Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
905 PM EDT Monday Mar 10 2014
an active polar jet stream will bring another bout of light wintry
precipitation tonight to the region...especially northern
Massachusetts and southwest New Hampshire. Thereafter the polar jet
lifts northward allowing milder weather to overspread the region
Tuesday with temperatures rising into the 50s! A powerful area of
low pressure then develops Wednesday and tracks over or near
southern New England...bringing heavy rain and snow to the area.
Still too early to determine exactly how much rain and snow will
fall. Dry but bitterly cold weather briefly returns later Thursday
into Friday. Much warmer weather is likely to begin next weekend.
Near term /until 6 am Tuesday morning/...
905 PM update...
A fast moving shortwave will bring a few brief rain/snow showers to
the region overnight...mainly to the north of the Massachusetts Turnpike. The
highest risk of measurable precipitation will be across southern
New Hampshire...where will go with a brief period of likely probability of precipitation.
As for ptype...soundings are warming but cold enough for some light
snow at the start at least in higher terrain of northern Massachusetts/southern
New Hampshire. We could see a coating to perhaps up to 1 inch of snow across
the higher terrain of far northern Massachusetts/southern New Hampshire. There also is a
low probability for a touch of freezing drizzle as thermal profiles
warm at the end and lifts becomes very shallow. Will continue to
monitor overnight...but confidence on any freezing drizzle is too
low to hoist any advisory at this time. Temperatures will pretty much
remain in the 30s overnight.
Short term /6 am Tuesday morning 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 Monday/...
*** trending warmer and wetter for Wednesday/Wednesday night storm ***
*** typical large temperature swings for March this period ***
Model guidance and synoptic overview...
All model guidance including the 12z GFS/NAM/UKMET/gefs/ECMWF and
ecens have all trended north with the surface low now and showing
good clustering around a track along the coastal plain /i95
corridor/ of southern New England Wed-Thu. This is a warmer solution
than seen in previous model runs. While this is the more likely
track/scenario at this time...not expecting major changes in future
model runs but keep in mind model projections at 60+ hours rarely
verify exactly. Thus need to keep the door open for slight colder
or warmer solutions in later model runs. This directly impacts the
evolution of the rain-snow and accompanying snowfall forecast. Thus
still too early to lock into precise snow totals or transition
The two packets of jet energy that will merge and result in
explosive cyclogenesis over the northeast are currently coming into
the Pacific northwest and the other packet over northwest Canada and
Alaska...not a data rich area. The amplitude of the trailing jet
energy over northwest Canada and Alaska will be key...as models
agree this feature will provide enough amplitude to back the middle
level flow sufficiently for a storm track farther northwest. As
mentioned above...still 60+ hours out so for now will blend all 12z
model guidance. However we will stay away from the 12z NAM thermal
fields which are displaying their typical cold bias at this longer
Sensible weather details...
Good model agreement that precipitation overspreads the region from west to
east...possibly holding off until early afternoon over southeast Massachusetts.
12z model guidance suggest precipitation may begin as snow somewhere along
and north of the Mass Pike and into southern New Hampshire...then the rain-snow
line lifting northward into southern or central New Hampshire before crashing
southward Wednesday night as middle level low moves east across the region
and wrapping colder air southward. Rain-snow likely to crash
southeast all the way to the coast. Then issue becomes how much quantitative precipitation forecast
is left once cold air arrives. GFS and European model (ecmwf) handle the evolving
comma head differently...so low confidence on how much snow will
fall on the backside. Based on the current storm track most
confidence of 6"+ across northwest into southwest New Hampshire. That is a
combination of snow on the front end Wednesday...mixed precipitation Wednesday evening
then back to snow overnight Wednesday night into early Thursday. Thus Winter
Storm Watch remains in effect for this area. Was tempted to bring
the watch farther south into northern Worcester County and northwest
Middlesex...but given ptype issues/uncertainty in evolution in comma
head snows and event still 48-60hrs out plenty of time to Iron out
Less snow southward but a risk of a wintry mix for a time Wednesday from
northern CT-Rhode Island to the Mass Pike followed by a period of wrap around
snow Wednesday night into Thursday am. Elsewhere across much of central-
southern Rhode Island and southeast Massachusetts little if any snowfall expected on the
front end Wednesday with periods of heavy rain more of a concern. Risk of
urban poor drainage flooding as precipitable waters climb to +2 Standard above climatology
along with the chance of thunderstorms as nose of dry slot approaches
/Theta-east decreasing with height/ late Wednesday-Wednesday night. Will leave
thunderstorms out of the forecast given the time range.
Wednesday night could be some concern regarding a flash freeze given
standing water followed by very strong cold air advection.
Thu/Fri...some comma head snows possible Thursday morning. Then focus
becomes anomalous cold air advection with ensemble 850 and 925 mb
temperature anomalies on the order of -2 Standard from climo! Core of the cold
air is over New England 06z-12z Friday. Gusty northwest winds will provide
bitterly cold wind chills. Looking at a superblend of all model
guidance for lows Thursday night/Friday am...we are within a few degrees of
record lows at Boston/Providence/Bradley and Worcester!
Weekend...likely milder Sat /40s to near 50 possible!/ As ensembles
have low pressure tracking across southeast Canada. Ensembles suggest
attending frontal passage should be mainly dry crossing the area
sometime later Sat/Sat night/early sun. Trending cooler behind the
front for Sunday.
Aviation /01z Tuesday 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...VFR except brief period of MVFR with a chance of a snow
shower in southern New Hampshire and far northeast Massachusetts.
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 Saturday...moderate confidence.
Wednesday...MVFR to start then lowering to IFR and possibly LIFR in heavy
rain most of CT/Rhode Island and southeast Massachusetts including Boston with heavy snow
northwest Massachusetts and southwest New Hampshire.
Preliminary snowfall forecast...
Bos...1-2" possible Wednesday night/Thursday am
pvd...1-2" possible Wednesday night/Thursday am
bdl...1-2" possible Wednesday night/Thursday am
orh...3-6" possible Wednesday/Thursday
mht...5-8" possible Wednesday/Thursday
Thursday...IFR early improving to MVFR-VFR. Gusty northwest winds up to 35 knots
Fri/Sat...VFR and dry weather likely.
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 Saturday...
Wednesday...intensifying low pressure tracks along the southern New England
coast. Low visibility in fog and heavy rain.
Thursday...gale center exits southeast Massachusetts into the Gulf of Maine with northwest
gales likely. Light freezing spray likely with a low risk of
moderate freezing spray.
Fri/Sat...winds ease Friday but then shift to the SW Sat and become
gusty as low pressure tracks across southeast Canada.
no flooding expected given relatively low astro tides and not much
wind and surge anticipated as track of surface low directly over or
very close to the region.
near record cold possible Thursday night into early Friday. Here are
record low temperatures for Friday March 14th...
Bradley Airport... low...10
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.
Marine...Small Craft Advisory from 5 am to 2 PM EDT Tuesday for