Area Forecast Discussion
Issued by NWS Boston, MA

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973
FXUS61 KBOX 141146
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
646 AM EST Sat Jan 14 2017

.SYNOPSIS...

High pressure moves E of the region today with a weak low pres
sliding well S of the coast overnight. Some light snowfall is
possible mainly across Connecticut, Rhode Island and Southeast
Massachusetts late today and tonight. High pressure maintains dry
and seasonable conditions Sunday and Monday, then milder temperatures
return for the rest of the week with a wet period around midweek.

&&

.NEAR TERM /UNTIL 2 PM THIS AFTERNOON/...

7 am update...No major changes to the forecast.

Low lvl pres gradient and a persistent band of CI continue to
influence the temps across New England this morning, primarily,
keeping them warmer than previously forecast. Even Meso-west data
shows the coldest valleys have not fully decoupled this morning.
2m temps are handling this better than MOS which is as much as
10-15F colder than current temps.

Used this blend through the early afternoon hours, especially
since the CI band will give way to a BKN-OVC AC band in advance of
weak low pres developing near the Delmarva. Have highs reaching
the upper 20s and low 30s. Dry wx prevails everywhere through mid
afternoon thanks to 1040+ high pres slowly sliding offshore. Winds
remain light, but will back to the S-SW by afternoon.

&&

.SHORT TERM /2 PM THIS AFTERNOON THROUGH 6 PM SUNDAY/...

Late today and overnight...

Weak low pres developing off the Delmarva will slide well S of the
40/70 benchmark just after midnight tonight. With center of high
pres more E of S New England overnight than N, this will allow
weak mid lvl f-gen band N of the developing low pres to just brush
S Coastal New England during the evening hours.

Sounding data suggests moisture loading from H7-sfc, but mainly S
of a line through the border of MA with RI/CT and continuing E.
Areas N remain under the subsidence of high pres and are not able
to moisten enough to be of impact. S of this line, where PWATs
reach about 0.75 inches just offshore light snowfall is possible,
mainly from late afternoon into the early overnight hours. F-gen
is weak and omega from this is below the primary snow growth
regime but within the region saturated in respect to ice.
Therefore, some light accumulations are possible below an inch,
and likely even below a half inch most locations, especially as
one heads N, where only flurries can be expected.

Overnight mins dip mainly into the 20s, as the cloud cover
associated with the wave will limit the ability for radiational
cooling until late.

Sunday...

Secondary high pres/ridging will allow for clearing and weak pres
gradient/winds and dry wx after clouds clear from exiting low
pres. H92 temps hover between -6C and -8C, but once again
subsidence inversion could limit mixing. In spite of sunrise, will
be limiting highs to the low-mid 30s primarily.

&&

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

*/ Highlights...

 - A warmer than average, wet weather pattern by midweek
 - Low confidence forecast going into the late-week

*/ Discussion...

Signals of mild and wet-weather outcomes into late January continue.
E CONUS / E Canada beneath favorable H5 ridging on the order of +1-2
standard deviations with H85 temperature anomalies in excess of +20C
for portions of Canada based on a consensus of forecast N Hemisphere
atmospheric teleconnections. Winter appears to be taking a vacation.
Much of impacts of the nuisance variety there may be only two things
to be concerned about: 1) Breezy S winds that could turn out strong,
and 2) Areas of dense fog at times.

Despite discrepancies among forecast solutions in handling mid-level
energy emerging out of the Pacific as well as the cut-off low across
the SW CONUS, there is a general trend of rain moving in on Tuesday.
This subsequent of low-mid level isentropic over-running of a decent
plume of sub-tropical moisture with precipitable waters in excess of
an inch, brought N via a H925-85 SW low level jet of 35 to 45 mph. A
risk of freezing rain with onset given lingering high pressure over
SE Canada which yields undercutting cold air as low pressure sweeps
across the Great Lakes. Area of concern mainly N/W MA and CT within
the low-lying valleys, sheltered from S flow. Prior to the inside-
runner low, it is more than likely will see some N funneling winds
ahead of the aforementioned low that may keep the cold air and thus
the freezing rain threat. Otherwise, storm-total rainfall consensus
of around half an inch through Wednesday along a lifting warm-front
prior to a sweeping cold front. Persistence the last several days,
will lean towards likely PoPs. Mild temperatures.

Hereafter a low confidence forecast as deterministic and ensemble
solutions struggle with handling individual shortwaves. In addition
there appear to be complications between preferred ridging across
the E CONUS along with a potential downstream block. It`s possible
high pressure and colder air out of Canada may sneak S into the area
despite atmospheric teleconnections suggesting milder temperatures.
Leaning with ensemble means.

&&

.AVIATION /12Z 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/...

12z update...No major changes to the forecast.

Through 18Z...High confidence.
VFR. Winds NW, shift mainly to SW this afternoon, but remain
light.

This evening and overnight...Moderate confidence.
VFR remains N of a line along the MA border with CT/RI into SE MA.
S of this line, light snowfall is possible, with some light
accumulations (less than an inch) possible especially near the
coast and over the Islands. This could yield a period of MVFR
conditions in lowered vsbys and CIGS. Conditions clear during the
early morning hours Sun. Winds S-SW, but shift back to the NW
after snows end.

Sun...High confidence.
VFR. NW flow, mainly 10 kt or less.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF overall. Low risk for very light
snowfall this evening, but VFR likely to dominate.

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Sunday night through Monday night...

VFR. Increasing SW winds. Increasing cigs, lowering down to low-end
VFR late.

Tuesday through Thursday...

Lowering to IFR with -RA. Continued breezy S winds. Potential LLWS
impacts. Improving late.

&&

.MARINE...

Forecaster Confidence Levels...

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

Short Term /through Sunday/...

12z update...No major changes to the forecast.

Through mid morning...High confidence.
Have extended small craft advisories until after sunrise
everywhere as winds/seas are slower to decline than previously
forecast, however they should diminish within a few hours of
sunrise.

Late today into Sunday...High confidence.
Winds will shift to the S-SW but remain below small craft
thresholds into the overnight hours before they turn back to the
NW late tonight and early tomorrow morning. Even with this shift,
gusts should remain below small craft thresholds. Seas will
diminish this morning, and then remain below 5 ft.

Some rain, even mixing with snow in spots late today and overnight
will yield brief vsby restrictions.

Outlook /Sunday Night through Wednesday/...Moderate confidence.

Breezy NW winds shifting out of the W/SW early. Seas diminishing
below 5 feet into Monday morning. Quiet into Tuesday. Will then be
watching a warm front lift N across the waters with rain behind
which S/SW winds will become breezy with a low risk of gales. Seas
potentially building 8 to 10 feet on the S/SE waters. Will see
conditions improve late Thursday.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...

CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 AM EST this morning for
     ANZ231>234-251-255-256.
     Small Craft Advisory until 10 AM EST this morning for ANZ250-
     254.

&&

$$

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



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