BOX issues Area Forecast Discussion (AFD) at Jul 11, 7:56 PM EDT936
FXUS61 KBOX 112356
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
756 PM EDT Thu Jul 11 2024
.SYNOPSIS...
Mainly dry and sunny Friday outside a few isolated showers and
thunderstorms possible during the afternoon. A frontal boundary
dropping south will bring showers and embedded thunderstorms to the
region sometime Friday night into Saturday with localized torrential
rainfall possible. Hot and humid weather returns for Sunday
into at least the middle of next week leading to high heat
indices. Heat-related headlines are likely to be needed for
portions of this period of time. While Sunday is dry, the risk
for daily thunderstorms increases Monday through Wednesday.
&&
.NEAR TERM /THROUGH FRIDAY/...
750 PM Update:
A humid but generally tranquil evening for most of Southern New
England, with a bit of a SWly breeze. The exception is on Cape
Cod and the Islands where a narrow stream of low clouds has
developed with intervals of mist and hit-or-miss light showers.
This is associated with a stalled frontal boundary that is
expected to shift back northwestward tonight and overnight.
This area of lower cloud cover and mist over Cape Cod and the
Islands should gradually expand in areal coverage over the
broader waters and also northwestward towards the Providence to
Plymouth corridor in southeast New England thru the early morning
hrs. There may be some spotty widely scattered showers but
should see more of those showers closer to morning. But
otherwise, remainder of Southern New England should be clear and
dry but still quite humid.
Previous discussion:
Tonight
Very subtle upper level ridge passes overhead overnight with the
stalled front still sitting offshore near the Cape and the Islands.
With very dry midlevel, and dropping dewpoints at the surface, skies
should remain clear overnight with the exception of the Cape and
Islands due to the stalled front. Overnight lows still remain above
normal in the upper 60s to low 70s even with clear skies and
decreasing winds across the interior.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH 6 PM FRIDAY/...
Tomorrow
The stalled front retrogrades back inland tomorrow as a weak
shortwave traveling through the SW flow approaches the region from
the south. This could set off a couple of isolated showers and
thunderstorms in the late morning to early afternoon with MUCAPE
values AOA 1000 J/kg. There is little to no sfc-6km shear with weak
mid level lapse rates which will keep severe weather from occurring
with any thunderstorms that form. There could be some heavy rain
with any showers or thunderstorm with PWATS around 1.8-2.0 inches
and warm cloud depths around 11kft. With little to no shear,
updrafts will not be able to sustain themselves for long or cause
training, therefore, not expecting a flash flood threat. High temps
tomorrow remain in the mid to upper 80s with dewpoints increasing
back into the low 70s.
Tomorrow Night
The weak shortwave in the SW flow moves through overnight along with
increasing moisture. Widespread rain with embedded thunderstorms are
possible overnight, however, guidance remains mixed on exact timing
and placement, with some hi-res guidance showing rain holding off
until late Saturday morning. With PWATS increasing AOA 2.0 inches
and better forcing to bring possibly multiple rounds of heavy
showers and thunderstorms, flash flooding could become possible
esspically in urban and poor drainage areas. Overnight lows continue
the above normal trend stay in the low 70s region wide.
&&
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Highlights:
* Showers and embedded t-storms continue into Sat; heavy downpours
with potential for localized flash flooding is possible, but still
uncertain which area(s) may see the heaviest rains. Humid but not
as warm (highs mid 80s).
* Hot and Humid weather returns Sunday through Wed, with high heat
indices looking likely. Heat headlines seem likely to be needed
for portions of this timeframe.
* Dry weather most of the time, but a risk for daily t-storms
Mon thru Wed, lingering into southeast New England Thurs.
Details:
Saturday:
Carrying over from Fri evening, Sat looks generally active as a
deamplifying shortwave disturbance over the Gt Lakes region
interacts with disorganized subtropical energy from the northern
Bahamas. Substantial moisture advection (PWAT values 2 to 2.25" per
model ensemble consensus, which is about 2 to 3 standard deviations
above normal) will be associated with this interaction and favor
periods of rain, some locally heavy at times. Rather deep warm cloud
depths favoring efficient warm-rainfall processes as well as the
passage of a 300 mb jetstreak of 60 kt, with Southern New England
placed in the equatorward entrance region of that jet leading to
some enhancement to upward vertical motions, are factors which could
favor heavy rain in some areas. From a synoptic perspective, it
seems to be a pattern favorable for heavy rainfall somewhere in the
region; this is seen by some pretty notable QPF bullseyes in the
deterministic solutions. However there still is a bit of uncertainty
on where the heaviest rains would be more favored; GEFS/EPS ensemble
QPF percentiles and probabilities seem to favor the western MA/CT
area in particular, but there are still some members which bring
local maxima in rainfall to central and southeastern portions of
Southern New England. PoPs were increased into the Likely range for
Sat with a gradual shift south and east through the daytime hrs,
while generally drying out/shifting into the coastal waters by
evening. It looks to be a pretty soggy start to the weekend, and
while temps are in the mid 80s, dewpoints in the mid 70s will make
it continue to feel quite muggy.
