Area Forecast Discussion
Issued by NWS Boston, MA

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547
FXUS61 KBOX 152016
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
416 PM EDT Sun Oct 15 2017

.SYNOPSIS...

A strong cold front sweeps across the region overnight and will
be accompanied by scattered showers into early Monday morning.
Behind the front it turns sharply cooler and brisk Monday
afternoon with temperatures dropping down close to freezing by
daybreak Tuesday. Gradual warm-up through the week, possibly
into the weekend, while overall dry and quiet with scattered
cloud decks and breezy winds from time to time.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...

415 pm update...

Southwest low level jet will continue to increase this evening
ahead of a cold front. While inversion will limit mixing to some
degree, expect southwest wind gusts of 20 to 30 mph to persist
with a few gusts to 35 mph. While temps will fall a few degrees
after sunset, readings will remain in the 60s through midnight
in most locations. Enough wind should limit extent of fog, but
did opt to issue a dense fog advisory for just the outer islands
this evening through 10 pm based on current observations.

The strong cold front will approach western MA/northern CT by
late evening. It remains uncertain if a fine line of showers
will survive into western MA/northern CT, but if it does a very
brief period of 35 to 45 mph wind gusts will be possible. We did
go ahead and issue a Special Weather Statement to highlight this
concern. A few weakened trees and/or tree limbs may be knocked
down if this occurs.

Otherwise, enough forcing/moisture for a band of brief scattered
showers late this evening and toward daybreak across eastern MA
and RI. Temps by daybreak will probably have fallen into the
upper 40s and 50s across much of the region.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...

Monday...

A few left over showers will be possible across the far
southeast New England coast during the first part of Monday
morning. Otherwise, expect some strato-cumulus to work into the
region in the cool advection pattern but will also see some peeks
of sunshine. Temperatures late Monday morning and afternoon
will mainly be in the upper 50s to the lower 60s, but a bit
cooler in the higher terrain. Northwest wind gusts of 20 to 30
mph will make it feel chilly compared to our recent mild
weather.

Monday night...

High pressure will build in from the west allowing winds to
gradually diminish, except across the southeast New England
coast. Cool airmass in place should allow overnight low temps to
drop to around 30 to the lower 30s in the normally coolest
outlying locations. Some frost/freeze headlines will likely be
needed where the growing season is technically still in place.

Lastly, it will be milder across the Cape/Nantucket as NNW winds
will result in ocean effect cloudiness and holding low temps in
the 40s. 850T to seas surface temperature differential around
20C may even yield an isolated shower or two.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...

*/ Highlights...

 - Gradual warm-up through the week into the weekend
 - Perhaps a pattern change into late October, more active, cooler

*/ Overview and Discussion...

Change is on the horizon. A deeper polar low upstream shifting from
the Siberian Peninsula E into Alaska diminishes downshearing storm
development over the W CONUS and rather promotes ridging into late
October. Concurrent with a strong MJO phase 4/5/6 signal, and the
expectation is for mild, moist Pacific air to pump into the W CONUS
ahead of deep troughing over the NE Pacific. Meanwhile this also
promotes downshear deeper troughing over the E CONUS.

But prior to, as the polar low matures E into Alaska, individual up-
stream Pacific-origin waves continue to slam into the Cascades later
emerging downstream and undergoing cyclogenesis NE into Canada. High
pressure is promoted over the SE CONUS beneath preferred H5 ridging.
Subsequent SW pump of warmer air across the Central into E CONUS as
far N/E into NE Canada. Looking at a suppressed environment over S
New England.

Aside from a series of weak frontal passages concurrent with breezy
winds, Tuesday night into Wednesday, and again Thursday night into
Friday with light shower activity over N New England high terrain,
otherwise little to no wet-weather activity given abundant dry air
through the following weekend. Main story is the warming temperature
trend for late October beginning near-seasonable with highs around
the low to mid 60s warming into the 70s, possibly into the 80s by
the weekend.

Consensus of model guidance preferred which signals the low to mid
level high situated over the SE CONUS out to Bermuda round which the
heat pump flows, breaking down early next week as Pacific energy
shears off into the SW CONUS as high pressure builds around the
coast of CA. The pattern flips and troughing becomes promoted into
the NE CONUS. Looking at the next cold frontal passage and chance of
wet weather potentially beginning around Monday night into Tuesday.

&&

.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight...Moderate confidence. Mainly low end VFR to MVFR
conditions, except IFR to even LIFR conditions across the
immediate south coast, Cape, and Islands in areas of fog and low
clouds. Southwest wind gusts of 25 to 30 knots with a few gusts
to 35 knots possible this evening. A fine line of showers with
a cold front may bring a brief period of 30 to 40 knot wind
gusts across western MA/northern CT if it holds together between
10 pm and 2 am. Scattered showers may impact eastern MA/RI
after midnight in associated with a strong cold front.

Monday...Moderate to high confidence. A few left over showers
possible across the southeast New England coast into part of Monday
morning. Otherwise, a scattered to broken deck of VFR cigs
which may occasionally fall to MVFR thresholds. Northwest wind
gusts of 20 to 25 knots.

Monday night...High confidence. VFR other than perhaps a period
of some marginal MVFR ocean effect clouds across the Cape/ACK.
Winds diminish for most but northwest wind gusts of 20 to 25
knots continue for Cape/Islands.

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

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

Outlook /Tuesday through Friday/...Moderate confidence.

Tuesday through Friday...

VFR. W winds. Breezy at times, around late Tuesday and again late
Thursday

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Tonight...Moderate to high confidence. Southwest wind gusts of
25 to 30 knots expected this evening ahead of a cold front with
perhaps a gust or two near 35 knots. Cold front crosses the
waters near daybreak Monday. Small craft headlines posted for
all waters.

Monday and Monday night...High confidence. Northwest wind gusts
of 20 to 30 knots expected over the open waters in the cool
advection pattern. The strongest of those winds probably occurs
Monday night when the greatest 850T to sea surface temperature
differential exists. Small craft headlines for some waters may
need to be re-issued or extended.

Outlook /Tuesday through Friday/...Moderate confidence.

Overall W winds, breezy at times around late Tuesday and again late
Thursday. Waves for the most part below 5 feet, only issues worth
noting are on the S/SE outer waters early Tuesday, possibly again
Thursday night into Friday. Otherwise good boating weather.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Dense Fog Advisory until 10 PM EDT this evening for MAZ023-024.
RI...Dense Fog Advisory until 10 PM EDT this evening for RIZ008.
MARINE...Small Craft Advisory until noon EDT Monday for ANZ231>235-237-
     251.
     Small Craft Advisory until 8 AM EDT Monday for ANZ230-236.
     Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254>256.

&&

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



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