Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
1020 am EDT Monday Mar 10 2014
an active polar jet stream will bring a few bouts of clouds and snow
showers over the region this morning and again late tonight. Average
temperatures return to the region today with temperatures rising
into the 50s by Tuesday. 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 /until 6 PM this evening/...
1015 am update...
Regional radars...as well as surface observations...showing snow
winding down across southern New England. Expecting snow to be
completely offshore past the islands by noon at the latest.
Main change for this package is the issuance of a Winter Storm
Watch for middle week. Thinking there is enough potential for 6 or
more inches of snow...but there are still many details which need
to be worked out. This watch may be expanded later today...after a
review of the 12z guidance.
Otherwise...only minor tweaks to bring near term forecast back in
line with observed trends.
Warm air advection will increase today as warm front continues to
lift northwards. Departing shortwave will push any light snow
showers/flurries offshore by the middle-morning hours. Any snow
accumulations will be light or none as quantitative precipitation forecast is less than an
Weak ridging will occur behind the departing shortwave yet guidance
shows some low level moisture sticky round. This seems reasonable thanks
to the return flow. 850mb temperatures will warm from -8c to -2c and
although mixing will not reach that high...a sure sign that warm
air advection is occurring. Mixing will be shallow today and with
on and off breaks in the clouds in the afternoon...believe temperatures
will warm at or near average. Just a precursor for tomorrow.
Short term /6 PM this evening through 6 PM Tuesday/...
another upper level disturbance will ripple through the flow and
move into southern New England. There is some weak lift and
moisture as the shortwave moves through...so anticipate some
isolated showers. Guidance shows the better lift and moisture will
reside in northern New England with northern Massachusetts and southern New Hampshire
having the best shot for any precipitation. P-type could be an
issue...at 925mb a warm nose is noticed on some of the guidance
and if surface temperatures are cold enough then perhaps some freezing
drizzle is possible. Yet as we get closer to 12z...surface temperatures
should warm above freezing resulting in liquid precipitation.
Overnight temperatures will remain at or just above freezing south
of the Pike where the warm air will move into the region first.
North of the Pike will see temperatures at or just below freezing. Overall
radiational cooling is not anticipated as cloud cover will
upper level short moving across northern New England will exit
offshore allowing for return flow to the region. 850mb temperatures warm
from 0c to 4c...combined with departing clouds and March sunshine
we could see high temperatures warm into the low to middle 50s. NAM
soundings show the best mixing which could yield to warmer
temperatures. Like previous forecaster leaned towards the European model (ecmwf) 2 M
temperatures which are the warmest and seem the most reasonable as all
other guidance seems to cool. As mixing occurs...the westerly
downsloping winds will allow for gusts to increase near 20mph and
dewpoints drop into the 20s. This could turn into a potential fire
weather day...all depends on how deep the mixing gets.
Long term /Tuesday night 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.
Tuesday night...weak high pressure over the region should keep
weather dry most of the night. Increasing moisture at all levels
overnight points to increasing clouds. The clouds/a lack of cold
air drainage/a mild preceding day should keep overnight temperatures near
freezing. There is some concern that the increasing clouds may
bring slowly warming temperatures overnight which is not shown in the
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 /14z Monday through Friday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /through Tuesday/...high confidence.
Today...scattered MVFR/IFR ceilings/visibilities in snow showers across the
cape and islands through 16z at the latest. Snow accumulations
from a dusting to perhaps an inch. Improvement to VFR late this
morning and afternoon there. Already VFR north and west of a line
from kbos to kuuu.
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.
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence in taf.
Outlook...Tuesday night through Friday...moderate confidence.
Tuesday night...VFR with increasing sky cover. Potential MVFR in
light snow late at night especially in the CT valley and Berkshire
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
Today...snow showers possible limiting visibility to 5 miles...then
good visibilities by the afternoon. Light SW winds with a few gusts to
Tonight...modest SW wind with possibly snow showers across the
northern waters. Visibilities could drop to 5 miles.
front moves offshore with a modest west-northwest wind overspreading the
waters. Seas could build to 5ft across the southern outer waters.
Low confidence on if this will occur to held off on Small Craft Advisory. Good
visibility and dry weather.
Outlook...Tuesday night through Friday...
Moderate confidence through the period.
Tuesday night...winds and seas below small craft thresholds.
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.