BOX issues Area Forecast Discussion (AFD) at Oct 4, 1:29 AM EDT708
FXUS61 KBOX 040529
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
129 AM EDT Fri Oct 4 2024
.SYNOPSIS...
Mild temperatures Friday with no precipitation. A weak cold
front brings a brief wave of showers late Friday through early
Saturday. Decreasing cloud cover early Saturday gives way to a
nice weekend in store with dry weather and seasonable
temperatures. A cold front moves through Southern New England
overnight Sunday evening into Monday, bringing a period of rain
showers. This cold front will herald a cooler, Fall- like
weather pattern as we move into the middle part of next week.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
10 PM Update...
Dewpoints approaching 60F, thanks to southerly flow, across the
south coast have supported patchy stratus/fog development for
the Cape and Islands. Most notably, MVY and ACK have reported
vsbys as low as ~2SM in the last hour or two. Will note that
dewpoints are currently running 2-3F higher than forecast, so
did an adjustment to the forecast with this update.
While river valley fog remains possible in the CT River Valley,
some mid level clouds will delay fog development until after
midnight when the cloud deck finally pushes east.
800 PM Update:
No significant changes needed to the going forecast. Surface
high pressure continues to slowly sag southeast into the
offshore waters. Other than some high clouds streaming in from
the SW, mostly clear skies have allowed temps to cool off into
the lower to mid 60s for most. Good radiational cooling is
expected with lows bottoming out into the mid 40s to lower 50s
(mid 50s in the urban areas). Could see patchy fog develop in
the typical radiational fog-prone areas around NW MA, the CT
Valley, the I-495 corridor in MA. We also need to monitor for
patchy fog development toward early morning along the RI/MA
south coast as SE winds slacken off.
Previous discussion:
Southern New England remains under an area of surface high pressure
tonight with light south/southwesterly surface winds. Lower clouds
develop just off the Cape, potentially moving into those immediate
shore areas. Across the interior, it will be a favorable night for
cooling with lows dipping into the mid 40s and 50s. Model soundings
show potential for patchy fog with ample cooling at the low levels
and light winds. The best chances will be for the CT River Valley
after midnight. Could see some spotty areas along the I-495 corridor
as well leading up to sunrise. Higher clouds are possible overnight
which will also help keep fog confined to the usual prone areas and
less widespread.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Weak upper level ridging overhead on Friday with a weak shortwave
trough approaching from the west. Any lower clouds/patchy fog across
the interior and offshore areas erode and scatter out. 850mb
temperatures warm into the 10-12 degC range which will support a
slightly warmer day. This could allow temperatures in the low to mid
70s in most areas with some upper 70s readings possible for parts of
the CT River Valley. Clouds pushing eastward ahead of the incoming
shortwave trough may potentially dampen highs a degree or two. The
Cape/islands will stay cooler with highs in the mid to upper
60s.
A weak shortwave trough moves through the region Friday night into
early Saturday. This will bring along a weak cold front with a wave
of light showers overnight through early Saturday morning.
&&
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Key Points...
Highlights:
* Early-Saturday light rain showers trend dry by mid morning
Saturday, with dry weather and seasonable temps for the weekend.
* Stronger cold front moves in overnight Sunday night into Monday,
bringing wetting rains but significant rainfall totals are not
expected.
* Pattern change toward cooler, Fall-like weather for early to mid
next week, with possible frost in some locations.
Details:
Saturday and Sunday:
Passing mid-level shortwave disturbance responsible for light rain
showers during the overnight will continue to shift offshore as we
move into the mid-morning hours on Sat. High pressure to then build
in from NW NY and southern Ontario into Southern New England through
the rest of Sat and continuing into the daytime hrs of Sunday.
Early-Saturday low chance PoP will then trend to dry by the mid-
morning hours along with decreasing clouds and good diurnal ranges
between high and low temps. Highs on Sat should reach into the low
70s with increasing sun, and in the 60s to low 70s on Sunday,
coolest near the coast. Lows Sat night in the 40s, to upper
40s/around 50 in the urban centers.
