BOX issues Area Forecast Discussion (AFD) at Jul 23, 1:31 AM EDT890
FXUS61 KBOX 230531
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
131 AM EDT Tue Jul 23 2024
.SYNOPSIS...
A few isolated showers or thunderstorms in the interior this
afternoon. The weather pattern turns more active tonight with
the first in a series of storm systems and increasing humidity
through Thursday. Things dry out Friday through the weekend with
a return of hot and humid conditions.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
930 PM Update:
Light returns on radar have begun to overspread southern CT and
RI but with dewpoint depressions between 4-14F no observation
site in our CWA is reporting precipitation as of the top of the
hour.
With that said, a more robust precipitation shield has its eyes
on the Cape and Islands as we do expect rain to begin to fall,
especially on Nantucket, over the next couple of hours.
350 PM Update:
Highlights:
* Pop-up showers and thunderstorms this afternoon.
* Additional rain and thunderstorms overnight may lead to localized
flash flooding for portions of southern New England. Also there is
a low severe weather threat around sunrise Tuesday.
This afternoon: Storms have begun to fire along a quasi-stationary
front extending from southwest Connecticut through Rhode Island and
out to Cape Cod. As we head into this afternoon we expect a few more
widely scattered storms to develop along this boundary, with activity
diminishing after sunset. That said, more rain is anticipated
overnight into Tuesday morning, more on that in a moment.
As with past two days, storms should remain below severe criteria
given the poor mid-level lapse rates and lack of effective shear. A
few storms could produce a few stronger gusts of 40 mph, but for the
majority should be garden variety thunderstorm. That said, these
storms are capable of producing lightning and if you can hear
thunder roar, head indoors! Rest of the afternoon features
increasing cloud cover with warm temperatures in the mid 80s.
Overnight through Tuesday morning: Given the increased clouds, a
mild night with lows 70s to upper 60s. The active weather continues
into the predawn hours of Tuesday with two threats, potential for
tropical rains leading to localized flash flooding and a low threat
for severe weather. Let's breakdown those for you.
Flash Flood Potential: Tropical-like atmosphere with anomolously
high PWATs could lead to locally heavy rain fall across the south
coast of Rhode Island and Massachusetts. There is uncertainty with
exact track of the surface low and how the ongoing convection is
playing into the model output. But what we do know, BUFKIT soundings
have a warm cloud depth across parts of southern New England between
12,000 and 15,000 feet, which are efficient rain producers. Given
this setup, did collaborate with WPC to have parts of the region
included in a Marginal ERO overnight. The current track of the low
gives the greats threat to for flooding rains over Cape Cod and the
adjacent Islands, and a bullseye at Nantucket. Timing of the
heaviest rain is between 4am and 10am with improvements from
southwest to northeast.
Guidance has trended north the past 24 hours, bringing the heaviest
rainfall closer to southern New England. Will need to continue to
monitor tonight 00z model run if the surface low trends further
north, it it does there could be issues for the urban centers of New
Bedford, Fall River, and Providence.
Areas along and northwest of the I-95 receive least amount of rain,
around 0.25 to 0.5 inch, while Boston and points north may see even
less in the way of rain, less than 0.25 inch. Heaviest rain leading
to higher totals for the south coast, Cape, and Islands range
between 0.75 to 1.5 inch, with localized amount near 3 inches
possible at Nantucket. Have held off on a Flood Watch as flash flood
guidance is between 4 to 6 inches in 6 hours.
Severe Weather: Environment is also favorable for a short-lived
tornado early Tue morning near Cape Cod and Islands (and waterspouts
over south coastal waters). High-res models show plenty of
instability and shear in lowest levels with 0-3km CAPE well over 100
J/kg, 0-500m SRH near 200 m2s2, and LCLs down to 500m. These
parameters are well within the values that we often see with
tornadoes in southern New England. Some question as to whether or
not enough buoyancy will be present to sustain updrafts so it's not
a certainty, and HREF keeps higher updraft helicity values well
south of New England, but it's certainly something to keep an eye on
from roughly 5 AM to 9 AM Tue.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
350 PM Update:
Tuesday and Tuesday Night:
Showers ending my mid morning, with a drying trend for much of the
afternoon as there is mid-level ridging. A rouge thunderstorm not
out of the question as there are fairly high PWATs and a weakly
forced environment. Muggy with high dew points in the upper 60s to
low 70s, although with cloudy skies, highs are only in the upper 70s
to low 80s. Another shortwave and weak low moves through Tuesday
night into Wednesday morning and brings renewed rain chances.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
350 PM Update:
Wednesday and Thursday
The forecast continues to support unsettled weather Wednesday and
Thursday as additional disturbances progress over southern New
England in a tropical like environment. On Wednesday, PWATs rise to
values above 2.25 inches across southeastern MA and Rhode Island
ahead of a weak short-wave trough embedded in the broader deep
southwesterly flow. Model guidance is hinting at a period of
scattered showers and thunderstorms Wednesday morning into early
Wednesday afternoon. Heavy downpours will be a concern for the south
coast, Cape, and Islands for a second consecutive day as modest
instability and a deep warm cloud layer should support efficient
rainfall processes. Ensemble guidance is suggesting the potential
for widespread 0.25 to 0.75 inches of accumulated rainfall with
locally higher amounts from 1 to 2 inches in heavy
downpours/embedded thunderstorms. Confidence in the location of
heaviest rainfall is low given the weak forcing/tropical nature of
this disturbance, but we should have more details as we get into the
HREF window in the next 12 to 24 hours. Shower and thunderstorm
activity should diminish by Wednesday evening leading to a brief dry
period for much of the region through Thursday morning.
