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000
FXUS61 KBOX 252332
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
732 PM EDT Sat May 25 2019

.SYNOPSIS...
High pressure moves offshore, allowing a warm front to slip
through Southern New England. This will bring mild night to our
area, along with a few showers and chance of a thunderstorm.
Southern New England gets a taste of summertime heat on Sunday
along with isolated thunderstorms. A cold front moves through
and brings moderating temperatures, but still pleasantly warm
air. High pressure pushes off the coast early Tuesday. Low
pressure then moves through Tuesday bringing cooler temps and
rain, followed by periodic unsettled weather through Thursday
night. A cold front pushes offshore late next week, with drying
conditions and mild temperatures.

&&

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

730 PM update...

Showers to our west over NY and PA continue to diminish as they
approach eastern NY/PA and leave the area of instability
(200-1000J/kg CAPE) to the west. Marginal instability isn`t
expected move into southern New England until will into the
overnight hours with the next round of rain. For now, some
scattered light showers drifting south from NH are the only
precip to speak of for the next few hours.

Previous Discussion...

Northern stream shortwave races into
Northern New England overnight, with Southern New England at the
tip of the upper jet. This places our area in a zone of lift
that will be coincident with a PW max around 1.5 inches.
Stability parameters are mixed in terms of being favorable for
convection. For instance, totals are 46-48 and mid-level lapse
rates reach 6.5C/Km while the theta-e ridge remains to our west.
We will continue to mention showers and widely scattered
t-storms.

A 40-50 kt low level jet develops after midnight, which suggests
gusty S-SW winds around 25 kt.

Increasing clouds and increasing dew points due to the
approaching warm front support min temps in the 50s.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday...


Showers exit during the morning as the warm front moves off to
the north/east. Southern New England will be in the warm sector,
with dew points in the upper 50s and lower 60s. Mixing is
expected to reach 800 mb, with temps at that level supporting
max sfc temps in the low to mid 80s. Winds in the mixed layer
have a potential for 25-30 kt.

Stability parameters linger at/near unstable levels but drier
air moves in at all levels above 750 mb. The dryness suggests it
will be difficult to generate convection, but the parameters
suggest it is not out of the question. We will mention slight
chance pops in Eastern Mass for showers/tstms.

Sunday night...

West-northwest winds bring lower dew points move in behind the
cold front. Overall a dry night with temps falling back into the
50s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Highlights...

* Dry and mild conditions for Memorial Day
* Low pressure bring showers and cooler temps Tuesday
* A front lingers across the region Wed and Thu with unsettled
  conditions and warming temperatures
* Rain ending Friday with dry and seasonable conditions toward
  the weekend

Overview...

Progressive pattern in the extended forecast, with a persistent
subtropical ridge over the central/southern U.S. directing a
series of shortwaves through SNE during the workweek. This will
lead to periodic shower/thunderstorm chances with a bit of a
roller coaster of high temperatures, warmer Monday and even
moreso Thursday. By next weekend we see indications of a drier
regime with high pressure in the vicinity.

Details...

Memorial Day...

A cooler and drier post frontal airmass will be in place for
Memorial Day as high pressure builds in to the north.
Temperatures top out around 10 degrees cooler than Sunday,
in the mid 70s (near 80 for CT valley), while dewpoints in
the 40s and low 50s mean less humidity. The exception will
be along the immediate coast, where high pressure and light
winds will allow for light onshore flow, keeping temps in
the 60s.

Tuesday through Thursday...

Showers return early Tuesday with cooler temperatures as a
surface low pressure system approaches and crosses the region
from the west. Still some uncertainty on the track and
magnitude of this system. The EC has consistently brought
a stronger ~1004mb low directly over SNE while the GFS keeps
it weaker and further south. Given the associated greater
forcing at 925 in the EC solution, it paints a far wetter
pictureas well. For now, sticking with a blend of synoptic
guidance brining rain on Tuesday. Instability, though, looks
poor, so not expecting thunderstorms. Either way flow remains
onshore Tuesday keeping high temps in the upper 50s and low
60s...mid to upper 60s inland.

