838
FXUS61 KBOX 301647
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1247 PM 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 /18Z TUESDAY THROUGH SATURDAY/...

Forecast Confidence Levels:

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

18z TAF Update...

Through tonight...Moderate Confidence.

Mainly VFR conditions into early evening...but a cooling
boundary layer should result in MVFR-IFR conditions developing
tonight with even some localized LIFR conditions given moist
onshore flow. Another round of showers will move in from the
west after 23z/00z. We can not rule out isolated thunder with it
briefly across the distant interior...but we expect a weakening
trend as the activity pushes east into a less favorable
environment. So for much of the region mainly just showers but
a few downpours are also possible. A few showers linger
especially towards the Cape/Islands through daybreak...but the
vast majority of the activity will have passed the region by
06z/07z. E winds shifting to the NE at 5 to 10 knots tonight.

Wednesday...Moderate Confidence.

IFR-LIFR conditions early Wed morning will gradually improve to
MVFR and even VFR conditions in some spots through the
afternoon...but this will be a slow process and timing will need
to be refined. After any remaining showers depart early Wed
morning, mainly dry weather will prevail Wed other than perhaps
a brief spot shower. NE winds 5 to 10 knots.

Wednesday night...Moderate Confidence.

MVFR-IFR conditions will probably become dominant again as the
boundary layer cools again Wed night. A few showers may spill
into our northern zones through daybreak Thu...but much of Wed
night will feature dry weather with nothing more than a spot
shower. Winds becoming light S.

KBOS TAF...Moderate Confidence in TAF.

KBDL TAF...Moderate Confidence in TAF.

Outlook /Thursday through Saturday/...

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...Frank/Dooley
MARINE...Dooley/RM