Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 241105
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
705 AM EDT Fri Mar 24 2017

.SYNOPSIS...
High pressure along the eastern seaboard will move offshore
later today, resulting in warmer and gusty weather today. A
cold front will push south across the region Saturday. This
stalled front will move northward on Sunday, resulting in a
battle of airmasses. This could bring a period of wintry precip
Saturday night, and again Sunday night. Heavy precipitation is
possible Monday as low pressure system moves over southern New
England. Another shot of precip is possible late Tuesday from
passing cold front.

&&

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

7 AM Update...

Overall trend in the forecast remains on track. surface
temperatures have remain steady overnight as precipitation
begins to move into upstate NY. Precipitation is struggling
eroding the low and mid level dry air per model soundings. this
has slowed the timing down by a few hours. Then a battle of what
the surface temps will be when precip moves into the area. 2m
temps are indicating temps will be warm enough for just rain thanks
to southerly winds ahead of the system.

However, there is a shot that the profile could moisten up just
enough for a few flakes to develop out ahead of the system.
Still do not anticipate much of a hazard issue. SPS will
continue.

Previous Discussion...
Today`s forecast will critically hinge on timing, and strength
of precipitation. Very dry air remains in place near the ground.
This dry air will delay the onset of precipitation until after
sunrise. Given the late March sun, and an strengthening
southwest wind, expecting a transition to all rain across
southern New England by afternoon.

Until that time, wetbulb cooling and temperatures starting out
in the teens and 20s will mean a window where some snow is
possible. The harder this snow falls, the greater the wetbulb
cooling, and the longer it will persist. Not expecting much
snow accumulation, with the greatest amounts towards northwest
MA. Once the transition begins, cannot rule out a period of
sleet or freezing rain. Low confidence on the timing for this,
so no Winter Weather Advisory at this time.

High pressure moving offshore will shift the flow enough where a
strong southwest low level jet develops towards southeast MA and
the coastal waters. The core of this jet is approaching 50 kt
later this afternoon. Have some concerns for stronger gusts
reaching the ground, but not a lot of confidence in
sufficiently deep mixing to maximize momentum transfer. Will
hold off on Wind Advisories for the Cape and islands.

&&

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

Clouds and a southwest flow of milder air will keep temperatures
from falling too much, and most of that should be this evening.
Still thinking temperatures may even rise a little overnight.
With a front just to our north, maintained a chance of rain
across northern MA, but low values for pops.

Saturday...

This front slowly moves south across our region. Near normal
temperatures expected, so any precipitation should be rain. Not
expecting a washout. The greatest risk for these showers will be
toward the western half of southern New England.

&&

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

* A period of wintry precip is possible Saturday night and again
  Sunday night
* Unsettled weather pattern will continue into Wednesday
* Improving conditions during the later half of next week

Pattern Overview...

00z models and ensembles are in agreement with the general
synoptic pattern for the extended. Still some timing and
thermal issues but overall confidence is improving. Active
pattern for the region with split flow aloft and several
shortwaves ejecting in from the Pacific. First wave is a 500mb
closed low over the Midwest on Sunday. This low deamplifies into
an open wave as it approaches the Northeast Monday. Due to the
confluent flow aloft, high pressure persists over northern New
England keeping surface temperatures cool, resulting in mixed
precip at times for the weekend into early next week. Heavier
precip possible on Monday as first open wave moves overhead. A
second wave will follow a similar path from the Plains towards
the Northeast before meshing or partially interacting with the
northern jet stream on Tuesday. This will result in another
system for New England Tues/Wed with high pressure to follow.

Details...

Saturday night into Sunday...Moderate confidence.

Confluent flow aloft with surface cold front south of southern
New  England. Cold air drainage from the high pressure over
northern New England will drop surface temps below freezing.
This is shown in surface winds which are due north. Mid-level
ridging will keep a warm layer around 850 mb which would aid in
the potential for mixed p-type. Biggest question is if there is
enough low level lift and/or overrunning for precipitation to
develop overnight. The higher theta- e values are well south of
the Pike and moreso near the south coast, which would limit the
mixed precip type as surface temps should remain above freezing
that far south. Still a lot of uncertainty with this time, but
believe that with the flow aloft, there appears to be enough low
level moisture for some spotty precip. If this occurs than a
winter weather advisory may be needed for the freezing rain
potential.

For Sunday, cold front will stall near the Mid-Atlantic as high
pressure moves southeast into the Gulf of Maine. Guidance
indicates that low levels will dry out Sunday morning keeping
the first half of the day dry. However, with mid-level ridge
axis overhead will see and increase in moisture thanks to
southwesterly flow aloft. At the surface easterly flow will
begin to dominate increasing the low levels throughout the day.
This could result in low clouds and drizzle. Surface temps will
warm above freezing thanks to mid-level ridge, but some areas
may struggle as cold air may be slow to dislodge/cold air
damming. Still a lot of uncertainty with this time frame.

