BOX issues Area Forecast Discussion (AFD) at Jul 29, 3:19 AM EDT326
FXUS61 KBOX 290719
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
319 AM EDT Mon Jul 29 2024
.SYNOPSIS...
Occasional showers and a few thunderstorms with localized downpours
are expected today as an upper level low pressure moves across the
region. It is trending drier for Tuesday before more widespread
showers and scattered thunderstorms develop on Wednesday as another
system moves through. It then turns hot and humid for Thursday
through next weekend, but an unsettled weather pattern will continue
with chance of showers or thunderstorms at times.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Forecast overnight behaved well with the south coast/Cape and
Islands cashing in on more than an inch of rain, with much lesser
amounts observed from the PVD to HFD line, north.
No better way to describe the next 12-16 hours than unsettled with
surface low pressure to our east and the mid level cutoff
centered directly overhead. This setup will yield waves of
widespread showers for the daylight hours. Do anticipate
downpours will develop at times, with PWATs as high as 1.8", and
warm cloud depths around 11,000-12,000ft. Additionally, there
will be modest instability today that may be supportive of some
isolated thunderstorms, but given a total lack of bulk shear,
generally less than 20kt, and very poor mid level lapse rates
(less than 6C/km), anticipate it will be difficult to sustain
any sort of organized convection across any given location for
an extended period of time. Given the aforementioned parameters,
not particularly keen on any sort of severe weather this
afternoon.
Will note that while confidence is pretty low in the exact location
of showers at any given time, the overnight hi-res guidance appeared
to have confidence that downpours and isolated thunder would be most
likely across western MA and CT; generally where instability is
greatest this afternoon. Overall, the thought is that most areas
will see an additionally 0.1-0.25" of QPF today thanks to
intermittent showers, but isolated convective downpours could drop a
quick inch or two of rain somewhere in our CWA this afternoon. For
what its worth, the HREF LPMM places the threat for greater than 1"
of QPF today over the Springfield/Chicopee area.
In any case, do expect showers to wane closer to sunset as low
pressure continues to move into the Gulf of Maine.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
With the surface low moving to our northeast, will see shower
chances decrease overnight. Winds will shift to the south region
wide, which will begin a long period of building humidity this week.
Do anticipate that, given residual moisture from showers and
increasing moisture on southerly flow, we'll have fog develop along
the south coast, as well as across the CT River Valley. It will be
more mild overnight tonight, thanks to increasing dewpoints, with
lows generally in the upper 60s to near 70F.
Mid level low is slow to shift north of our region on Tuesday, so
while we'll be "out of the woods" when it comes to any showers
generated by the surface low, do anticipate some cold pool showers
will develop by Tuesday afternoon, particularly across western MA
and CT. Will note it wont be a washout of a day, and showers will be
much less widespread tomorrow compared to Monday. The best chance
for some afternoon sunshine will come across SE MA, away from the
greatest instability. Dewpoints will again grow to uncomfortable
levels, greater than 70s, by Tuesday afternoon. Highs will top out
in the 80s region wide.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights...
* Oppressive humidity with widespread showers and scattered t-storms
Wednesday. Locally heavy rainfall is the primary threat
* Drier Thursday, then unsettled pattern Friday through the weekend
with chance of showers or thunderstorms at times
* Hot and humid conditions Thu through the weekend with heat indices
in the mid-upper 90s possible
Details...
Tuesday night and Wednesday...
A more robust mid-upper level trough will be moving into New Eng
late Tue night into Wed. Modest forcing for ascent ahead of this
system acting on anomalous PWAT plume of 2 to 2.25 inches will
result in widespread showers developing and moving into western New
Eng late Tue night before overspreading rest of SNE during Wed. Mid
level lapse rates are poor but high dewpoints and diurnal heating
will help to contribute to moderate instability with potential for
SBCAPES 1000-2000 J/kg so expect scattered t-storms to develop.
However, lots of cloud cover could limit instability somewhat. Severe
weather threat appears low at this time due to unfavorable low and
mid level lapse rates which will limit updraft strength, and deep
layer shear is relatively weak around 20 kt. Locally heavy rainfall
is the greater risk given high PWATs and warm cloud depths around
13k ft leading to very efficient warm rain processes. Cloud cover
will limit how warm it will get, with expected highs in the upper
70s and lower 80s. But humidity levels will be oppressive as
dewpoints climb into the low-mid 70s.
Showers could linger into Wed evening, but do expect a drying trend
overnight as weak front pushes offshore.
Thursday through Sunday...
