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354
FXUS61 KBOX 051157
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
757 AM EDT Wed Jun 5 2024

.SYNOPSIS...
Rather warm and mainly dry today outside the risk for an isolated
afternoon shower or thunderstorm across northeast MA. Our weather
pattern then changes to a cloudy and more unsettled outlook by
Thursday and continuing into early next week. Widespread rain
showers and embedded thunderstorms are expected on Thursday with
locally heavy rainfall possible. Shower and thunderstorm
coverage for Friday into Monday then becomes more scattered with
some dry periods at times. Temperatures trend slightly cooler
than normal.

&&

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

-- Changed Discussion --
755 AM Update...

* Scattered showers/isolated thunder exit central/eastern MA by
  late morning

* Mainly dry & quite warm the rest of the day, but low risk for
  a few additional showers/isolated t-storm impacting NE Mass

Quick update this morning to account for a cluster of showers
and isolated t-storms moving across central/eastern MA early
this morning. This activity should push east of the over the
next few hours with a mainly dry and very warm afternoon.

The one caveat is we will have to watch another shortwave
rotating south across northern New Eng which will result in
scattered convection across NH/ME. There is a low risk an
isolated shower or t-storm could spill southward into NE MA this
afternoon, but the greater risk is to the north where moisture
and instability is more favorable.

It will be a rather warm day away from the south coast as high pres
shifts further offshore setting up a SW flow with warming low level
temps. Highs will reach well into the 80s away from the south coast,
and a few locations in northern MA may reach 90 as 925 mb temps
increase to 22-23C in this area. Otherwise, expect highs in the 70s
along the immediate south coast where SW flow will result in cooler
low level temps. SW winds 10-20 mph expected.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Key Points...

* Widespread showers and a few t-storms move across the region
  late tonight into Thu

* Another round of showers and t-storms develop in western New
  Eng during the mid-late afternoon Thu

* A few strong storms are possible Thu afternoon but the greater
  risk is for localized heavy rainfall capable of flash
  flooding

Tonight...

Dry this evening, although expecting stratus and patchy fog to
develop along the south coast and expand north overnight as higher
dewpoint air advects northward. A subtle shortwave approaches late
tonight as the mid level ridge slides to the east. Good moisture
transport and modest forcing for ascent will result in an area of
showers and perhaps and isolated t-storm overspreading the region
from SW to NE toward daybreak. It will be a mild night with lows in
the 60s, and humidity levels will be increasing as dewpoints climb
into 60s.

Thursday...

Widespread showers and a few t-storms assocd with this shortwave
will lift NE across SNE during the morning, lingering into early
afternoon across eastern MA. Given PWATs increasing to 1.5-2.0"
locally heavy rainfall is possible. A dry slot will move in behind
the shortwave during the afternoon which will result in a lull in
the rainfall. However, a more potent shortwave rotating around the
Gt Lakes upper low will be approaching toward evening. It is
possible a few breaks of sunshine may develop in western New Eng
during the afternoon which will help to generate up to 1000 J/kg of
SBCAPE. As a result, all the CAMs are indicating another round of
showers/t-storms moving into western New Eng later in the afternoon.
0-6km shear up to 30 kt so can`t rule out a few strong storms
although low and mid level lapse are not favorable. However, HREF is
indicating some updraft helicity swaths and CSU ML probs and HRRR
Neural Network are indicating low probs of severe wx in western New
Eng with wind the main threat. While we can`t rule out a strong to
severe storm, heavy rainfall will likely be the greater threat given
high PWAT airmass. HREF localized PMM indicating potential for
localized rainfall amounts of 3+ inches and WPC ERO has a slight
risk of rainfall exceeding flash flooding across interior MA.

