Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 131112
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
712 AM EDT Fri Oct 13 2017

.SYNOPSIS...
Strong high pressure builds southward across New England today,
providing dry and seasonably cool weather. Warmer and more
humid conditions arrive over this weekend as high pressure moves
offshore and a cold front approaches from the west. This setup
will also result in scattered showers at times, but a washout is
not expected. This front moves offshore late Sunday night or
early Monday morning, followed by drier, less humid and cooler
weather next week.

&&

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

7 AM update...

Some ocean effect strato-cu clouds coming onshore across eastern
MA/RI and CT. Cool airmass (+6C at 925 mb) streaming across
relatively warm ocean temps of +17C yielding steep low level
lapse rates. Guidance has this low level moisture becoming more
widespread and overspreading most of the region today as ENE
winds become ESE. These clouds have resulted in temps coming up
a bit faster, cutting off radiational cooling. Thus have
cancelled the Frost Advisory given temp trends at 7 am.
Otherwise previous forecast on track. Earlier discussion below.

================================================================

Expect dry conditions through the day as temps recover nicely
during the day even with the onshore winds. Temps will top off
in the lower-mid 60s, which are close to seasonal normals for
mid October.

&&

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

Tonight and Saturday...
As the ridge moves further offshore, the SW wind flow becomes
established as a cold front slowly works E out of the Great
Lakes. The low level moisture will increase as well milder air
moving in. Some question as to whether spotty light precip may
start to break out after midnight, as models showing some
solution spread in how far E that moisture may push in
overnight. Kept slight chance POPs going for tonight. May also
see patchy fog develop overnight. Low temps will be mainly in
the upper 40s to mid 50s, maybe a bit milder along the S coast.

Better lift and moisture feed will work in during Saturday as
the high sits S of Nova Scotia and the approaching cold front
remains well W of the region. With the onshore flow, should see
scattered showers develop during the mid day and afternoon hours
mainly near and S of the Mass Pike. It will be mild though, with
highs mainly in the upper 60s to lower 70s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...

Highlights...

* Much warmer than normal and humid Sat night/Sunday
* Scattered showers Sat into Sun morning, then again Sun night
* Dry weather much of next week and chilly Mon night/Tuesday

Saturday night...

Anomalous 591 dam subtropical ridge over the southeast states
builds into the Mid Atlc region and results in a warm front
moving across southern New England. This boundary and associated
moisture plume of PWATs +2 standard deviations above normal
will result in a chance of showers. Very mild night for mid Oct
given dew pts in the low to mid 60s! This will also yield a risk
for patchy dense fog.

Sunday...

Chance of morning showers as warm front lifts northward across
the area. Warm sector overspreads the area by late morning/early
afternoon with 925 mb temps surging to +17C to +18C at 925 mb!
This will support highs easily 75-80 away from the south coast
with a low prob of a few interior locations getting into the low
80s, which will approach new record highs for the day. Quite
anomalous when you consider the normal high temp for mid Oct is
60-65. After warm front exits late morning a period of dry
weather is expected in the warm sector. It will become windy as
991 cyclone exits the northern Great lakes and intensifies to a
sub 980 low as it tracks across southern Quebec during the day
Sunday. This strengthening pres gradient combined with
steepening low level lapse rates in the warm sector will support
southwest wind gusts up to 40-45 mph, which may be strong
enough for isolated wind damage given fully leaved trees.
Greatest risk appears eastern MA given location of low level
jet.

Sunday night...

Strong low level convergence along approaching cold front and
robust upper level jet streak with RRQ over southern New
England. This will support a deep layer of ascent accompanied by
adequate deep layer moisture. This setup may provide a broken
line of low top convection along and ahead of approaching cold
front. Given strong wind fields a few of the heavier showers may
produce gusty winds. Instability appears to be lacking but with
dew pts in the mid 60s will have to monitor instability trends
on later model runs. If instability is greater than what models
are simulating this could be a sneaky low top convective event.
Fropa occurs later Sun night with much drier/less humid post
frontal airmass ovespreading the region 06z-12z Monday.

Next Week...

