526
FXUS61 KBOX 281937
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
337 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 PM THIS EVENING/...

While it took some time for the clouds to burn off this morning,
abundant sunshine has allowed temperatures to warm into the 60s to
near 70F this afternoon. With a few hours left before sunset, it`s
likely that temps continue to warm a few degrees thanks to mid level
ridging and healthy 850mb temps (exceeding 10C) centered over the
region. Mainly clear skies will give way to increasing cloud cover
this evening as the ridge begins to break down. Convection over
central and northern New York will ride the ridge axis, leading
to some spillover shower activity across western southern New
England early this evening. A few rumbles of thunder are
possible across western MA between 22 and 00Z this evening, but
instability is rather sub par for thunderstorm activity to
maintain strength as showers creep into our CWA, with CAPE
around 100J/kg confided to our NW zones.

As ridge breaks down, weak cold front will seep south across the
region tonight, which will generate some shower activity through
03/06Z from north to south. QPF will be rather spotty with these
frontal showers, generally less than 0.10", so the greatest impact
from this front will be decreasing dewpoints; which, aided by a wind
shift from the SW to the NW, will drop from the high 50s to the
upper 40s north of the MA Pike by daybreak.

Given anomolously high dewpoints for this time of year, overnight
lows will be starkly different compared to the last week or so,
generally bottoming out in the mid 50s. 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 PM THIS EVENING THROUGH 6 PM MONDAY/...

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 /MONDAY NIGHT 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 /19Z SUNDAY THROUGH FRIDAY/...
Forecast Confidence Levels:

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

18Z Update...

Through tonight... Moderate confidence in fog formation

Scattered showers and an isolated rumble of thunder possible
this evening, between 22-03Z. Generally VFR conditions through
03Z with low end VFR to MVFR cigs developing behind departing
showers away from the Cape and Islands. IFR with localized LIFR
likely as fog forms on the Cape/MVY/ACK after 06Z tonight.

Winds SW becoming NW overnight. Gusts to 15kt possible through
early evening, generally less than 10kt thereafter.

Tomorrow... High Confidence in Trends

MVFR/IFR may persist through ~15/16Z but will
eventually improve to VFR at all terminals by mid day. Winds NW
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. Winds around 10kt expected.

Tomorrow Night..

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

KBOS TAF...High confidence in TAF.

VFR to MVFR behind scattered showers this evening, between
23-03Z. Expecting fog to stay well south of the terminal as the
winds shift from the SW to the NW overnight. Seabreeze tomorrow
with NE winds by 13Z and ESE winds by 16Z. VFR redevelops
quickly tomorrow morning.

KBDL TAF...High confidence in TAF. Scattered showers this
evening between 22Z and 03Z, an isolated rumble of thunder is
possible but confidence is much too low to include in the TAF.
Winds SW becoming NW overnight and maintaining direction through
Monday. VFR through the period with a chance for MVFR late
Monday evening.


Outlook /Monday Night 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 /Monday Night 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...Frank/KS
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...Frank
AVIATION...KS
MARINE...Frank/KS