744
FXUS61 KBOX 291111
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
711 AM EDT Mon Apr 29 2024

.SYNOPSIS...
Enjoy the warm and partly sunny conditions today, a backdoor
cold front will bring much cooler conditions, clouds, and spot
showers on Tuesday. The greatest risk for a period of showers
will be Tuesday night into Wednesday morning. Temperatures for
late this week and next weekend are uncertain given the
positioning of a backdoor cold front...but are looking more
likely to end up on the cooler side especially along the coast.
After a slight chance of showers Thursday, another round of
showers may arrive late next weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
A mixture of clear sky and some lower clouds early this morning. Fog
and low clouds have been tough to come by, while there has been a
few instances of isolated fog, do think there is enough mixing to
preclude fog formation across southeast Massachusetts, Cape Cod, and
the islands. Looking at the nighttime RGB product, can see some low
clouds well to the northeast in the Gulf of Maine. While this
feature is shifting from north to south, confidence in this reaching
eastern Massachusetts remains low. The latest 07z HRRR does show the
bank of low clouds/fog clipping the outer end of Cape Ann and
Cape Cod between 5AM and 8AM. Something to monitor, though
should have no real impacts - though, it could reduce visibility
for our mariners.

Bigger picture, a weak area of high pressure at the surface and a
mid-level ridge is centered aloft. There will be much drier air to
our northeast into Maine, but we will hold on to a bit of mid-level
moisture. A partly sunny day with should help to warm us into the
70s for many locations, but the immediate coast remains cooler. With
a weak pressure gradient, do expect a sea breeze develops 10am to
12pm, the onshore flow limits the day time heating for those coastal
communities. Essentially an east-northeast wind for the eastern coast
of Massachusetts and a south-southeast wind for the southern coast
of Rhode Island and Massachusetts. Wind speeds are 10 to 15 mph. Here
temperatures are in the 50s to the low 60s. While further inland, a
north-northwest wind will allow for minor downsloping in the CT
River Valley, and could push temperatures close to 80 degrees. While
this isn`t a record, in fact the record for KBDL is 91F, set in
1974, but still, a high near 80F is warmer than the normal high of
67F.

Think the day will remain dry, but there is a low chance of a brief
and localized shower for the locations southwest of Hartford due to
the chance of convective showers developing north and west of the
NYC Metro. HREF ensembles have a few hundred to a thousand units of
surface based CAPE here in addition to PWATs one inch and better.
Once again, this is  Since there is high pressure, little steering
for these storms and a good chance the will not drift towards our
neck of the woods. As for now, kept the mention of any showers out
of the forecast grids.

Increasing cloud cover post sunset as a 850mb warm front lifts from
southwest to northeast. Can`t rule out a few widely sct`d showers
around midnight to 5/6am Tuesday. Maintained 20 to 40 POPs, `Slight
Chance` to `Chance` POPs, mainly across northern Connecticut and
western Massachusetts. A mild night as well with overnight lows in
the upper 40s and low 50s.

&&

.SHORT TERM /TUESDAY/...
Highlights:

* Much cooler on Tuesday, by as much as 10 or 15 degrees cooler due
  to a backdoor cold front.

* Spot showers possible ahead of an approaching cold front late
  Tuesday.

A noticeable difference come Tuesday, temperatures are roughly
10 to 15 degrees colder than the day prior, plus cloudy skies
and chance for spot showers. We can thank a backdoor cold front
for the cooler temperatures, brought on by an east to east-
southeast wind throughout the day. This knocks back the warm
temperatures to a range of what is considered `normal` for late
April. There will be a spread in temperatures from the low/mid
50s in Boston to the mid/upper 60s in Hartford to Springfield.
In between, many locations achieve a high temperature in-between
the lower and middle 60s. Coastal towns are much cooler, with
highs in the low to mid 50s! As for precipitation, have
maintained `Slight Chance` POPs across western Massachusetts and
northwest Connecticut for the early afternoon, but the POPs
increase into the late afternoon. Do think the bulk of any rain
will arrive overnight, which is discussed in the Long Term
section of the AFD.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Key Points...

* Cool Wed with highs in the 50s coast & 60s inland.

* Main threat for a period of showers Tue night into Wed morning.

