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Area forecast discussion 
National Weather Service Taunton Massachusetts
926 am EST Monday Dec 29 2014

Synopsis...

Strong high pressure builds south from western Canada and then
spreads across the USA for much of the week. This will mean a dry
and cold spell for New England through the end of the week. A
storm may impact the region sometime later in the weekend but
there is much uncertainty regarding possible outcomes.

&&

Near term /through tonight/...

935 am update...

A strong and sprawling 1060 mb high pressure across western Canada
will allow chillier air to slowly ooze into our region. A mixture
of clouds and sun expected through the afternoon. High temperatures mainly
in the middle 30s across the higher terrain...and around 40 to the
lower 40s across the coastal plain. These readings are still a
touch above normal for this time of year...but will be the mildest
temperatures for the rest of the work week. Winds generally less than 15
miles per hour will make it quite tolerable for this time of year.

&&

Short term /tonight and Tuesday/...

The large high pressure from western Canada builds south into the plains
during Tuesday with ridging extending to the East Coast. Continued dry
northwest flow will bring moclear skies tonight and Tuesday as low level
moisture decreases...but turning even colder as 850 mb temperatures drop to
-13 to -16c Tuesday. Lows tonight will be in the teens to lower
20s...with high temperatures Tuesday recovering to low/middle 30s...except upper
20s higher terrain. Modest northwest breezes expected Tuesday.

&&

Long term /Tuesday night through Sunday/...
highlights...

* dry through at least Friday night
* seasonable to a little below normal temperatures
* chance of rain or snow developing sometime over the weekend

Overview...

Medium range models remain in good agreement through the work week
but are depicting widely varying solutions for next weekend in
handling the trough being ejected out of the southwest USA. The timing
of the ejection of that trough will be critical. A faster timing would
seem to result in better phasing with the northern stream and a
potent system heading toward the Great Lakes. The 00z GFS and UKMET
operational runs as well as ensemble members from prior runs depict
this type of scenario. The result for southern New England would be
a period of very mild...wet and windy sensible weather. A slower
ejection of the trough would appear to allow the northern stream to
establish greater dominance and cause the SW trough to shear toward
the East Coast with a surface low passing southeast of New England with
cold and possibly snowy or dry sensible weather late in the
weekend or early the following week. With signals of a return to a
positive nao by the end of the week...it seems that the eventual
solution should be fairly progressive with a deep coastal low
unlikely.

Bottomline...confidence in nearly all elements of the forecast for
this weekend is very low. There is an exceptionally wide range of
possibilities for temperature...wind direction/speed...ptype...
quantitative precipitation forecast...and timing of any precipitation.

Day to day...

Tuesday night through Wednesday...generally dry and colder than normal
temperatures supported by broad trough aloft centered over Hudson Bay
and strong high spreading S and southeast from the Canadian and USA High
Plains. Tuesday night/Wednesday am looks to be the coldest night with 850 mb
temperatures of -15c to -17c...probably mostly clear skies and light
winds. Will likely experience surface temperatures in teens across
most of interior southern New England with possibly pockets of 5 to
10 above temperatures northwest Massachusetts. Lack of snowcover prevents what might
otherwise be colder temperatures. High temperatures on Wednesday will
likely top out in the middle 20s to lower 30s most locations.

Wednesday night and Thursday...there are a couple of issues during this time
period. One is that believe there is a chance of some light ocean
effect snow showers over Nantucket late Wednesday night and Thursday morning.
Given sea surface temperatures still middle to upper 40s off the New
England South Coast...anticipate steep enough lapse rates to
support scattered flurries or snow showers in west-southwest flow that
develops across south coastal areas late Wednesday night and Thursday. BUFKIT
soundings support low chance probability of precipitation at Nantucket...mainly in the 2
to 10 am time frame. Second issue is the tightening surface
pressure gradient that should result in brisk winds with gusts 20
to 25 miles per hour over land and possibly marginally gale force over the
outer coastal waters south and southeast of New England.

Thursday night through Friday night...anticipate dry conditions through this
period with temperatures near or a little below normal.

Sat through sun...this is when the forecast gets very challenging.
Have gone with a model consensus due to the extreme uncertainty. As
noted above...there exists a wide range of possible outcomes
depending upon the timing of the ejection of the trough energy from
the southwest USA. For now...have low chance probability of precipitation for much of the
weekend due to uncertainty in timing but do not really anticipate a
prolonged event. Have lowered high temperatures some from prior
forecasts but here again there exists an extraordinary wide range of
possibilities depending upon whether we experience a robust system
passing well west of the region or a weak system passing southeast
of our area.

&&

Aviation /15z Monday through Friday/...
forecaster confidence levels...

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

Today through Tuesday...continued high confidence. VFR with
northwest winds but gusts mainly less than 20 knots.

Kbos terminal...high confidence.

Kbdl terminal...high confidence.

Outlook...Tuesday night through Friday...

High confidence of mainly VFR through the period. The only exception
is a risk of MVFR ceilings and visibilities in possible ocean effect snow
showers in vicinity of Nantucket late Wednesday night into Thursday morning.

&&

Marine...
forecaster confidence levels...

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

Short term /through Tuesday/...high confidence.

Northwest winds likely to remain below Small Craft Advisory thresholds through Tuesday with
gusts to 20 knots...but a few higher gusts possible this morning.
Small Craft Advisory in effect until 8 am for outer waters for seas up to 5
feet...otherwise seas below Small Craft Advisory thresholds.

Outlook...Tuesday night through Friday...

Tuesday night through Wednesday night...expect winds and seas below Small
Craft Advisory thresholds.

Thursday...west wind will likely increase above Small Craft Advisory
thresholds all waters with a chance of gale force gusts over the
outer coastal waters.

&&

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

&&

$$
Synopsis...kjc/Thompson
near term...Frank
short term...kjc
long term...Thompson
aviation...Frank/kjc/Thompson
marine...Frank/kjc/Thompson

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