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583
FXUS61 KBOX 032343
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
743 PM EDT Fri May 3 2024

.SYNOPSIS...
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High pressure brings dry weather with cooler onshore breezes through
Saturday. A slow-moving frontal boundary brings clouds and rain showers on
Sunday into early Monday, along with a period of cooler high
temperatures. Though clouds and off and on showers may linger in
southeast New England in vicinity of the slowing front, drier
weather prevails for most of interior Southern New England.
Turning warmer on Tuesday with abundant sunshine, and though
temperatures will be significantly cooler near the coast,
interior areas could see high temperatures reach near 80
degrees. Our next chance for rain is around midweek.
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&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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740 PM Update:

Tranquil early-evening underway across Southern New England,
governed by a 1024 mb high pressure area located in the waters
east of Ipswich Bay. This high pressure remains generally
stationary over at least the next 24 hours, maintaining dry
weather but with an increase in cirrus/high clouds as the
evening progresses. Used some of the RAP to show a decrease in
sky cover for most of the evening, thus pleasant conditions for
any Friday evening outdoor plans.

However the fly in the ointment arrives by the pre-dawn hrs and
mainly in eastern MA, in the form of marine-layer stratus which
is evident in satellite imagery over Nova Scotia and the Bay of
Fundy. These low clouds should gradually build/spread
southwestward through the Gulf of Maine into Cape Cod and the
adjacent eastern coastal waters toward daybreak. Think greatest
extent of low cloud cover should be restricted to the immediate
eastern MA coast, with scattered lower clouds further inland to
around central MA/RI by daybreak.

Low temps in the low-mid 40s seem on track for now with
expectation of generally clear skies for most of the evening,
with cooling likely not to be impeded by advancing stream of
high clouds.

Previous discussion:

Good amount of wind shear visible on the satellite this afternoon
with mid level clouds moving NE to SW and upper level cirrus moving
NW to SE this afternoon. As for those mid clouds, the May sun is
helping to increase our breaks of sun but partly cloudy is about the
best we can hope for in much of southern New England for the rest of
the day. By the overnight hours we`ll see some marginal clearing of
both mid and high clouds, especially after midnight, but fully clear
skies aren`t expected. Even so, given the high overhead and calm
winds, did lower temps a but to account for some potential to
radiate. Lows bottom in the low to mid 40s; right around average for
early May.
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&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
High pressure nudges further south into New England from Nova Scotia
bringing continued quiet weather for the first half of the weekend.
This means continued cool, moist onshore flow from the northeast so
low clouds will be moving in from the northeast while high clouds
move in from the southwest. High temperatures won`t be too different
than Friday, with the warmest spot (the CT valley) in the upper 60s
and the coolest spot (eastern MA) in the mid 50s. Cloudcover
continues to increase overnight as deeper moisture (PWATs over 1
inch) move into western SNE on SW flow ahead of the approaching
system. However, rain should hold off until after 8am.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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Highlights:

* Cloudy, cooler with rain on Sunday into early Mon, with continued
  lighter showers on Mon for southeast New England.

* Dry and turning mild on Tue, though cooler onshore flow near the
  coasts. Spot 80s in the CT Valley?

* Next chance for rains around midweek (Wed/Thu), though still
  unclear which day has the higher rain chances.

Details:

Sunday and Monday:

The 12z suite of guidance continues to come into better congruence
regarding our next chance for steadier light rains associated with a
passing frontal boundary and a rather disorganized 500 mb trough.
Chances for rain increase during the morning in most areas, with the
period of greatest rain chances focused during the Sunday afternoon
to early Monday morning period as the frontal boundary slowly shifts
eastward. With the front becoming parallel to the 500 mb flow with
time as we move into the early Monday period, expect lingering rain
showers during the morning hrs along the RI/MA South Coast, Cape Cod
and the Islands. Further north and west, we should see dry weather
but with a mix of clouds and sun. Overall not a soaking rain, but
enough to likely put a damper on outdoor plans for many on Sunday,
with rain showers lingering into Monday for the southeast New
England coastal areas. To that end, model-ensemble probabilistic QPF
assessment shows high (70-90%) probs of 24 hr rain totals over a
tenth of an inch, but lower to moderate (25-50%) probs for rain amts
at or over a half inch. Official forecast has rain amts around a
quarter to third of an inch.

