795
FXUS61 KBOX 182342
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
742 PM EDT Wed Sep 18 2024

.SYNOPSIS...
Rain chances increase from south to north tonight into tomorrow,
with the best chances across the Cape and Islands decreasing
significantly to the north and west. Rain chances continue
through the first half of the weekend, highest over the Cape
and island. Gusty northeast winds will keep temperatures near or
below normal for much of the region tomorrow into the weekend.
Next chance of rain comes around mid week.

&&

.NEAR TERM /THROUGH THURSDAY/...
An area of low pressure makes its way north and eventually stalls
somewhere south of Cape Cod and the Islands. Guidance remains in
disagreement on how far south the low stalls, making the QPF
forecast somewhat uncertain for being 12 to 24 hours out. The HREF
ensemble has a large spread between the 25th and 75 percentiles due
to the unknowns on how far south the low stalls. The 25th percentile
QPF from the HREF through 8 am Friday shows 1.75 inches for the Cape
and Islands and 0.5 inches for the I-95 corridor from Boston to
Providence. The 75th percentile shows 3-3.5 inches for the Cape and
Islands, with 1.0-1.5 inches from Boston to Providence. Further
west, rain amounts drop off very quickly due to dry air on the NW
side of the low. There may not even be measurable QPF north and west
of Worcester.  Overall, any rain that falls will be beneficial and
likely not cause flooding impacts, given the antecedent dry
conditions. Regardless of the rain, tonight and tomorrow will
feature overcast skies with a blustery northeast wind. Temperatures
tonight stay warmer in the upper 50s to low 60s with an abundance of
cloud cover and increasing winds. With the onshore flow tomorrow,
high temps in eastern MA and RI will struggle to top 70F, while in
western MA and CT, temps will reach the mid-70s.

&&

.SHORT TERM /THURSDAY NIGHT/...
Uncertainty continues to remain high into Friday night as guidance
struggles with where the low stalls south of the region. Rain should
continue through Friday night with the best chances over the Cape
and Islands, but how far inland rain continues remains a big
question mark.  Low clouds and gusty NE winds will keep far from
ideal radiational cooling conditions from occurring and hedged
toward slightly warmer overnight lows in the low to mid-60s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
* Rain chances linger through Friday. Things will improve through
  the weekend but some rain likely lingers into Saturday, especially
  in eastern MA.

* Temperatures will trend below normal with the lowest on Sunday
  before steadily increasing next week.

* Minor coastal flooding possible along the east coast of MA during
  Friday and Saturday afternoon`s high tides.

Details...

Friday the rainy and windy pattern remains rooted overhead thanks to
a mid level trough and a coastal low at the surface spinning south
of Long Island and Nantucket. This low will be the main player with
our rain chances Friday into Saturday wrapping moisture around
itself and into southern New England, especially eastern MA and RI.
For this reason these are the locations with the best chance of
seeing widespread rain during the period. Even so, areas further
inland (north and west) will see less rain than those further south
and east (the Cape and Islands) thanks to the proximity to the
source of lift and moisture. This low will be relatively slow to
exit but eventually a high pressure ridge pushes in from the north
and the low exits east allowing for drier conditions, improving
through the weekend.

Another factor that will have an impact during the Friday and
Saturday period will be the gusty winds thanks to an increased
pressure gradient and the placement of a 35-45 kt low level jet
overhead. This leads to wind gusts of 15-25 mph inland, 25-30 mph
over the Cape and Islands both Friday and Saturday afternoons. This
also makes for rough seas and, given existing higher astronomical
tides, some very minor coastal flooding is possible during the
Friday and Saturday afternoon high tides.

