Area Forecast Discussion
Issued by NWS Boston, MA

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996
FXUS61 KBOX 250849
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
449 AM EDT Sat Mar 25 2017

.SYNOPSIS...
A cold front will push south across the region today. This
front will stall just to our south tonight, then will try to
push northward as a warm front Sunday. Active weather pattern
continues into Tuesday, with the potential for wintry precip
Sunday night. Below average temperatures return by mid-week
with another shot of precip by the end of next week.

&&

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

A cold front will work its way south across our region this
morning. Winds turn north, then northeast behind this front.

Even though this front should be to our south, most of the
guidance continues to show an impressive back of Q-vector
convergence and upper level divergence to the north of this
boundary. Enough moisture should remain where there is a high
probability for light rainfall at times, especially from mid
morning into this afternoon.

Nearly steady temperatures today.

&&

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

A high pressure over southeast Canada and northern New England
will nudge slightly farther south tonight into Sunday. Still
expecting dry weather for much of tonight. The high pressure to
the north is a near classic cold air damming signature. It will
also provide an excellent overrunning surface.

Low level ageostrophic winds become north late tonight at 1000
mb and 925 mb. The ageostrophic winds at 925 mb shift east to
southeast Sunday morning, a sign of increasing warm air
advection aloft.

Depending upon the timing of precipitation tonight into Sunday,
there is a window for a period of sleet or freezing rain across
the interior. The areas most a risk are central and western MA,
northern Ct and northern RI. Expecting temperatures to rise
above freezing by noon Sunday, ending the threat of mixed
precipitation. Will need to monitor the extent of the low level
cold pool very carefully. This timing may change with later
forecasts.

Near normal temperatures expected tonight, and Sunday.

&&

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

Highlights...

* A period of wintry precip including sleet/frz rain Sunday night
* Unsettled weather pattern will continue into Tuesday
* Improving conditions for mid-week
* Active weather returns late in the week into the weekend

Pattern Overview...

00z models and ensembles continue to show an active weather pattern
for the region with split flow aloft and several shortwaves ejecting
in from the Pacific. First wave is the closed 500mb low currently
over the southern Plains. This low deamplifies into an open wave as
it approaches the Northeast on Monday. Surface high pressure
persists over northern New England keeping surface temperatures
cool, resulting in mixed precip at times 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 interacting with the northern jet stream on Tuesday
bringing another shot of precip. Lots of uncertainty with the next
southern stream wave and its potential interaction with the northern
stream late in the week.

Details...

Sunday night into Monday...Moderate confidence.

*** Increasing chances for a period of sleet/freezing rain across
the higher terrain Sunday night into Monday morning ***

Stalled front south of the region will begin 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 due to the nearby surface high pressure. Both the NAM
and high-res versions of the EC and GFS are indicating northerly
winds across the CT Valley, a clear sign of cold air damming.

While the surface cold air is in place, the focus then turns to
precipitation amounts and timing. Spotty light precip may start out
during the first half of the night, but as the upper level shortwave
approaches, there appears to be enough synoptic lift for higher qpf
chances. While there is 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. Sleet and freezing rain are the main concerns, with the chance
that freezing rain could be ongoing during the Monday morning
commute. Keep in mind that a difference of a degree or two in the
thermal profiles will change the p-type. Winter weather
headlines may be needed.

Surface temps will eventually warm above freezing during the later
half of the day, with the chance that some sites may struggle to get
into the 40s due to cold air damming. Models continue to advertise
that Monday morning into the early afternoon will see the highest
QPF thanks to synoptic lift from passing open wave and the
development of a secondary low over the region. PWAT values also
increase above an inch, so widespread rainfall is possible. Precip
chances will begin to wind down by the evening hours. Overall it
appears that Monday will be a chilly, raw, damp day especially north
of the Pike. South of the Pike has the chance of getting into a warm
sector with temps near 50F.

Monday night into Wednesday...Low confidence.

Weak ridging in the mid-levels will result in a break in the precip.
Focus then turns to the secondary Pacific wave which is just now
moving onshore. This wave will interact with the northern stream but
the question is how soon and will this slow the precip chances down
per previous runs. EC has become less amplified and more progressive
compared to the GFS which could result in a more zonal flow during
this period. This difference could result in a slow down to
precipitation timing and temperature differences Tuesday into
Wednesday. However both models continue to show arctic front passing
through by the second half of Wednesday. Overall expect near
seasonable temperatures for this period with precip chances sometime
between Tuesday and Wednesday. Confidence will increase once models
have a better sampling of onshore Pacific wave.

Thursday...Moderate confidence.

Upper level trough overhead as a few shortwaves moves through the
flow. Canadian high pressure will build into the Northeast leading to
a break in the precip chances.

Friday into the weekend...Low confidence.

Active pattern remains for the region with the next southern stream
wave interacting with the northern stream. The EC continues to be
more amplified than the GFS stalling the timing of any precip on
Friday. Latest ensembles appears to be trending this way as well.
Overall this portion of the forecast will depend on the strength and
timing of the upper level wave and thus surface reflections. Because
of the large spread in the guidance will continue with low
confidence forecast.

&&

.AVIATION /08Z 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/...Moderate confidence.

Today...A cold front moves north to south across the region
this morning. An area of light rain should develop, with cigs
and vsbys lowering to MVFR. Winds shift from the north this
morning, then northeast this afternoon and evening.

Tonight...Mainly VFR as high pressure builds from the north.
MVFR will lurk to our southwest, preparing to move north again.
East flow through the night.

Sunday...mainly VFR, with areas of MVFR in precipitation. Some
freezing rain or sleet possible Sunday morning.

KBOS TAF...High confidence in TAF trends. Moderate confidence in
timing.

KBDL TAF...High confidence in TAF trends. Moderate confidence in
timing.

Outlook /Sunday Night through Wednesday/...

Sunday night...Moderate confidence. Cigs lower to MVFR/IFR in
due to increasing low level moisture. Spotty precip will
increase closer to daybreak. Anticipate areas of -FZRA/-PL
across the interior overnight.

Monday-Monday night...Moderate confidence. Any leftover
-FZRA/-PL Monday morning will end across higher terrain.
Otherwise MVFR-IFR CIGS in rain.

Tuesday into Wednesday...Low confidence.
MVFR conditions within any passing rain showers with improving
cigs to VFR by Wednesday. N/W winds continue.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Sunday/...

Today...High confidence. W winds shift to N this morning and
early afternoon as a cold front moves north to south. Winds then
shift from the northeast by afternoon as high pressure moves in
from Quebec. Winds will be less than 25 knots through the day.
Seas will linger at 5 feet on the southern outer waters and
parts of RI Sound much of the day. Small Craft Advisories
continue where needed.

Tonight...High confidence. Northeast winds turn from due east
overnight. Speeds remain below 20 knots through the night. Seas
will remain less than 5 feet through the night.

Sunday...High confidence. East winds continue less than 20 kt
Sunday. Seas remain less than 5 feet.

Outlook /Sunday Night through Wednesday/...

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

Tuesday into Wednesday...Moderate confidence. Frontal system
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 until 8 PM EDT this evening for
     ANZ254>256.
     Small Craft Advisory until noon EDT today for ANZ235.

&&

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



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