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fxus61 kbox 231950 
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Area forecast discussion
National Weather Service Taunton Massachusetts
350 PM EDT Thu Mar 23 2017

Synopsis...
high pressure along the eastern USA coastline will move offshore
later tonight bring windy and milder conditions Friday.
Unsettled weather this weekend, with potential for a variety of
precipitation types.

&&

Near term /until 6 am Friday morning/...

Tonight...

High pressure will move off the mid Atlantic coast. Expect
winds to become light and variable for a time as the Ridgeline
moves overhead. A light south-southwest flow is possible late at
night as the ridge moves offshore.

Some high thin clouds moving over Ontario will reach our area
early tonight. But thicker mid level clouds should hold off
until after midnight, allowing a period of light winds and fair
skies. So we expect radiational cooling the first part of the
night, shutting down later tonight as the clouds thicken. Dew
points start in the single numbers below zero and climb into the
teens by late night. We favored going a couple of degrees below
guidance with a range from the high single numbers in the
interior to near 20 along the coastline. Most areas would be in
the teens.

&&

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

Friday...

High pressure offshore will provide a flow of milder air. Winds
above the surface will climb to 30-40 knots by midday. That will
provide a flow of moist air with precipitable water values
reaching near an inch by Friday evening. Weak overrunning
created by this southwest flow will create clouds and light
precipitation starting in the morning. Temperatures will be cold
enough at the start for snow, but quickly moderate to rain by
afternoon if not sooner. The transition period may feature some
sleet.

The best chance for this precipitation will be in northern and
western mass. But frozen amounts will be light, with any
snow/sleet accumulation less than an inch.

Have high confidence in the overall trend, but only moderate
confidence in the precipitation types.

The strong southwest low level jet will also provide the
momentum for gusty winds, especially during the afternoon when
mixing is greatest. It still appears the greatest risk for gusts
over 30 mph to be along the Boston-Providence corridor and
southeast from there.

Max temperatures should make a 5-10 degree rise from today, but
values in the mixed layer Friday are supportive of highs in the
low to mid 40s so still below March normals.

Friday night...

Clouds and a southwest flow of milder air will keep
temperatures from falling too much, and most of that should be
in the evening. Temps may rise a little overnight. We maintained
a chance of showers in far northern mass, but low values for
pops.

&&

Long term /Saturday through Thursday/...
highlights...

* above average temps on Saturday with a few showers
* low confidence next sun-tues with unsettled weather possible at
times with some rain, ice and/or snow possible
* moderating temperatures by mid-next week

Pattern overview...

00z models and ensembles are in agreement with the general synoptic
pattern for the long term. Uncertainty increases in the extended do
to mesoscale and thermal issues. Split flow aloft with closed low
over the Southern Plains and northern stream across southern Canada.
The initial closed 500 mb will slowly move into the Midwest over the
weekend. This low deamplifies into an open wave as it comes towards
the northeast early next week. 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. The models have slowed again compared
to 22.00z guidance but are similar in timing. Another open wave
moves through the flow during the mid-week with the GFS more
amplified versus the progressive ec. Still a lot of uncertainty with
this timeframe.

Details...

Saturday...moderate confidence.

850 mb temps Saturday morning will be close to 8c but drop
through the day as cold front begins to slide southward. Surface
temperatures will reach into the mid 50s, cannot rule out a few
60s if the mid- level ridge continues to build and slows the
timing of the front. Along the front, there could be a few rain
showers but not expecting widespread rainfall as heights
continue to build overhead.

Saturday night into Sunday...moderate confidence.

Cold front will pass through southern New England dropping surface
temps below freezing. The timing of the cold air drainage from the
high pressure over northern New England will determine if precip
type remains all rain, or if snow and/or mixed precip develops. Mid-
level ridging could keep a warm layer around 850 mb which would aid
in the mixed p-type. This is something to watch in the coming days.

For Sunday, cold front will stall somewhere between southern New
England and the mid-Atlantic as high pressure begins to move
southeast into the Gulf of Maine. Depending on how close the high
pressure gets, we could see a dry Sunday or a few showers. One thing
to keep an eye on is the easterly flow, which could keep the low
level moist resulting in drizzle. Still a lot of uncertainty with
this time frame.

