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Area forecast discussion
National Weather Service Taunton Massachusetts
1029 PM EDT Sat Mar 25 2017

Synopsis...
a cold front lingers offshore well south of New England tonight.
This front will then push northward as a warm front Sunday.
A weather system lifts through the Great Lakes Sunday and
Monday, bringing a wintry mix inland and wet weather near the
coast. Another low pressure will move across southern New
England Tuesday, bringing some rain showers. High pressure
brings dry but cooler weather Wednesday and Thursday. Then more
precipitation possible late Friday into Saturday.

&&

Near term /until 6 am Sunday morning/...
1029 PM update...

Forecast remains largely on track this evening. Mainly clear
skies away from the immediate South Coast of New England.
Temperatures already below freezing at many locations north of
I-90 and outside of the urban centers. This may result in some
icy spots on untreated surfaces Sunday morning.

Tweaked temperatures and winds to reflect observed conditions.
Also slowed the return of precipitation chances later tonight.

715 PM update...

Skies had begun to rapidly clear across northern Massachusetts early this
evening. This trend should continue across our area by
midnight. Per composite guidance, the cloud shield motion stalls
over SW CT and Long Island between midnight and 3 am, then
slowly builds north again.

Shortwave ridge aloft builds east into our area tonight. This
turns our upper flow from the northwest. This allows surface
high pressure centered over Quebec to build south into New
England.

So expect clearing or partial clearing most places. A northeast
marine wind will not carry any low dew points, but we should see
a small lowering trend through early tonight. Min temps expected
to be a little above dew point, in the mid 20s to lower 30s.

&&

Short term /6 am Sunday morning through Sunday night/...
Sunday...

High pressure shifts east into the Maritimes. The pressure
builds southwest through New England with a typical cold air
damming signal. Ageostrophic winds at 1000 mb turn from north
Sunday morning at 10-15 knots...would like to see that a little
higher, but the direction is good.

The ggem is most aggressive in bringing precip north into New
England...and even that is west of Hartford at 12z Sunday. Most
of the others are not even in New England. The strongest low
level winds and resulting lift will be in New York/PA, with little
wind over here. Expect most of the precip to be to our west,
with light quantitative precipitation forecast in western New England...about 0 to 0.03 inches.

Temperature profiles suggest that if there is any precip, it
would involve rain or a rain/sleet mix and mainly for the
western and central hills. Consensus timing would bring any
chance for the precip into western New England late morning. If
anything reaches farther east it would be in the
afternoon/evening, by which point temperatures should be above
freezing.

Model high temps show upper 30s in the hills and low-mid 40s
lower down. With clouds, cold air damming, and the chance of
pcpn, we opted to undercut this by 2-4f. Forecast Max temps will
be in the mid 30s to low 40s.

Sunday night...

The stronger low level south winds shift farther east Sunday
evening and bring a greater potential for lift and precip
production. The upper ridge also shifts east at this time,
bringing under the influence of the approaching Great Lakes
shortwave and associated upper jet. This will mean an increasing
chance of precip during the night.

Temperature profiles show a layer of above-freezing air between
800-900 mb with Max temps around 3c. This indicates a sleet
potential, especially overnight as cooling surface temps may
allow the precip to refreeze below the warm layer. A 3c
temperature is on the low side for freezing rain production, but
close enough to consider the possibility.

Precip amounts start the evening light, but will build up
overnight as the shortwave and low level lift increase. This
will be a concern just as the early Monday morning commute gets
started. We are anticipating the need for winter weather
headlines starting sometime during the night.

&&

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

* rain Monday and showery on Tuesday
* sunshine mid-week
* more precipitation late Friday into Saturday

Upper level pattern overview...

Several short wave troughs moving through our region through the
upcoming week. The first is weak and moves through on Mon. The
next is stronger and closes off an upper low as it moves through
northern New England on Wed. Then large model differences occur,
with the European model (ecmwf) much more amplified with a ridge over our region
Thu and a sharp trough approaching by Sat. Other models have a
more benign west-southwest flow aloft over the region in that
time frame.

Details...

Monday...moderate confidence.

Southerly low level jet of 30-40 kt will usher warmer air into
the region Monday morning, changing any leftover freezing rain
in the hilly terrain of western and north-central Massachusetts over to all
rain by mid to late morning. A weak surface warm front will
become stationary over southern parts of the region while a weak
wave of low pressure develops along the front. Due to cold air
damming, areas north of the Mass Pike will take longer to reach
the lower 40s but in northern CT, RI, and southeast Massachusetts we are
forecasting highs to reach the upper 40s.

Rain is likely across the region...and it could be briefly
moderate to heavy at times...with generally about one-half inch
of rainfall expected in most places. Mon. Afternoon total totals
reach 50 and k reaches 25-30 but with no cape, have not
mentioned any thunder.

