-- Discussion containing changed information from previous version are highlighted. --
287
FXUS61 KBOX 131956
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
356 PM EDT Thu Jun 13 2024

.SYNOPSIS...

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Warm and muggy Friday with dewpoints in the 60s. Scattered
severe thunderstorms possible with the passage of a cold front
Friday afternoon and evening. Canadian high pressure will
provide a comfortable Father`s Day weekend along with dry
conditions. Turning unseasonably hot next week as an anomolous
mid-level ridge develops across the eastern third of the
country. Prolonged period of heat and humidly could linger well
into the end of next week.
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&&

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

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Pleasant conditions are expected through the overnight with
early summer like humidity building into the region on southwest
flow. Coastal sea breezes that developed, much to the chagrin
of guidance, will flip back to the SW after sunset this evening.
While dewpoints are already in the mid 60s along the south
coast and Islands, dews will continue to climb overnight to
similar values region wide. Given high dewpoints and SW flow,
saw a bit of marine stratus flirt with Nantucket and Block
Island around the lunch hour. Do expect stratus and fog to
impact the islands and perhaps immediate south coast, especially
around Buzzards Bay, this evening as dews continue to increase.
Fog will be hard to come by away from the immediate coast given
gusty winds, with 925mb LLJ of around 25-30kt, keeping gusts
elevated between ~07-12kt overnight.

So, while mainly clear tonight, dewpoints will be the bound on lows,
which will range in the mid 60s overnight.
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&&

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

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With overnight lows only bottoming out in the mid 60s, temperatures
will very quickly warm into the 80s by late morning, which will
provide a sounding board for convection driven by a cold
front/shortwave crossing the region tomorrow afternoon/evening. As
mentioned by previous shifts, we continue to favor a more linear
convective line compared to discrete cells given deep layer shear
between 30-40kt.

The 12Z HREF provided a window of greatest certainty regarding when
the convective line will begin to impact our northwestern zones, but
uncertainty remains between individual members, with the ARW and FV3
firing off storms as early as 16Z and the NAMNest delaying the
convective potential until as late at 19Z across western MA and
Central CT. While forcing continues to look robust with generous
height falls and reasonably strong jet dynamics, tomorrow`s
convective potential will rely heavily on a narrow band of
instability and timing of the line.

So, lets talk instability. Hi-res and global sounding continue to
portray a rather significant amount of uncertainty regarding how
much fuel will be available. The RAP, perhaps one of our most
aggressive pieces of guidance, depicts and environment of MUCAPE
values exceeding 2000J/kg ahead of the cold front. Conversely,
the NAM and GFS show much more modest instability values ranging
from about 600-1200J/kg MUCAPE, with greater instability to our
north and west across VT and NY. The best lapse rates will also
be to our north and west, but model soundings show that MLLR
may exceed 6.5C/km across the western half of the CWA tomorrow
afternoon (which, for southern New England isn`t too shabby).
MLLR wane quickly approaching the I-95 corridor where they fall
to about 6C/km along the I-495 corridor and less than 5.5C/km SE
of I-95. Given the gradient in both instability and lapse
rates, do expect a rather robust line of convection that will
reach approximately the Worcester area between 22-00Z tomorrow
evening before the line wanes quickly as it progresses
eastward. There remains a distinct possibility that storms decay
so quickly tomorrow evening that places from Boston to
Providence, south and east, see just some light to moderate rain
with any convection dissipating before moving into the more
stable airmass. DCAPE values climbing to near 700J/kg and robust
low level lapse rates continue to pinpoint strong to damaging
wind gusts as the primary severe threat with the convective
line. Temperatures aloft remain too mild for a substantial hail
threat and near zero helicity/0-1km shear quells any tornado
concerns.

PWATs have trended downward compared to yesterday, dropping from
~1.7-1.8" to around 1.5", which is a trend that will, combined with
the lack of training storms, mitigate widespread flooding. Still,
"long skinny CAPE" is supportive of downpours, depicted by the HREF
PMM that highlights pixels of 1.5-2", especially across the CT River
Valley, in some convective cells tomorrow afternoon, which could
generate urban and poor drainage flooding in places like Springfield
and Hartford.

While the primary convective line will wane after sunset, trailing
weak surface low/mid level shortwave will allow some showers to
backfill across the region tomorrow night through early Saturday.
Models are poorly depicting how robust these lingering showers will
be, but ultimately expect them to shift southeast of the region by
12Z. Trough axis clears the region around the same time which will
allow much drier airmass to filter into the region.
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&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...

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Highlights:

* A few showers possible Saturday morning, otherwise a dry and
  comfortable Father`s Day weekend.

* Seasonably warm on Monday, becoming hot and humid Tuesday through
  the end of next week with heat indicies potentially reaching
  between 95F and 104F.

* Early summer heat could challenge daily record high temperatures.


Father`s Day Weekend...

Few showers linger Saturday morning, mainly across southeastern
Massachusetts and Rhode Island as a mid-level trough moves east and
away from the region. By no means a washout for Saturday, PWATs fall
dramatically as Canadian high pressure moves into the area. This
yields a comfortable air mass, dewpoints fall from the 50s into the
40s! As for highs, low to mid 70s near the coast and upper 70s to
low 80s inland. Overnight into Sunday morning will be cooler, given
the dry atmosphere and weaker wind fields, should have effective
radiational cooling for many locations, thus have deviated away from
the NBM and favored the cooler MAV and MET blend. Areas like KORE
could experience morning lows in the low 40s! Elsewhere, low
temperatures are expected to drop to the upper 40s and low 50s along
the coast, the exception would be Boston, where lows are generally
in the mid 50s. Comfortable conditions follow on Father`s Day, with
mainly sunny conditions thanks to high pressure, low humidity values
and highs in the mid 70s to 80 degrees.