Beyond Saturday high pressure continues to build in through at least
Monday allowing for the return of quiet and dry weather. Flow
becomes more southerly by Tue into Wed allowing for moderating high
temperatures, back toward 70. This precedes the next shortwave but
confidence on if/when this arrives remains low at this point.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Forecast Confidence Levels:

Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

Tonight...Moderate Confidence

Winds turn NE this evening, which will bring CIGS down to
IFR/LIFR east of the I-95 corridor, while to the west, CIGS
should remain VFR with pockets of MVFR possible. LIFR cigs are
most likely for the Cape and Islands, but could work into BOS
and PVD. Light rain begins to work its way from south to north
overnight, mainly just affecting the Cape and Islands northward
to BOS. ORH and BDL should stay mainly dry.

Tomorrow...High Confidence

IFR continues as winds increase from the NE at 10-15 knots
inland, and 15-30 knots near the waters. Rain becomes moderate
to heavy for the Cape and Islands. The extent that rain reaches
inland remains uncertain, but should remain light outside of the
Cape. Western terminals may see no rain with MVFR/VFR conditions
tomorrow afternoon.

Tomorrow Night... Low confidence

Guidance tries to show some improvements in CIGS, but am rather
skeptical given the continued on shore NE winds. The low stalls
south of the Cape and Islands, but rain could still continue for
eastern terminals, esspically the Cape and Islands.


KBOS TAF...Moderate Confidence

VFR this afternoon with east winds. Winds turn NE overnight,
bringing in IFR CIGS by 00-02z. CIGS could go LIFR late
overnight, but confidence is low at this time. light rain is
possible early Thursday morning, possibly lasting into Friday
morning

KBDL TAF...High confidence in TAF.

VFR today with light winds. Mainly VFR overnight and tomorrow,
but pockets of MVFR possible. Expecting the rain to stay east
of the CT river valley

Outlook /Friday through Monday/...

Friday: MVFR/IFR conditions possible. Windy with local gusts up
to 30 kt. Chance SHRA.

Friday Night: Mainly VFR, with areas IFR possible. Breezy.
Chance SHRA.

Saturday: Mainly VFR, with local IFR possible. Windy with local
gusts up to 30 kt. Chance SHRA.

Saturday Night: Mainly VFR, with local MVFR possible. Breezy.
Chance SHRA.

Sunday: Mainly VFR, with local MVFR possible. Windy with local
gusts up to 30 kt. Slight chance SHRA.

Sunday Night through Monday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.

Marine

Today through Tomorrow night

Worsening marine conditions starting tonight, with northeast
winds increasing to 20-30 knots by tomorrow morning and seas
increasing to 5-8 feet by tomorrow afternoon.  Moderate to heavy
rain moves from south to north tonight and lasts through Thursday
night.  Seas continue to rise into Thursday night and Friday to 7-10
feet.

Rip Currents/High Surf With gusty NE winds, increasing surf and long-
period swells, we decided to issue a Rip Current Statement for
tomorrow. Much of the south and east-facing beaches will have a
high risk of rip currents. The rip current statement will likely
be extended or upgraded to a high surf advisory on Friday as
seas rise up to 10 feet in outer waters.

Outlook /Friday through Monday/...

Friday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Rough seas up to 10 ft. Rain showers likely.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 10 ft. Chance of rain
showers.

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain
showers.

Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain
showers.

Sunday: Strong winds with gusts up to 30 kt. Rough seas up to
11 ft. Slight chance of rain showers.

Sunday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 11 ft.

Monday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 11 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Risk for Rip Currents from Thursday morning through Thursday
     evening for MAZ007-019-020-022>024.
RI...High Risk for Rip Currents from Thursday morning through Thursday
     evening for RIZ006>008.
MARINE...Small Craft Advisory from 1 PM Thursday to 8 AM EDT Friday for
     ANZ231-251.
     Small Craft Advisory from 5 AM Thursday to 8 AM EDT Friday for
     ANZ232>235-237.
     Small Craft Advisory from 8 AM Thursday to 8 AM EDT Friday for
     ANZ250.
     Small Craft Advisory until 8 AM EDT Friday for ANZ254>256.

&&

$$

SYNOPSIS...BW/KP
NEAR TERM...BW/KP
SHORT TERM...KP
LONG TERM...BW
AVIATION...BW/KP
MARINE...BW/KP