Sunday through Thursday:
Very warm to hot and humid weather again resumes for this period.
Steady warming trend to temperatures are expected, with the peak of
the heat being on Tue. It is looking like high temps are in the
lower to mid 90s (low to mid 80s South Coast, Cape and Islands) with
dewpoints in the mid 60s to lower 70s, leading to the risk for high
heat indices. At the moment it is looking like heat indices could
reach levels which would support heat headlines being needed, with
little nighttime relief. While Sunday looks generally dry, there is
potential for t-storms Mon thru Wed. It isn't clear if severe
weather is favored in that timeframe, although the trained machine
learning datasets from Colorado State show lower probs for severe
weather in the Days 5-7 period. This added cloud cover could add a
level of uncertainty as to how high heat indices get; regardless,
hot and humid weather resumes with heat indices also on the rise for
late in the weekend into at least the middle portion of next
week.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight: High confidence.
VFR for the interior to about I-95. MVFR-LIFR stratus over the
Cape and Islands to gradually expand northwestward, especially
after 04z, moving into the PVD-PYM corridor toward daybreak.
Initial hit or miss showers should increase a bit more in
number for these southeastern terminals by daybreak. SW winds
begin around 10-15 kt with gusts 20-24 kt, though should stand
to decrease to around 6-12 kt overnight.
Friday...Moderate Confidence
VFR with the exception for the Cape and Islands once again could
still be stuck in MVFR/IFR. Low chance for isolated showers and
thunderstorms in the afternoon.
Friday Night...Low Confidence
MVFR with localized IFR possible. Widespread rain and
thunderstorm chances increase towards morning.
KBOS TAF...Moderate confidence in TAF.
VFR today with gusty SSW winds up to 25 knots. Winds remain SSW
but gradually decrease this evening, but become gusty again
tomorrow afternoon up to 20 knots. Low chance for a shower or
thunderstorm tomorrow afternoon
KBDL TAF...Moderate confidence in TAF.
VFR today and tonight with gusty SSW winds. Winds diminsh
tonight but could become gusty again tomorrow afternoon. Low
chance for a shower or thunderstorm tomorrow afternoon.
Outlook /Friday Night through Tuesday/...
Friday Night: Mainly VFR, with local IFR possible. Chance SHRA,
isolated TSRA.
Saturday: MVFR/IFR conditions possible. Chance SHRA, slight
chance TSRA.
Saturday Night: VFR. Slight chance SHRA.
Sunday through Sunday Night: VFR.
Monday: VFR. Breezy. Slight chance SHRA, isolated TSRA.
Monday Night through Tuesday: VFR. Breezy. Slight chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Marine
Tonight though Tomorrow Night
Winds remain gusty out of the SSW tonight up to 25 knots through
tomorrow afternoon. Waves begin decreasing through tomorrow night
back to 4-5 feet for the outer waters, and 2-3 feet for the
near coastal waters. With decreasing waves, will allow the high
surf advisory to expire tonight and will not reissue for
tomorrow.
Outlook /Friday Night through Tuesday/...
Friday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.
Saturday: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.
Sunday through Sunday Night: Winds less than 25 kt. Seas
locally approaching 5 ft.
Monday: Winds less than 25 kt.
Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft.
Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Heat Advisory until 8 PM EDT this evening for MAZ005>007.
High Surf Advisory until 8 PM EDT this evening for MAZ020-
022>024.
RI...High Surf Advisory until 8 PM EDT this evening for RIZ006>008.
MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ230-
231-251.
Small Craft Advisory until 11 AM EDT Friday for ANZ232>235-237.
Small Craft Advisory until 8 PM EDT this evening for ANZ236.
Small Craft Advisory until 8 AM EDT Friday for ANZ250.
Small Craft Advisory until 9 PM EDT Friday for ANZ254>256.
&&
$$
SYNOPSIS...Loconto/KP
NEAR TERM...Loconto/KP
SHORT TERM...KP
LONG TERM...Loconto
AVIATION...Loconto/KP
MARINE...Loconto/KP
Source:
BOX issues Area Forecast Discussion (AFD) at Jul 11, 7:56 PM EDT----------------
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