* Generally dry Thu & Fri but can`t rule out some scattered
  showers on Thursday...large spread in potential high temps.

* Another round of showers possible next weekend.

Details...

Tuesday Night and Wednesday...

High pressure remains in control directing cool, NE flow into
southern New England keeping highs once again in the low to mid 50s
(east) and mid 60s (CT valley). A shortwave passing overhead coupled
with a surface low moving from the mid-Atlantic passing south of the
region will bring a round of showers moving in Tuesday night and
continuing through at least Wednesday morning; there is a low
probability that showers continue well into the evening before weak
ridging moves in and things dry out a bit.

Thursday and Friday...

An upper level ridge tries to build in for the latter half of the
week, but latest guidance now indicates a shortwave suppressing the
eastern periphery of the ridge over SNE on Thursday, so things
aren`t looking as dry for Thursday as they did 24 hours ago. Even
so, weak forcing and PWATs <1" will keep any rainfall from being to
impactful. By Friday with the ridge closer dry weather is more
likely. The biggest forecast challenge for this period will be the
potential for another backdoor cold front to accompany this
shortwave on Thursday which would keep the earlier expected 70s from
materializing. At this point there is a considerable amount of
uncertainty, but odds shifting toward a cooler solution with temps
more likely to be in the 50s and 60s each day rather than the 70s.

Saturday and Sunday...

The ridge axis arrives on Saturday with our next shortwave on its
heels which brings the return of widespread rain chances as early as
Saturday night. Confidence is low given significant spread in how
the pattern evolves.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

Today... High confidence.

Any lingering lower clouds or fog across the Cape and Islands
will dissipate by mid morning, otherwise expect VFR Cigs
throughout. Winds are north-northwest 5 to 10 knots across the
interior, but a sea breeze develops along the coast 14z to 16z
from the east-northeast to the east-southeast along the eastern
MA coast and from the south-southeast around Narragansett Bay.

Tonight... Moderate to High confidence.

VFR, localized MVFR within widely scattered showers. Winds are
generally light and variable in direction.

Tuesday... High confidence.

VFR east, MVFR west. Showers develop late afternoon across
northwestern terminals. Wind direction becomes east-southeast
with speeds 8 to 12 knots.

KBOS TAF...Moderate confidence in TAF.

There is uncertainty with how low Cigs will fall this morning,
feeling a bit more optimistic that the terminal remains VFR
with lowering to 4000ft around 08z to 12z. West-southwest wind
will become northerly by 12z, then sea breeze occurs 14z to 16z
with a wind direction east-northeast late morning becoming east-
southeast by mid afternoon.

KBDL TAF...High confidence in TAF.

VFR. Light west-southwest wind becoming northerly by 12z. Wind
direction is generally north through today with winds 10 knots
of less. Lowering Cigs tonight to MVFR after 03z/05z.

Outlook /Tuesday Night through Friday/...

Tuesday Night: MVFR/IFR conditions possible. Chance SHRA.

Wednesday: Mainly VFR, with areas IFR possible. Chance SHRA.

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

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

Thursday Night: VFR. Slight chance SHRA.

Friday: VFR. Breezy. Slight chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Tuesday... High confidence.

Low chance for coastal fog to develop early this morning across
the eastern waters, nighttime RGB product does show an area of
low clouds/fog across the Gulf of Maine and high-res model
guidance shows the potential for this to drift south between 6AM
and 10AM. Otherwise, dry and partly sunny Monday with east-
southeast winds along the eastern coast of Massachusetts and
south-southeast winds along the south coast of Massachusetts and
Rhode Island. Winds are 10 to 15 knots and seas 2 to 4 feet.

Tonight winds are light and variable. Tuesday, winds are east to
southeast 8 to 12 knots, gusts around 15 knots. Seas 1 to 3
feet. A few showers are possible ahead of an approaching front
during the afternoon.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Winds less than 25 kt. Chance of rain showers,
isolated thunderstorms.

Wednesday: Winds less than 25 kt. Chance of rain showers.

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

&&

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

&&

$$

SYNOPSIS...BW/Dooley
NEAR TERM...BW/Dooley
SHORT TERM...Dooley
LONG TERM...BW
AVIATION...BW/Dooley
MARINE...BW/Dooley