BOX issues Area Forecast Discussion (AFD) at Sep 5, 1:37 PM EDT737
FXUS61 KBOX 051737
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
137 PM EDT Thu Sep 5 2024
.SYNOPSIS...
High pressure will continue to provide dry and seasonably warm
conditions today. While mainly dry weather is expected to
persist Friday into much of Saturday, low pressure moving
northward over the Atlantic will bring a period of increased
cloud cover, as well as the potential for rough surf and rip
currents on east-facing beaches. A cold front brings rain
showers late Saturday into early Sunday, but no washouts
expected this weekend. Drier early to mid next week with
seasonable day time highs, but cool nights.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1100 AM Update...
Gorgeous conditions are underway, last bit of valley fog has
lifted over the past hour, now bountiful sunshine. Have noticed
translucent high-clouds on satellite, is smoke from wildfires
out west. The forecast has stayed on track, no changes made
during this update.
Previous discussion...
Surface ridging will remain in control across New Eng with
subsidence and dry air in the column leading to another sunny day
with seasonably warm conditions. Not much change in low level temps,
although some cooling near the coast due to E-SE flow developing.
Highs will reach upper 70s to near 80, except low-mid 70s along the
immediate coast. Dewpoints will be in the lower 50s this afternoon
so comfortable humidity.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Tonight...
As high pres moves further offshore, low pres well east of the NC
coast will begin to drift northward. Persistent easterly flow to the
north of the low will lead to increasing low level moisture which
will lift north across SNE later tonight. As a result, we expect
stratus developing and expanding across the region overnight, along
with patchy fog. Some of the hi-res guidance is indicating some
light QPF which is likely a signal for patchy drizzle given
soundings indicate moisture is quite shallow, mainly below 900 mb,
with dry air above 900 mb through the mid levels. With increased
cloud cover, lows will be mostly in the 50s.
Friday...
The low pres will continue moving northward, reaching east of the
benchmark by evening with surface ridging and subsidence to the west
across SNE. Stratus expected to linger into the morning with patchy
drizzle possible, but heating and mixing of a shallow boundary layer
should lead to lifting cloud bases and partly sunny skies developing
as low level moisture becomes quite shallow below the subsidence
inversion. Highs expected to reach mid-upper 70s, possibly near 80
in the CT valley where low level temps are warmer. But a bit cooler
across east coastal MA with E-NE flow which may gust to 20 mph
Cape/Islands.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights
* Dry for much of Sat with rain chances increasing late. Showers
anticipated to exit early on Sun. Temperatures roughly 5 degrees
cooler than seasonable.
* Main concern for the weekend is high surf leading to moderate to
high rip currents across eastern facing beaches. Peak of the risk
is on Sat.
* Dry with seasonable conditions later on Sun through at least
midweek. Strong radiational cooling leading to some cool nights.
Friday Night through Sunday...
A deep trough/cutoff will initially be situated over the central
Great Lakes/Ontario late on Fri, with a coastal storm to the east of
SNE. Between these two features a shortwave ridge will be over New
England. The ridge builds offshore by early Sat, while the
cutoff/trough digs into the central/eastern Great Lakes. The trough
makes its closest pass by late Sat over the eastern Great
Lakes/western New England before lifting into Quebec on Sun. High
pressure nudges in for much of Sat, but will gradually move offshore
during the afternoon. This allows a cold front to slide into and
through southern New England late Saturday into early Sun.
Main concern through this timeframe is the high surf due to the
coastal storm east of SNE on Sat lifting toward Nova Scotia by late
in the day. Associated with the system will be a roughly 30-40 kt E
to N low level jet just offshore of SNE. This will bring 20-30 kt
gusts over the waters and seas of 7-11 ft across the eastern waters.
These diminish to 3-5 ft by Sun. This will result in a high risk for
Rip Currents across eastern facing beaches on Sat. The risk lowers
to moderate for Sun. A Rip Current State or High Surf Advisory may
be needed heading into Sun for portions of the region.
