Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
930 PM EDT Sat Mar 15 2014
dry and unseasonably cold conditions for the remainder of the
weekend under breezy west-northwest winds as Arctic high pressure
builds across the region. A coastal storm is expected to pass far
enough to our south Monday to spare our region a winter storm. A
cold front will bring more precipitation sometime Wednesday into
Near term /until 6 am Sunday morning/...
930 PM update...
***colder air will work back into the region overnight on gusty
A strong cold front will move across southern New England over the
next few hours. The front will generally come through the region
dry...but a few brief flurries are possible across our far western
and northern zones.
The main story will be the much colder air that will be returning
overnight. Given that the cold air is coming in more from the west
as opposed to the north...this airmass will not be as cold as the
one from a few days ago. Nonetheless...by daybreak Sunday lows have
fallen into the middle to upper teens across the interior high
terrain to mainly the 20s elsewhere.
In addition...westerly winds will increase overnight in the cold air
advection pattern. Gusts of 25 to 30 miles per hour are anticipated resulting
in wind chill values in the high single digits and teens by daybreak.
Short term /6 am Sunday morning through Sunday night/...
The combination of a well-mixed boundary layer and fast west/northwest flow
aloft continues breezy conditions across the region. Combined with
the return of diurnal mixing processes...and there is likely an
enhancement of the mix-down of drier air and faster momentum.
Winds of 25 to 30 miles per hour expected the strongest of which will be
across higher terrain and more towards the North/East of Massachusetts into S New Hampshire.
Such winds should diminish during the afternoon into evening with
lesser diurnal mixing and increasing influence of high pressure.
Will also see a reduction in moisture availability with the
increasing influence of high pressure. Will keep the forecast
period dry with scattered cloud decks.
Unseasonably cold with 850 mb temperatures dropping to -15 to -20c by dusk.
Highs should get into the upper-20s to low-30s /below-normal on
the order of 15 to 20 degrees/. Greater abundance of the higher
March sun should provide some relief and warm those areas more
considerably that do not have a snowpack.
Some fire weather concerns...please see the discussion at the very
High pressure across the region keeping a 850 mb airmass of -15 to
-20 degrees in place. Winds should be light...perhaps calm within
the sheltered valleys. But am anticipating increasing middle- to
high-level clouds overnight with the advancing storm out of the
central Continental U.S. Remaining mostly S of New England. This will limit
overnight radiational cooling. Lows around the upper-single digits
to low-teens. Coldest to the north/west Massachusetts into S New Hampshire. Its possible we
could reach record lows...but feel they may be in jeopardy with
the increasing clouds /Boston 10 1916 - Hartford 6 1916 -
Providence 7 1916 - Worcester 5 1967/.
As for the storm...blended the latest guidance with the previous
forecast. This keeps slight-chance to chance probability of precipitation from the
immediate South-Coast of New England southward over the waters.
Best chances for snow will be across the islands. With just a few
hundredths of precipitation possible coupled with the high snow-
to-liquid ratios...its possible to see a few tenths of snowfall
out on Cape Cod.
But even considering the more robust GFS...feel the enhanced
northerly component in response to the storm will drive cold dry
air southward beneath 800 mb limiting any possible precipitation
north. The isentropic component above 800 mb is confined well south of
the region and per the mass fields there appears to be a more
confluent structure across the region.
Do not have a lot of confidence in the current forecast outcomes
but did not want to jump ship just yet. Do have the feeling though
that the storm may skirt US altogether as any over-running precipitation
would evaporate/sublimate before reaching the ground.
Long term /Monday through Saturday/...
overview and model preferences...
15/12z guidance suite is in very good agreement through the
middle of next week...both at the surface and aloft. This
agreement breaks down late next week...which is not uncommon at
that time range in the forecast. The main source of disagreement
involves another surge of Arctic air south into eastern Canada.
The international models...namely the CMC and European model (ecmwf)...favor a
strong surge of colder air than does the GFS and gefs.
The resulting changes in the flow aloft then impact the track and
timing of a low pressure projected to move through the Great Lakes
into Quebec late next week. What is interesting..is the CMC
becoming a fast outlier...while the European model (ecmwf) is only slightly farther
south than the GFS and gefs mean. With the European model (ecmwf) rather close to the
GFS and gefs...will discount the CMC and use a consensus solution
from the GFS and European model (ecmwf) to minimize the differences between the
Monday...a strong high pressure over the Great Lakes should force a
low pressure to remain well to the south of New England. The
expectation is for a lot of dry air which would need to be overcome
across most of New England for significant precipitation to fall.
