid 50s
seem reasonable enough to yield surface based CAPEs of around 500
J/kg or less; phrased as isolated to scattered showers with 20-40%
PoP though as BUFKIT soundings from even the bullish NAM indicate
the layer of instability doesn`t reach into the -10C isothermal
layer for lightning. 12z HREF 1-hourly thunder probs are also
zero, with low probs confined to northern ME/NH closer to where
the upper low is progged. The risk for scattered showers should
be limited to just the MA/RI coastal plain around or within a
few miles either side of I-495; westerly non-convergent flow
further inland into CT and western MA should result in mainly
dry weather there. QPF amts likely no higher than a few
hundredths of an inch in any one area, so a few showers to dodge
but nothing too significant.

Wednesday Night:

Cloud cover with scattered light showers should dissipate shortly
after sundown towards mostly clear skies for the overnight.
Temperatures warm a bit aloft and that should help offset
radiational cooling to an extent with lows in the 50s, to low 60s in
the urban areas. With clear skies and light winds, there`s an
outside chance at patchy radiational fog, with somewhat better
chances of development where showers developed during the daytime
hrs.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights:

* Increasing heat and humidity Thursday into Friday. A cold front
  brings showers and thunderstorms on Friday afternoon and evening
  with drier and more comfortable conditions for Father`s Day
  Weekend.

* There is potential for significant warm-up next week as
  highlighted by a moderate risk for excessive heat.

Thursday...

Looking at a sunny and warm day ahead with surface high pressure is
off shore and shortwave ridging aloft. Southwest flow ushers in warm
temperature aloft, 925mb temperatures are in the neighborhood of
+19C to +23C, yielding highs between 85-90 degrees. Southwest wind
keep coastal Rhode Island, south coast of Massachusetts, Cape Cod,
and the islands slightly cooler in the 70s. While it is not overly
humid, it will be noticeable as dewpoints creep into the upper 50s
and low 60s, highest near the coast and lowest in the interior.

Friday...

As advertised, a cold front passage with the associated near-neutral
shortwave trough pushes across the northeast during Friday afternoon
and evening. Ahead of the front, robust southwest flow will increase
our temperatures and especially the humidity. Temperatures aloft are
very similar to Thursday, thus expecting another day with highs
between 85-90 degrees. Though the main difference are the higher
dewpoints, with PWATs surging to either side of 1.7 inch, dewpoints
are largely in the mid 60s. Combination of the heat and humidity
will fuel storms during the afternoon. Depending on which guidance
source, there is roughly 800 to 1200 J/km of SB CAPE. In addition,
modest jet dynamics provide roughly 40 knots of 0-6km shear. Leading
to a few storms during the afternoon, but will largely depends on
the timing of the frontal passage. In addition, high PWATs may lead
to locally heavy downpours, which may cause nuisance flooding, as
highlighted by the Marginal Risk for Excessive Rainfall Outlook.

Father`s Day Weekend...

Drying out and falling humidity this coming weekend, a nice reprieve
from the humidity, as surface high pressure moves down from Canada.
PWATs drop in most cases below 0.3 inch on Saturday and 0.5 inch on
Sunday. That said, we are looking at mainly clear skies both days
with highs in the upper 70s to low 80s, and dewpoints in the 40s to
low 50s. With clear skies and potential for light winds on Saturday
night, there is the possibility for radiational cooling, which could
lead to a cooler than normal start on Sunday, Father`s Day. Early
risers or golfers could be greeted by temperatures in the upper 40s
across the interior.

Next Week...

Dry weather continues into early next week as surface high pressure
sits along the east coast. Though the bigger talking point is the
potential well above normal temperatures... not only during the day
but also overnight. This is highlighted by the moderate risk for
excessive heat mid to late next week.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

00z TAF Update: High confidence.

Isolated showers in central MA will dissipate soon after sunset
but VFR ceilings will linger into tonight before many areas
clear out overnight. Similar conditions expected Wed with
another round of VFR ceilings and isolated showers, primarily in
eastern MA and perhaps RI, with VFR ceilings gradually clearing
out Wed night.

Light winds will give way to coastal sea breezes again Wed.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: VFR. Breezy.

Friday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, slight chance TSRA.

Friday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA, slight chance TSRA.

Saturday through Sunday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

215 PM Update:

Winds and seas/waves to remain below small craft advisory
levels through this portion of the marine forecast period. Light
mainly southerly winds around 10 kt or less should be the rule
tonight through Wednesday night, though could turn easterly
nearest the shoreline with seabreezes. Seas mainly 3 ft or less,
with 1-2 ft seas near shore.

There could be a hit or miss shower Wed aftn near the
coastlines. Could see fog develop Wed evening over the outer
waters.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt.

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

Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers.

Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers, isolated thunderstorms, patchy
fog. Areas of visibility 1 to 3 nm.

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

Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft.

Sunday: Winds less than 25 kt.

&&

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

&&

$$

SYNOPSIS...Loconto/Dooley
NEAR TERM...KP/JWD
SHORT TERM...Loconto
LONG TERM...Dooley
AVIATION...JWD
MARINE...Loconto/Dooley