Rain clears out briefly early Wednesday before the next
system approaches Wednesday night into Thursday. This one with
several hundred J/kg of CAPE so we could see some thunderstorms
overnight into early Thursday. A brief break in the rain
follows, early-mid day Thursday, before the approaching cold
front brings more widespread rain and potential for
thunderstorms to all of southern New England late Thursday into
early Friday.

Wednesday and Thursday we`ll see increasing temperatures each
day as a warm front slowly makes its way north on southerly
flow, placing southern New England fully in the warm sector by
Thursday. This is associated with a surface low over the Great
Lakes moving into southeast Canada. Cloudcover will limit solar
insolation Wednesday but temps manage to get into the 60s-70s.
Thursday is our warmest day of the week, with 850mb temps
approaching 16-18C, leading to surface highs in the 80s. Some
deterministic model runs continue to predict even hotter temps
Thursday, but for now keeping things in the low to mid 80s.
Glancing at the EPS, only 1-2 of the 50+ members want to bring
90+ highs to PVD or BDL Thursday (even less for BOS). This of
course depends on the timing of the approaching cold front which
if it were to speed up could limit our warming.

Friday and Saturday...

The cold front passes sometime around late Thursday night/early
Friday morning, bringing showers to an end as PWATs drop to
<0.5" and cooler NW winds return. Under large scale troughing
but generally zonal flow, things look to dry out as we head into
the weekend under high pressure. Seasonable temperatures are
expected, in the mid to upper 70s for most with increasingly
clear skies.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...

Tonight...Moderate confidence.

VFR, at least for the first half of the night. Potential that
oncoming showers will lower cigs/vsbys to MVFR during the night.
In addition to showers, expect widely scattered thunderstorms.

Sunday...Moderate confidence.

Showers move offshore in the morning with partial clearing
taking place. Lingering instability hints at potential for
midday/afternoon thunderstorms, but with the air drying out this
will be difficult to accomplish. We will expect isolated
shower/t-storm in Eastern MA. West winds gusting to 25 kt.

Sunday night...High confidence.

VFR with clearing skies and diminishing wind.

KBOS Terminal...Moderate confidence in timing of lower
conditions in showers tonight. Otherwise high confidence.

KBDL Terminal...Moderate confidence in timing of lower
conditions in showers tonight. Otherwise high confidence.

Outlook...

Memorial Day through Monday Night: VFR.

Tuesday: VFR. Breezy. Chance SHRA.

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

Wednesday: Mainly VFR, with local IFR possible. Breezy. Chance
SHRA, isolated TSRA.

Wednesday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA, isolated TSRA.

Thursday: VFR. Breezy. Chance SHRA, isolated TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday Night/...High confidence.

Tonight...Increasing SW winds as a low level jet moves across
the waters. Gusts to 25 kt possible after midnight with building
seas. A Small Craft Advisory is being issued with this forecast.
Showers move through, mostly during the overnight, with reduced
vsbys.

Sunday...Low level jet exits SE waters early with diminishing
winds. Another pulse of west gusts to 20-25 kt may develop in
the afternoon over Boston Harbor and Narragansett Bay. Also some
concern for a second round of showers/t-storms along the Eastern
MA coast, but important conditions for shower growth are not
showing in our data. We will forecast isolates showers/thunder
along the North Shore and South Shore waters.

Sunday night...Diminishing northwest wind and diminishing seas
as high pressure builds from the west.

Outlook...

Memorial Day: Winds less than 25 kt. Seas locally approaching
5 ft.

Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Rain showers likely.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Rain showers likely.

Wednesday through Wednesday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain showers, isolated
thunderstorms.

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 2 AM to noon EDT Sunday for
     ANZ231>235-237.
     Small Craft Advisory from midnight tonight to 5 PM EDT Sunday
     for ANZ250.
     Small Craft Advisory from 2 AM to 10 PM EDT Sunday for
     ANZ254>256.

&&

$$
SYNOPSIS...WTB/BW
NEAR TERM...WTB/BW
SHORT TERM...WTB
LONG TERM...BW
AVIATION...WTB/BW
MARINE...WTB/BW