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Area forecast discussion
National Weather Service Taunton Massachusetts
245 PM EST Sat Jan 20 2018

Synopsis...

A couple of weak cold fronts in the neighborhood bring a few
clouds, but otherwise fair and mild weather tonight and Sunday.
A storm system will bring the potential for heavy rain and
strong coastal winds on Tuesday, but this will be preceded by a
risk of some wintry mix/ice across the interior late Monday into
Tue morning. Blustery, dry and colder weather follows Wednesday
through Friday.

&&

Near term /through tonight/...

The remains of a weak cold front were moving through this afternoon
and evening. But the air was so dry that all we saw were an area of
clouds above 15k feet. Mixing did bring gusty winds, some reaching
30-40 knots, but these will be diminishing this evening.

High pressure builds in with dry weather. Fair skies, light wind,
dew points in the 20s... expect min temps in the mid 20s to low 30s.

&&

Short term /Sunday through Sunday night/...

High pressure in place Sunday with fair skies and light wind.
Moisture fields do show some increasing mid and high level moisture,
so expect some increasing clouds mostly in the afternoon/evening.
With mixing to 950 mb, expect Max temps in the mid to upper 40s, a
few spots around 50.

The clouds increase Sunday night. A cold front in northern New
England dips south and may slip through southern New England. But
with the upper flow west-east we do not expect a lot of push to it,
and potential that it stalls either over or near US. The net change
in the airmass is nil, so min temps Sunday night should be similar
to tonight.

Low level southerly winds reach only to western New York/PA by 12z
Monday...still west winds over US at that time...which means little
lift to be generated Sunday night. So the probability of precip
should be low. If the precipitation were to move in faster,
low level temperatures would support a mix with sleet and
freezing rain. But that scenario looks unlikely at this time.

Our forecast shows slight chance pops in western Massachusetts/CT by 12z
Monday, and that may be overplaying the liklihood.

&&

Long term /Monday through Saturday/...
highlights...

* risk of light wintry mix/ice interior Massachusetts late Mon into Tue am
* a period of heavy rain and strong coastal winds likely Tue
* dry and colder Wed-Fri

Sunday night into Monday night...

Subtle cold front will drop south across southern New England late Sun night
into Mon as strong high pres builds across southeast Canada. Weak
overrunning to the north of this stalled boundary and a gradual
moistening of the column will result in light precip developing
across sne, mainly Mon afternoon into Mon night. Pronounced
cold air damming signature noted with high pres over the
Maritimes and sfc ridging nosing down across southern New England will set the
stage for some wintry precip in the interior. Thermal profiles
initially support mixed precip with some light snow/sleet/freezing
rain into the evening, with risk transitioning to areas of
freezing rain during Mon night interior northern Massachusetts as warming
aloft becomes more pronounced while low level cold air hangs
tough. Some uncertainty with how long low cold air near the
surface hangs on but some of the guidance has it lingering into
Tue morning for interior northern Massachusetts. Increasing risk for some
travel impacts.

Tuesday...

Other than a risk of some freezing rain lingering across interior
northern Massachusetts in the morning, ptype will be all rain. Period of heavy
rain appears likely on Tue moving west to east across southern New England as strong
low level jet develops ahead of the cold front. Precipitable water anomalies +2sd
with low level wind anomalies up to 2-3sd which is a good signal for
heavy rainfall. In addition, marginal elevated instability develops
supporting a risk of some convection and elevated thunder.
Deterministic GFS/ECMWF/ggem all show potential for quantitative precipitation forecast of 0.75 to
1.5 inches and ensemble guidance supports this with moderate to high
probs of 1+ inches. This system is rather progressive which should
prevent rainfall from exceeding these amounts.

Other concern for Tue is potential for strong winds accompanying the
65-70 kt low level jet. Low level lapse rates are forecast to be
near moist adiabatic which would allow for decent mixing, especially
where temps get into the 50s across Rhode Island and eastern Massachusetts. Potential for
Wind Advisory gusts, especially in any heavier showers/convective
activity.

Not expecting much impact to river ice as there is only a brief
window of higher temps/dewpoints on Tue followed by colder
conditions.

Wednesday through Friday...

Turning colder and blustery behind the departing storm in northwest flow
pattern. Temps near normal Wed trending below normal Thu/Fri.
Coldest day expected to be Thu as gefs and eps showing ensemble mean
850 mb temps dropping to -12 to -14c across southern New England. Temps on Thu likely
remaining below freezing across much of southern New England with 20s interior.
Mainly dry weather expected during this period, although a
brief flurry/snow shower can't be ruled out Wed/Thu over higher
terrain as a few shortwaves move through.

&&

Aviation /20z Saturday through Thursday/...
forecaster confidence levels...

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

Short term /through Sunday night/...

Tonight...high confidence.

VFR. Diminishing west wind this evening.

Sunday...high confidence.

VFR. West-northwest winds around 10 kt or less as pressure gradient
relaxes.

Sunday night... moderate confidence.

VFR. Increasing sky cover late at night.

Kbos terminal...high confidence in taf.

Kbdl terminal...high confidence in taf.

Outlook /Monday through Thursday/...

Monday: MVFR/IFR conditions possible. Chance ra, pl, snow.
Slight chance freezing rain.

Monday night: mainly MVFR, with areas IFR possible. Rain likely,
freezing rain likely interior northern Massachusetts.

Tuesday: mainly MVFR, with local IFR possible. Windy with gusts
to 30 kt. Rain. Pockets of freezing rain possible early interior northern
Massachusetts.

Tuesday night: VFR. Windy with local gusts to 30 kt.

Wednesday: VFR. Windy with areas gusts to 30 kt.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday night/...high confidence.

Tonight...

Diminishing wind this evening and overnight as high pressure builds
over the waters. Expect winds below gale this evening and dropping
below Small Craft Advisory levels tonight. Seas also subsiding
tonight with the southern outer waters the last to drop below 5 feet
late tonight. We are dropping gales with this forecast, and holding
on to Small Craft Advisory for a few hours tonight.

Sunday and Sunday night...

High pressure over the waters should provide fair weather with light
winds and seas below 5 feet. Clouds will increase overnight, but
support for any precipitation will remain well to our west during
the night.

Outlook /Monday through Thursday/...

Monday: winds less than 25 kt. Slight chance of rain.

Monday night: winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain.

Tuesday: low risk for gale force winds with gusts up to 35 kt.
Rough seas up to 12 ft. Rain.

Tuesday night: moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Rough seas up to 11 ft.

Wednesday: low risk for gale force winds with gusts up to
35 kt. Rough seas up to 11 ft.

&&

Hydrology...
a Flood Warning remains in effect for the Connecticut River at
Middle Haddam, where ice jams are causing river fluctuations.

For details on specific area rivers, including observed and
forecast river stages, please visit the advanced hydrologic
prediction service (ahps) graphs on our website.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Gale Warning until 4 PM EST this afternoon for anz232>235-237-
250.
Small Craft Advisory until 4 PM EST this afternoon for anz230.
Small Craft Advisory until 10 PM EST this evening for anz231-
251.
Small Craft Advisory until 6 PM EST this evening for anz236.
Gale Warning until 6 PM EST this evening for anz254-255.
Gale Warning until 5 PM EST this afternoon for anz256.

&&

$$
Synopsis...wtb/kjc
near term...wtb

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