841
FXUS61 KBOX 042002
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
402 PM EDT Tue Jun 4 2024

.SYNOPSIS...

Mainly dry and warm weather is on tap for Wednesday outside the risk
for a few spot showers. 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. 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 AM WEDNESDAY MORNING/...

4 PM Update...

* Spot shower/t-storm possible near Berks early this evening
* Mainly dry/mild overnight outside a spot shower...lows 55-60

Diurnal instability coupled with interaction on the terrain may
generate a few spot showers & possibly a t-storm near the Berks
early this evening. This activity should dissipate this evening with
the loss of daytime heating. Another piece of shortwave energy may
allow for a few spot showers elsewhere mainly after midnight. That
being said...dry weather will dominate the vast majority of the time
and region tonight.

We will need to watch for some low stratus and fog to possibly
impact areas near the south coast...Cape and Islands as boundary
layer cools. Should not be an issue though away from that region. It
will be mild tonight with low temps only dropping into the 55 to 60
degree range.

&&

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

Key Points...

* Warm Wed with highs 85-90 away from the south coast
* A few showers/iso t-storm possible Wed afternoon in NE Mass
* Main risk for showers/iso t-storms develop near daybreak Thu

Details...

Wednesday...

Shortwave energy may result in a few leftover spot showers across
eastern MA early Wed morning...but any of this activity should be
pushing east of the region by mid-late morning. Otherwise...mainly
dry weather is on tap for Wed with partly to mostly sunny skies and
warm temperatures. 850T near +14C/+15C should result in afternoon
high temps between 85 and 90 away from the cooling marine influence
near the south coast, Cape and Islands. Ridge axis building to our
west should result in a mainly dry weather too. That being said...a
few showers/iso t-storm are possible mainly across northeast MA with
some shortwave energy focused to our north and east. Greatest risk
will north of our region...but northeast MA may be brushed by this
activity depending on how far south it can build.

Wednesday night...

Mainly dry weather expected Wed evening as upper level ridge axis
crosses the region. Once this ridge axis crosses the
region...shortwave energy approaching from the west. Timing is a bit
uncertain...but a cluster of showers/isolated t-storms may approach
the region from the southwest toward daybreak Thu. Pwats increasing
to between 1.5 and 2 inches may allow for downpours within this
activity as well. It will be quite mild too with increasing low
level moisture. This may result in low clouds and fog patches to
develop as well. Overnight lows will only drop into the lower to
middle 60s as a result.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...

Highlights:

* Slow-moving upper level disturbance favors several chances for
  showers/t-storms Thurs thru Mon, with temps trending slightly
  cooler than normal.

* Thurs looks to be a washout with widespread showers/t-storms.

* More scattered/hit-or-miss showers/t-storms Fri thru Mon with dry
  periods in between.

Details:

There are no substantial changes in the anticipated pattern for late
in the week on into the early next week period. An anomalous upper
low for early June over the Gt Lakes region will bring lower than
normal 500 mb heights to the Northeast states. While it won`t be
raining the whole period of time with drier periods interspersed, it
is an unsettled pattern with several chances at showers and t-
storms. This upper level low will close off and gradually fill into
the weekend into early next week. It remains uncertain when we might
see this upper-level feature leave our area; a North Atlantic omega
blocking pattern indicated by GEFS/EPS ensembles would favor very
slow eastward progression through the weekend. There are indications
on Mon that the upper low may make greater northeast inroads then,
with the latest 12z ensembles indicating the North Atlantic blocking
pattern weakening, but that is still to be determined.

Thurs still looks to be a washout and is the wettest day in this
period. PoPs were increased into the Categorical range, as leading
edge of stronger 500 height falls combined with an axis of anomalous
moisture (PWATs 1.2 to 1.4") and warm cloud depths 10-11kft will
favor showers and embedded t-storms with localized downpours,
focused by a surface frontal occlusion. Wouldn`t rule out isolated
instances of street flooding but we still are not anticipating any
significant hydro problems as it has been pretty dry of late and FFG
is on the higher side. Most of these rains move in during the
daytime hrs, then lift into interior New England by early evening
with a decrease in PoPs.

For Fri, the weekend on into Mon, still expect partly to mostly
cloudy conditions with a general sameness to PoPs for showers/t-
storms. More specifically, higher PoPs during the daytime hrs in the
30-55 percent range with the highest north and west closer to the
upper low. Lesser/reduced PoPs around 15-25% for the nighttime hours
during the diurnal-heating minimum. Later shifts will need to adjust
this up/down but level of predictability at this time horizon is too
limited to get into those details. It won`t be raining the entire
time, but the message is that there will be showers/t-storms to
dodge however severe weather potential is quite low.

