Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
1047 am EDT Wednesday Mar 12 2014
an intensifying low pressure system approaching from the west will
result in steady rain developing this afternoon. Rain will
transition to freezing rain/sleet then snow later tonight as
temperatures crash allowing for a flash freeze. Bitterly cold air
and strong winds are expected on Thursday as lingering snow showers
taper off during the afternoon. Milder weather returns Friday and
Sat...before another installment of colder air arrives Sunday into
early next week.
Near term /until 6 PM this evening/...
***steady rain will not affect most locations until this afternoon
and possibly not reaching the coastal plain until early evening***
1045 am update...
12/12z observed soundings indicate a pronounced warm nose already
in place across southern New England. Regional radars showing
precipitation on our doorstep...but drying up somewhat as it
moves east. 12/14z observations still had rather large dew point
depressions...particularly toward southeast Massachusetts and Rhode Island. Expecting
these conditions to change as the afternoon progresses. Did adjust
the arrival time of rainfall later this afternoon...leaning
heavily upon the 12/12z NAM and 12/13z rap guidance.
Otherwise...made some minor tweaks to near term conditions to keep
them in line with observed trends. No changes to existing
headlines at this time.
Previous discussion follows...
Low pressure across the Ohio Valley will move east northeast today
as it intensifies. The bulk of the forcing/lift will be well to our
northwest this morning. Therefore...other than scattered showers
across the interior this morning..mainly dry weather will prevail.
Ptype should be liquid across most of the region this morning...but
a few wet snow flakes are possible across the higher terrain of
southwest New Hampshire but no accumulations are expected.
Steady rain will move into areas northwest of I-95 during the middle to
late afternoon. It may take until early evening for the steady rain
to reach the coastal plain. Given the track of the storm...bulk of
the middle level forcing/frontogenesis will be across the interior this
As for ptype...models soundings indicate it will be warm enough for
rain for much of the afternoon for southern New England.
However...will have to watch for some pockets of sleet/freezing rain
developing by late afternoon in southwest New Hampshire/northwest Massachusetts as shallow
cold air begins to work into the area.
Across the rest of the region high temperatures will mainly be in the 40s
but some lower to middle 50s are possible in the warm section of
interior Rhode Island/southeast Massachusetts.
Short term /6 PM this evening through 6 PM Thursday/...
***rain changes to brief period of sleet/freezing rain and then to
snow from northwest to southeast tonight***
***flash freeze overnight with impact on Thursday am rush hour a
much bigger concern than snow accumulations***
Intense low pressure will track across Rhode Island and southeast Massachusetts
tonight. Once the low passes to the east...temperatures will crash
an rain will change to snow. The cold air initially comes down
shallow...so a brief period of sleet/freezing rain is possible
especially north of the Massachusetts Turnpike. The rain should change to
sleet/freezing then snow across southwest New Hampshire/western Massachusetts by late
evening...then between 11 PM and 3 am on the coastal plain.
The middle level centers of the storm track to the west of our region.
That means that the very heavy snow amounts will confined to
northern New England. The one thing will have to watch is northern
Cheshire/northwest Hillsborough counties where some 6+ inch snow
amounts are possible. We were not confident enough that these
amounts would cover a large enough portion of the counties for an
upgrade to a warning...but something later shifts may have to
consider. Best chance for that will be across Cheshire County.
Across most other areas...have hoisted a Winter Weather Advisory
except for the South Coast/cape and islands. For most locations
were just expecting 1 to 2 inches of snow...with perhaps 2 to 4
inches north of Route 2. However...given the potential for a brief
period of sleet/freezing rain and flash freeze with temperatures expected
to crash into the teens and lower 20s...felt an advisory was Worth
it. Especially with an impact expected on the Thursday am rush hour.
Very impressive temperature fall as some locations in Rhode
Island/southeast Massachusetts may be near 50 this evening and into the upper
teens lower 20s by early Thursday am!
***bitterly cold with northwest wind gusts of 40 to 50 mph***
Potent upper trough will be lagging behind surface low pressure.
