Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
720 am EDT sun Mar 16 2014
mainly dry and unseasonably cold weather is on tap for early this
week. Low pressure will pass far enough to our south on Monday to
spare our region a winter storm. After a period of dry weather
into Wednesday a cold front will bring more precipitation sometime
Wednesday night into Thursday.
Near term /until 6 PM this evening/...
***dry but much colder and blustery today***
7 am update...
brief lull in winds somewhat as Arctic front continues offshore
push and high pressure begins its nose in from the northwest. Still a fairly
robust low level jet and good cold advection should promote mixing through
the day allowing wind gusts to once again reach 20-30 miles per hour at
times. Otherwise this morning...a few returns on radar from a
combination of upslope flow across Vermont/northern New Hampshire and lake effect
moisture...likely not even reaching the ground but if they
are...its a very brief...very light flurry. These will dissipate
as mixing commences now that the sun is rising. Regarding
temperatures...it/S a balancing act as strong cold advection
continues at the low-middle levels and decent middle-late March mixing
continues. Still feel final highs will be some 5-10 degrees below
normal and wind gusts will lead to wind chills only in the teens
and low twenties. Forecast right on track with this thinking.
Northwest winds will continue to usher in colder air into southern
New England. Despite partly to mostly sunny skies...850 mb temperatures
dropping to between -14c and -18c will result in well below normal
temperatures. Highs should only recover to between 25 and 30 across the
interior high terrain...to the lower to middle 30s on the coastal
Excellent mixing with steep lapse rates will result in northwest wind
gusts of 25 to 35 miles per hour. This will keep wind chill values in the
teens to lower 20s all day.
Short term /6 PM this evening through 6 PM Monday/...
***winter storm misses US to the south but well below normal
temperatures continue tonight and monday***
Tonight and Monday...
Low pressure will emerge off the middle Atlantic coast tonight into
Monday. Models are in good agreement that a piece of the polar
vortex across eastern Canada along with surface high pressure
building in will suppress a winter storm and its associated snow
shield to our south. Perhaps a brief period of very light snow
showers/flurries may make it onto the immediate South
Coast/cape/islands towards 12z Monday. However...it will be
fighting a lot of dry air coming down from the north...so if it
happens it should be short lived. Any accumulations in this region
would be less than an inch. The main affects from this storm will
just be a period of middle/high level cloudiness tonight into Monday
morning...south of the Massachusetts Turnpike.
Otherwise...unseasonably cold air will remain entrenched across the
region with high pressure in control. As winds diminish...low temperatures
tonight will likely drop to around zero across southwest
New Hampshire/northwest Massachusetts. Across the rest of the region...lows should
mainly be in the high single digits and teens. Highs on Monday will
only reach between 25 and 30 degrees. These readings are 15 to 20
degrees below normal for the middle of March!
Long term /Monday night through Saturday/...
overview and model preferences...
16.00z model guidance continues to show generally good synoptic
scale agreement through at least the middle term. This looks to be
defined initially by middle level ridging through middle week before
giving way to phased Arctic and western Continental U.S. Waves by the latter half
of the week. With this...guidance is beginning to show better
agreement in the timing of the attendant low pressure with this wave
but continues to struggle with thermal profiles once the low
pressure/cold front moves through.
Following this wave...a mainly zonal flow develops by along the
base of a longwave trough extending through eastern Canada. This may
suggest another round of colder air and possibility of a southern wave
track. However there are some differences regarding the overall
depth or southern extent of the wave which. This will have significant
impacts on the final track and sensible details for another low
pressure by this coming weekend. Given the general agreement...a
consensus blend of models will take into account various
Monday night into Wednesday...
mainly dry period as Arctic high pressure settles across /Mon night
into Tuesday/ then moves east /Tue night into Wednesday/ of southern New England.
Monday night into Tuesday...temperatures expected to remain mainly below
normal as 850 mb temperatures settle around -8c. This suggests lows in teens
and low 20s...then highs in the 30s. By Wednesday as high pressure moves east
allowing for return flow and 850 mb temperatures to approach -2c...which
suggest highs finally approach seasonal normals allowing for full
mixing...a good possibility in late March sun angles.
Wednesday night into Thursday...
low pressure with western Continental U.S. Origins is expected to follow the ridging
flow across the western Continental U.S....moving into Canada Wednesday night into Thursday.