Sunday night Monday into Wednesday...low confidence.

While guidance is in agreement synoptically, still a lot of details
to work out for this portion of the forecast. Biggest uncertainties
will be the placement of the upper level low and how quickly it will
diffuse early next week.

Right now, the stalled front 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. Another open wave right behind this one
will push through the flow developing around shot at precip on
Tuesday.

As mentioned before, still a lot of uncertainty as to the thermal
profiles. Continue to believe that there could be a period where the
region could see a mixed bag of precip with the highest confidence
Sunday night into Monday and another shot Monday night into Tuesday
due to surface temps falling overnight. Still a lot of uncertainty
with this timeframe as thermal profiles will change. Will continue
the mentioning of snow, sleet, ice and/or rain for the forecast
until thermals come better in alignment.

Lastly, weak ridging in between waves may allow for temps to
moderate back to seasonable during the day light hours Monday
and Tuesday.

&&

Aviation /19z Thursday through Tuesday/...
forecaster confidence levels...

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

Short term /through Friday night/...

Tonight...VFR. High confidence

Northwest winds with gusts 20-25 kt this evening, becoming light and
variable for a time tonight. Winds become light south to
southwest late tonight.

Friday and Friday night...VFR with some MVFR mainly north of
the Mass Pike. Moderate confidence.

Increasing and lowering clouds during the morning. Areas of MVFR
cigs/vsbys in light snow or sleet, with best chance along or
north of Boston and the Mass Pike. All frozen precip should
change to rain during late morning/early afternoon. Southwest
winds will gust 25-30 knots during the day, highest along the
coast and in higher terrain. Winds diminish Friday night.

Kbos taf...high confidence in taf.

Kbdl taf...high confidence in taf.

Outlook /Saturday through Tuesday/...

Saturday into Sunday...moderate confidence. A period or two of
showers along with some MVFR cigs are possible at times as cold
front sags southward over the region. Could see a period of mixed
precip overnight.

Sunday into Monday...low confidence. Showery weather to start with
possible MVFR cigs. Precip chances increase overnight into Monday
which could result in mixed precip.

&&

Marine...
forecaster confidence levels...

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

Short term /through Friday night/...

Tonight...high confidence.

Diminishing northwest winds becoming light SW overnight. Seas near 5
feet on the outer waters east of Massachusetts early, but
subsiding during the night. Seas elsewhere less than 5 feet. A
Small Craft Advisory lingers on those eastern outer waters for a
few more hours until seas subside.

Friday...moderate confidence.

High pressure moves well offshore, bringing southwest winds to
the waters. Potential for wind gusts 25-30 knots. This will
build seas with 5 foot heights on many of the waters by the
afternoon. Patchy light rain may bring brief visibility
restrictions. Small craft advisories are being issued for most
waters. An advisory for the eastern outer waters for Friday will
be issued once we move clear of the existing headline.

Friday night... moderate confidence.

Southwest winds 25 to 30 knots may become west toward morning.
Seas of 5-7 feet will linger through the night on the outer
waters and all southwest-exposed waters such as Rhode Island Sound. Small
Craft Advisory will lower on Boston Harbor and Narragansett Bay,
but linger on the remaining waters.

Outlook /Saturday through Tuesday/...

Saturday...high confidence. Increased pressure gradient with
approaching systems may result in gales across the eastern
waters. Cold frontal passage on Saturday may bring some showery
weather for the waters.

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

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

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 10 am Friday to 6 am EDT Saturday
for anz232>235-237-255-256.
Small Craft Advisory from noon to 8 PM EDT Friday for anz230.
Small Craft Advisory from 10 am Friday to 3 am EDT Saturday
for anz231-251.
Small Craft Advisory from 10 am to 10 PM EDT Friday for anz236.
Small Craft Advisory until 2 am EDT Friday for anz250-254.

&&

$$
Synopsis...wtb/dunten
near term...wtb/dunten

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