Sunday Night into Monday:
500 mb height rises transitions to height falls later Sun night as a
cold front brings our next chance for showers. PoPs increase into
the Likely range for the overnight period into Monday. Rainfall amts
do not appear to be too significant per 12z ensemble percentile
analyses; however what we will need to monitor for is the potential
for a weak low pressure area to develop along the front, as
indicated more bullishly by recent ECWMF solutions. Net effect this
would have, were it to develop, would be to delay the eastward
progress of the front and perhaps continue lighter rain showers into
eastern and southeastern sections of Southern New England into a
greater part of Monday. With more clouds than sun for Monday, expect
highs in the 60s.
Tuesday through Thursday:
Pretty significant pattern change toward cooler, Fall-like weather
for Southern New England, as a pronounced closed low and cold pocket
of air aloft settles in across the Northeast. 925 mb temps tumble to
around +4 to +6C, representing an airmass that is slightly cooler
than normal by early October standards. Highs may struggle to reach
into the low 60s; we could also see nighttime lows cool down enough
to the point where frost would be possible in the outlying valleys
which radiate well. However there does appear to be at least some NW
breeze that could keep nighttime temps from falling faster than they
would in a clear/calm night. While the daytime hrs should feature a
good deal of diurnal cloud cover, dry weather is expected.
&&
.AVIATION /05Z FRIDAY THROUGH TUESDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
06z TAF Update:
Through today... High Confidence
Patchy radiation fog yielding LIFR to IFR across the CT River
Valley will give way to VFR. VFR elsewhere except along the
immediate south coast where higher dewpoints and southerly flow
have led to some marine stratus/fog formation. By the lunch
hour, expect all terminals to be VFR. SSW winds today less than
10kt, with east coast seabreezes possible around 16Z.
Tonight... Moderate confidence
Approaching cold front will deteriorate conditions from VFR to
MVFR with showers developing between 06-12Z. Light winds shift
to the NW behind the frontal passage.
Saturday... Moderate Confidence
Rain showers most likely during the morning hours, tapering by
afternoon. MVFR improves to VFR, though isolated pockets of IFR
possible. Winds generally N, around 10kt with gusts to 15
possible.
BOS TAF...High confidence in TAF.
VFR. For Friday, sea breeze develops likely in the 15-16z time
frame with SSE/SE winds. Showers likely by 12Z Saturday.
BDL TAF...High confidence in TAF.
VFR, although localized patches of ground fog may come in and
out of the terminal through 13Z this morning. Light rain showers
possible by 06Z Saturday. Light SW/SSW winds Friday.
Outlook /Saturday Night through Tuesday/...
Saturday Night through Sunday: VFR.
Sunday Night: VFR. Chance SHRA.
Monday: Mainly VFR, with local MVFR possible. Chance SHRA.
Monday Night: VFR. Slight chance SHRA.
Tuesday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight and Friday...High Confidence.
Waves 2-4ft. SSW winds tonight, less than 15kt expected. Marine
stratus and patchy fog possible tonight across the southern
waters. S/SE winds Friday through Friday night less than 15
kts, waves 2-4 ft.
Saturday...High Confidence
NW winds less than 25 kts. Waves 2-4 ft.
Outlook /Saturday Night through Tuesday/...
Saturday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft.
Sunday: Winds less than 25 kt. Seas up to 5 ft.
Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.
Monday: Winds less than 25 kt. Seas up to 5 ft. Rain showers
likely.
Monday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers.
Tuesday: Winds less than 25 kt. Seas up to 5 ft. Slight chance
of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Loconto/Mensch
NEAR TERM...Loconto/Mensch/KS
SHORT TERM...Mensch/KS
LONG TERM...Loconto
AVIATION...KS
MARINE...Loconto/Mensch
Source:
BOX issues Area Forecast Discussion (AFD) at Oct 4, 1:29 AM EDT----------------
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