BOX issues Area Forecast Discussion (AFD) at Aug 1, 1:56 AM EDT927
FXUS61 KBOX 010556
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
156 AM EDT Thu Aug 1 2024
.SYNOPSIS...
Very warm and humid weather with full sun is expected Thursday
and Friday, with generally dry weather. Still very warm and
humid this weekend, but with daily shower and thunderstorm
chances.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
2 AM Update:
Mid level trough and associated surface wind shift moving
through SNE early this morning. Slightly drier/not as humid
airmass advecting in from the west, with dew pts dropping off
into the 60s across NYS. Clouds are eroding across SNE, except
along the south coast of MA/RI, where low clouds and areas of
fog are impacting this area. Slow improving trends toward
sunrise, along with dry weather prevailing.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/...
340 PM Update:
Thursday and Thursday Night:
Upper trough moves northeast early on Thursday, with weak
subsidence/height rises most of the day. This will allow for more
sun than the past couple days, very warm temperatures, with modest
westerly winds. There could be a spot shower during the afternoon
but the vast majority of the area is dry.
Heat and humidity will be the main story for Thurs, with rising heat
indices. High temps should rise into the mid 80s to lower 90s.
However the strong heating should allow for more mixing (as
indicated by multiple models) and with westerly downsloped flow,
dewpoints seem likely to drop (potentially into the mid 60s) as peak
heating occurs. The NBM's handling of dewpoints seems curious and
likely too high in light of this, as it shows dewpoints in the low
to mid 70s despite westerly flow. It still will be humid, but not to
the degree of the past couple days. Heat indices on Thursday thus
look to peak in the lower to a few areas in the mid 90s. After
coordination with ALY, GYX and OKX, given the mixing we all agreed
to refrain on heat headlines at this time. We'll need two days of at
least 95+ heat indices, and it will be close but we may end up
falling just short of that if dewpoints do mix lower on the basis of
today's guidance. However we still encourage appropriate heat-
related precautions. Drier weather is expected to continue into
Thursday evening, though still fairly muggy with lows in the mid 60s
to low 70s.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Friday through Sunday
A mid-level ridge axis builds east of southern New England during
the day Friday. Increasing south/southwest winds will support
increasing temperatures and humidity which will support heat indices
in the mid to upper 90s for much of southern New England. Height
rises and weak surface high pressure should support mostly dry/sunny
conditions on Friday afternoon, but can't rule out late afternoon
shower or thunderstorm across western MA and CT ahead of the next
approaching batch of short-wave energy. If we exceed 95 degree heat
indices on Thursday, we may get to heat advisory criteria on Friday
with a second consecutive day of 95+ degree heat indices. A tricky
part of the forecast will be the coastal locations where a sea-
breeze may keep the coastal areas including Boston a bit cooler.
Nonetheless, dewpoints are forecast to be in the upper 70s which
will support oppressive humidity regardless of how high surface
temperatures can rise.
As we head into the weekend, a short-wave trough will approach
southern New England and support a cloudy/unsettled day on Saturday.
Scattered showers and thunderstorms will be in the cards with the
potential for heavy downpours with PWATs over 2 inches. There is
forecast to be a modest amount of shear with 20 to 30 knots in the 0-
6 km layer, but a lack of steep mid-level lapse rates and strong
synoptic forcing should fend off any substantial severe weather
threat. Details with respect to timing and location of showers and
storms are vague given the weakly forced summertime pattern, but we
should have more details as we get into the hi-res model window
later this week. Saturday may feature another round of heat indices
in the low to mid 90s.
The aforementioned short-wave trough axis progresses east across
southern New England during the first half of Sunday. This may
result in more scattered showers and thunderstorms Sunday morning
into perhaps early Sunday afternoon, but the latest suite of
ensemble guidance supports this disturbance getting east of the
region by Sunday afternoon, so we should be trending toward drier
conditions as the weekend comes to a close.
Monday through Wednesday
We will trend toward drier conditions early next week as more zonal
flow aloft should support periods of westerly winds that will rid
southern New England of the tropical air mass that will be in place
through much of the weekend. After a dry/seasonable start to next
week with temperatures in the low to mid 80s,a renewed southwest
flow regime may bring another round of humid/unsettled weather by
mid-week.
&&
.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06Z TAF Update:
Thursday...high confidence.
VFR, except IFR/LIFR along the south coast, including Cape Cod
and Nantucket, but improving to VFR by mid morning. SW winds
10-15 kt becoming west after sunrise. Very low probability
(10-15%) of an isolated shower, otherwise dry weather prevails.
Thursday night...high confidence.
VFR with light SW winds becoming WNW. Low probability of
MVFR/IFR along the south coast and islands.
Friday...high confidence.
VFR, dry weather and light S-SE winds. MVFR in scattered
showers possible late in the day across CT and western/central
MA.
KBOS TAF...High confidence for VFR and SSW predawn becoming west
after sunrise at 10-15 kt, precluding seabreeze from developing.
Low probability (10-15%) of a brief spot afternoon shower,
otherwise dry weather prevails.
KBDL TAF...High confidence for VFR with SW winds predawn
becoming west after sunrise. Low probability (10-15%) of a brief
spot afternoon shower, otherwise dry weather prevails.
Outlook /Friday Night through Monday/...
Friday Night through Saturday: Mainly VFR, with local MVFR
possible. Chance SHRA, isolated TSRA.
Saturday Night: VFR. Chance SHRA, isolated TSRA.
Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, isolated TSRA.
Sunday Night: VFR. Breezy. Chance SHRA, isolated TSRA.
Monday: VFR. Chance SHRA, isolated TSRA.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
345 PM Update:
SCA on the southern ocean waters continues into the overnight
hours for seas around 5 ft.
Scattered showers with embedded thunderstorms to end early
tonight. SSW winds around 15-20 kt most of tonight, with a
windshift to WSW around 10-15 kt toward overnight. Seas 3-5 ft,
decreasing to 4 ft or less on all waters around early Thursday
AM. Patchy fog will re- develop tonight on the southern waters
and reduce visibility.
Tranquil conditions then expected for mariners Thurs and Thurs
night with W winds around 10-15 kt and seas 4 ft or less all
waters.
Outlook /Friday Night through Monday/...
Friday: Winds less than 25 kt.
Friday Night: Winds less than 25 kt. Slight chance of rain
showers.
Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain showers, isolated thunderstorms.
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain showers, isolated
thunderstorms.
Sunday through Sunday Night: Winds less than 25 kt. Local rough
seas. Chance of rain showers, isolated thunderstorms.
Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain showers, isolated thunderstorms.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 6 AM EDT early this morning for
ANZ254>256.
&&
$$
SYNOPSIS...Loconto/RM
NEAR TERM...Nocera
SHORT TERM...Loconto
LONG TERM...RM
AVIATION...Nocera/RM
MARINE...Loconto/RM
Source:
BOX issues Area Forecast Discussion (AFD) at Aug 1, 1:56 AM EDT----------------
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