Monday night into Tuesday night...moderate confidence.

As the upper level shortwaves trough moves away from our region,
it will be replaced by a weak mid-level ridge Monday night.
There will be a lull or complete break in the precipitation
Monday night. Skies will remain cloudy with perhaps some
drizzle, which will keep low temperatures in the upper 30s and
lower 40s.

Another weak low pressure area will be moving through on
Tuesday, accompanied by positive vorticity advection with the upper shortwave trough axis
late in the day. There is a chance of showers anywhere during
the day. Model high temperatures have come way up, due to 925 mb
temperatures possibly nearing 8c to 9c. Have split the
difference between the warm GFS and the cooler European model (ecmwf) and am
forecasting highs mainly in the 55 to 60 range...cooler along
the coast.

That system departs Tuesday night with shower chances
diminishing. Lows mainly 35 to 40.

Wednesday through Friday morning...

Cold air aloft will overspread southern New England as strong
high pressure over Hudson Bay Wednesday morning builds across
the New England region by Friday morning. Late March sunshine,
however, will allow high temperatures to still reach into the
lower 50s Wednesday and mid 40s to lower 50s Thursday and
Friday. Mostly clear skies could allow nighttime lows to dip
well into the 20s in northern and western areas each night, with
the coldest being Thursday night.

Friday afternoon into Saturday...low confidence.

All models agree on an increase in cloudiness Friday afternoon.
But there is much uncertainty as to whether low pressure will
track across the region or skirt the area to the south.
Currently, we have a chance of showers in the forecast.
However, depending on timing, there is a low chance that
Northwest Hills of Massachusetts could have a touch of freezing rain early
on Saturday morning - April 1...no foolin'. Again confidence is
low that far out.

&&

Aviation /02z Sunday 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/...moderate confidence.

Tonight...high pressure builds from the north. This will bring
clearing skies between 8 PM and midnight, as well as an
improvement to VFR. Patchy IFR in fog, some of which may be
fzfg. Light east-northeast flow through the night. Areas of
MVFR may redevelop after midnight in CT. GFS implies an area of
low ceilings moving onshore of eastern Massachusetts overnight, too. Will
need to watch for that.

Sunday...

Mainly VFR. Areas of MVFR cigs/vsbys in possible precipitation,
especially in CT and western Massachusetts. Some sleet or freezing rain
possible Sunday morning.

Sunday night...

Conditions lower to MVFR, with IFR in the central hills and the
Berkshires. Increasing chance of precipitation with time.
Increasing chance of sleet or freezing rain in areas north and
west of Boston-Providence. Best chance of precipitation will be
late at night, as the Monday morning push starts to gear up.

Kbos taf...high confidence in taf trends. Moderate confidence in
timing.

Kbdl taf...high confidence in taf trends. Moderate confidence in
timing.

Outlook /Monday through Thursday/...

Monday-Monday night...moderate confidence. Any leftover
-fzra/-pl Monday morning will end across higher terrain by mid
to late morning. Otherwise MVFR-IFR ceilings in rain.

Tuesday and Tuesday night...moderate confidence. MVFR
conditions within any passing rain showers.

Wednesday through Thursday...high confidence. VFR.

&&

Marine...
forecaster confidence levels...

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

Short term /through Sunday night/...

This evening...high confidence.

North to northeast winds less than 20 knots. Lingering 5 foot
seas on the southern outermost coastal waters. Seas less than
5 feet all other waters.

Tonight...high confidence.

East-northeast winds less than 20 knots. Seas will remain less
than 5 feet.

Sunday...high confidence.

East winds less than 20 knots. Seas less than 5 feet.

Sunday night...moderate-high confidence.

Approaching weather system from the west will spread rain across
the waters from west to east. Winds will remain below 20 knots
and seas below 5 feet through the period.

Outlook /Monday through Thursday/...

Monday...moderate confidence. Warm front with weak low pressure
along it may kick up southeast to south winds to near 25 kt
gusts and seas could build to 5-6 ft over the outer waters.
Small Craft Advisory may be needed.

Monday night...winds diminishing to below Small Craft Advisory gusts but seas
will only slowly subside.

Tuesday/Tuesday night...expecting winds and seas below Small Craft Advisory
levels.

Wednesday and Thursday...Small Craft Advisory likely. Northwest winds ahead of advancing
strong high pressure, along with cold air aloft over the
relatively warmer waters, will lead to good momentum Transfer
over the waters. Should see gusts to at least 25-30 kt over the
outer waters, especially off of eastern Massachusetts. Seas building to 5-8
ft over the eastern waters and 5-6 ft over the southern waters,
south of the islands.

&&

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

&&

$$
Synopsis...wtb/gaf
near term...wtb/Belk/gaf

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