750
FXUS61 KBOX 301312
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
912 AM EDT Tue Apr 30 2024

.SYNOPSIS...
A backdoor cold front will bring much cooler conditions with
considerable cloudiness today. Unsettled mid to late in the
week due to a backdoor cold front nearby. This could bring
spotty showers and keep us a bit cooler, but there is a
significant amount of uncertainty with the fronts location.
Better shot for more widespread showers late Saturday into
Sunday as a frontal system slides through.

&&

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

910 AM Update...

* Considerable cloudiness but generally dry for most of today
* Highs in the 50s at the coast and 60s further inland

Shortwave energy and a burst of mid level instability was still
resulting in a cluster of showers and embedded t-storms from
parts of upstate NY into southern NH and southern Vermont. Some
building upper level ridging will likely keep the bulk of this
activity to our north today. We may see a few brief showers
graze areas near the NH border through lunchtime.
Otherwise...expect light onshore to result in considerable
cloudiness with mainly dry weather.

The clouds and onshore flow will hold highs in the 50s along the
coast with 60s further inland. Mildest of the readings will be
found in the Lower CT River Valley...where some middle to even
upper 60s are possible. Meanwhile...along the immediate eastern
MA coast temps will generally remain between 50 and 55.

We should mention that additional showers and embedded t-storms
will develop to our west later today across NY State. But this
activity will not impact us until this evening and probably in a
weakening form.

&&

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

A modest frontal wave associated with a mid-level low at 850 hPa
moves across southern New England overnight bringing additional
rounds of precipitation. Not expecting any convective activity as
there is not expected to be any instability in the atmosphere.
Precipitation accumulations will be limited to around a tenth of an
inch or less. Overcast skies will limit overnight low temps to the
low to mid 40s across most of southern New England with easterly
winds becoming more northeasterly after midnight.

Tomorrow

Tomorrow, northeasterly winds develop behind the departing mid-level
low allows a backdoor cold front to push over the eastern portions
of southern New England. This will continue to support cloudy skies,
cool temperatures, and perhaps a few sprinkles or drizzle along the
east coast through the mid-morning hours. Across the interior and
western MA/CT however, a mid-level ridge axis is expected to build
far enough east to advect a substantially warmer air mass over the
CT River Valley where high temps in the mid to upper 60s will be in
the cards while the areas east of the backdoor cold front across
eastern MA and RI would stay in the low to mid 50s. Confidence is
pretty low with respect to how far west the cooler air mass will
extend, but generally expect locations east of the I-95 corridor to
be much cooler than locations west of the I-495 corridor with a
gradual cooling trend from west to east for the areas inbetween.
While cloudy conditions are expected during the morning into perhaps
the early-afternoon hours, there should be at least partial sunshine
across the interior developing by mid-afternoon.

&&

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

* Good amount of uncertainty in the extended forecast with timing
  and expect location of showers.

* Backdoor cold front on Friday. This could bring spotty showers and
  keep us a bit cooler, but there is a significant amount of
  uncertainty with the fronts location.

* Unsettled with rain chances continues this weekend as a front
  moves across the region.

Wednesday Night:

Cloudy conditions overnight with any lingering showers coming to an
end before midnight. Wind shifts to the south, this will help keep
it mild overnight, minimum temperatures lower and middle 40s. Not
out of the question patchy ground fog develop as the dewpoints are
in the 40s overnight.

Thursday and Friday:

There is some uncertainty with this part of the forecast as global
guidance remains in some disagreement. A weak surface low pressure
system moves from northern New York towards southern New England
along a frontal boundary. The good news, much of the deterministic
models are showing minimal QPF, no threat for a washout. In fact,
much of the guidance over southern New England supports only a few
hundredths of an inch to a tenth of an inch. For what it is worth,
the NAM at 00z kept much of the area dry, while the GFS being the
wetter of the models. The uncertainty lies with the position of the
front and the path the low takes. Kept the highest POPs, 20 to 30
percent mainly areas northeast of ORE, ORH, and TAN. But given the
uncertainty, did leave minimal POPs for areas southwest which would
give us `Slight Chance`, the lowest category for precipitation. As
for temperatures, still fairly mild despite the clouds and rain
chances, generally in the 60s with the immediate coast, Cape, and
Islands in the upper 50s. CT River Valley will likely be the warm
spot yet again, highs are in the upper 60s to lower 70s.

