008
FXUS61 KBOX 261915
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
315 PM EDT Sun May 26 2024

.SYNOPSIS...

Downpours and thunderstorms persist through early evening.
Widespread shower activity tomorrow ahead of approaching cold
front that will bring renewed heavy rain and thunder chances to
SNE. Cold front moves offshore early on Tuesday, with decreasing
clouds and drier weather conditions. A cooler more seasonable
air mass then builds into Southern New England for the remainder
of the workweek into much of the weekend. Mainly dry weather
prevails as well, though there is a chance for rains on
Wednesday night. &&

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

Downpours have begun to fire along the seabreeze boundary
across the far southern Hudson River Valley with a few rain
showers cropping up along the same boundary across northern CT
and central RI. Fortunately, storms are forming quickly but
transitioning to "orphan anvils" within a few scans, suggesting
our forecast of mainly sub severe storms is on track.

While storms remain innocuous as of this writing (at 19Z), do
continue to anticipate some slow moving strong storms to develop
along the I-90 corridor and perhaps south into northern Bristol
and Plymouth counties. 12Z CAMs continued to show initiation
"prime time" around 21Z with storms persisting through 00-01Z
this evening before subsiding quickly after sunset as
instability wanes. As for instability, models continue to
support 1500 J/kg SBCAPE combined with decent low and mid level
lapse rates of 7.5-8C/km and 6.5-7C/km respectively. Bulk
shear, while lackluster, will increase to between 30-40kt along
the MA/NH border later today, which will likely keep storms on
life support this evening.

Pockets of heavy rain continue to be the greatest threat associated
with storms this afternoon with PWATs around 1.25" and weak flow
aloft to keep storms moving. In general, many communities will
remain dry, but those under a potent cell could see upwards of 1 to
even 2" of rain, which may lead to some poor drainage flooding
especially if storms set up in the Boston metro.

As mentioned, storms wane quickly after sunset but with easterly
flow, marine stratus and fog will expand from the nearshore waters
to at least the coastal plain. Places like the Cape and Islands can
expect to see dense fog, comparative in coverage to last night.
Prevailing wind direction should support more expansive fog
coverage overnight that may overspread inland to the I-95
corridor.

&&

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

Low pressure over the Great Lakes continues east-northeast into
Ontario and Quebec as mid level trough digs into the Ohio River
Valley and mid-Atlantic. Warm front lifts from the mid-Atlantic
towards New England tomorrow but will fail to lift of ~central NJ by
mid day tomorrow. While we remain north of the warm sector, will
still have some prefrontal showers beginning as early as 12Z across
the western portions of the CWA before tracking east through early
afternoon with rain holding off in places like Boston and Providence
through around 15/16Z. Cold front will fuel more potent line of rain
after 20Z, with the 12Z guidance speeding up the front`s
arrival and departure by several hours compared to last
evening`s guidance; in fact, had to stray significantly from the
NBM given it`s know lag time to derive PoPs through early
Tuesday morning.

The greatest concern with tomorrow`s forecast will be the threat for
additional heavy rainfall, with PWATs climbing to near 2" by late
tomorrow afternoon and a decent southerly oriented LLJ of between 30-
40kt. Could certainly see some upslope enhancement across the
Berkshires and Worcester Hills, but fortunately the jet lacks an
easterly component that would really "ring out the rain". HREF
PMM and 24 hour MAX QPF ending early Tuesday morning depicts
local max QPF of 1.5-2" across the aforementioned terrain
features, with lesser amounts elsewhere. Warm cloud depths near
12,000ft combined with very high PWATs should draw one`s
attention to the potential for tropical-like downpours tomorrow
afternoon, but the progressive nature of the front should limit
any flooding concerns to just poor drainage areas, which is
corroborated by WPC placing the entirety of the region under
just a "marginal" excessive rainfall outlook. Given a lack of
evidence pointing to widespread urban or flash flooding, did not
consider a flood watch with this package issuance.

Convective elements will likely be present, particularly along the
cold front, with tomorrow`s rain with modest instability of 200-
600J/kg CAPE. With that said, convection looks to be elevated, with
really poor low level lapse rates below 5C/km. Hodographs look quite
curly tomorrow, but with no surface based convection, the severe
weather potential remains low. The one saving grace for more
prolonged convective showers would exist due to bulk shear
values approaching 50kt late tomorrow evening, which may result
in some locally gusty winds.

As previously mentioned, cold front should be east of the area
between 06-09Z Tuesday, which will lead to rapidly improving
conditions by sunrise Tuesday. Winds will shift from the E to
the south behind the front, which combined with residual
moisture, may drive another night of coastal fog.

&&

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

* Cold front moves offshore on Tue with decreasing rain chances by
  later Tue AM and temps warming into the 70s to low 80s.

* Temps cool off to more seasonable levels starting Wed into the
  weekend.

* Other than a chance for rain on Wed night into Thurs, much of the
  rest of the workweek into the early weekend are generally dry.

