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Area forecast discussion
National Weather Service Taunton Massachusetts
134 PM EDT Tue Mar 28 2017

Synopsis...

Wet weather continues through tonight. Some improvement expected
on Wednesday. High pressure brings dry and cool weather Wednesday
night and Thursday. Low pressure from the Ohio Valley passes south
of New England over the weekend. This brings a mix of precipitation
Friday and Saturday, followed by dry weather Sunday and Monday.

&&

Near term /until 6 PM this evening/...

1 PM update (updated previous discussion)...

Low clouds persist ahead of later day showers / widespread rain
and an isolated risk of thunderstorms.

First, low clouds. Despite daytime heating, the kinked frontal
boundary remains, unlikely to budge until the surface low off
the mid-Atlantic sweeps by. Plenty of moisture trapped beneath
the h925 inversion within the shallow cool airmass, clouds not
expected to go anywhere. Not much rise in temperatures, highs
in the mid to upper 40s. North/East winds.

Secondly, wet-weather and isolated risk of thunderstorms. Generally
speaking, low pressure presently across the mid-Atlantic pushes
east. Parent with a weak open-wave mid level impulse, associated
lift and ascent, frontogenetically along attendant surface
frontal boundaries of a decent moist- instability axis, and weak
cyclogenesis, deep layer forcing is expected.

Moderate rain is expected with forcing of anomalous precipitable
waters, widespread over S New England given the environment of
strong Omega forcing. Yet focus along the S coast of New England
and adjacent S waters where instability converges. Already seeing
activity emerging around the NYC tri-state region where Storm Prediction Center meso-
analysis shows a nose of low instability (mucape) creeping north with
values of 100 j/kg. Several convective indices meeting or exceeding
thresholds as well. Some uncertainty on the better convergence
area. Consensus of near-term high-res guidance there is some subtle
discrepancy north-S across the aforementioned S region. Will come down
to near-term trends. Will be interesting to see what develops over
Virginia / NC and anything offshore, whether better instability and
moisture are robbed north. Again, however, widespread rain is expected
with the heaviest more in the vicinity of the S coast.

So overall, still thinking we'll see a decent slug of rain going
into this afternoon and evening. Amounts of 0.50 to 0.75 with
the heavier amounts focused S/E. Some locations, especially along
the S coast may see higher amounts where there is a greater risk
for convection.

&&

Short term /6 PM this evening through 6 PM Wednesday/...

Tonight...
frontal wave once again shifts east of the region during the
overnight hours. This will once again allow a mix of cold
advection and drier air to entrain from west-east especially from
about 03z to 09z. Rainfall gradually dissipates, but it may take
some time for the lowest lvl moisture to fully erode.
Therefore, some fog and low clouds may linger beyond the precip
ending times. May need to monitor for a few spots of patchy
dense fog as a result. Otherwise, another mild/damp night for
the most part, but cooling will occur within a few hours of
sunrise such that min temps could drop back into the mid 30s.

Wednesday...
finally a break from the prolonged damp conditions. Drier air
will entrain through the entire column through the day allowing
skies to clear and sunshine to poke through. Although some cold
advection clouds may increase through the peak afternoon
heating. 850 mb temps, although cooling are still near 0c by early
afternoon. Therefore, highs could easily still reach the upper
40s and low 50s especially where enough sunshine is observed.
Breezy with north-northwest flow increasing through the day, gusts could
reach 25-30 mph at times.

&&

Long term /Wednesday night through Monday/...

Big picture...

A rather flat longwave pattern with individual shortwaves moving
east through that flow. One shortwave moves off through the
Maritimes Wednesday night. Another ejects out of the southwest USA
and crosses New England Friday-Saturday.

Models continue to change run-to-run, leaving low confidence in the
details.

Details...

Wednesday night-Thursday...

Surface low pressure passes south of Nova Scotia as high pressure
builds in from Canada. Strong pressure gradient between the systems
will maintain north breezes along the eastern Massachusetts coastline with
lighter winds farther inland. The resulting cold advection should be
sufficient to maintain mixing from at least 950 mb where winds will
be 30-35 knots. This will mean gusty winds in at least eastern
Massachusetts early in the night, diminishing overnight as the
pressure gradient diminishes.

High pressure builds over New England Thursday, bringing fair skies
and mixing to between 850 and 900 mb. Temps at these levels support
Max sfc temps in the 40s.

Friday-Saturday...

