Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
703 am EDT Friday Mar 14 2014
high pressure moving off the coast will allow temperatures to moderate
through Saturday...with just a brief period of scattered rain
showers very late tonight/Sat am. High pressure will lead to below
normal temperatures Saturday night into Sunday. A coastal storm
to the south will have to be watched closely for possible impacts
to southern New England Sun night into Monday. More precipitation
Near term /until 6 PM this evening/...
7 am update...
very weak surface warm front already moving across the area this
morning...draped from southern Vermont to southern Rhode Island as of about 11z /7am/. This
has mostly manifest itself as a rapid rise in dewpoints from the
negative single digits to positive single digits near 10f...a weak
wind shift to the SW and some scattered-broken low-middle level altocu. This
will be the general trend through the morning...with skies
becoming partly cloudy once again in the afternoon. Also...modest
low level jet should allow for gusty SW winds to pick up with
afternoon mixing...looking for mainyl 20-30 miles per hour gusts at times.
Bias corrected NAM actually doing best at the moment on
temperatures/dewpoints so used it for baseline adjusments.
After a very cold start early this morning...temperatures will
moderate significantly this afternoon. High pressure will move off
the middle Atlantic coast allowing for a return southwesterly flow of
milder air to work into the region. Expect a mixture of sun and
clouds this afternoon with high temperatures recovering well up into the
30s to near 40. Still below normal for middle March standards...but a
big improvement over yesterday. Southwest winds will become gusty
by late afternoon at speeds of 20 to 30 miles per hour.
Short term /6 PM this evening through 6 PM Saturday/...
tonight and Saturday...
Dry weather will prevail this evening. However...a southwest low
level jet up to 50 knots will develop out ahead of an approaching
shortwave. This will allow for clouds to increase along with a band
of scattered rain showers roughly between 8z and 15z Saturday. This
is supported by a decent instability burst as models depict total
totals exceeding 50.
Most of the precipitation will be short lived in a given location and
in the form of rain. However...a brief period of wet snow is
possible at the onset across the higher terrain of northwest
Massachusetts/southwest New Hampshire. Any accumulations should just be a dusting to less
than 1 inch. There also is a low probability for a touch of
freezing rain across our far northwest zones...but given the fact
that winds will be southwest that potential looks limited at this
point. However...later shifts will have to re-examine this later
Otherwise...any left over scattered showers should depart by middle to
late morning on Saturday. Skies should become at least partly sunny
and with a relatively mild start...temperatures should respond nicely.
Highs should reach into the middle to upper 40s across the interior
high terrain...to the lower to middle 50s across most other areas.
It will again be breezy.
Long term /Saturday night through Thursday/...
* below normal temperatures but dry weather through sun.
* A coastal low may brush south coastal region Sun night-Mon.
Overview and model preferences...
long term still looks marked primarily by the polar vortex
initially...following by its shift to the north toward the middle and
end of next week. Both deterministic and ensemble guidance
continues to support this general trend...there are sub-synoptic
differences in the final amplitude of the ridging building across
the eastern Continental U.S. As the vortex shifts out. This will effect both
temperature moderation and the timing/strength of an inside runner
low pressure toward the latter half of the week. Given there is
overall agreement...will continue with a general blend of guidance
as a baseline.
The key with the polar vortex will culminate in a digging
shortwave trough and attendant coastal low pressure for sun into Monday. As
mentioned by the previous forecaster...there was initial
disagreement in the final placement of 1030 Arctic high
pressure...which has been settled somewhat...suggesting it crests
across Ontario and Quebec. This is the northern solution. Given
the phasing of both Arctic and western Continental U.S. Energy is the key to this
low pressure initialization/track and moisture...it appears the western
Continental U.S. Energy will dominate...digging the trough further west and
pulling in Gulf of Mexico moisture. However as it slides off the
Carolina coast it will be interacting with strong confluent and
zonal flow associated with the positive nao/ao regime across the
Atlantic. Therefore...it looks to shear out as it approaches. See
below for more sensible weather details.
Sat night into sun...
Arctic high pressure gradually settles across southeast Canada following a
cold frontal passage on Sat. Mainly dry but colder weather is
expected to follow. Min temperatures will not fall off as quickly as
possible given northwest flow remains elevated and the overnight period
will begin with cloud cover. Therefore...expect Sat night mins
only in the low to upper 20s. Sun...850 mb temperatures continue to decline
to around -12c by late day. So suspect highs only reach the upper
20s to middle-upper 30s.