Details:

Cold front from Monday will continue to move offshore during the
morning hrs of Tuesday. There might still be some steadier rain
during the morning commute in eastern and southeast New England but
improving conditions are expected by later-morning, with decreasing
clouds allowing for temps to warm into the 70s to low 80s, with
upper 60s/near 70 for the Cape and Islands.

A deep longwave trough becomes established over the Northeast states
as we move through the rest of the workweek into the early part of
next weekend. This trough will bring cooler than normal 925-850 mb
temps to Southern New England, bringing temps closer to late-
May/early-June climatological values (upper 60s to lower to mid
70s). Though it is a generally dry weather regime, we do have to
watch around Wed night into Thurs for chances for showers as an
embedded shortwave disturbance aloft rotates around the trough.
There are differing answers as far as the placement and track of
this shortwave trough, with the ECMWF the most bullish on bringing
steadier rains to SNE for Wed night into Thurs, with the GFS
interestingly being dry while the Canadian GEM too far south for any
significant precip. NBM guidance was showing 25-40% PoP for rains
and opted to stay close to that until there`s better agreement on
the shortwave trough. Other than the Wed night into Thurs timeframe,
overall it looks to be a decent stretch of weather. Our next chance
of rain may not arrive until very late Sunday or into next Mon.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Today...High confidence in trends, moderate in timing.

VFR across the interior today, but will need to keep an eye out
for hit or miss showers/storms this afternoon. Timing wise am
thinking things initiate at roughly 18-21Z. If a shower/storm
can move over a terminal then will have risk of gusty winds and
and small hail. IFR in low clouds across the south coast. Though
think we improve for PVD-FMH-HYA with some heating around
roughly 14-16Z. Winds out of the S/SE at 5-10 kts. Will have
localized sea breezes developing roughly 14-17Z.

Through tonight... moderate confidence in storm location, high
confidence in trends

Thunderstorms will bubble up along the I-90 corridor, between
Springfield and Boston, north, after 21Z and will be scattered
in nature. Sea breeze will likely keep storms away from the
immediate coast, including Logan, but it is possible for a
strong cell to produce heavy rain and gusty winds at several
terminals through 01Z tonight.

IFR develops quickly after storms subside overnight with stratus
and fog advecting from the east. Uncertainty regarding how far
inland fog develops, but it is almost a surefire thing for
terminals on the Cape and islands.

Tomorrow... High Confidence in Trends

IFR/LIFR for most. Scattered showers develop between 12-16Z.
Lull in shower activity expected from 16-19Z or so from west to
east. More robust line of rain associated with a cold front
develops after 19Z. Some embedded Thunder possible with the
second round of rain. Winds remain from the east, may gust as
high as 20kt tomorrow afternoon.

Tomorrow night... Moderate Confidence in timing

Rain will come to an end between ~03-06Z yielding improving
conditions with improvement from IFR to VFR around sunrise.
Winds shift from the E to the S, gusting to 20kt, behind frontal
passage.

KBOS TAF...High confidence in TAF trends, moderate in timing.

Generally VFR through 00Z except if a thunderstorm is able to
develop over the terminal. Thunderstorms more likely just
northwest of the city of Boston. Winds from the E/ESE through
the period building late tomorrow to around 20kt. Several rounds
of rain for Monday. IFR developing quickly after sunset this
evening as stratus develops.

KBDL TAF...High confidence in TAF trends, moderate in timing.

Generally VFR, hit or miss Thunderstorms likely stay north of
the terminal but cant rule out impactful TSRA between 21-01Z.
IFR develops overnight, winds from the south shift to the ESE
tomorrow.


Outlook /Tuesday through Friday/...

Tuesday: Mainly VFR, with local IFR possible. Breezy. Slight
chance SHRA.

Tuesday Night: VFR.

Wednesday through Thursday: VFR. Chance SHRA.

Thursday Night through Friday: VFR.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Memorial Day... Moderate Confidence in fog.

Another night of dense marine fog expected as winds prevail from
the east. Increased shower activity early Monday before a cold
front brings the chance for more potent rain and embedded
thunder to the waters late tomorrow evening and early Tuesday
morning. Winds increase, gusting between 25-30kt from the east
before turning south behind the front. Waves climb in excess of
5 feet across the outer waters. SCA has been hoisted for the
eastern outer, and southern waters, including Nantucket sound
late tomorrow/tomorrow night.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain
showers, patchy fog.

Tuesday Night through Wednesday: Winds less than 25 kt. Seas up
to 5 ft.

Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers.

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

Friday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 9 PM Monday to 11 AM EDT Tuesday for
     ANZ232-233-235-237.
     Small Craft Advisory from 6 PM Monday to 5 AM EDT Wednesday
     for ANZ250-254.
     Small Craft Advisory from 9 PM Monday to 5 AM EDT Wednesday
     for ANZ255-256.

&&

$$

SYNOPSIS...Loconto/KS
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...Loconto
AVIATION...KS
MARINE...Loconto/KS