Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 131835
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
135 PM EST Fri Jan 13 2017

.SYNOPSIS...
High pressure slowly builds over the region into Saturday, with a
return of colder, more wintry temperatures. Surge of colder air
continues over the weekend with a perhaps snow flurries or a brief
period of light snow Saturday night across the Islands with a
passing offshore low. A mild more wet weather pattern going into
the next week.

&&

.NEAR TERM /THROUGH TONIGHT/...

115 PM update...

Previous forecast on track. Thus no major changes with this
forecast update. Earlier discussion below.

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

Cold advection will be the primary influence in today`s weather.
H92 temps will drop to -8C to -10C by 00Z this evening. This cold
advection will impact mixing but subsidence inversion will suppress
the mixing through the day. Warmest temps are likely to occur
early in spite of mix of sun and clouds. Therefore, did not go
with a typical diurnal trend with hourly temps/dwpts today,
highlighting the warmest temps this morning.

Otherwise, the cold advection/mixing should tap some of the 35-45
kt LLJ in place across the region, however the suppressed mixing
will limit sfc gusts mainly to 25-35 mph, still breezy, but below
wind advisory thresholds.

Wind chills therefore will remain in the 30s and begin dipping below
by late afternoon, in spite of ambient highs in the 40s / upper 30s
early.

&&

.SHORT TERM /SATURDAY/...

Tonight...

Initially, breezy conditions will yield wind chills in the teens
and low 20s. However, strong subsidence inversion and slackening
pres gradient will lean way from wind chills and toward radiational
cooling. Top of the inversion is about -12C, so plenty of room for
early morning mins to drop into the teens (and even single digits
in the usual cold valleys of NW MA). Only urban heat-islands
remain in the 20s.

Saturday...

1040+ high pres will settle across N New England, suppressing a
weak low pres which will move off the Delmarva Sun night. This
should suppress the precip shield well to the S late tomorrow
afternoon and evening, for now only highlighting a low risk for
flurries mainly across the Islands.

This will lead to a shift in winds back to the S-SW and allow for
some warming at H92, which reach -6C to -8C by tomorrow evening.
However, the cold start, building CI/AC shield attendant to the
low pres to the S and suppressed mixing should limit highs to the
mid-upper 20s with a few low 30s. Nearly 30F colder than Thu
highs.

&&

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

*/ Highlights...

 - Despite a slight chance of snow for the S-coast Saturday night, a
   warmer than average, more wet weather pattern for next week

*/ Discussion...

Clash of N Hemispheric patterns signal a mild, more wet pattern into
late January across the NE CONUS. Absence of wintry weather. Several
features: 1) +EPO / +WPO indicating a progressive jet of mild Pacific
air into the W CONUS, 2) PNA largely neutral during a weak La Nina
ENSO episode supports a variable ridge-trough pattern across the W
half of the CONUS, and 3) Increasing -NAO with an altering pressure
pattern over the N Atlantic indicating a downstream blocking setup.
Hints of a rex block.

So no surprise the E CONUS / E Canada becomes a region of favorable
ridging with ensemble means continuing to signal a +1-2 standard
deviation in H5 heights with potential H85 anomalies on up to +20C.
Leaning towards inside-runner lows with New England within the warm
side of the envelope. Sorry all you skiers / snowboarders out there.

After some significantly cold air over the weekend with some snow
skirting the S shore Saturday night, overall light, flurries mostly,
looking at mainly S winds, warmer than average temperatures, and
with any disturbances outcomes will be mostly rain with a low risk
of a wintry mix with onset, as is the case around Tuesday into
Thursday with a leading initial warm front followed by a weak cold
front. Talking highs averaging in the 40s to 50s with lows in the
30s with continued support from ensemble probabilistics. Ridging
across the region, expecting emerging disturbances from the W to
weaken while remaining progressive. Only noteworthy targets of
opportunity may be perhaps blustery S winds with limited confidence
to suggest the possibility of wind advisories. The draw of warmer,
more moist air N, may also contend with low cloud / fog issues at
times with wet-weather anticipated.

Already this winter we`ve seen an altering WPO / EPO pattern with a
variable Pacific jet during a weak La Nina ENSO event. Don`t expect
this mild, wet pattern to hold for long given upstream variability.
It`ll be interesting to see how the AO / NAO evolves, but aside do
expect with the remaining 2+ months of winter that we`ll see the
return of some colder air, but it would appear that January will end
with an above-average monthly average temperature.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

18z update...

Thru 00z...VFR and dry with gusty WNW winds up to 35 kt.

After 00z...VFR, dry along with diminishing winds. Low risk MVFR
ceilings east of MA over the ocean may clip the outer Cape.

Saturday/Sat night...VFR with light winds. Low risk for MVFR a
few flurries along the immediate coast and Islands late in the
day.

KBOS TAF...VFR and gusty WNW winds up to 30 kt until sunset...then
slowly diminishing thereafter.

KBDL TAF...VFR and gusty WNW winds up to 30 kt until sunset...then
slowly diminishing thereafter.

Outlook /Sunday through Tuesday/...Moderate confidence.

Sunday through Wednesday...

VFR through Monday. Lowering cigs into Tuesday down to IFR with RA
and increasing S/SW winds. Low risk of LLWS impacts.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

135 pm update...No major changes to the forecast. WNW winds up to
30 kt this afternoon then slowly diminishing tonight. Earlier
discussion below.

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

Through tonight...High confidence.
Winds across the waters will reach 25-30 out of the W-NW as seas
also reach 8-10 ft on the outer ocean waters. Winds drop late this
evening, and seas will take much of the overnight to subside.
Therefore, small craft advisories continue today, but will be
dropping this evening and overnight. Some light freezing spray is
possible, mainly across the E waters and mainly this evening until
winds recede.

Saturday...High confidence.
High pres will yield a period of quiet boating wx through the
day. Winds will remain light, but shift from NW to S-SW by
afternoon.

Outlook /Saturday Night through Tuesday/...Moderate confidence.

An offshore area of low pressure sweeping W to E yields light snow
across the S waters, perhaps some lower visibility Saturday night.
Behind the low, breezy NW winds which could result in 5 foot seas on
the outer waters. Seas subsiding and winds remaining light while
turning S into midweek beneath high pressure will make for good
boating weather. Winds increasing beginning Wednesday as does wave
action as rain overspreads the region.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EST Saturday for ANZ231>234-
     251.
     Small Craft Advisory until 7 PM EST this evening for ANZ230-
     236.
     Small Craft Advisory until 10 PM EST this evening for ANZ235-
     237.
     Small Craft Advisory until 7 AM EST Saturday for ANZ250-254.
     Small Craft Advisory until 5 AM EST Saturday for ANZ255-256.

&&

$$
SYNOPSIS...Doody/Sipprell
NEAR TERM...Nocera/Doody/Sipprell
SHORT TERM...Doody
LONG TERM...Sipprell
AVIATION...Nocera/Doody/Sipprell
MARINE...Nocera/Doody/Sipprell


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