454
FXUS61 KBOX 011355
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
955 AM EDT Wed May 1 2024

.SYNOPSIS...
Considerable cloudiness persists today, but peeks of sunshine
are expected by early afternoon. A nearby front may bring a few
showers near the coast Thursday. High pressure north of the
region will bring dry and seasonable weather Friday and most of
Saturday with onshore winds. An approaching front should bring
showers late Saturday into Sunday. Dry and warmer weather is
expected early next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
10AM Update

Today

The last of the showers are now moving offshore this morning,
leaving only dreary low clouds in its wake. Expecting clouds to
continue to linger today for much of the region, with the best
chance for breaks of sun being across CT. If any sun can be
realized, this would allow for 100-200 J/kg of surface based
CAPE to build. Hi-res guidance has started to show isolated
weak showers across western MA and CT, so added a 15% PoP for
the afternoon.


Northerly flow behind the departing low will aide in advecting
cooler air from the north over over eastern MA for this afternoon.
Further west however, a mid-level ridge axis at 850 hPa will build
eastward into western MA and CT with substantially warmer
temperatures. Locations east of the ridge axis that experience
prevailing north/northwesterly winds will be substantially cooler
than those locations beneath the ridge axis where 925 hPa temps will
be in the 10 to 13C range. As a result of this setup, we expect
there to be a rather tight temperature gradient from west to east
this afternoon. Generally expect the coolest locations to be east of
the I-495 corridor and the warmest locations west of I-495 and
especially in the CT River Valley. The area of greatest temperature
uncertainty will be along I-495 where temperatures will depend on
how far west the cooler air mass from the north/northeast is able to
penetrate. Best guess is for high temps in the low to mid 50s along
the immediate east coastline and upper 60s to low 70s in the CT
River Valley. Central MA and RI will range from the upper 50s to
upper 60s with temperatures gradually increasing from west to east.
Expect cloud cover for most of the areas across eastern MA and RI
with some breaks of sun likely for locations west of Worcester
beginning in the early afternoon hours. While it is likely to be a
dry day for most there is a low chance for a pop up shower or two.

&&

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

Winds shift to the south overnight as weak surface high pressure
builds east of southern New England. Generally expecting a quiet,
cloudy, and seasonable night with lows in the mid to upper 40s.
Shower chances increase toward day break across eastern and
northeastern MA as a short-wave trough originating from over
Ontario digs south/southeast over southern New England.

Tomorrow

Somewhat of another tricky forecast tomorrow, particularly across
eastern MA where some showers will be possible during the day. A
broad upper-level ridge axis will be building in from the west with
a warmer air mass tomorrow, but east of the ridge axis an embedded
short-wave trough at 500 hPa will be digging southeast over southern
New England. Vorticity advection east of the short-wave trough axis
should provide enough forcing to support periods of rain across
portions of New England tomorrow, but how far south these showers
develop is still a challenge in the forecast. There is fair
agreement in recent model guidance that the best forcing associated
with this disturbance will stay to the north and east leaving most
of southern New England dry. Eastern MA and The Cape/Islands will
have greater chances for seeing some showers develop as the short-
wave digs east over The Gulf of Maine this afternoon. Forcing and
moisture are limited, so we have set PoPs between 20 and 40 percent
for areas generally along and east of the I-95 corridor. High temps
across eastern MA and The Cape/Islands will be cooler than the rest
of southern New England thanks to the showers/cloud cover associated
with the short-wave aloft, but interior MA is set to have a very
warm day with highs getting into the low to mid 70s west of I-495.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Key Points:

 * Overall quiet weather pattern ahead
 * Scattered showers late Saturday into Sunday
 * Warmup early next week

Fairly good agreement among models that upper ridge will build over
New England Fri and most of Sat maintaining dry weather. Normally we
would expect a significant warmup but in the lower levels, high
pressure to the north of the region will maintain an onshore
flow of cooler air, even into the interior (though it will be
warmer there).

There are some timing differences with respect to arrival of showers
in Sat-Sun timeframe. 00z GFS is most aggressive and is an outlier
when compared to its ensembles as well as other medium range models.
Additionally, it maintains upper ridge over SNE through most of day
Sat which by pattern recognition would keep any showers to our west.
It does appear that scattered showers will arrive late in the day
but especially Sat night into Sun as upper ridge shifts offshore and
cold front approaches from Great Lakes.

Beyond the weekend, looks dry with springtime warmth early next week
as high pressure builds offshore and brings milder S/SW flow, though
usual south-facing coastlines along South Coast, Cape Cod, and
Islands will be kept cooler with onshore flow. Our next chances for
showers looks to be Wed as closed upper low lifts into Great Lakes
and next cold front approaches SNE.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

12Z TAF Update: Moderate confidence.

Last of -SHRA will move offshore through 14z as dense fog near
ORH/ACK gradually lifts. Ceilings stay MVFR through morning but
could dip to IFR for a time, mainly near coast. We do think
ceilings improve to lower-end VFR during afternoon, but
ceilings return to MVFR/IFR tonight, then slowly improve to VFR
Thu.

E/NE winds prevail today before veering to S tonight and Thu.

KBOS TAF...Moderate confidence. Ceilings may briefly lower to
IFR through 14-15z.

KBDL TAF...High confidence.

Outlook /Thursday Night through Sunday/...

Thursday Night: Mainly VFR, with local IFR possible. Slight
chance SHRA.

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

Friday Night: VFR. Chance SHRA.

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA.

Saturday Night through Sunday: Mainly VFR, with local IFR
possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tomorrow

Low pressure moves east of the coastal waters today supporting
northeast winds over the coastal waters for the first half of the
day. As the day progresses, weak high pressure will build over the
coastal waters leading to continued light/easterly flow across the
marine zones. Overnight, winds shift to the south but remain modest
around 5 to 10 knots. Winds increase out of the south/southwest
tomorrow as an area of modest low-pressure moves over the coastal
water. While winds will be stronger in the 10 to 12 knot range
tomorrow, we don`t anticipate conditions deteriorating enough to
warrant SCY headlines. Seas will persistently be 2 feet or less
through the end of the week.


Outlook /Thursday Night through Sunday/...

Thursday through Friday: Winds less than 25 kt. Slight chance
of rain showers.

Friday Night: Winds less than 25 kt.

Saturday through Sunday: Winds less than 25 kt. Chance of rain
showers.

&&

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

&&

$$

SYNOPSIS...RM/JWD
NEAR TERM...RM/KP
SHORT TERM...RM
LONG TERM...Belk/JWD
AVIATION...RM/JWD
MARINE...RM/JWD