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489
FXUS61 KBOX 231625
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1225 PM EDT Sun Jun 23 2024

.SYNOPSIS...

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Warm and humid today with another round of diurnal showers and
thunderstorms, with the focus across western and central MA/CT
later today into this evening. Some storms may become severe,
with strong to damaging winds and perhaps a few tornadoes.
A few diurnally driven showers will remain possible Monday but
lowering humidity. Dry and very warm weather is on tap for
Tuesday but with comfortable humidity. Hot and humid weather
returns later Wednesday. Another round of showers and
thunderstorms is possible later Wednesday, perhaps lingering
into Thursday. Otherwise...drier weather with lower humidity
returns by Friday.
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&&

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

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10 AM update...

Elevated convection has now moved off shore for most, but
continue to monitor a line of towering cumulus stretched NE to
SW from Boston to Eastern CT. As for this afternoon, no major
changes to severe weather forecast. First look at the 12z
guidance indicates better chances still remain north of MA, but
scattered severe convection still remains possible in the late
afternoon to early evening.

645 AM update...

Cluster of showers and a few t-storms moving through SE MA
assocd with weak shortwave and LLJ riding over low level warm
front to the south. This activity will move offshore during the
next hour or so. Still can`t rule out an isolated shower or
t-storm this morning as the shortwave moves through, otherwise
it should be mainly dry into the early afternoon before next
round of convection develops/moves into the region.

Previous discussion...

Key Points...

* Potential high-end severe weather event western-central MA
* Primary threat is strong to damaging winds and tornadoes
* Hot and humid conditions continue with heat indicies 95-100

This afternoon...

Once lead short wave over northern New England this morning exits
into ME, the backdoor front over SNE early this morning, lifts
northward as warm front and gives way to an impressive warm sector.
For example, this afternoon, 925 mb temps rise to around +24C to
+26C along with dew pts climbing into the low and mid 70s, a classic
mid summer airmass over SNE, yielding very robust instability with
SB Capes of 1500-2500 j/kg across western-central MA/CT. Less
instability southeast into the I95 corridor given duration of low
clouds this morning and SW flow off the cool ocean this afternoon.

Trailing short wave currently across the Great Lakes this morning,
enters NY state this afternoon and then across SNE this evening.
This provides synoptic scale lift/height falls for ascent and is
enhanced by the RRQ of an 80 kt upper level jet streak over SNE late
in the day. Moreover, both of these features contribute to 35-40 kt
of deep layer shear, highest across northern portions of CT and MA.
In fact, even low level wind fields are robust for late June, with
up to 40 kt at 850 mb and 925 mb. Thus, spring jet dynamics acting
on a mid summer airmass will potentially yield a high end severe
weather event this afternoon/early evening across western-central
MA, possibly into northwest CT, including Hartford county.

Given strength of wind field throughout the column, combined with
high instability and steep low level lapse rates, greatest risk is
for strong to damaging winds, with highest probabilities across
western CT, including Hartford county into western and central MA.
In addition, anomalous wind fields thru the column combined with
model soundings showing large curved hodographs and high STP values
of 1.5-3, yielding an elevated risk for tornadoes. CSU machine
learning probs, updraft helocity swaths from the HREF and NCAR wind
probs all support the potential for a high end severe weather event
18z-00z across western-central MA, possibly into northwest CT.
Convection is expected to arrive in RI and eastern MA in a weaken
state, as greatest shear and instability remain northwest of I-95
corridor. Secondary concerns are large hail and brief heavy
downpours.

As mentioned above, impressive warm sector will yield highs this
afternoon in the upper 80s to lower 90s and combined with dew pts in
the low to mid 70s, heat indices will soar into the 95-100 deg
range. Thus, we will continue the heat advisory for CT and southwest
MA.

Becoming breezy to windy at times this afternoon, as strong low
level SW jet streams across southeast MA. Surface winds of 15-25 mph
with gusts up to 35 mph at times expected. This will help to provide
some relief from the hot and humid conditions.

As for sunshine, low clouds and fog will erode and give way to at
least partial sunshine away from the south coast. Despite the high
sun angle of late June, low clouds and fog may only lift into a deck
of SCU clouds along the south coast given the increasing low level
SW jet.
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&&

.SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...

355 AM update...

Sunday night

The threat for severe thunderstorms will quickly wane after 8pm-10pm
with only lingering showers and thunderstorms thereafter. A drying
trend overnight, however without a change in airmass, another warm
and humid night, yielding low clouds and fog. Lows only in the upper
60s and lower 70s.

Monday...

Deep layer moisture exits offshore. However, potent northern stream
closed low over NYS and VT, with cyclonic flow across New England.
This will yield lots of diurnal clouds and possibly a few diurnal
scattered showers, but by no means a washout. Remaining warm and
humid with highs in the low to mid 80s and dew pts in the 60s.
Although, a WSW breeze of 15-20 mph will provide some relief from
the warm conditions.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...

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Key Points...

* Dry & very warm Tue with tolerable humidity
* Humid with showers/t-storms later Wed which may linger into Thu
* Dry & seasonable Fri
* Humidity increases next weekend with risk of showers/t-storms Sun

Details...

Tuesday...

Shortwave ridging briefly builds across the region on Tue. This will
result in abundant sunshine and a very warm afternoon...but with
tolerable humidity. Highs Tue should mainly be in the middle to
upper 80s.

Wednesday and Thursday...