Next Week...

As advertised, we continue to expect well above normal temperatures
heading into next week. Starting Monday, mid-level high pressure
should be located over the southeast, leading to increasing mid-
level heights across the northeast. Could be a rouge shower Monday
afternoon with shortwave energy passing to our north, albeit a low
chance at this point. Highs warm into the low and middle 80s.

Tuesday into Thursday, the mid-level high expands into the northeast
with continued signals this will be an anomolous event. NAEFS
ensemble situation table indicates the 500mb heights and surface
temperatures could exceed forecast model climatological reference
points, in addition to PWATs nearing 97th to 99th percentile!

So, hot and humid conditions are expected with peak intensity around
Wednesday and Thursday. Given this is still a week away, there is
still time to iron out off the wrinkles/details. Additionally, there
are high probabilites, greater than 60 percent, that highs could
exceed 90 degrees across northern Connecticut, the majority of
Massachusetts (away from the southeastern portion of the state, Cape
Cod, and the Island), and northern Rhode Island starting Tuesday,
with the peak Wednesday, Thursday, and Friday. It is not out of the
question a few spots could reach 100F from Wednesday to Friday.
There are low probabilities on DESI, around 20 to 40 percent, for
areas such as the northern Connecticut River Valley and Merrimack
Valley. Likely will challenge daily record highs, see the climate
section for those details.

This period appear more dry than not, but with a juiced up atmosphere
and a few bouts of shortwave energy passing through, can`t rule out
pop-up showers during this period as well.
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&&

.AVIATION /20Z THURSDAY THROUGH TUESDAY/...
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Forecast Confidence Levels:

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

20z TAF Update...

Through tonight: High Confidence

Coastal sea breezes will dissipate near sunset with dominant SW
flow takign hold overnight. Gusts will remain between 10-15kt.
Saw some stratus and fog flirt with the islands around lunchtime
on Thursday, and with dewpoints surging into the mid 60s and
strong SW, do expect it to redevelop tonight at least at
Nantucket, with greater uncertainty for Cape terminals. Fog
unlikely across the interior.

Tomorrow: Moderate Confidence

VFR and dry in the morning with southwesterly flow.
Thunderstorms will develop across eastern NY and Western MA and
CT in the mid to late afternoon. Thunderstorms then move east
and begin to weaken in the evening. Some storms may have strong
winds and torrential rainfall. High confience in impact to
western terminals, low confidence in thunder at BOS and PVD as
storms will wane very quickly as they approach the coast around
sunset. Winds shift the W/NW behind frontal passage.


Tomorrow Night: Moderate Confidence

Convection dissipates quickly after 00Z, but lingering shower
activity will backfill across the region, pulling east from
about ORH to the Cape betwen 06-12Z. Will see a period of lower
cigs associated with these showers but do not expected
tremendous vsby reductions. VFR redevelops from west to east
early Saturday morning.

KBOS TAF...Moderate confidence in TAF.

High confidence in VFR throgh 16Z tomorrow, lesser confidence in
convective potential tomorrow evening as storms weaken.
Seabreeze dissipates with sunset this evening, with winds SW
10-20kt head of cold front. Winds shift to the W/NW behind the
frontal passage tomorrow evening. MVFR to possible IFR in
showers and potential thunderstorms.

KBDL TAF...High confidence in TAF.

VFR through tomorrow morning, with strong line of thunderstorms
impacting the terminal between 17-21Z, though confidence is
moderate on exact timing. Winds SW around 10 kt until frontal
passage when winds become more W/NW. MVFR to even IFR possible
in passing storms.

Outlook /Saturday through Tuesday/...

Saturday: VFR. Slight chance SHRA.

Saturday Night through Tuesday: VFR.
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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.

Tonight through Friday Night...

Areas of marine stratus and fog are possible overnight into Friday
morning, this likely will reduce visibilities to less than one-half
mile at times. Surface high pressure moves off shore Friday
afternoon with the approach of a strong cold front. Ahead of the
front, periods of gusty south/southwest winds produce locally
stronger gusts, around 25 knots, for the northeast waters off the
coast of Cape Ann. Have held off on issuing a SCA at this time, do
think the window for this to occur is during the early afternoon, if
confidence in stronger gusts increases a SCA may become needed.
Showers and thunderstorms possible Friday afternoon and evening,
with rain lingering into Saturday morning. Seas tonight into Friday
are between 2 and 3 ft, but building to 3 to 4 ft for northeast
waters, with potential to reach 5 ft on the outermost waters. Seas
diminish Friday night into Saturday to around 2 to 3 ft.
Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers.

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

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

Sunday Night through Tuesday: Winds less than 25 kt.
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&&


.CLIMATE...

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Daily Record High Temperatures...

Tuesday, June 18th

BOS - 94F (1929)
BDL - 95F (1994)
PVD - 94F (1929)
ORH - 93F (1929)

Wednesday, June 19th

BOS - 96F (1923)
BDL - 95F (1995)
PVD - 94F (1923)
ORH - 93F (1923)

Thursday, June 20th

BOS - 98F (1953)
BDL - 97F (2012)
PVD - 95F (1941)
ORH - 93F (1953)

Last Day of 100F (or greater)

BOS - 100F (07/24/2022)
BDL - 100F (07/21/2019)
PVD - 100F (07/28/2020)
ORH - 102F (07/04/1911)
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&&


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

&&

$$

SYNOPSIS...Dooley/KS
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...Dooley
AVIATION...KS
MARINE...Dooley
Climate...Dooley