Therefore...expect snow showers to continue throughout the morning
before tapering off during the afternoon. Temperatures will remain
in the upper teens and lower 20s all day...which is very impressive
cold for this time of year. Wind chills will be below zero. In
addition...northwest wind gusts of 40 to 50 miles per hour in strong cold
advection will likely require the need for a Wind Advisory. Since
its a 3rd period event and there is a lot going on will let the next
Long term /Thursday night through Tuesday/...
*** typical March weather with a mix of Spring and winter-like
temperatures this period ***
Overview and model preferences...
12.00z model guidance suite is in fairly good synoptic scale
agreement through the weekend at least but then begins to show
typical spread/biases by early to middle next week.
The key to the extended period will be an Arctic cutoff...that is
a piece of the polar vortex which will gradually settle across
northern Quebec. This will be embedded within a general positive
nao/ao regime...suggesting a progressive storm track from the eastern
Continental U.S. Into the northern Atlantic. Therefore...the key to the ultimate
storm track for early next week will be exactly where the vortex
and its longwave trough extension into the eastern Continental U.S. Sets up. Latest
European model (ecmwf) as well as some of the gefs/ecens members suggest a slightly
less progressive track...allowing the trough to set up mainly from
the Great Lakes into the Gulf of Mexico...picking up energy and
moisture as it does. It is this solution that would bring the best
shot at another coastal storm for early next week. The GFS
solution is more progressive and suppressed to the S. Once again
though...aside from the longwave trough it will require additional
shortwave energy...both from Arctic the northern Pacific. Each of these
waves will not be in an observation rich area for about 48+
hours...so expect the track to settle better by the weekend. For
now...will blend operational guidance to take into account all
Thursday night into Friday night...
mainly dry weather through the period as a ridge of high pressure noses
over the region from the S. Thursday night is expected to start
cold...with ambient mins dropping into the single digits and low
teens. This will be combined with gusty northwest winds and may yield
wind chills approaching -10f to -15f...so not out of the question
wind chill advisories may be needed. Otherwise...temperatures
rebound by Friday...shifting into the low to upper 30s and only
dropping back into the middle 20s to low 30s thanks to increasing
clouds Friday night.
Sat into Sun night...
moderating temperatures expected under weak warm advection ahead
of a cold front Sat. This should allow highs to reach into the middle
40s to low 50s. The cold front is expected to slide through by
afternoon...lift with it is weak...mainly from the isentropic
support within the warm advection ahead of it. Moisture is also
lacking...with only about a quarter to half inch precipitable water values.
So...a few showers may accompany this front as it passes...but
certainly not a washout and some areas may stay dry altogether.
Cold and drier air settles in behind the front Sat night into Sun
night. Lows in the low to upper 20s expected Sat night under
cloud cover and highs sun only in the 30s. Another round of cold
mins Sun night...settling in the teens and low 20s.
Monday into Tuesday...
the cold front settles offshore sun...orienting along the mean
storm track...which remains a bit in question based on the
overview discussion above. There are ingredients for another
coastal wave of low pressure to develop...but its potency and track
are uncertain. As mentioned above...current European model (ecmwf) /as well as
gefs/ecens members and even the global CMC/ suggest it may make a
close enough pass for some wrap-around snows across southern New
England...but the more progressive pattern /GFS and some ensemble
members/ would keep it too far offshore. Will need to monitor once
shortwave energy in the Pacific and Arctic are better sampled.
Toward the middle of next week...
in either case...another round of Arctic high pressure looks to
settle across the region as any storm system moves further
offshore...so a period of temperatures below normal looks
Aviation /15z Wednesday through Sunday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term...through Thursday.
Today...high confidence in trends...lower confidence in exact
VFR to start the morning. A few light showers possible mainly
terminals north of Route 2 this morning...but suspect bulk of the
morning remains dry. Expecting conditions to gradually lower to
MVFR this afternoon...then to IFR from about 17z-21z across the
western half of southern New England as rain arrives. Rainfall
becomes heavier this evening with most locations seeing IFR
conditions after 22z. May see pockets of low level wind shear out of the S at
times this afternoon...mostly Cape/Island terminals.
Tonight...aside from slight adjustments to timing...mostly on
track for 12z update....mainly IFR with some MVFR conditions.