We could perhaps see some light measurable snowfall as far north
as the South Coast of Rhode Island and Massachusetts. The most likely scenario is for
measurable precipitation to stay south of the islands. The
position of the high should mean temperatures struggle to break
freezing during the day...which is about 10 degrees below normal
for this time of year.
Monday night into Tuesday night...the high pressure from the Great
Lakes moves across southern New England. This will mean dry
conditions with below normal temperatures. Temperatures will
gradually rise respective to each day and night as this high
pressure moves offshore.
Wednesday into Thursday...a low pressure should move through the
Great Lakes into southeast Canada sometime during this period. Our
region will first see the warm front...then the cold
front...associated with this system. Current expectations are for
near normal temperatures Wednesday...followed by above normal
temperatures Thursday. Will not try to get too precise with the
timing of these fronts...but will target Wednesday night as the most
likely period for scattered rain/snow showers.
Thursday night into Friday night...expecting mainly dry conditions with
seasonable temperatures...as our region is under the influence of
a high pressure ridge centered along the middle Atlantic coast.
Saturday...timing and track differences between the 15/12z
guidance start to make their presence felt in this time range.
While the track is still uncertain...there are some hints at
common ground. For instance...the southernmost track still crosses
southern New England...rather than off the coast. Depending upon
timing...this would favor a snow to rain situation over an all
snow situation. Will mention a chance for rain or snow showers for
now...and give some time to work out the details with later
forecasts this week.
Aviation /01z Sunday through Thursday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /today through Sunday night/...high confidence.
VFR. Overall theme. Breezy west/northwest flow with gusts around 25 kts
with scattered-broken ceilings 6-8 kft. Shower activity dissipating into this
evening remaining dry through the rest of the forecast. Lesser
confidence of -sn along the S-coast...though high confidence of
increasing middle- to high-level clouds Sunday night into Monday
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence in taf.
Outlook...Monday through Wednesday.
Monday into Tuesday...high confidence. Mainly VFR. Continued snow
chances along S-coast Monday...but very light. North winds on Tuesday
Wednesday and Thursday...mainly VFR...with scattered MVFR in
showers. Most likely period for MVFR would be late Wednesday into
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /today through Sunday/...high confidence
* small craft advisories for west/northwest winds gusting 25 kts through sun
* light freezing spray especially for the east waters
SW winds gusting 15 to 20 kts backing west/northwest with Arctic front
sweeping the waters overnight. Will see winds increase especially for the
east water with near gale-force gusts for the northern reaches of the
stellwagen bank. Combination of winds with seas of 6-8 feet on the
outer waters will yield the likelihood of minor freezing spray for
the majority of the forecast period.
Outlook...Monday through Thursday...moderate confidence.
Monday...moderate confidence. Northwest wind gusts approaching 25 knots
gradually subside during the day. Small craft advisories will
likely end sometime during the day. At this time it appears the
coastal storm will stay well to the southeast of the waters. This will
permit more Arctic air to arrive...which could lead to areas of
freezing spray...particularly across the outer coastal waters
south of New England.
Tuesday and Wednesday...high confidence.
Mainly quiet boating weather as high pressure crests over the waters.
Wednesday night and Thursday...moderate confidence. Scattered
showers result in lower visibility. Increasing south winds will
build seas across the outer coastal waters. Small craft advisories
may be needed for this time period.
minimum relative humidity values will fall below 25 percent during
the day Sunday across the southern and eastern interior coastal
plains as Arctic air and high pressure builds into the region.
Combined with gusty west-northwest winds...and there is an
elevated fire weather potential for Connecticut...Rhode Island...
and eastern-southeastern Massachusetts where snow-pack is in parts
Considering how cold it is...will only highlight the threat in
this discussion and not issue out any headlines with the forecast.
Marine...Small Craft Advisory until 2 PM EDT Sunday for anz232>235-237.
Small Craft Advisory until 8 PM EDT Sunday for anz230.
Small Craft Advisory until 11 PM EDT Sunday for anz231-251-256.
Small Craft Advisory until 11 am EDT Sunday for anz236.
Small Craft Advisory until 8 am EDT Monday for anz250-254-255.