Friday does look to be on the drier side, at this point, with weak
surface high pressure in place and the mid-level just to the west.
While this would typically mean a milder day, the signal is there
for another backdoor cold front to sweep across southern New England
and the temperatures cooler than normal. Wind direction on Friday
becomes northeast and drives cooler airmass over the region. Highs
are generally in the mid 50s along the eastern Massachusetts coast
and away from the water the temperatures are generally 59F-62F, with
a few spots in the lower CT River Valley reaching 63F-66F.

Saturday through Monday:

Mid-level ridge shifts east and is planted over the New England
states with a warm front arriving during the afternoon with the
potential for scattered showers, it is not until Sunday the ridge
moves off shores and a cold front moves through - the timing on this
still is uncertainty and leaned on NBM guidance given how far out in
the forecast we are reaching to. With this uncertainty kept with NBM
temperatures, highs 60F-65F, and lows 45F-50F. A ridge sets up to
our west on Monday and trends drier and mild with highs creeping
back to the low 70s.

&&

.AVIATION /13Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

06Z TAF Update

Through 12Z... high confidence in flight categories, moderate
confidence in precipitation potential.

VFR for locations east of ORH continue through morning with MVFR
at and west of ORH. Generally light easterly winds at the
terminals. A few showers with perhaps VCTS is possible at and
west of ORH but confidence is low as and thunderstorms should be
isolated in nature. Have only mentioned VCSH in the 06Z TAFs.

Today... High confidence.

MVFR ceilings continue to stay focused generally west of the
I-495 corridor. Persistent easterly winds. East of I-495 expect
mid-level clouds around 050 for the day with some possible
breaks above 10 thousand feet during the afternoon over The
Cape/Islands terminals.

Tonight.. Moderate confidence.

IFR/MVFR ceilings overspread the rest of southern New England
overnight. Winds persist out of the east through about 06Z
before shifting northeast between 06 and 12Z. Expect periods of
SHRA between 00 and 06Z.

Tomorrow... Moderate confidence

MVFR/IFR conditions should persist through late morning with
some improvements to VFR possibly during the early to mid
afternoon hours. Northeast winds become more easterly by the
evening hours.


KBOS TAF...High confidence in VFR, moderate confidence on
afternoon cloud bases.

Generally onshore flow prevails through the TAF period with a
steady sea-breeze settling in by 15Z. High confidence in VFR
ceilings. While cloud bases are generally expected to persist
around 5000 feet, there is expected to be a region of higher
bases over east/southeast MA this afternoon. Not expecting the
higher bases to extend north over BOS, but can`t rule out the
possibility of higher cloud bases up to 10000 feet after 18Z
before falling back to MVFR/IFR tonight.

KBDL TAF...High confidence in TAF.

MVFR persists today before possible deterioration to IFR
overnight. Some showers and a rumble of thunder possible over
the next couple of hours (06-09Z).

Outlook /Wednesday Night through Saturday/...

Wednesday Night: MVFR/IFR conditions possible. Patchy BR.

Thursday: Mainly MVFR, with areas VFR possible. Breezy. Slight
chance SHRA.

Thursday Night: Mainly VFR, with areas MVFR possible. Breezy.

Friday: Mainly VFR, with local MVFR possible.

Friday Night: Mainly VFR, with local IFR possible.

Saturday: Mainly VFR, with local MVFR possible.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tomorrow

Generally calm/quiet conditions across the coastal waters through
tomorrow afternoon with modest east/northeasterly winds and seas
generally between 1 and 3 feet.


Outlook /Wednesday Night through Saturday/...

Wednesday Night: Winds less than 25 kt. Patchy fog. Areas of
visibility 1 to 3 nm.

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

Friday through Saturday: Winds less than 25 kt.

&&

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

&&

$$

SYNOPSIS...RM
NEAR TERM...Frank
SHORT TERM...RM
LONG TERM...Dooley
AVIATION...Dooley/RM
MARINE...Dooley/RM