BOX issues Area Forecast Discussion (AFD) at Oct 16, 8:19 PM EDT633
FXUS61 KBOX 170019
AFDBOX
Area Forecast Discussion
National Weather Service Boston/Norton MA
819 PM EDT Fri Oct 16 2026
.WHAT HAS CHANGED...
Gale Watches have been replaced with Small Craft Advisories for the
applicable waters, excluding the outermost zones where Small Craft
Advisories are not issued. Post-frontal NNW winds are expected to
gust 25-35 kt Saturday, with occasional gusts approaching gale force
possible, especially across the southern and southeastern outer
waters Saturday night into early Sunday.
&&
.KEY MESSAGES...
- Morning showers exit, followed by a brief lull this afternoon
before a cold front brings additional showers and
thunderstorms this evening. A few strong to isolated severe
thunderstorms are possible.
- A few showers may linger along the southern coast early
Saturday. Otherwise, drier and noticeably colder conditions
are expected Saturday.
- Dry with a modest warmup through mid next week, but monitoring
coastal storminess near or south of the mid-Atlantic waters
which could bring periods of light rain, enhanced northeast
winds and building waves/possible erosion to southeast New
England.
&&
.DISCUSSION...
KEY MESSAGE 1...Morning showers exit, followed by a brief lull this
afternoon before a cold front brings additional showers and
thunderstorms this evening. A few strong to isolated severe
thunderstorms are possible.
As anticipated, gloomy conditions to wrap up the workweek. Earlier
this morning, a warm front lifted through southern New England,
bringing the first round of showers. The region is now positioned
within the warm sector. Dew points are increasing into the lower 60s
along the coast, while interior locations remain in the 50s.
However, by midafternoon, anticipate temperatures and dew points
continuing to climb into the 60s. Increasing dew points could lead
to pockets of instability. High-resolution guidance suggests limited
surface-based CAPE; however, as we've previously mentioned, the jet
dynamics associated with the approaching cold front are impressive.
A line of showers and embedded thunderstorms is developing across
western New York and extending southwest into Ohio. This activity is
associated with our cold front, which is marching eastward, aided by
a fairly robust mid-level trough. Ahead of the trough, SSW flow
allows for WAA, supporting mild afternoon temperatures despite the
clouds and rain. Highs should reach the middle 60s across northern
areas, while upper 60s to near 70 degrees are possible farther south.
Today is not anticipated to be a high-end severe weather day by any
stretch of the imagination; however, it is a day we cannot
completely ignore. Instability remains limited, generally 100-300
J/kg of MUCAPE, though strong bulk shear may compensate for the
limited instability and support a few stronger storms. Over the last
24 hours, the greatest shear has shifted a bit farther south,
favoring areas around NYC and points southwest. Nevertheless, a
couple of stronger storms remain possible. Feel as though these
storms could produce sub-severe wind gusts of 40 to 50 mph, with a
much lower chance of severe gusts exceeding 60 mph. CAMs continue to
indicate that the greatest potential for thunderstorms across
southern New England will be between 5 PM and 11 PM as the cold
front progresses from west to east.
Additional rainfall amounts of 0.25 to 0.50 inches are expected.
KEY MESSAGE 2...A few showers may linger along the southern coast
early Saturday. Otherwise, drier and noticeably colder conditions
are expected Saturday.
Heading into the overnight hours, the area of low pressure
associated with the cold front tracks northeast through the Saint
Lawrence Valley as broad high pressure expands across the Great
Plains. The surface low deepens to below 990 mb, with some guidance
suggesting it could reach 985 mb by Saturday afternoon. A tightening
pressure gradient supports gusty NNW winds at the surface, while
northerly flow strengthens aloft. Meanwhile, 850 mb temperatures
fall to between -6C and -4C, a rather significant drop considering
values were between +15C and +17C Friday afternoon.
While the majority of precipitation should exit with the cold front,
some guidance suggests the potential for an anafrontal wave to
develop along the departing boundary early Saturday. This could
allow showers to linger across the southern coast, Cape Cod, and the
Islands into Saturday morning. Highs Saturday afternoon are not
anticipated to be much warmer than the lower 50s across the coastal
plain and middle to upper 40s farther inland. However, with gusty
winds, apparent temperatures are expected to be 5 to 10 degrees
colder than the actual air temperatures.
Very cold conditions are expected Saturday night into Sunday morning
as strong high pressure builds into the region. With the combination
of very cold temperatures aloft, diminishing winds, and favorable
radiational cooling, temperatures are expected to fall below
freezing across much of southern New England, leading to widespread
frost/freeze conditions. However, since we are outside the
climatological growing season, our frost/freeze program ended on
October 11, and no Frost or Freeze headlines will be issued.
Nevertheless, if you purchased any sensitive tropical plants or
palms from the garden center this summer, now would be a good time
to bring them indoors!
