869
FXUS61 KBOX 061403
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1003 AM EDT Mon May 6 2024

.SYNOPSIS...
Partial sunshine develops today with much warmer temperatures.
A brief band of scattered showers is expected Monday afternoon/
evening...but the majority of the time will feature dry weather.
Tuesday will be the pick of the week with abundant sunshine and
above normal temperatures. Then an unsettled weather pattern
develops Wednesday and beyond, with cooler than normal
temperatures and the risk of showers at times. However, there
will also be periods of dry weather. The weekend may feature a
drying trend, with shower potential not as widespread and
limited to the afternoon/evening hours.

&&

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

10 AM update...

The back edge of the rain shield has finally exited the islands
and we expect mostly dry weather to persist through the rest of
the day. The biggest question this morning is how quickly those
clouds can erode and allow the temperatures to jump up. We`re
currently sitting in the in the upper 50s across much of the
region but where those breaks in the clouds have started we see
low 60s. The next few hours should see some continued clearing
and temperatures climbing. No significant changes to thinking
for this afternoon.

Previous Discussion...

Today

Short-wave energy and associated showers at the surface
exit east off the coast of southern New England this morning.
This will be followed by increasing temperatures and dewpoints
today as southerly flow advects a more warm/moist air mass over
southern New England. 925 hPa temps rise close to 15 Celsius, so
we should experience very warm temperatures in the low to mid
70s across the interior this afternoon. While the sun is likely
to break out at times, there will continue to be a fair amount
of low clouds in place as well, especially over the south coast,
Cape, and Islands where the sun may not break out at all with
low-stratus persisting into tonight. With not as much sunshine
and the expectation that sea-breezes will develop, these
locations near the coast will be noticeably cooler than across
the interior with highs in the low to mid 60s more common. While
most areas should stay dry today, there will be chances for
some mid-afternoon showers to develop as another embedded short-
wave traverses over the region. Can`t rule out a rumble of
thunder either as there will be modest amounts of instability in
the atmosphere to the tune of 100-300 J/kg of CAPE. Expect any
shower/thunderstorm activity to be limited to the interior as
sea-breezes would be expected to stabilize the atmosphere near
the coast.

&&

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

Low clouds fill back in after sunset tonight as the boundary layer
cools. Light winds and high dewpoints will likely result in areas of
fog developing this evening as well. However, low-level winds in the
925-850 hPa layer shift northwest as a mid-level trough axis shifts
east of the region. This will support winds shifting to the north at
the surface which will allow drier air to displace the fog/low-
stratus gradually overnight. Expect clearing skies by sunrise. Low
temps in the low to mid 50s.

Tomorrow

Beautiful day on tap for Tuesday. High pressure and a dry air mass
will support very warm and sunny conditions. 925 hPa air temps in
the mid to upper teens will support another afternoon with temps in
the mid to upper 70s. Can`t rule out a few locations in  the CT
River Valley topping 80. Light northerly winds to start will become
more westerly as the day progresses. By far the pick of the week if
you enjoy warm/sunny weather.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
* Progressively cooler this period, especially Fri and Sat

* Wet weather at times Wednesday through Friday, but also
  periods of dry weather too

* Possibly trending drier next weekend, with showers not as
  widespread and limited during the afternoon/early evening

Synoptic Overview...

By late Tue/Tue night, a high amplitude closed low will be located
over the Dakotas. Models, including ensembles then differ on the
evolution of jet energy ejecting eastward from this closed low
eastward into New England. This will impact frontal position across
SNE, along with timing and amplitude of frontal waves. Hence, a low
confidence forecast this period. Forecast confidence increases
slight for next weekend, as ensembles in better agreement, with mean
trough axis over SNE, displacing deep layer moisture well offshore.
This will favor drier weather with shower threat more diurnally
driven across SNE.

Precipitation...

As mentioned above, anomalous closed low over the Dakotas late Tue
moves slowly east mid to late week. Models, including ensembles
displaying a large spread in the timing of jet energy ejecting
eastward out of this low and eventually into New England. This
results in a low confidence forecast this period, specifically in
regards to frontal boundary placement, including magnitude and
timing of frontal waves traversing this boundary. Hence, rain likely
at times, although periods of dry weather too. Unfortunately, given
model spread, too difficult at this time range to nail down exact
timing of specifics. Ensembles offer some support of drier weather
for the weekend, with mean trough axis over SNE. This will shift
deep layer moisture and frontal wave offshore. However, cyclonic
flow aloft and cold pool will yield a risk of diurnal instability
showers. Not widespread, but unfortunately timing will be in the
afternoon and evening hours.