Sun night into Monday...
given the recent trends suggested in the overview above...it
appears low pressure will slide off the Carolina coast but then shear
out to the east...passing southeast of the 40/70 benchmark. However...given
the northward trend in Arctic high pressure...it appears to be a close
enough pass that precipitation wrapping within the warm conveyor and then
to the north of the low center may scrape the southern reaches of southern New
England late Sun night into the early day Monday. Indeed even gefs
mean shows a 40 percent chance of 0.5 inches along the S
coast...not bad for an event over 48 hours away. For now will
blend a mix of the European model (ecmwf)/GFS/CMC quantitative precipitation forecast...which takes into account
the envelope of possible quantitative precipitation forecast solutions. Arctic high pressure suggests
only snowfall...with potential for decent ratios assuming the warm
conveyor lift remains within the dendritic regime...but that will
have to be ironed out. Dry air will be filtering in from the north
with high pressure...so at this time...it appears areas north of the Mass
Pike may struggle to see little if any accums. But given the trend
to the north this will have to be watched...especially if the final
phasing of shortwaves occurs further west than current forecast.
Tuesday into Wednesday...
the Arctic high settles across southern New England then slides
offshore during the day on Wednesday. Tuesday...as the high settles
over...850 mb dips to around -12c...which suggests a period of highs
and lows below normal. That until temperatures rebound Wednesday as high pressure
slides east and warm advection develops under return flow.
Thursday into Friday...
some uncertainty here...but mainly in timing. Deterministic
guidance and even ensembles agree that a strong inside runner low
pressure will move in proximity to the St. Lawrence...dragging a cold
front across the region with precipitation. The more amplified and
slower solution is represented by the European model (ecmwf)...while the more
progressive is represented by the GFS. In either case...increasing
moisture warm advection could yield some showers for either day.
Aviation /12z Friday through Tuesday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term...today through Saturday...
Mainly VFR. A few broken ceilings 050-100 through the early half of the
day with a gradual progression toward scattered clouds late. Winds
continue a shift toward the SW through the day...with gusts up
around 25 knots at times this afternoon and evening.
Tonight and Saturday...moderate to high confidence. VFR conditions
the majority of the time. However...a period of MVFR conditions in
a brief band of scattered rain showers between 8z and 15z. There
could be a bit of wet snow at the onset across the higher terrain of
southwest New Hampshire/northwest at the onset...but no accumulations expected.
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence through about 08z tonight...lower
confidence on any MVFR ceilings...and -shra thereafter.
Outlook...Saturday night through Tuesday.
Saturday night into Sunday...high confidence.
Mainly VFR. West-northwest winds may gust 20-25 knots at times.
Sun night through Monday...moderate confidence.
A coastal low pressure will pass well S of the area...but there is the
possibility of some MVFR/IFR ceilings/visibilities in snowfall especially S
of the Mass Pike.
Monday night into Tuesday...moderate confidence.
Any snows gradually end...VFR follows.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /today through Saturday/...high confidence.
Today...winds continue to diminish early this morning as high
pressure build overhead. However...as the high moves off the
coast...southwest wind gusts of 25 knots will develop by middle to late
afternoon. Small Craft Advisory will once again be needed for all waters...but will
start some of them later this afternoon where conditions have
temporarily diminished below criteria.
Tonight and Saturday...southwest flow out ahead of our next cold
front will continue to yield 20 to 30 knots wind gusts. Have kept
Small Craft Advisory headlines in place for most waters.
Outlook...Saturday through Tuesday...
Saturday through Sunday...high confidence.
Small craft advisories likely needed as winds shift to the
W-NW...with gusts around 25 knots. Seas 5-7 feet expected on the outer
Sunday night through Monday...moderate confidence.
A brief period of quiet boating weather is expected late day sun
into the overnight hours Sun night...but some light snow may
spread over especially the southern waters during the overnight hours.
Low pressure associated with this snowfall may lead to a period of
Small Craft Advisory winds and building seas...but if the low
passes further offshore conditions would be more quiet. Aside from
the possibility of small craft advisories...if the low makes a
closer approach...wind gusts may approach gale force. Still some
uncertainty to work out.
Depending on how close low pressure comes to the southern
waters...winds and seas may remain above Small Craft Advisory
Marine...Small Craft Advisory from 3 PM this afternoon to 11 PM EDT
Saturday for anz231>234.
Small Craft Advisory from 2 PM this afternoon to 11 PM EDT
this evening for anz230-236.
Small Craft Advisory until 8 PM EDT Saturday for anz235-237-