Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
301 PM EDT Monday Mar 10 2014
an active polar jet stream will bring a few bouts of clouds and snow
showers over the region late tonight. Maximum temperatures should
be above normal Tuesday...with values around 50. A winter storm
is likely Wednesday into Thursday...but the details of how much
rain or snow will fall is uncertain. Cold and dry weather
follows...but a warm up is possible Friday and Saturday.
Near term /through tonight/...
snow has pretty much ended across southern New England. We will
still be dealing with lower clouds across the cape and islands for
a couple more hours. Thinner spots were developing farther
The trick will be how much clearing we get late this afternoon...
before another band of isentropic lift arrive this evening. The
majority of the dynamics should remain to our north...so only
expecting scattered snow or rain showers. Conditions expected to
dry/clear out after midnight across southern New England.
Temperatures will be tricky...and largely dependent upon how
quickly the skies clear. At this point...thinking is there will be
enough clouds lingering to prevent ideal radiational cooling
conditions. Stayed close to MOS consensus for min temperatures
overnight. Temperatures right around freezing does open the door
for some icing potential...particularly across portions of
northern Massachusetts...where the 925 mb temperatures are above freezing.
This is a low probability at this point...so not planning any
advisories at this time.
Short term /Tuesday through Tuesday night/...
mainly dry with plenty of sunshine. As mixing occurs...the
westerly downsloping winds will allow for gusts to increase near
20 miles per hour and dewpoints drop into the 20s. This could turn into a
potential fire weather day...all depends on how deep the mixing
increasing clouds associated with a broader...but weaker...area of
isentropic lift Tuesday night. Low levels look fairly dry until
rather late in the night. At this point...thinking precipitation
will hold off until later in the day Wednesday.
Stayed close to MOS consensus for these periods...but did try to
account for some recent biases.
Long term /Wednesday through Sunday/...
big picture...Pacific shortwave moves ashore this morning. By
Tuesday night it will be over the Central Plains phasing with a
shortwave moving around the Arctic low. Meanwhile...a southern
stream shortwave moves along the Gulf Coast. The two northern
waves phase Tuesday night...digging a trough over the eastern USA
that draws the Gulf shortwave moisture up the coast. The trough
sweeps across New England Thursday. The Arctic low moves south to
James Bay late in the week generating a broader cyclonic flow over
the Great Lakes/northeast while an upper ridge builds along the
West Coast. The below normal heights suggest a core of cold air
either in the neighborhood or overhead during the weekend.
Model preferences...with the northern Pacific shortwave still
feet- wet overnight...and thus less-well sampled...it is still too
soon to converge on a definite solution. We continue to prefer a
blend of model data.
Wednesday-Thursday...low pressure in the plains moves up the
front. Operational model data points to a passage along or just
south of the coast. Isentropic lift fields continue to show
favorable conditions moving into CT and the Berkshires around 12z
Wednesday and then moving east across the region middle morning. This
timing of onset is similar to previous packages. Middle level
frontogenesis lines up across the eastern Great Lakes/central
New York/ncentral PA at 12z...then move across New England by midday.
The most favorable values line up across Vermont/NH/Maine during
Wednesday...then move east Wednesday night.
As the parent system was still over the Pacific at the time of
initial conditions...insufficient confidence to move to categorical
probability of precipitation. Instead we have held at high-end likely...68 to 74 percent.
The parent system moves ashore this morning...and so one would
expect confidence to increase during the day.
Aside from precipitation...question remains as to precipitation type.
Climatologically...the nearshore track would suggest rain south of
the Mass Pike and snow or a mix to the north. Thermal fields from
the European model (ecmwf) and GFS show rain to the New Hampshire border Wednesday afternoon. As
the surface low passes Wednesday night the colder air banked over
the St Lawrence Valley gets drawn south and changes the thermal
fields to snow-favorable. Several hours of snow are then possible
Wednesday night and Thursday morning as the trailing portion of the
frontogenesis maximum sweeps southern New England...with several inches
of accumulation possible.
This analysis is of course based on the 00z models...and as noted
earlier this could change as the parent system moves into the North
American weather balloon domain. A headline may eventually be needed when
forecast confidence increases.
Thursday night-Friday-Saturday-Sunday...strong gusty winds
trailing the storm will draw colder air across New England. This
will mean another chilly night...model temperatures in the single numbers
and expected winds will mean wind chills in the single numbers
below zero. A weak ridge builds aloft and pushes the coldest air
out...allowing a trend to more seasonable temperatures Friday and
Saturday. Clipper low moves across Canada Saturday and swings a
cold front across New England. Best support is in the north...less
south. So low-end chance probability of precipitation in southern New Hampshire and slight chance
farther south. Dry weather returns for Sunday.
Aviation /18z Monday through Saturday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /through Tuesday/...high confidence.
Through 00z...conditions improving to VFR across cape and islands.
Tonight...marginal MVFR-VFR in another round of snow
showers....focus on northeast Massachusetts and southern New Hampshire.
Tuesday...VFR and dry along with a modest northwest wind.
Tuesday night...VFR with increasing sky cover. Potential MVFR in
light snow late...especially in the CT valley and east slopes of
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence in taf.
Outlook...Wednesday through Friday...moderate confidence.
Wednesday-Thursday...well developed low pressure passes just
south of New England. This will likely bring precipitation to all areas.
Thermal profiles suggest mainly rain Wednesday except snow or a
rain/snow mix in southern New Hampshire. Any rain will change to snow
Wednesday night as colder air gets drawn south...with IFR/LIFR
continuing. Expect IFR or LIFR ceilings/visibilities in rain and snow. Winds
at 2000-3000 feet will reach 50-60 knots Wednesday night creating
concern for low-level wind shear. Conditions slowly improve
Thursday with surface winds shifting to northwest and gusting to
Friday...high pressure builds Friday with VFR conditions. A
clipper moves across from the Great Lakes Friday night and
Saturday...and may bring MVFR ceilings/visibility in rain or snow showers.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
High confidence through tonight...moderate confidence on seas for
Tuesday and Tuesday night.
Increasing southwest winds ahead of a cold front...shift west
during Tuesday. While maximum wind speeds are expected to remain
beneath 25 knots...there cold be a strong enough fetch for a
sufficient period of time to generate 5 feet seas across the outer
coastal waters late tonight into Tuesday. It is marginal...but
will issue a Small Craft Advisory later this afternoon for the
southern outer coastal waters.
Outlook...Wednesday through Friday...
Moderate confidence through the period.
Wednesday-Thursday...low pressure moves through the Middle Atlantic
States and approaches the coast Wednesday evening. Winds and seas
will increase...reaching small craft levels late afternoon/evening
and potentially reaching north-northeast gales later Wednesday night
and Thursday. Seas may reach 10-16 feet on the eastern waters and 7
to 10 feet on the exposed southern waters. A Gale Warning may be
needed. Winds become northwest at 30 knots
Friday...winds and seas slowly diminish as high pressure builds
high tide Wednesday night at Boston is 8.6 feet. High tide Friday
morning is 9.4 feet. A surge of 2.5 to 3 feet might cause minor
flooding along the mass East Coast. Seas of 10-16 feet being pushed
toward shore could result in splashover/minor erosion during the
period. This will be monitored.
Massachusetts...Winter Storm Watch from Wednesday morning through Thursday
morning for maz002-003-008-009.
New Hampshire...Winter Storm Watch from Wednesday morning through Thursday
morning for nhz011-012-015.