The next shortwave trough will slide southeast across the Great
Lakes Wed. This will induce southwest low level flow and increasing
humidity. The amount of solar insolation will determine the high
temps Wed...but currently thinking upper 80s to lower 90s away from
the south coast.

Diurnal heating along with increasing dewpoints will likely allow
for modest instability to develop Wed. The bigger question remains
the timing of the shortwave and associated cold front.
While...timing is uncertain...the threat for showers & t-storms will
increase late Wed into Wed night. It is too early to assess the
severe weather potential...but given that a remnant EML looks to be
in place with modest effective shear will have to watch this closely.

Not sure if Thu will turn out dry or the threat for a few showers/t-
storms will continue. The current guidance seems to favor a more
drier solution Thu...but that certainly is subject to change.

Friday...

High pressure builds in behind the cold front and should result in a
very nice end to the work week. Plenty of sunshine expected on Fri
with highs in the upper 70s to the middle 80s along with
low/comfortable humidity.

Next Weekend...

The high pressure system moves east of the region on Sat...but
current indications favor mainly dry weather with a gradual increase
in humidity. It is a long way off...but by Sunday it looks like it
may be rather humid and the threat for some showers & t-storms will
increase ahead of the next shortwave trough/cold front.
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&&

.AVIATION /18Z SUNDAY THROUGH THURSDAY/...

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Forecast Confidence Levels:

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

12z update...

Thru this morning...high confidence on trends, lower on exact
timing and details.

Showers with embedded thunder moving offshore. Otherwise,
widespread IFR/LIFR in low clouds and fog this morning. Light
NE winds trending southeast through the morning. Cigs and vsbys
will be trending upward to IFR/MVFR 14z-16z. Most improvement
inland and slowest improvement along the south coast.

This afternoon...high confidence on trends, lower on exact
timing and details.

Cigs and vsbys improving to VFR, except along the south coast,
including Cape Cod and the Islands, only to IFR/MVFR in low
clouds and areas of fog. Increasing low level southwest jet
increases to about 50 kt at 2 kft over Cape Cod and Islands by
00z. This will yield LLWS, less inland with better low level
mixing and surface winds SW 15-20G30 kt over RI and eastern MA.
A line of strong thunderstorms is likely 19z-01z northwest of
I-95. Strong winds, large hail and very heavy rain with reduced
vsby are the main concerns.

Sunday night...Moderate to high Confidence.

Lingering thunderstorms at 00z across eastern MA will be
weakening and moving offshore. However, cigs and vsbys lower to
IFR/LIFR in low clouds and fog. Southwest winds remain robust at
15-25 knots. LLWS lingers over southeast MA with low level jet
up to 50 kt at 2 kft at 00z, but slowly moving offshore by
morning.

Monday...high confidence.

IFR/LIFR in the morning lifts and improves to VFR all terminals.
Mist/drizzle possible early, but dry runways late morning into
the afternoon. Low risk of a few spot showers inland in the
afternoon.

KBOS TAF...high confidence in TAF trends. Strongest storms this
afternoon should remain west of the terminal, with weakening
storms impacting the terminal 22z-02z. Frequent lightning, gusty
winds and heavy rain are the main impacts.

KBDL TAF...high confidence in TAF trends. Strong thunderstorms
may impact the terminal 20z-00z. Strong winds, large hail and
heavy rain are the main concerns.

Outlook /Tuesday through Thursday/...

Monday Night: VFR. Breezy.

Tuesday: VFR.

Tuesday Night: VFR. Breezy.

Wednesday: Mainly VFR, with areas MVFR possible. Breezy. Chance
SHRA, chance TSRA.

Wednesday Night: Mainly MVFR, with areas VFR possible. Breezy.
SHRA likely, isolated TSRA.

Thursday: Mainly MVFR, with areas VFR possible. Chance SHRA.
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&&

.MARINE...
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Forecaster Confidence Levels:

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

*** SCA remains in effect Sunday afternoon & night ***

Sunday...

SW winds increase 15 to 25 kt by this afternoon, with some gusts
possibly up to 30 kt at times. Low vsby in morning fog will improve
during the afternoon.

Sunday Night...

Scattered showers and thunderstorms in the early evening, dissipate
and move out to sea in the late evening. Low clouds and fog fill
back in. Winds remain gusty out of the SW at 15-25 knots. Sea
increase to 5-8 feet.

Monday...

Improving weather, especially vsby in the afternoon along with WSW
winds easing to 15-20 kt.

Outlook /Tuesday through Thursday/...

Monday Night: Winds less than 25 kt. Local rough seas.

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

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain
showers.

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers,
isolated thunderstorms.

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

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 7 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 7 PM EDT this evening for MAZ010-011.
     High Surf Advisory until 7 PM EDT Monday for MAZ020>024.
RI...High Surf Advisory until 7 PM EDT Monday for RIZ006>008.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230-
     250-251.
     Small Craft Advisory until 8 AM EDT Monday for ANZ231.
     Small Craft Advisory until 3 PM EDT Monday for ANZ232>235-237.
     Small Craft Advisory until 9 AM EDT Monday for ANZ236.
     Small Craft Advisory until 9 PM EDT Monday for ANZ254>256.

&&

$$

SYNOPSIS...Nocera/Frank
NEAR TERM...KJC/Nocera/KP
SHORT TERM...Nocera
LONG TERM...Frank
AVIATION...Nocera/Frank
MARINE...Nocera/Frank