Dry and seasonably cool Monday behind initial cold front late
Sun night/early Mon morning. Coolest air arrives Mon ngt/Tue
morning with secondary/trailing short wave trough. Guidance has
850 mb temps cooling off to about -2C across New England. So
slightly cooler than normal Mon ngt into Tue along with patchy
frost possible as MOS guid offers lows in the 30s, some upper
20s possible. GFS and EC ensembles lower 850 temps to about -3C
12z Tue with deterministic guid as cool as -6C. Nonetheless a
cool shot of air Mon ngt/Tue. Ensembles and deterministic
guidance both indicate northern stream reloads middle of next
week with new jet energy diving into the northeast mean trough.
This will support a reinforcing shot of seasonably cool airmass.
Regarding precip, this looks to be a rather dry pattern.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...High confidence.

11z update...

SCT-BKN CIGS coming onshore. These MVFR cigs will become more
widespread as the day progresses due to ENE winds shifting to
ESE. Otherwise previous TAFs on track. Earlier discussion below.

==================================================================

Today...Mainly VFR. Local MVFR VSBYS in patchy fog through 14Z
across interior E Mass and parts of the CT valley. E wind gusts
up to around 15 kt along immediate E coast and on the islands.
May see MVFR CIGS move into S coastal areas around 22Z.

Tonight and Saturday...Mainly VFR. CIGS lowering to MVFR to
local IFR across central and western areas around or after
midnight with MVFR VSBYS in patchy fog. Chance of showers
central and western areas after midnight.

KBOS TAF...trend will be for SCT030 to become BKN030 cigs as the
day progresses in response to winds becoming SE later this
morning.

KBDL TAF...High confidence in TAF. May see brief patchy fog
through 12Z-13Z with local MVFR VSBYS possible. MVFR CIGS after
04Z and MVFR VSBYS at times in patchy fog. Chance of showers
around or after midnight.

Outlook /Saturday Night through Tuesday/...

Sat night/Sunday morning...MVFR with IFR possible in the higher
terrain. Scattered showers and patchy fog. Moderate confidence
with some uncertainty on areal coverage of IFR.

Sunday afternoon...MVFR and VFR. Mainly dry but gusty SW winds
up to 30 kt, possibly higher. High confidence.

Sunday night...MVFR with scattered showers, a few gusty showers
possible. SW winds up to 30 kt, possibly slightly higher.
Moderate confidence with some uncertainty on areal coverage and
intensity of showers.

Mon and Tue...VFR and dry. High confidence.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

Today...
Winds and seas remain at or above small craft criteria across
the waters E of Cape Cod southward. Expect E wind gusts up to 25
kt across the southern waters early then will diminish, but
seas remain around 5-7 ft through the day. Seas should slowly
subside across the waters E and S of Cape Cod and Nantucket
during the afternoon.

Tonight and Saturday...
Seas around 5 ft will linger across the southern waters S of RI
into early Saturday morning, then should subside. Otherwise
expect E-SE winds to slowly diminish during tonight, shifting to
S-SW on Saturday. Visibility may lower in patchy fog, along
with spotty showers that may push across the waters during
Saturday.

Outlook /Saturday Night through Tuesday/...High confidence,
except some uncertainty how strong southwest winds become Sun
afternoon and evening.

Saturday night...Poor vsbys in areas of showers/drizzle and
fog.

Sunday...Poor vsbys in areas of morning showers/drizzle and
fog, improving by midday. SW winds become gusty especially near
shore with gusts up to 30 kt, possibly higher. Cold frontal
passage Sunday night.

Mon and Tue...Cold front moves offshore early Mon followed by
dry weather and good vsby.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 PM EDT this afternoon for ANZ254.
     Small Craft Advisory until 4 PM EDT this afternoon for ANZ255.
     Small Craft Advisory until 11 AM EDT Saturday for ANZ256.

&&

$$
SYNOPSIS...Nocera/EVT
NEAR TERM...Nocera/EVT
SHORT TERM...EVT
LONG TERM...Nocera
AVIATION...Nocera/EVT
MARINE...Nocera/EVT



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