Guidance starting to hammer down the timing of the cold front
sliding into/through the region, though there are some slight
differences. At this point though appears front moves in Sat
afternoon and moves through overnight. So, looks like for a good
portion of Sat the weather will be dry. Did have to dial back NBM
precip chances as they are still a bit too quick with the onset of
precip and also holds onto precip too long. Best shot for rainfall
amounts AOA 0.10 inches are across CT, RI, western and central MA
where probs are moderate to high (50-90%+). These fall off low to
moderate further east. Risk for heavier rain/higher amounts solely
over western MA/CT with low (10-30%) 24 hr probs of AOA 0.50 inches
per EPS/GEPS and GEFS guidance. Really not a whole lot of
instability to work with with MUCAPE values < 100 J/kg, so have
removed thunder at this point, despite the strong forcing.
High temperatures on Saturday will be in the 70s for much of the
region. Anticipating a nice, albeit breezy day on Sun once any
lingering showers exit quickly during the AM. Highs generally in the
low to mid 70s.
Sunday Night through Wednesday...
Cyclonic flow in place late Sun through a good portion of Tue as the
cutoff lifts into northern portions of Quebec, Newfoundland and
Labrador. A ridge builds into the Great Lakes region for midweek.
High pressure nudges in for much of this timeframe, but plants more
overhead or just to our south by Tue/Wed.
Dry and quiet weather anticipated through this timeframe.
Temperatures will generally be around seasonable levels through the
daytime hours. However, given the high building in should have
relatively clear skies and light winds. This combination should lead
to strong radiational cooling. Nudged low temps down to the 25th
percentile of guidance for Sun Night, Mon Night and Tue Night as the
NBM tends to be much too warm in these situations. Held off from
going lower as winds could be elevated enough on Sun/Mon Night along
with some cloudiness that we don't radiate as well as the lower end
of guidance indicates.
&&
.AVIATION /17Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
This Afternoon and Tonight...High confidence through 06z,
moderate confidence afterwards.
VFR then areas of MVFR and IFR stratus developing 06Z to 10z
with patchy drizzle possible. East to northeast winds up to 10
knots along the coast, with light and variable wind across the
interior. Cape Cod and Islands remain VFR during this period.
May have areas of patchy fog develop between KBED to KORH to
KPVD.
Tomorrow...Moderate confidence.
MVFR-IFR ceilings in the morning with patchy drizzle possible,
improving to VFR in the afternoon. East to Northeast wind 8 to
15 knots.
Tomorrow Night...Moderate confidence.
Widespread MVFR ceilings, lowering to IFR. Northeast winds near
the coast 10 to 15 knots, light from the northeast across the
interior.
KBOS TAF...Moderate confidence in TAF.
VFR through 10z, quickly lowering to MVFR/IFR shortly after,
have the prevailing cloud base as MVFR, though there will be a
tight gradient of IFR ceilings around the terminal, have opt to
use a SCT IFR group to signal this threat. May scatter out to a
low end VFR ceiling around 16z to 18z. East to Northeast winds
throughout the TAF period.
KBDL TAF...High confidence in TAF.
VFR, then MVFR stratus possibly moving in early Friday around
10z to 13z, lifting to lower end VFR, BKN040 by 14z to 15z.
Light wind from the North/Northeast.
Outlook /Friday Night through Monday/...
Saturday: Mainly VFR, with local MVFR possible. Breezy. Slight
chance SHRA.
Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.
Sunday through Monday: VFR.
&&
.MARINE...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Today through Friday... High confidence.
E-SE winds 10-15 kt with gusts to 20 kt over south coastal waters
later today through tonight. NE winds increase later Fri and Fri
evening over south coastal waters with potential for 25 kt gusts
south and east of Cape Cod as low pres tracks east of the waters.
Building seas to 5+ ft tonight into Friday over south coastal waters
where SCA has been issued.
Outlook /Friday Night through Monday/...
Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas.
Saturday: Winds less than 25 kt. Areas of rough seas.
Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance
of rain showers.
Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Slight chance of rain showers.
Sunday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT Friday
for ANZ254>256.
&&
$$
SYNOPSIS...KJC/BL
NEAR TERM...KJC/Dooley
SHORT TERM...KJC
LONG TERM...BL
AVIATION...Dooley/BL
MARINE...KJC/BL
Source:
BOX issues Area Forecast Discussion (AFD) at Sep 5, 1:37 PM EDT----------------
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