With cloud cover, showers/t-storms around and with 850 mb temps in
the upper single digits to lower teens, reduced NBM high temps
downward with slightly cooler than normal temps in the lower to
middle 70s and lows in the 50s to lower 60s. Humidity levels are
highest on Thursday and could be pretty muggy with dewpoints in the
mid to upper 60s, then with lower humidity levels Fri thru Mon.



Thursday through the Weekend:

Heading into a period of unsettled weather with several
opportunities for showers and t-storms starting Thurs into
potentially a good portion of the weekend. An upper level closed low
over the Gt Lakes slowly builds into the Northeast for Thurs into
Fri, and remains in place through at least Sat and potentially into
Sunday as well. Though this expected rain should be welcome news to
wash out the clouds of pollen around our area of late, although far
from ideal weather for outdoor plans.

Wettest period still looks to be on Thurs; PWAT values of 1.2 to 1.4
inches along with warm cloud depths between 10000-11000 ft favor
localized downpours in showers and embedded t-storms. Severe weather
potential appears to be low at this time with limited instability
and a general lack of stronger surface heating through abundant
cloud cover. From a hydro perspective, we can`t rule out isolated
issues but probably not anything more than that given the
progressive nature to the rain, and we`ve also been pretty dry of
late. While the international guidance lends support to this
solution, did note the past couple cycles (06/12z) of the
deterministic GFS are cloudy but depict a dry weather pattern.
However there`s a good majority of GFS ensemble members which show
rain for Thurs so we view this as a dry outlier outcome as of now.
NBM probs of 24 hr rain for Thurs have increased into the the
moderate to high (40-60%) range for totals at or above 0.5 inches
for much of the area, and indicate moderate (30-40%) probs for rain
totals at or over 1 inch in portions of RI and SE MA. PoPs were
raised into the high Likely range and Categorical PoP could be
warranted in later updates.

For Fri into the weekend, the upper level low parks itself over or
in the vicinity of Southern New England. This will maintain
cloudier/unsettled weather conditions with more periodic/hit-or-miss
showers or t-storms. Felt NBM based PoPs in the 30-50% range were a
little too high and opted to following a more diurnal approach Fri
into Sunday, with higher PoP during the daytime and lower (20-25%)
at night. Here too, severe weather potential looks on the low side.

Temperatures trend a little cooler than normal for this period, with
cloudy weather and periods of rain, along with 850 mb temps in the
upper single digits to low teens C range. Highs mainly in the lower
to middle 70s and lows in the upper 50s to mid 60s. Though it will
be cooler, humidity levels still looks somewhat elevated.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...

Forecast Confidence Levels:

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

18z TAF Update...

This afternoon and tonight...High Confidence except low
confidence near the south coast, Cape and Islands tonight.

VFR conditions will persist tonight in most locations, but a spot
shower or even a t-storm is possible near the Berks this
evening. A few spot showers can not be ruled overnight across
the rest of the region...but dry weather dominates. The main
uncertainty revolves around the potential for some low stratus and
fog to impact areas near the south coast, Cape and Islands
tonight. This remains uncertain given marginal low level
moisture...but greatest risk is our Nantucket terminal
so will need to monitor this closely. Sea breezes come
to an end early this evening...otherwise light S winds
becoming SW tonight.

Wednesday...High Confidence.

Any low clouds/fog patches should burn off Wed morning across
the Cape and Islands. Otherwise...VFR conditions with winds SW at 10
to 15 knots. We will need to watch for a few showers/isolated t-
storm mainly across NE MA Wed afternoon. Greatest risk will be north
of our region...but this area may be impacted depending on how far
south it builds.

Wednesday night...Moderate Confidence.

Low end MVFR-IFR ceilings and possibly reduced vsbys will
overspread the region from south to north...but specific timing
remains uncertain. The evening will mainly be dry...but a
cluster of showers and perhaps an embedded t-storm or two may
begin to overspread the region from southwest to northeast
towards daybreak. Light S winds.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday: Mainly MVFR, with areas IFR possible. Breezy. SHRA,
isolated TSRA.

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

Friday: VFR. Slight chance SHRA, isolated TSRA.

Friday Night: VFR. Chance SHRA.

Saturday: VFR. Chance SHRA, isolated TSRA.

Saturday Night: VFR. Slight chance SHRA.

Sunday: VFR. Chance SHRA, isolated TSRA.

&&

.MARINE...

Forecaster Confidence Levels:

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

Tonight through Wednesday night...High Confidence.

The pressure gradient should remain weak enough to keep winds/seas
generally below small craft advisory thresholds through Wed night.
We may see some 20+ knot wind gusts Wed afternoon and night across
the waters. The best chance for these winds will be near the south
coast Wed afternoon with good mixing nearshore...so seas might be
bit choppy near the south coast Wed afternoon.

The other concern will be for areas of fog impacting the waters
especially tonight and again Wed night. Greatest risk for this will
be across the southern waters.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Rain showers, isolated thunderstorms.

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

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

&&

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

&&

$$

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