KEY MESSAGE 3...Dry with a modest warmup through mid next week, but
monitoring coastal storminess near or south of the mid-Atlantic
waters which could bring periods of light rain, enhanced northeast
winds and building waves/possible erosion to southeast New England.
Expansive area of high pressure will maintain itself over most or
much of Southern New England through midweek and potentially longer
as it becomes reinforced by another strong high pressure coming out
of the northern Canadian Prairie region by midweek. This will at
least drive dry weather and a gradual warming trend away from the
southeast coast with pretty strong diurnal temperature ranges (mild
days, cool nights). These conditions could linger into much of the
upcoming workweek, away from the southeast coast.
However we continue to monitor coastal storminess depicted across
the NWP and ensemble suite near the mid-Atlantic waters Sunday.
There seem to be an increasing number of model guidance which brings
a portion of this feature's moisture northward or northeastward into
a weakness in the above surface ridge at some point Monday into
Wednesday, mainly impacting the coastal plain and southeast New
England. Exactly when and/or for how long it rains is still quite a
bit unclear as the rain will be moving into a very dry ridge and
should create a sharp NW to SE gradient in rain, but it doesn't look
to be a soaking rain in looking at ensemble QPF probabilities. The
bigger potential issue is mainly for the southern waters/coastlines
with respect to increasingly gusty ENE winds and building rough seas
which could lead to beach erosion for east- or northeast-facing
beaches. With a persistent easterly fetch over several days, it's a
conduit for building waves and latest significant wave heights are
in the 12-15 ft range south and east of Nantucket and Martha's
Vineyard. ECMWF probabilities of gale force gusts have increased
into the moderate to high (50-70%) range for Monday into Tuesday,
while the GFS is more tempered at around 30-50%, with lower
probabilities for the northeast waters. It may also turn breezy over
the land as well with gusts up to 30 mph at times. We'll re-evaluate
the risk for coastal flooding given several tidal cycles, but astro
tides are decreasing through midweek, which should mitigate
significant issues. So as it looks right now, there appears to be a
growing risk for at least impacts to mariners, including potential
gale force gusts that could warrant headlines in the coming days as
well as rough seas. Some risk for rains would exist as well for
southeast New England, but at the moment rainfall doesn't look
particularly significant or substantial at this point.
&&
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
00z TAF Update:
Tonight: Moderate confidence.
Mix of flight categories with IFR/LIFR for PVD, Cape and Islands
and VFR/MVFR ceilings from ORH westward. Line of gusty showers
moving through eastern MA and RI to clear offshore by 02z, with
a windshift to W around 10-12 kt upon frontal passage and
either very light rain or even dry.
After 04-06z, another round of light rain showers then develops
from SW to NE as NW winds increase and become gusty. These
shouldn't reduce visby with VFR/MVFR ceilings. Rain showers
should begin to taper off between 08-12z from the Berkshires
southeast to a rough BED/IJD line, but continue into Sat south
and east from there. NW winds increase to around 13-15 kt with
gusts 23-27 kt by daybreak.
Saturday: High confidence in TAF/trends, but moderate on when
SHRA clears southeast New England.
Ceilings should improve to VFR before daybreak, but rain
showers could linger until early afternoon for PVD, and
potentially into midafternoon for the Cape and Islands. North
and west from there, VFR prevails. Gusty NW winds around 13-17
kt with gusts 25-30 kt.
Saturday Night: High confidence.
VFR. Easing NW winds to around 5-10 kt by midnight, continuing
to ease to light NW overnight.
Sunday: High confidence.
VFR. Light north winds, though becoming NE around 8-12 kt for
the Cape and Islands.
KBOS Terminal...Moderate confidence in TAF.
KBDL Terminal...Moderate confidence in TAF.
Outlook /Sunday through Wednesday/...
Saturday Night through Sunday: VFR. Breezy.
Sunday Night: VFR.
Monday: VFR. Breezy.
Monday Night: VFR. Breezy. Slight chance SHRA.
Tuesday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Outlook /Sunday through Wednesday/...
Saturday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 8 ft.
Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft.
Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt.
Monday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Chance of rain showers.
Monday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Chance of rain showers.
Tuesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Slight chance of rain showers.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT Saturday for ANZ230-236.
Small Craft Advisory until 2 AM EDT Sunday for ANZ231-251.
Small Craft Advisory until 8 AM EDT Sunday for ANZ232>235-237-
250.
Small Craft Advisory until 11 AM EDT Sunday for ANZ254>256.
Gale Watch from Saturday evening through Sunday morning for
ANZ281>283.
&&
$$
DISCUSSION...Loconto/Dooley
AVIATION...Frank/Loconto
MARINE...Loconto/Dooley
Source:
BOX issues Area Forecast Discussion (AFD) at Oct 16, 8:19 PM EDT----------------
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