Forecast is trending drier on Thu as the upper trough begins to push
to the east, but timing of when this occurs will determine if Thu
ends up a dry day. We trended drier and lowered PoPs to 10-20
percent, but if the upper trough is slower to depart the risk for
showers and storms would continue into Thu, mainly in the east. The
forecast details for Thu still have to be worked out. Higher
confidence in temps reaching upper 80s and lower 90s Thu as 850 mb
temps approach 18C. Humidity will remain high but likely a bit lower
than Wed as PWATs temporarily drop leading to afternoon dewpoints
upper 60s to lower 70s. Heat indices will reach the mid 90s.
Then forecast confidence is low for Friday through next weekend due
to uncertainty in the upper level pattern and timing and amplitude
of approaching shortwaves from the Gt Lakes. The pattern looks
unsettled as showers and t-storms will be possible as shortwaves
approach but plenty of dry periods as well, especially behind these
shortwaves. Exact timing of these features will determine when the
best chance of showers are. Ensemble mean 850 mb temps 18-19C so hot
and humid conditions likely to continue Fri through the weekend with
persistent dewpoints in the lower 70s and temps upper 80s and
lower 90s leading to heat indices into the mid-upper 90s.
&&
.AVIATION /07Z MONDAY THROUGH FRIDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z Update:
Really tricky forecast today regarding coverage of rain
showers/isolated thunder chances given upper low is directly
overhead. Unfortunately for most sites, its going to be
VCSH/-SHRA through at least 20Z this evening. Do think better
chances for thunder/heavy downpours this afternoon across the CT
River Valley (BAF/BDL) but confidence too low to include any
deviation from VCSH/-shra in the TAF.
Generally MVFR east to VFR west, though isolated pockets of IFR
are possible across the Cape. Boston will go down to MVFR after
13Z today. MVFR will gradually retract to the northeast as low
pressure pulls to the northeast later this evening.
Winds will shift from the E/NE to more S/SW as low pressure
moves up the eastern MA coast today. Gusts will subside this
morning with 15-20kt gusts mainly isolated to the Cape.
Tonight...
Patchy fog possible thanks to residual moisture. Should see MVFR
to IFR develop away from the coastal plain, almost a complete
flip from conditions during the daylight hours. Persistent
southerly flow expected. Isolated to scattered showers may
persist across the interior.
Tomorrow...
Scattered showers and isolated thunderstorms again possible,
though the greatest chance for additional precipitation will be
across northwestern MA. IFR/MVFR will improve to VFR. Southerly
winds continue.
KBOS TAF...Moderate confidence in TAF (40 percent). Showers
possible at any point today. VFR through 13Z. MVFR 13-20Z,
improving to VFR after 20Z. Shower chances diminish this evening.
E/NE winds become southerly as low pressure moves into the Gulf
of Maine. Southerly flow persists for the foreseeable future.
KBDL TAF...Moderate confidence in TAF (60 percent). Showers
possible all day, cant rule out an isolated rumble of thunder.
Generally VFR until late tonight when MVFR develops. Shower
chances less but still present on Tuesday.
Outlook /Tuesday Night through Friday/...
Tuesday Night: Mainly VFR, with local IFR possible. Chance
SHRA, isolated TSRA.
Wednesday: Mainly MVFR, with local IFR possible. Breezy. SHRA
likely, chance TSRA.
Wednesday Night: VFR. Chance SHRA, slight chance TSRA.
Thursday: VFR. Slight chance SHRA, isolated TSRA.
Thursday Night: VFR.
Friday: VFR. Chance TSRA, slight chance SHRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Overall high confidence.
Scattered showers expected today as low pressure pulls north
into the Gulf of Maine. Winds diminish this afternoon and shift
to W/SW behind departing low pressure as it heads to our north.
Showers become less numerous overnight and on Tuesday. Some
coastal fog is likely due to southerly winds and increasing
dewpoints.
Residual swells along the eastern coast will remain near 6ft
this afternoon and into early evening. Small crafts remain in
effect for most of the outer waters and the northeast inner
waters.
Outlook /Tuesday Night through Friday/...
Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers, isolated thunderstorms.
Wednesday through Wednesday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain showers, slight chance
of thunderstorms.
Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Thursday Night through Friday: Winds less than 25 kt.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Surf Advisory until 6 PM EDT this evening for MAZ007-015-
016-019-022.
RI...None.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
ANZ232>235.
Small Craft Advisory until 8 PM EDT this evening for ANZ250-
254>256.
Small Craft Advisory until 1 PM EDT this afternoon for ANZ251.
&&
$$
SYNOPSIS...KJC/KS
NEAR TERM...KS
SHORT TERM...KS
LONG TERM...KJC
AVIATION...KS
MARINE...KJC/KS
Source:
BOX issues Area Forecast Discussion (AFD) at Jul 29, 3:19 AM EDT----------------
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