Expect Sunday to be a cooler day with cloud cover and rains around,
with narrower diurnal range in high and low temps. Highs Sunday in
the mid 50s, and lows in the upper 40s to near 50. High temps are
more challenging on Monday with more clouds south of the Mass Pike
and especially near southern coast, with some sunny breaks further
north. Highs along the southern coast probably struggle to
reach 60, but you don`t have to go much further inland before
highs reach into the low to mid 70s; with lows in the mid 40s to
low 50s.

Tuesday:

High pressure over interior northern New England governs weather
conditions into Southern New England Tuesday, supplying dry weather
and mostly sunny conditions. An early look at model forecast
soundings in interior MA/CT show potential for temperatures to
overachieve guidance with progged deep mixing; with 850 mb temps
around +7 to nearly +10C, highs could reach around 80 degrees in the
CT Valley with readings well into the 70s eastward into RI and into
the MA coastal plain. Northeast flow near the coast will keep temps
several degrees cooler than well inland though, in the mid to upper
60s. Very difficult to show that level of granular detail given
model-resolution limitations at this forecast time horizon and
utilized some of the bias-corrected temperature fields given a
similar regime. Did note NBM was advertising some low PoPs in this
period for spot showers, but feel this is pretty overdone given
progged mixing.

Wednesday and Thursday:

Though this period offers the next best chance for rain associated
with an elongated warm front from low pressure over the Plains
states, there is more uncertainty in timing when chances are
greatest. Really will need those uncertainties to become more in
clearer focus before delving into specifics. Didn`t make too many
adjustments to NBM in this period, except capped PoPs at the higher
end of Chance range (40-50%) given stated timing uncertainties.
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&&

.AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
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Forecast Confidence Levels:

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

00z TAF Update:

Tonight: High confidence.

VFR with increasing stream of high clouds. Could see patchy
mist/fog develop mainly in eastern/northeast MA but too unlikely
to mention in the TAF. Toward daybreak, advancing SCT-OVC
marine stratus at VFR/MVFR levels and while there`s stronger
confidence of MVFR bases over the Cape and Islands, it may lie
just offshore of the remaining portion of the eastern MA
coastline. Light E winds (light/variable at times), before
trending NE/ENE around 6-10 kt by daybreak.

Tomorrow...Moderate confidence.

Any lingering MVFR may improve to VFR for much of the day. Some
uncertainty here given we are still stuck in persistent onshore
easterly flow at 5-10 kts. Confidence higher for VFR away from
eastern MA coastline.

KBOS TAF...High confidence in TAF. VFR, with marine stratus
nearing BOS after 09z; outside chance at MVFR bases early Sat
AM but should trend more BKN VFR levels. Light east winds
tonight (variable at times) before becoming ENE around 10 kt
starting early Sat.

KBDL TAF...High confidence in TAF. VFR, light southerly winds
becoming light easterly early Sat AM.

Outlook /Saturday Night through Wednesday/...

Saturday Night: Mainly VFR, with local IFR possible.

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

Sunday Night: MVFR/IFR conditions possible. SHRA.

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

Monday Night through Tuesday: VFR.

Tuesday Night: VFR. Chance SHRA.

Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA.
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&&

.MARINE...
Forecaster Confidence Levels:

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

Marine

This evening through Saturday night...

High pressure supports fairly calm conditions across the coastal
waters through Saturday night. Winds will prevail out of the
northeast from 10 to 15 knots with some gusts to 20 knots
possible. Seas generally 1 to 3 feet.

Outlook /Saturday Night through Wednesday/...

Saturday Night: Winds less than 25 kt.

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

Sunday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Rain showers likely.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Tuesday: Winds less than 25 kt. Slight chance of rain showers.

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

&&

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

&&

$$

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