Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kbox 171756 
afdbox

Area forecast discussion
National Weather Service Taunton Massachusetts
1256 PM EST sun Dec 17 2017

Synopsis...
cold and dry today but with light winds as high pressure builds
across the region. A weak wave of low pressure may bring spotty
light snow to the region late tonight into Monday morning,
mixed with rain along the South Coast. Temperatures will be
milder on Tuesday ahead of a cold front, then turning blustery
and colder Wednesday into Thursday. A wave of low pressure which
may track to our west will bring the potential for a wintry
mix/rain sometime Friday and/or Saturday.

&&

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

100 PM update...

Trend in the forecast remains on track for today. High levels
clouds are beginning to push across the region from west to
east. Anticipate this trend to continue through the remainder
of the day. Temperatures have warmed into the upper 20s across
the region, with a few spots hitting 30s. Temperatures will warm
another degree or two as upper level cloud deck will limit
diurnal heating for the rest of the afternoon.



&&

Short term /6 PM this evening through 6 PM Monday/...
tonight...
high pres gradually retreats to the NE as weak warm front
approaches from the south. Weak warm advection develops which
will bring increasing clouds. Initially, low levels will be
quite dry in the evening, then gradually moisten after midnight
from SW to NE. As low level moisture increases, some patchy
light snow is possible, especially in western new eng. Lows
mainly in the teens to lower 20s.

Monday...
the weak warm front will lift north into southern New England bringing lots of
clouds with some light snow possible, especially in the morning.
Any snow would change to rain along the South Coast as milder
air advances northward. Forcing is weak so not much precip and
any accum would be limited to a coating to less than an inch.
During the afternoon, it looks mostly dry although can't rule
out some spotty light precip given the moist low levels. Given
that the ice Crystal growth region is fairly moist through the
day, any precip would likely be in the form of light snow vs
freezing drizzle where temps remain near freezing. It appears
the warm front will get hung up near the South Coast as a weak
wave develops on the front. This will result in a north-south
gradient of temps. Highs may climb into the lower 40s near the
immediate South Coast but cooler as you head north with coldest
temps near or a bit below freezing in northern and especially
northeast Massachusetts.

&&

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

* dry conditions Monday night into Tuesday, then rain and/or
snow showers across northwest mass Tue afternoon/evening
* mainly dry and much milder Tue
* blustery and colder with mainly dry weather Wed into Thu
* a period of snow and/or wintry mix possible Fri morning to
midday, changing to rain

Overview...

00z model suite continues to signal progressive steering flow
across the lower 48 through about the middle of this week as a
nearly zonal northern stream flow is in place. Models then
transition around the late Tue as 500 mb trough begins to dig across
central Canada into Hudson Bay, while another long wave trough
moves into the Pacific northwest. The central Canadian trough
progresses across the region Wed, but appears the weak surface
reflection will remain far enough north of the region for mainly dry
conditions.

Models showing another high amplitude ridge from Alaska south
across the eastern Pacific by late this week. As the downstream
long wave trough digs from the Great Lakes to the desert SW,
noting another short wave in the northern stream flow with
another shot of Arctic air trying to work south from the North
Pole into the northern plains states into early next weekend.
Model solution spread increases, since each member handling this
feature somewhat differently, but the GFS/ggem and European model (ecmwf) all
appear to have a similar idea in digging a long wave trough
across the central U.S. Late this week into the Holiday weekend,
with moderating temperatures possible by Fri-Sat.

A lot of questions with the potential of low pressure and the
approach of an Arctic front sometime next weekend, but with wide
model solution spread due to the timing and track of this
potential feature, have low forecast confidence beyond Thursday.

Details...

Monday night and Tuesday...

