Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 201443
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1043 AM EDT Sat Oct 20 2018

.SYNOPSIS...
Today`s mild weather will come to an end tonight as a cold
front crosses the region. This will bring the return to
blustery and chilly weather overnight and into Sunday.
Temperature swings roll on through the following week. Warm ups
out ahead of sweeping cold fronts associated with light showery
weather and breezy conditions, frost / freeze conditions
following as high pressure builds across the region. A potential
Nor`Easter for the following weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

1015 AM Update...

Breezy SW winds have begun to diminish mainly across the
interior, with some leftover gusts up to 25-30 mph across the
Worcester hills and into NE CT/N RI into SE Mass. Should see
these winds diminish from midday through the afternoon as the
low level jet shifts away from the region.

Still noting spotty showers with last of the band of precip
shifting SE of Nantucket as seen on latest NE regional 88D
radar imagery. Also noting spotty lower clouds crossing the
region from time to time. Should see slow improvement as drier
air works in, though will likely linger through at least mid
afternoon across NE CT/RI/SE Mass. However, can not rule out a
few spotty showers into this afternoon as a secondary trough
moves quickly across.

Temps were mainly in the mid-upper 50s, with a few spots along
the S coast touching 60 at 14Z. As the clouds tend to break,
temps should slowly rise through midday or early afternoon.
Agree with previous forecaster that readings should make it to
the lower-mid 60s, but could remain a bit cooler across the
higher inland terrain.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...

Tonight...

A strong cold front will cross the region this evening with perhaps
a few showers. However, the better chance for more widespread
showers will be overnight as a strong upper level shortwave/cold
pool aloft moves into southern New England. 500T drop below
-30C and there is a period of decent forcing with a bit of
elevated instability. We think some of the model guidance is too
dry tonight and feel the GFS/ECMWF are more realistic with QPF.

Certainly not expecting a lot of precipitation but do expect some
showers across the region. In fact, temperatures may become
cold enough for even some wet snow flakes across the high
terrain.

Low temperatures by daybreak should drop into the 30s across
portions of the interior with lower 40s elsewhere.

Sunday...

A blustery and much chillier day across the region. We may have
a few left over showers into part of the morning and perhaps
even a few wet snow flakes in the high terrain.

Otherwise, partial clearing expected with 850T dropping to
between -6C and -8C. This should hold high temperatures mainly
in the upper 40s to the lower 50s. Good mixing should yield
northwest wind gusts of 25 to 35 mph.

&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...

*/ Highlights...

 - Coastal frost / freeze headlines Sunday night - Monday
 - Rolling temperature trend through midweek
 - Best wet-weather chances Tuesday - Wednesday with clipper low
 - First-season Nor`Easter potential the following weekend

*/ Overview...

A first-season late week / following weekend Nor`Easter? Very wavy
longwave pattern into October-end. Persistent NE Atlantic block that
promotes -NAO / -AO trends, a N Atlantic ridge and upstream Eastern
N American H5 trof. Meanwhile a progressive Eurasia to NE Pacific H3
jet max, flipping EPO to positive, +PNA maintained while the split-
flow W CONUS regime deamplifies. The longwave pattern amplifying and
tucking equatorward into the S-stream per tag-team teleconnections,
an opportunity emerges in where ejecting NE Pacific energy carves S
within preferred Eastern N America H5 trof, promoting height falls,
usurping while stretching / ejecting E Pacific tropical energy. Any
interaction / phasing unclear, there`s increasing signal of S-stream
obtaining greater cyclonic curvature within the aforementioned
H5 trof promoting potentially our first-season Nor`Easter by the
weekend, more warm-core / maritime-tropical, potential
significant rains as CPC notes a moderate risk for heavy
precipitation within their 8-14 day forecast, EC preference in
handling the -AO with their forecast.

Until then, an undulating temperature trend. Clipping Canadian lows
and highs up against an upstream split-flow. NW vs. SW flow. Flip-
flop back and forth, temperatures averaging overall below-seasonable
with the best chance of wet-weather Tuesday - Wednesday per Canadian
clipper-low. Breezy conditions at times but seemingly below advisory-
level criteria. Of remaining forecast areas where the growing season
is still considered, only Sunday night - Monday there`s the greatest
chance of closing out frost / freeze headlines for those areas, the
end of their growing season. Otherwise, not much else with
respect to targets of opportunity.

Consensus weighted forecast with greater weighting to EC / ECens out
at longer ranges into late October.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...

Forecaster Confidence Levels...

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

Short Term /through Sunday/...Moderate confidence.

14Z Update...

Through this afternoon...
Noting mainly low end VFR conditions, but still some leftover
MVFR CIGS across portions of the CT valley/S central Mass into
NE CT/N RI, but should improve from NW-SE this afternoon.

Gusty SW winds, up to 20-25 kt at times across the Worcester
hills and across RI/SE Mass. May see brief gusts up to around 30
kt through midday, then will diminish.

Tonight...
Mainly VFR but some showers overnight may result in briefly lower
conditions.

Sunday...
Any left over showers should exit the region Sunday morning.
Otherwise, VFR with NW wind gusts of 25 to 30 knots.

KBOS Terminal...Moderate to high confidence in TAF.

KBDL Terminal...Moderate to high confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday: VFR. Windy with gusts to 30 kt.

Sunday Night: VFR. Windy with areas gusts to 30 kt. Areas
frost.

Monday: VFR. Breezy. Areas frost.

Monday Night: VFR.

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night through Wednesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

14Z Update...

Through this afternoon...
Winds and seas are slowly but steadily diminishing late this
morning. Noting gusts mainly in the 20-30 kt range over the open
waters and some of the S sounds. Only exception appears to be
Boston Harbor, which winds have diminished below small craft
criteria.

Still noting higher seas, up to 8 ft with a 2 ft ground swell,
on the southern outer waters (ANZ255-256) along with some
leftover gusts to gale force, so have kept the Gale going there
into this afternoon. Elsewhere, have lowered Gales to Small
Crafts of the remaining waters except Boston Harbor as noted
above. Small craft gusts and seas AOA 5 ft will linger through
part of the afternoon, then may briefly diminish on more of the
open waters. Will continue to monitor.

Tonight...
A cold front crosses the region this evening. This should allow
small craft wind gusts to redevelop towards daybreak.

Sunday...
Strong cold advection over the relatively mild ocean will result
in northwest wind gusts of 30 to 35 knots. Strong small craft
or gale headlines will be needed...but given current headlines
will let the next shift decide based on the latest data.

Outlook /Sunday Night through Wednesday/...

Sunday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Chance of rain showers.

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.

Monday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Slight chance of rain showers.

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Local rough seas. Slight chance of rain showers.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft.

Wednesday: Low risk for Small Craft Advisory winds with gusts
up to 20 kt. Seas locally approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232.
     Small Craft Advisory until 11 PM EDT this evening for ANZ233-
     234.
     Small Craft Advisory until 4 PM EDT this afternoon for ANZ231-
     236.
     Small Craft Advisory until midnight EDT tonight for ANZ235-237.
     Small Craft Advisory until 5 PM EDT this afternoon for ANZ250.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ251.
     Small Craft Advisory until 6 AM EDT Sunday for ANZ254.
     Gale Warning until 1 PM EDT this afternoon for ANZ255-256.

&&

$$
SYNOPSIS...Frank/Sipprell
NEAR TERM...EVT/Sipprell
SHORT TERM...Frank
LONG TERM...Sipprell
AVIATION...Frank/Sipprell/EVT
MARINE...Frank/Sipprell/EVT


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