Rain transitions to snow from northwest to southeast as the night
wears on. A brief period of sleet/freezing rain is possible during
the transition especially north of the Massachusetts Turnpike. Northerly
winds will gust between 20 and 30 knots behind the storm by late
evening into the overnight hours. Some low level wind shear possible as winds
shift to the northwest rapidly.
Thursday...MVFR to IFR conditions in snow showers in the morning
should improve some during the afternoon from west to east. Expect
conditions to improve to MVFR if not VFR by middle to late afternoon.
Northwest wind gusts of 30 to 45 knots expected.
Preliminary snowfall forecast...
Bos...1 to 2 inches overnight/Thursday am
pvd...1/2 to 2 inches overnight/Thursday am
bdl...1/2 to 2 inches overnight/Thursday am
orh...1-3 inches late overnight/Thursday am
mht...2-5 inches late overnight/Thursday am
Kbos terminal...high confidence in taf through 18z today.
Moderate confidence thereafter. Rain transitions to a brief period
of sleet/freezing rain between 04z and 06z tonight. Then a change
to all snow between 06z and 08z.
Kbdl terminal...high confidence in taf through 18z today.
Moderate confidence thereafter. Rain transitions to snow between
02z and 05z tonight with a brief period of sleet/freezing rain
possible during the transition.
Outlook...Thursday night through Sunday.
Thursday night through Friday night...high confidence.
Mainly VFR. Strong northwest winds diminish Thursday night then shift back to
the SW on Friday and Friday night.
Mainly VFR...but occasional MVFR possible in light rain/snow
showers ahead of a cold front.
Mainly VFR...but low probability of a late day ocean low pressure
leading to some snow showers particularly southeast mass. MVFR/IFR would
be possible should this occur.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /tonight through Thursday/...high confidence.
Today...winds/seas will be below Small Craft Advisory thresholds through the morning.
Southerly flow ahead of low pressure will result in 20 to 25 knot
gusts and 3 to 6 foot seas develop during the afternoon across the
southern Atlantic waters.
Tonight and Thursday...northwest gale force wind gusts of 40 knots
develop late tonight and Thursday as intense low pressure passes to
our east. In addition...moderate freezing spray will develop during
Thursday afternoon as an usually cold air mass for middle March invades the
region. Later shifts will likely need to issue a freezing spray
advisory. In addition...seas across the eastern Atlantic waters
will build to between 7 and 13 feet on Thursday.
Outlook...Thursday night through Sunday...
Thursday night...moderate confidence northwest gales likely along with
moderate freezing spray possible by late day Thursday. Visibility reduced in
light snow during the day. Very rough seas especially south waters
from leftover south swells combining with new northwest wind waves.
Northwest wind becoming SW during the afternoon. A few gusts to 25 knots
possible during the afternoon...with seas remaining elevated above
5 feet especially on the ocean waters.
Friday night into Sat...moderate confidence.
SW winds shift to the west during the day sate. Gusts should
generally remain below small craft criteria but a building swell
of 5-7 feet expected on the ocean waters.
modest northwest wind may increase by sun evening. Dry and good visibility.
no flooding expected given relatively low astro tides and not much
wind and surge anticipated as track of surface low pressure looks
to be directly over southern New England. This will limit the ability
for fetch in any one direction.
near record cold possible Thursday night into early Friday. Here are
record low temperatures for Friday March 14th...
Bradley Airport... low...9
CT...Winter Weather Advisory from 10 PM this evening to noon EDT
Thursday for ctz002>004.
Massachusetts...Winter Weather Advisory from 4 PM this afternoon to noon EDT
Thursday for maz002-003.
Winter Weather Advisory from 10 PM this evening to noon EDT
Thursday for maz004>019-026.
New Hampshire...Winter Weather Advisory from 4 PM this afternoon to noon EDT
Thursday for nhz011-012-015.
Rhode Island...Winter Weather Advisory from 10 PM this evening to noon EDT
Thursday for riz001>005.
Marine...Gale Warning from 8 am to 8 PM EDT Thursday for anz232>235-237-
Gale Warning from 5 am to 8 PM EDT Thursday for anz230-236.
Gale Warning from 2 am to 8 PM EDT Thursday for anz231-250-251.