Temps will hold steady Mon night, mainly in the upper 20s to
around 30 away from the coast and lower-mid 30s at the
shoreline. With light S-SW wind flow, expect dewpoints close to
the temps so will see patchy fog develop as well. For now, have
carried a dry forecast Mon night. Can't rule out some rain
and/or snow showers across northwest mass especially across the higher
terrain of the northern Berkshires, which may continue into
Tuesday but changing over to rain. Expect highs on Tue mainly in
the 40s, possibly touching 50 in a few spots along the S coast.

Tuesday night...

As a cold front approaches Tue night, most of the precip will
linger across the east slopes of the Berkshires Tue night. Main
energy/moisture remains closer to the parent low over central
Quebec, so looks like best shot for precip will be well north of the
region but can't rule out a few stray showers mainly across north
mass.

A cold front will cross the region Tue night into early Wed
with perhaps a few brief rain/snow showers. High temps will
recover well into the 30s to around 40, but a well mixed
atmosphere should result in northwest wind gusts of 30 to 40 mph
developing Wednesday and making it feel colder.

Wednesday through Thursday night...

The cold front should exit the coast by around 12z on
Wednesday with west-northwest winds. Will see excellent low level mixing,
so winds will be gusty. Could see gusts up to 30-40 mph Wed
afternoon. Highs will range from only 30-35 degrees across the
higher inland terrain up to the lower 40s along the immediate
coast.

Expect continued dry conditions on Thursday, but it will even
colder with highs only in the mid to upper 20s well inland
ranging to the lower-mid 30s at the coast. Expect light west
winds. Clouds will increase Thu night with a few snow showers
reaching into far northwest mass toward daybreak.

Friday and Saturday...

Low confidence forecast continues. As long wave trough digs
south out of central Canada into the northern plains, will see
backing mid level steering flow to SW, along with increasing 500 mb
heights. Arctic air starts to push S across Hudson Bay during
the weekend, with the Arctic cold pool pushing S. So, as high
pressure exits Friday morning, leading edge of precip ahead of
an approaching warm front will bring light snow during Fri.
Should see transition to a mix of sleet and rain during the
morning across central and western areas, with temps already
above freezing as the precip moves eastward Fri morning.

Some question whether snow or even a little freezing rain may
linger across the higher terrain of the northern Berkshires Fri
evening, but eventually should change over to all rain with a
non-diurnal temp trend Fri night with S-SW wind flow in place.
Next question will be how quickly the Arctic front will push out
of the Mississippi Valley into the Appalachians. Wide variance
in track and timing of the front toward the region, but at this
point should see mainly rain on Saturday with mild temps. Highs
look to approach 10 degrees above seasonal normals.

&&

Aviation /18z Sunday through Friday/...
forecaster confidence levels...
low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.

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

Today...VFR.

Tonight...mainly VFR with gradually lowering cigs, becoming
MVFR in western new eng after midnight. Patchy light snow
possible.

Monday...widespread MVFR cigs. Chance of light snow or rain.

Kbos terminal...high confidence.

Kbdl terminal...high confidence.

Outlook /Monday night through Thursday/...

Monday night: mainly VFR, with local IFR possible. Patchy br.

Tuesday: mainly VFR, with local MVFR possible. Windy with local
gusts to 30 kt.

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

Wednesday night through thursday: VFR. Breezy.

&&

Marine...
forecaster confidence levels...

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

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

Today...northwest winds diminishing through the morning to 15 kt or
less. Seas 4 ft or less early, and will continue to subside.

Tonight...light winds and seas.

Monday...winds becoming SW and increasing in the afternoon but
gusts below 20 kt. Seas below Small Craft Advisory. Chance of light snow changing
to rain.

Outlook /Monday night through Thursday/...

Monday night: winds less than 25 kt.

Tuesday: moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas.

Tuesday night: moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas.

Wednesday: low risk for gale force winds with gusts up to
35 kt. Areas of rough seas.

Wednesday night: moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Local rough seas.

Thursday: winds less than 25 kt. Seas locally approaching 5 ft.

&&

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

&&

$$
Synopsis...kjc/evt
near term...dunten

National Weather Service Glossary of Abbreviations