Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
311 am EST Monday Nov 30 2015


High pressure over Quebec Sunday afternoon builds slowly south into
the Gulf of Maine yielding dry and chilly weather through Monday
night. The exception will be tonight and early Monday over southeast
Massachusetts where scattered snow showers are expected. Coastal
low pressure passing Cape Cod and a storm coming out of the
western USA will together bring rain to New England later Tuesday
into Wednesday. There is a low risk of freezing rain at the onset
in northwest Massachusetts. High pressure then brings dry and
seasonable weather through the weekend.


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

Surface high pressure builds into the Gulf of Maine allowing winds
to diminish and shower activity to conclude. Though NE winds turning
east diminish ... there will be an opportunity for the low-level flow
to push lingering marine stratus onshore mainly across the E-half.
With a cool airmass in place aloft ... looking at chillier than
normal conditions. Warmest spots likely in the lower-CT valley with
abundant sunshine and away from onshore E-flow. Highs around the
upper-30s to low-40s.


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

Tonight ...

Greater confidence that it will stay dry. Surface high pressure is
to the east and offshore while the middle- to upper-level ridge is either
across or to the west of New England. Synoptically there is not a lot
of support to suggest that wet-weather will move in by morning. It
is with certainty that top-down moistening will occur as middle- to
high-level clouds increase and thicken...but overall forcing mostly
via isentropic ascent is weak as broader diffluence is absent. Will
see lows drop well below freezing considering the below-average
conditions earlier and an increasing north-component of ageostrophic
flow through the interior. Lows around the middle- to upper-20s.

Tuesday ...

Leaning a WRF/European model (ecmwf) solution holding precipitation off till midday.
This coincident with the consensus of forecast guidance synoptically
building in diffluence aloft with presence of surface high pressure
east. Prior to the ridge remains in place. North-component of ageostrophic
flow persists through the interior keeping temperatures chilly with
just a slight warming ... remaining steady but just above freezing
with precipitation onset. If there is any concern of freezing rain
the focus is across north/west Massachusetts. Meanwhile east-onshore flow
prevails along the coast. Looking at a coastal front setup with
upper-30s for highs across the interior ... low- to middle-40s along
the coast. So wet weather for the most part beginning around midday
and continuing into the evening hours.


Long term /Tuesday night through Sunday/...

Big picture...

Closed low west of the Great Lakes moves along the Canadian border
Thursday. A second shortwave races through on Friday. Upper ridge
then builds over the eastern USA for the weekend.

Models show general consistency and so we used a general blend.

The dailies...

Tuesday night-Wednesday...moderate confidence.

Continues to look like a two-phase period of wet weather across
southern New England. Coastal low pressure off New Jersey moves past
cape/Nantucket overnight with one period of wet weather...then a
break Wednesday morning...then more rain in the afternoon/evening as
the system cold front approaches. Small differences in timing of
frontal passage...consensus places it in the Hudson Valley Wednesday evening
and east of mass between 06z and 12z Wednesday.

Southern stream jet extends up the Ohio Valley with broad upper
divergence over New England Tuesday night. The jet curves north into
New York/PA overnight and the venting weakens over our area...but
strengthens again Wednesday afternoon as the jet shifts east over
New England.

With favorable jet dynamics and deep moisture in place...will
continue with high-end likely probability of precipitation. Clouds and an increasing south
flow overnight. There could be some evening cooling but
otherwise expect temperatures to slowly rise most of the night.

Precipitable water values maximize around 1.25 inches Wednesday
afternoon with highest values over cape/islands. This is well above
90 percent exceedance. Good venting and good supply of moisture
should support locally heavy downpours. Possibly some poor
drainage flooding.

Thursday-Friday...high confidence.

Generally dry but with upper low and cold pool concerns. On Thursday
it is the upper low supporting the midweek storm. Cold pool and
associated moisture will generate clouds and widely scattered
showers rain and snow showers across northern mass.

Second shortwave drops south from northern Ontario on Friday. This
one has less associated moisture with the cold core concentrated
farther north. Expect fewer clouds and little/no precipitation.

The mixed layer both days will reach near 925 mb. Temperatures in the layer
will support maximum surface temperatures in the 40s.

Saturday-Sunday...high confidence.

High pressure builds over New England with dry weather.


Aviation /08z Monday through Friday/...

Forecaster confidence levels...

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

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

East-winds taper as -shra/-shsn threat concludes. Scattered-broken MVFR ceilings
linger across the east-half S New England. Ceilings will erode overnight
as winds turn light. Broken-overcast ceilings into Tuesday lowering MVFR-IFR
towards midday and late with an increasing threat of -ra and visibility
impacts. Could be a threat of -fzra for northwest mass. Increasing
east-winds with gusts up to 25 kts possible for S/se-shore of New

Kbos terminal ... will prevail low-end VFR ceilings away from MVFR
today. -Shra/-shsn seen per tdwr should stay southeast while dissipating
during the morning hours. Will hold off Tuesday -ra till midday at

Kbdl terminal ... lowering conditions during the morning to midday
hours on Tuesday holding off -ra till then.

Outlook /Tuesday night through Friday/.....Moderate confidence

Tuesday night-Wednesday...IFR/LIFR especially along the cape and
islands. Conditions may improve to MVFR Wednesday morning but expect
mixed MVFR/IFR later afternoon and evening as a cold front moves
through. Easterly wind Tuesday night becomes west Wednesday
afternoon. Conditions improve to VFR behind the cold front Wednesday

Thursday-Friday...VFR. Northwest gusts to 25 knots on Thursday.



Forecaster confidence levels...

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

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

Winds and seas relax through today beneath the influence of high
pressure allowing small-craft advisories to conclude. Attention
then turns towards Tuesday with the onset of rain and increasing
east-winds with gusts up to 25 kts late in the day. Subsequently a
new round of small-craft advisories may be needed.

Outlook /Tuesday night through Friday/...moderate confidence

Tuesday night-Wednesday... coastal low pressure moves across the
waters Tuesday night and off to the northeast Wednesday morning.
Rain and fog will bring areas of poor visibility. Winds will stay
below 25 knots. Seas will build to 5 feet on the southern outer
waters. Cold front moves through late Wednesday or Wednesday night.
Winds become west to northwest behind the cold front. Small Craft
Advisory may be needed.

Thursday-Friday... winds increasing from the northwest with gusts 25-
30 knots. This will build seas to 5-7 feet...mainly on the outer
waters. Small Craft Advisory may be needed Thursday.


Box watches/warnings/advisories...

Rhode Island...none.
Marine...Small Craft Advisory until 1 PM EST this afternoon for anz231-
Small Craft Advisory until 4 PM EST this afternoon for



near term...sipprell
short term...sipprell
long term...wtb

National Weather Service Glossary of Abbreviations