By Thursday afternoon, a cold front is progged to push through
southern New England triggering another round of scattered showers
and thunderstorms. There is a low risk for storms to become strong
to severe as there will be modest CAPE (MLCAPE 500-1000 J/Kg) and
sufficient deep layer shear up to 40 knots. Lapse rates will be
somewhat favorable as well with steep low-level lapse from 7 to 9
C/km and even mid-level lapse rates may approach favorable values
between 6 and 6.5 C/Km in the 700-500 hPa layer. CSU machine
learning probabilities currently indicating a 5 to 15 percent chance
for severe weather across much of The Northeast and MidAtlantic
between Thursday and Friday morning. As with Wedneday's system,
we'll have more information later this week as we get into the
window of the more detailed hi-resolution model guidance.
Friday through Early Next Week
High pressure and an associated upper-level ridge build in behind
Thursday evenings cold front. This will support drier/sunnier
conditions as we head into the weekend. The upper-level ridge and
associated high pressure will support sunny, hot, and dry
conditions through early next week with high temperatures slightly
above normal through the weekend.
&&
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z TAF Update...
Tonight... Moderate Confidence.
VFR, becoming MVFR and IFR. SHRA developing from west to east
between 03z and 06z and TSRA possible across south coastal terminals
between 08z and 10z, with the greatest confidence for thunder at the
Cape and island terminals, as well as terminals along the immediate
south coast, KWST, KUUU, and KEBW. Winds overnight start off south
becoming east/southeast by daybreak. Localized stronger gusts are
possible within embedded thunderstorms.
Through Today... Moderate Confidence.
Rain showers overspread southern New England this morning with
the heaviest rain, and embedded thunder, focused south and east
of the I-95 corridor thru 15Z. VFR becoming MVFR to IFR/LIFR in
rain showers. Some improvement to VFR possible across the
interior after 15Z as clouds scatter out, with MVFR to IFR
expected across the Cape and Islands. E/NE winds gusting to
10kt.
Tuesday Night... Moderate Confidence.
MVFR to IFR, SHRA and isolated TSRA possible though
will be focused across interior southern New England. Winds are
southeast less than 10 knots. VFR becoming IFR to LIFR
overnight.
Wednesday... Moderate Confidence
Showers and isolated TSRA possible again on Wednesday, as low
pressure tracks south of the Islands. Heaviest rain again
centered over the Cape/Islands with more spotty precip expected
for the interior. Winds again generally less than 10kt. Gradient
of MVFR (west) to IFR/LIFR (east).
KBOS TAF... Moderate confidence in TAF.
Unsettled period with variable flight categories thanks to
several rounds of showers through Wednesday. Heaviest rain and
thunder risk generally remains SE of the terminal but can't rule
out some isolated pockets of thunder. MVFR develops with perhaps
some brief periods of VFR this afternoon as cloud scattered. IFR
to LIFR tonight into Wednesday with another round of showers.
KBDL TAF... Moderate confidence in TAF.
Ceilings lower to MVFR after 06z with the arrival of -SHRA,
lowering to IFR by 09z. Light south winds becoming light
east/northeast overnight into Tuesday. -SHRA ending after 10z
with vicinity showers possible through 12z. MVFR ceilings
continues through the morning push with a trend to VFR after
18z.
Outlook /Wednesday Night through Saturday/...
Wednesday: Mainly MVFR, with areas IFR possible. SHRA likely,
isolated TSRA.
Wednesday Night: Mainly VFR, with local IFR possible. Chance
SHRA, isolated TSRA.
Thursday: Mainly VFR, with local MVFR possible. Chance SHRA,
isolated TSRA.
Thursday Night: VFR. Chance SHRA, isolated TSRA.
Friday through Saturday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight...High Confidence.
A few spot showers this afternoon, increasing chances of rain
tonight as weak low pressure system exits the Mid Atlantic coast
and moves towards southern New England. Seas 2-3 feet.
Tuesday and Tuesday Night...High Confidence.
Showers and thunderstorms exiting the waters by late
morning/early afternoon. A second round of showers and storms
arrive Tuesday night into Wednesday morning. Seas 2-4 feet.
Outlook /Wednesday Night through Saturday/...
Wednesday through Wednesday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. Chance of rain showers, isolated
thunderstorms.
Thursday through Thursday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain showers, isolated
thunderstorms.
Friday: Winds less than 25 kt. Seas locally approaching 5 ft.
Friday Night through Saturday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Dooley/RM
NEAR TERM...Dooley/KS/JWD
SHORT TERM...Dooley
LONG TERM...RM
AVIATION...KS
MARINE...Dooley/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Jul 23, 1:31 AM EDT----------------
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