Highs will be mostly in the 70s and it will be rather humid with
dewpoints 65-70.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
Highlights:

* Unsettled through early next week with daily chances for
  showers/thunderstorms

* Many locations should experience dry/pleasant weather but with
  some cloud cover and slightly below normal temps

* Unsettled pattern breaks sometime early next week

Friday

A broad upper-level low approaches The Northeast from The Great
Lakes region on Friday. This will continue to support a period of
unsettled weather for southern New England. Available moisture and
forcing ahead of the upper trough axis on Friday will be limited,
but should be enough to trigger a few scattered showers and possibly
a rumble of thunder on Friday afternoon. With muggy conditions and
dewpoints in the mid 60s there should be a few hundred J/kg of CAPE
available, but not enough to make severe thunderstorm development a
concern. Latest suite of model guidance actually supports a bit of
dry air in the lower levels with most of the available moisture in
the mid-levels around 700 hPa. Because of this, many locations in
southern New England will experience a decent spring day on Friday
with a mix of sun and clouds and temps in the low 80s. The greatest
risk for showers/storms looks to be focused along and north of I-90
where there should be more moisture available. We should have more
details for Friday as we enter the window of hi-res model guidance
in the next 24 to 36 hours.

Saturday and Sunday

Upper-low remains parked over The Northeast this weekend. A surface
cold front pushes through The Northeast Friday night into Saturday
which will bring cooler temperatures to the region into early next
week. Dewpoints come down to more comfortable levels behind the
front, falling into the mid 50s by Saturday afternoon. The air mass
behind the front will be characterized by 925 hPa temps around 15C,
give or take a few degrees. This will support high/low temps in the
mid-upper 70s and mid-upper 50s respectively this weekend. The
presence of the upper-low and cold air aloft will support more
clouds than sun for most of southern New England and continued
chances for afternoon showers/thunderstorms, though no washouts look
to be in the mix this weekend, mainly just hit or miss
showers/storms.

Early Next Week

Forecast becomes fuzzy early next week, but it looks like we`ll have
at least one more substantial rainfall event before the quasi-
stationary upper-low over The Northeast finally departs over The
Atlantic. Model guidance differs in the timing of when this will
happen, but it could be as early as Monday evening or as late as
Tuesday evening. The timing of the departure of this feature will
govern what kind of weather we experience early next week. Stay
tuned for more details.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Forecast Confidence Levels:

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

12Z TAF Update:

Today...High Confidence.

Some VCSH near BED and ORH early should diminish by
13-14Z.Thereafter any remaining stratus will burn off quickly,
otherwise VFR. But patchy SCT stratus may develop around ACK by
this afternoon and become IFR- LIFR cigs by late afternoon.
There is a low risk for an isolated shower or t-storm across NE
MA this afternoon, but greater risk will be to the north. SW
wind increasing to 10-20 kt.

Tonight...Moderate Confidence.

IFR-LIFR stratus and patchy fog expected to overspread the
south coast by early evening then expand northward, but
specific timing remains uncertain. A cluster of showers and
perhaps an embedded t-storm may begin to overspread the region
from SW to NE 09-12z. Light S winds.

Thursday...High confidence.

Widespread IFR-LIFR may improve to MVFR in the CT valley during
the afternoon. Numerous showers and a few t-storms with locally
heavy rainfall possible. SE-S wind 5-15 kt.

KBOS TAF...High confidence today. Low risk for showers over
central MA reaching the BOS terminal, but expect they should
diminish prior to that. VFR into this evening. Lowering cigs to
MVFR and possibly IFR later tonight but exact timing is
uncertain. No sea-breeze today with SW wind 10-15 kt.

KBDL TAF...High confidence today. VFR today. Lowering cigs to
MVFR-IFR later tonight but exact timing is uncertain.

Outlook /Thursday Night through Sunday/...

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

Friday: VFR. Chance SHRA, isolated TSRA.

Friday Night: VFR.

Saturday: VFR. Chance SHRA.

Saturday Night: VFR. Slight chance SHRA.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Thursday...High Confidence.

Increasing SW winds today into this evening with gusts to 20 kt
developing. Winds become more S-SE during Thu with gusts to 20 kt.
Seas may build to near 5 ft over southern waters Thu afternoon.
Patchy fog may reduce vsbys over southern waters today, with
greater risk of fog tonight and Thu morning. A round of showers
and embedded t-storms will move through late tonight and Thu.

Outlook /Thursday Night through Sunday/...

Thursday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers.

Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.

Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.

Saturday through Saturday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Slight chance of rain showers.

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers.

&&

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

&&

$$

SYNOPSIS...KJC/RM
NEAR TERM...Frank/KJC
SHORT TERM...KJC
LONG TERM...RM
AVIATION...KJC/RM
MARINE...KJC/RM