As it does so...a cold front with a combination of both isentropic
and frontogentical lift looks to slide across southern New England.
However...despite the warm advection implied by the isentropic
lift in the middle levels...there is a bit of a question mark of
p-type especially in the northwest interior of Massachusetts and SW New Hampshire. Surface temperatures
may have enough time to fall off Wednesday night and mass fields show
just enough low level cold air damming signal such that h92 may
remain below 0c and 850 mb potentially below -4c. Therefore...not out
of the question that precipitation starts as snow in some of the areas
mentioned while areas further S and east look to be warm enough for
only rainfall. May need to keep an eye on this as dependent on
whether some Gulf moisture is tapped /models currently keep the
system disconnected/ there could be modest snow accums especially
during the overnight hours. In any case...the precipitation gradually
ends Thursday morning before another round of blustery and slightly
colder weather follows /though not as cold as early in the week/
especially after warmer weather since the cold advection lags the front
Thursday night into Friday...
brief ridge of high pressure crests across the region suggesting dry
weather...but this time airmass associated with it supports
temperatures closer to normal for late March.
model guidance has been reasonably persistent with another wave
of low pressure...but continue to struggle with both track and timing.
GFS is much weaker and more progressive while European model (ecmwf) is stronger
and slower. Recent trends has also been to push this wave further
S...from an inside runner in early runs...to now almost directly
across southern New England where the zonal jet sets up. This is a
result of that deepening and digging of the longwave trough
mentioned above. Will suggest some probability of precipitation for unsettled weather...but
continue with a blend for thermal profiles.
Aviation /12z Sunday through Thursday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /tonight through Monday/...
Today...high confidence in VFR conditions. West to northwest wind
gusts between 20 and 30 knots.
Tonight...high confidence in VFR conditions. Gusty winds diminish
during the evening.
Monday...high confidence in VFR conditions. Low probability
in brief MVFR conditions across the cape/islands in a few light snow
showers/flurries...mainly during the morning.
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence in taf.
Outlook...Monday night through Thursday.
Monday night into much of Wednesday...high confidence.
Late day Wednesday and Thursday...moderate confidence.
Periods of MVFR possible in low ceilings and showers with a cold front
Wednesday night. Some snows possible especially north of a line from psf-
orh-mht with light accumulations. Conditions improve during the
morning Thursday as winds shift to the west. Wind gusts Thursday may reach
25-30 knots at times.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /today through Monday/...
Today...high confidence. Strong cold advection will result in
excellent mixing and 25 to 30 knot wind gusts. Small Craft Advisory headlines remain
posted for all the waters.
Tonight...high confidence. Small Craft Advisory wind gusts diminish this evening as
high pressure builds in from the west. However...left over swell
will require Small Craft Advisory headlines into at least a portion of the overnight
hours across the eastern Atlantic waters.
Monday...moderate to high confidence. Low pressure passing well to
our south will result in marginal Small Craft Advisory wind gusts from the northeast
at 20 to 25 knots along with 3 to 5 foot seas across our southern
Atlantic waters. Small Craft Advisory headlines may be needed...but its 3rd period
and marginal so will defer to the next shift.
Outlook...Monday night through Thursday...moderate confidence.
Monday night into Wednesday...high confidence overall.
Mainly quiet boating weather after seas subside Monday evening and
high pressure builds across the waters through the period. Low
probability of some 5 feet swells along the S ocean waters through
the period from storms well offshore.
Wednesday night into Thursday...moderate confidence.
SW winds increase through the overnight Wednesday night as seas build to
5-7 feet. Following a cold front late night...winds shift to the west
with gusts expected around 25-30 knots at times during the day Thursday.
Given these factors...a period of small craft advisories looks
northwest wind gusts of 25 to 35 miles per hour are expected today. In
addition...minimum afternoon relative humidities will fall to
between 20 and 35 percent. However...given the cold temperatures and
at least patchy snow cover across much of the region...no fire
weather headlines will be issued.
Marine...Small Craft Advisory until 5 PM EDT this afternoon for
Small Craft Advisory until 2 am EDT Monday for anz250-254-255.
Small Craft Advisory until 8 PM EDT this evening for anz256.