445
FXUS61 KBOX 282237
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
637 PM EDT Sun Apr 28 2024

.SYNOPSIS...
Scattered showers and perhaps a rumble of thunder tonight give
way to a mild Monday. A backdoor cold front will bring cooler temperatures
Tuesday and Wednesday. 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 may end up
on the cooler side especially along the coast. Another chance
for a period of showers also arrives sometime next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

630 PM Update...

* Period of showers this evening with focus western MA/CT
* Mild tonight with overnight lows mainly in the 50s

A shortwave coupled with some diurnal heating allowed for a
cluster of showers to develop across NY State earlier today.
Northwest flow aloft was allowing these showers to move into
western MA/CT early this evening. A few showers may also impact
eastern MA/RI for a brief time...but the bulk of them will be
across interior southern New England. Low risk for a rumble of
thunder, but thinking its not worth inserting in the forecast
given areal coverage would be so limited.

The shortwave and associated showers will come to an end
by or just after midnight. Otherwise...a rather dry and very
mild night is in store for the region. Given anomolously high
dewpoints for this time of year, overnight lows will be starkly
different compared to the last week or so. Lows should bottom
out in the upper 40s to lower 50s near the immediate south
coast...but middle to even a few upper 50s are expected for the
rest of the region. Given SW flow early this evening and small
dewpoint depressions, expecting fog to form across the Cape,
Islands, and far SE MA, but aforementioned wind shift and drying
flow should keep fog well south of the I-90 corridor/Boston
Metro area.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...

Ridge restrengthens tomorrow and broadens, building back
towards the west, which will keep very mild temperatures aloft
pinned over our area; 925mb temps will climb towards 16C in the
CT River Valley! With morning fog and stratus burning off by
15/16Z, we should see very mild temperatures develop,
particularly across the interior, but early afternoon as highs
surge well into the 70s to perhaps 80F in places like Hartford
and Springfield. Given weak pressure gradient, seabreeze
development looks like a lock, with climatology telling us it
will develop between 14-16Z tomorrow, so, as is usually the case
in April, the immediate coastline will be significantly cooler
than inland zones, with Boston proper struggling to warm into
the low 60s! The only potential snag to temperatures tomorrow
would be, as we saw on Sunday, a pesky cloud deck that struggles
to erode, but given the high sun angle as we head into the
final days of April, hedging our bets that partly cloudy skies
will support optimal daytime heating. Given the expected
temperature gradient, derived temperatures using the NBM50th
percentile away from the coast, and the CONSSHORT for the
immediate coastline.

A seasonable night is in store for Monday night as dewpoints
continue to drop into the 40s area wide. With light and variable
winds, there is a distinct possibility that patchy fog will develop,
especially in CT and RI where dewpoints are a bit slower to dry
out.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...

Key Points...

* Cool Tue & Wed with highs in the 50s coast & 60s inland
* Main threat for a period of showers Tue night into Wed am
* Generally dry Thu & Fri...but large spread in potential high temps
* Another round of showers possible sometime this weekend

Details...

Tuesday and Wednesday...

High pressure across eastern Canada will result in an onshore flow
and cooler temperatures Tuesday and Wednesday. Onshore flow will
hold highs into the 50s along much of the coast and 60s further
inland for both afternoons. In fact...the immediate eastern MA coast
may see high temps only in the lower 50s.

The other issue will be for a round of showers mainly Tuesday night
into Wednesday morning. Shortwave and some instability to our west
will allow showers and possibly a few thunderstorms to develop
across NY State Tue afternoon. Enough westerly flow aloft should
allow some of this activity to survive into our region sometime
Tuesday night into Wednesday morning. The activity will be on a
weakening trend given our stabilizing marine environment...so for
now did not include thunder but later shifts may have to take an
other look.

Thursday and Friday...

An upper level ridge axis will again build to the west of southern
New England. As this happens will have to watch for some shortwave
energy to dive southward from the Canadian Maritimes. This may be
enough to send a backdoor cold front southward across southern New
England. The ensembles indicate a large spread in the potential
outcomes and temperatures. If this front remains to our north high
temps will be well into the 70s...but if it does come through like
some of the 12z guidance suggests highs will be held in the 50s and
60s. We think much of this time may feature dry weather with the
lack of synoptic scale forcing.

Next Weekend...

Approaching shortwave/cold front may bring a round of showers to the
region sometime later Sat into Sun...but timing is uncertain given
this is a 6-7 day forecast. Thinking temps may end up on the cooler
side given the potential for onshore flow...so thinking mainly highs
in the 50s and 60s coolest readings most likely on the coast.

&&

.AVIATION /22Z SUNDAY THROUGH FRIDAY/...

Forecast Confidence Levels:

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

00z TAF Update...

Tonight...Moderate Confidence.

Mainly VFR across interior southern New England this evening
despite a round of showers which should come to an end by
midnight or shortly thereafter. Meanwhile...moist southwest
flow has allowed MVFR conditions to develop across the
Cape/Islands early this evening. These conditions should lower
to IFR levels for a time and may have a period of LIFR
conditions in fog too. We do not expect the low clouds to
advance too much further northwest than the Boston to
Providence corridor. SW winds 5 to 10 knots shift to the NNW
after midnight.

Monday...High Confidence.

Any lingering low clouds/fog patches across the Cape/Islands
quickly dissipate by late morning...otherwise expect VFR
conditions on Monday. Winds NNW 5-10 knots across the interior
but a seabreeze will develop along the coast...from the E/ESE
along the eastern MA coast and from the ESE/SE around
Narragansett Bay.

Monday night..

Mainly VFR with localized MVFR in widely scattered shower
activity. Winds generally light and variable in direction.

KBOS TAF...Moderate confidence in TAF.

Biggest uncertainty is do we see a period of low clouds for a
time late tonight ahead of the cold front. We only indicated
some MVFR conditions as we think the bulk of the lower clouds
and fog stay south of the terminal. Seabreeze tomorrow with NE
winds by 13Z and ESE winds by 16Z.

KBDL TAF...High confidence in TAF.

Showers come to an end this evening...otherwise expect mainly
VFR conditions to prevail.

Outlook /Tuesday through Friday/...

Monday Night: Mainly VFR, with local MVFR possible.

Tuesday: Mainly VFR, with areas MVFR possible.

Tuesday Night: Mainly MVFR, with local IFR possible. Chance
SHRA.

Wednesday: MVFR/IFR conditions possible. Breezy. Chance SHRA.

Wednesday Night: Mainly VFR, with local MVFR possible.

Thursday: VFR.

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

Friday: VFR/MVFR conditions possible. Breezy. Slight chance
SHRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Through Monday... High confidence.

Widely scattered showers possible this evening with a very low
chance of a rumble of thunder across the waters. Fog development
likely for the near shore waters around the Cape/Islands/south
coast with SW winds shifting gradually overnight to the NW.
Winds continue to shift on Monday with seabreeze development;
from the ESE along the eastern MA coastline and the SSE along
the south coast. Regardless of wind direction, winds generally
less than 10kt with gusts to 15kt. Seas mainly 3ft or less all
waters.

Outlook /Tuesday through Friday/...

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Patchy fog.

Tuesday: Winds less than 25 kt.

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

Wednesday Night through Thursday: Winds less than 25 kt.

Thursday 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...KS/Frank
NEAR TERM...Frank/KS
SHORT TERM...KS
LONG TERM...Frank
AVIATION...KS
MARINE...KS/Frank