Temperatures...

High forecast confidence on a cooler temperature regime this period,
in response to lowering heights across New England. Seasonably cool
Wed with highs in the 60s, but then cooling off into the 50s Thu,
especially in eastern MA behind departing wave with N-NE winds
across SNE. Coolest weather could arrive Fri pending track and
intensity of surface wave tracking SE of New England. Depending on
amplitude of wave, could be chilly with onshore only yielding highs
in the 50s. Ensemble 850 mb temp anomalies are impressive, about -6C
cooler than normal. In fact, ensemble probs of 50+ highs Friday drop
to less than 50% across northern MA. Hence, could see highs only in
the 40s there. Chilly weather likely lingers into Saturday given
below normal heights/cold pool aloft. Temps may moderate to seasonal
levels by Sunday, as flow becomes NW aloft and cold pool moves
offshore.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

12Z TAF Update...high confidence in trends, but some uncertainty
on exact timing.

Forecast theme remains for upward trends today with IFR/MVFR
conditions lifting to VFR bases by late morning and continuing
into the afternoon. Rain across RI and southeast MA at 11z will
exit offshore by 12z. Then mainly a dry day, however widely
scattered showers develop this afternoon and early evening.
10-20% chance of an isolated thunderstorm. Light WSW winds with
local seabreezes possible along the eastern MA coast.

-----------------------------------------------------------------

Tonight...High Confidence

MVFR/IFR conditions fill back in across the interior and persist
over the south coast, Cape, and Islands through about 06Z. Winds
shift to the north after that time frame and allow ceilings to
gradually improve to VFR by 09-12Z.

Tomorrow...High Confidence

VFR. Light northerly winds becoming light out of the west. Sea-
breezes likely along the coast with very warm temps forecast
over land.


KBOS TAF...Moderate Confidence in TAF. BOS should scatter out
for a few hours this morning into early afternoon before
returning to MVFR by early to mid afternoon. Moderate
confidence in a sea- breeze circulation developing today between
14 and 16Z. Higher confidence in a sea- breeze for Tuesday.

KBDL TAF...High Confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR. Slight chance RA.

Wednesday: Mainly MVFR, with local IFR possible. Chance RA.

Wednesday Night: Mainly VFR, with local IFR possible. Chance
RA.

Thursday: Mainly VFR, with areas MVFR possible. Breezy. Chance
RA.

Thursday Night: Mainly MVFR, with areas IFR possible. Breezy.
Chance RA.

Friday: Mainly VFR, with areas IFR possible. Breezy. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Tomorrow...High Confidence

Modest winds and seas continue today and tomorrow. Expect areas of
fog over the coastal waters this morning and this afternoon as
moisture increases from southerly winds. Fog should dissipate
tonight into tomorrow as a weak cold front ushers drier air over the
coastal waters.


Outlook /Tuesday Night through Friday/...

Tuesday Night: Winds less than 25 kt.

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

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

Thursday: Winds less than 25 kt. Chance of rain.

Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of
rain.

Friday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Seas up to 5 ft. Chance of rain.

&&

.TIDES/COASTAL FLOODING...
.Coastal Flooding...

High astro tides this week and concern becomes late Thu into Fri
with potential frontal wave tracking south of New England,
generating onshore flow into eastern MA. Magnitude of potential
inundation and erosion will depend on strength and timing of surface
low. Too early for specifics with any certainty, but given astro
tides are already over 11 ft at Boston, it will only take a 1 ft
storm surge and modest wave action to yield minor inundation and
erosion. Stay tuned throughout the week for updated information.

&&

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

&&

$$

SYNOPSIS...Nocera/RM
NEAR TERM...Nocera/BW/RM
SHORT TERM...RM
LONG TERM...Nocera
AVIATION...Nocera/RM
MARINE...Nocera/RM
TIDES/COASTAL FLOODING...