Sunday night into Monday...Moderate confidence.

Stalled front south of the region looks to return back north as
a  warm front late Sunday into Monday, as surface low pressure
moves into the Great Lakes. Although warmer air aloft should
move easily back into the region, the low-level cold air may be
a little tougher to dislodge this time due to the nearby surface
high pressure. Believe this is the timeframe where we will see
the heaviest precip due to passage of the open wave and
development of a secondary low over the region. Still some
uncertainty with the thermal profiles but cross-sections,
soundings and even CIPS analogs show this timeframe has the
potential for icing especially north of the Pike. Still some
uncertainty with this timeframe as a difference of a degree or
two in the thermal profiles will change the p-type. Will
continue the mentioning of snow, sleet, ice and/or rain. Winter
weather advisories may be needed.

Monday night into Wednesday...Moderate confidence.

Weak ridging aloft as surface low moves offshore. Any lingering
showers will come to an end. 850 mb temps will continue to warm
overnight which will help keep surface temps above freezing.

Second wave will move into the region late Tuesday into
Wednesday.  this wave will drag a cold front across the region
bringing a periods of rain. Temperatures will remain seasonable
for both days.

Thursday into Friday...Moderate confidence.

Cold front will be offshore as upper level trough begins to take
hold over the Northeast. Appears to be the potential for another
arctic front with high pressure to follow.

&&

.AVIATION /12Z 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/...Moderate confidence.

Today and Tonight...

Mainly VFR with scattered MVFR in heavier showers. The greatest
risk for MVFR conditions will be north of the Mass Pike, and
especially across the higher terrain. Any frozen precipitation
should change to rain during late morning/early afternoon.
Southwest winds will gust 25-30 knots during the day, highest
along the coast and higher terrain. Winds diminish later
tonight.

Saturday...Periods of light rain with areas of MVFR cigs and
local MVFR-IFR vsbys.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday night...High confidence. Northerly winds with spotty
precip overnight. Terminals north of the Mass Pike have the best
chance for wintry precip.

Sunday into Monday...Moderate confidence. Showery weather to
start  with possible MVFR to IFR cigs. Precip chances increase
into Monday which could result in mixed precip for terminals
north of the Mass Pike.

Tuesday...Moderate confidence. Dry to start with showers in the
afternoon from passing cold front. Cigs may start out as VFR
lowering to MVFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

Today...Moderate confidence.

High pressure moves well offshore, bringing southwest winds to
the waters. Potential for wind gusts 25-35 knots. This will
build seas with 5 foot heights on many of the waters by this
afternoon. Patchy light rain may bring brief visibility
restrictions.

Gale Warnings for the eastern outer coastal waters, where
confidence is highest for a period of 35-40 kt gusts. Potential
for similar gusts across the other coastal waters near the Cape
and islands, just not enough confidence there will be a long
enough duration to warrant a Gale Warning. Will continue the
Small Craft Advisories across the remaining southern New England
coastal waters.

Tonight...High confidence.

Southwest winds diminish overnight, and become west toward
morning. Rough seas linger across the outer coastal waters, and
ocean-exposed south coastal sounds. Small Craft Advisories
will lower on Boston Harbor and Narragansett Bay, but linger
on the remaining waters.

Saturday...High confidence.

West winds becoming north to northwest as a cold front pushes
slowly south across the waters. This front is not expected to
push south of the waters until late afternoon.

Outlook /Saturday Night through Tuesday/...

Sunday...Moderate confidence. Cold front will be south of the
waters  as surface high pressure moves northeast of the region.
Conditions should remain below SCA but if the front gets closer
than seas and winds may be a bit stronger.

Monday...Moderate confidence. Approaching upper level system and
passing warm front will increase precip as well as wind and seas
of  the waters. SCA may be needed.

Tuesday...Moderate confidence. Cold front will pass over the
waters  increasing them to above 5 feet. SCA may be needed.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 10 AM this morning to 6 AM EDT
     Saturday for ANZ232>235-237.
     Small Craft Advisory from noon today to 8 PM EDT this evening
     for ANZ230.
     Gale Warning from 4 PM this afternoon to 9 PM EDT this evening
     for ANZ231.
     Small Craft Advisory from 10 AM this morning to 10 PM EDT this
     evening for ANZ236.
     Gale Warning from 1 PM this afternoon to midnight EDT tonight
     for ANZ250-254.
     Small Craft Advisory from 10 AM this morning to 3 AM EDT
     Saturday for ANZ251.
     Small Craft Advisory from 10 AM this morning to 6 PM EDT
     Saturday for ANZ255-256.

&&

$$
SYNOPSIS...Belk/Dunten
NEAR TERM...Belk/Dunten
SHORT TERM...Belk
LONG TERM...Dunten
AVIATION...Belk/Dunten
MARINE...Belk/Dunten


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