Questions continue with end-of-week system. General model agreement
on surface low moving up the Ohio Valley and then jumping to the mid
Atlantic coast Friday night, passing south of New England Saturday
or Saturday night. Projected low level winds show 25-30 knot
southeast jet from New Jersey through eastern PA and central New York at 12z
Friday. Light south flow into western CT and western Massachusetts. Meanwhile
model quantitative precipitation forecast shows measurable pcpn almost all the way to Boston.
We passed on a straight importing of the model values in favor
of limiting morning pops and quantitative precipitation forecast to areas Worcester and
west...then spreading east to the rest of our area during the
afternoon/evening. Timing and track of the surface low and
resulting northeast winds supports likely pops across all of
southern New England. Precipitable water values reach .75 to
1.00 inches over our area.

Temperatures and resulting precip type are also a lingering
question. High pressure departing through the Maritimes provides a
small cold air damming signal, both in the pressure pattern and a 25
knot low level ageostropic flow. Surface winds off the Gulf of Maine
should keep coastal areas above freezing, and daytime temps may
nudge above freezing each day. But interior locations may at least
have a rain/snow mix and may see a period of sleet or freezing rain
especially Friday night and Saturday morning.

Sunday-Monday...

High pressure builds in with dry weather. Building heights and
warming temps aloft suggest Monday will be several degrees milder
than Sunday.

&&

Aviation /18z Tuesday through Sunday/...

Forecaster confidence levels...

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

Short term /through Wednesday/...

18z update...

Today into tonight..high confidence.
Hold with IFR/LIFR with ceilings below 1900ft. Vsbys remain mostly
VFR. Lowering MVFR-IFR with -ra/ra, low risk thunderstorms and rain. North/East flow.
Improving towards morning west to east. VFR into the CT River Valley
however remaining S New England likely to remain beneath IFR-LIFR.

Wednesday into Wednesday night...high confidence.
Improving conditions through morning with VFR everywhere by 18z,
lingering longest over the cape and islands. North-northwest winds. Gusts to
20-25 kt at times.

Kbos taf...will hold with IFR through 12z Wednesday. Cigs 800
feet or less. -Ra/rain moving through 20z-6z. Some variability in
visibility during this time frame, though a lowering trends
prior to North/East winds shifting out of the west.

Kbdl taf...will hold with IFR through roughly 9z Wednesday with
cigs 800 feet or less. -Ra moving in presently becoming rain late
afternoon into evening, improving shortly before midnight. Vsbys
variable though a downward trend overnight with North/East flow before
winds become west.

Outlook /Wednesday night through Saturday/...

Thursday...

VFR. Winds diminishing through Thursday.

Friday-Saturday...

MVFR lowering to IFR in the afternoon, then IFR/LIFR cigs/vsbys
Friday night and Saturday. Rain expected but with a period of sleet
and freezing rain possible inland Friday night-Saturday. East-
southeast winds Friday become northeast by Saturday.

&&

Marine...

Forecaster confidence levels...

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

Short term /through Wednesday/...

1 PM update...no major changes to the forecast.

Today and tonight...high confidence.
Mainly quiet boating weather as winds and seas remain below
Small Craft Advisory thresholds. These winds will shift, mainly
east today, then veer around to the northwest by early tomorrow morning.
Fog/drizzle along with showers may lead to low visibilities at
times. Low risk for a modest thunderstorm on the waters late
today through the early overnight hours, especially on the
southern waters.

Wednesday...high confidence.
Northwest flow increases with gusts 25-30 kt at times through the day
and seas on the east waters increasing to 5-7ft by late Wed
afternoon. Small craft advisories will be needed.

Outlook /Wednesday night through Saturday/...

Wednesday night...low-moderate confidence.

Low confidence for low-end north gales along the eastern waters.
Otherwise moderate confidence for north winds gusting 25-30 knots,
diminishing overnight. Seas 5 to 8 feet, mainly on the eastern and
southeast outer waters. A Small Craft Advisory will be needed.

Thursday...high confidence.

Diminishing north wind with speeds near 25 knots during the morning.
Seas 5 to 8 feet on the eastern outer waters diminishing through the
day. Lingering Small Craft Advisory will be needed in these areas.

Friday-Saturday...moderate-high confidence.

Midwest weather system moves to the mid Atlantic coast Friday and
passes south of New England Saturday. Increasing southeast winds
during Friday but speeds remain below 25 knots until Friday night.
Winds turn from the northeast Saturday and from north Saturday night
with speeds 25-30 knots. Seas build Friday night and Saturday with
heights 5 to 7 feet. Small Craft Advisory will be needed.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...wtb/doody
near term...sipprell

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