Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
715 PM EDT Tuesday Mar 11 2014
dry and mild weather continues this evening. A strong coastal
storm will track across the southern New England coast Wednesday into
early Thursday. Heavy rain will be the primary precipitation type...
except across far northwest Massachusetts and southwest New
Hampshire where a wintry mix is likely Wednesday before changing over to
snow Wednesday night. Most locations will end as a bit of snow
Thursday morning...but the highlight Thursday will be an Arctic
surge overspreading the region on strong northwest winds. Milder
weather returns Friday and Sat...before another installment of colder
air arrives Sunday into early next week.
Near term /until 6 am Wednesday morning/...
715 PM update...made a few minor adjustments to the temperatures
and dewpoints to account for the latest trends /temps still in the
upper 40s to lower 50s across much of the area/. Otherwise...the
forecast is in good shape...just waiting on the precipitation to move
into the area late tonight/early tomorrow morning.
Made some adjustments to temperatures for the rest of this
afternoon to reflect the latest observations. Plenty of
sunshine...combined with a downsloping west wind...has pushed
temperatures well above normal.
Dry weather should prevail...despite an abundance of middle level
cloudiness arriving overnight. Warm advection well in advance of a
low pressure may allow some scattered light precipitation to
develop towards daybreak...mainly northwest of a line from
Manchester New Hampshire...to Worcester Massachusetts...to Hartford CT. The greatest
risk for precipitation will be toward the New York border.
Soundings continue to show it will probably be warm enough for
light rain across most of Massachusetts...with any light snow
confined to southern New Hampshire. Cannot rule out a strip of freezing rain
or sleet to be sandwiched between these two areas. Best estimate
would be along the Route 2 corridor west of Gardner Massachusetts. Any
accumulations across southern New Hampshire should just be a dusting to less
than an inch through 12z Wednesday. Low temperatures will mainly
be in the 30s.
Still thinking it is too uncertain to commit areas or timing for a
Freezing Rain Advisory just yet. Will need to keep an eye on
trends to see if this becomes more of a risk.
Short term /6 am Wednesday morning through Wednesday night/...
* storm continues to trend toward a warmer outcome
11/12z model guidance continues to favor a warmer solution. Stayed
close to model consensus for track. At this time...the low track
would move from New York City to near the Cape Cod canal before
moving offshore. Have the greatest confidence in winter weather
advisories at this time...so that is what we have done with this
afternoon package. Will need to keep a very close eye across
southern New Hampshire and northwest Massachusetts. It is still possible these areas
could be upgraded to warnings should the transition to snow occur
more quickly than currently forecast.
Moisture is not really going to an issue. Thermal profiles will be
critical. Expecting rainfall to become more widespread during the
day Wednesday...with the majority of the area experiencing
precipitation by late in the day. Temperatures should rise enough
to be all rain for most of the day...with the exception of areas
north of Route 2 in Massachusetts and New Hampshire. Those areas could see some wintry
precipitation in the morning. Rainfall will likely be heavier at
Strong cold air advection Wednesday night on the backside of the
precipitation will transition all precipitation back to snow.
Cannot rule out a period of sleet or freezing rain. Temperatures
will plummet...which could lead to a rapid freeze late Wednesday
night into Thursday morning. For some /especially CT...RI...
southern Massachusetts/ this may actually be the bigger issue where any
standing water/wet roadways are observed.
Did not use a diurnal trend Wednesday night into Thursday.
Thinking highs for the calendar day Thursday will be near or
shortly after midnight Thursday...then falling thereafter.
Long term /Thursday through Tuesday/...
*** typical March weather with a mix of Spring and winter-like
temperatures this period ***
Amplified northern stream offers several intrusions of colder than
normal air masses into New England this period. First shot of Arctic
air arrives Thursday behind departing coastal storm. This cold airmass
briefly retreats into southeast Canada Friday/Sat however quickly on
its heels is another intrusion of Arctic air as a piece of the
polar vortex breaks off and plunges equatorward into southern Quebec
sun into early next week. This likely keeps the area mainly dry
/other than some light nuisance frontal showers Sat/ as any southern
stream moisture most likely gets shunted south of our latitude.
Sensible weather details...
Arctic air spills across the region on the backside of the departing
coastal storm with 850 and 925 mb temperature anomalies dipping to about
-2 Standard colder than climatology. 2 meter temperatures from 12z ec/NAM and GFS all
have temperatures in the teens across much of the area at 18z Thu! Combine
this anomalous airmass with gusty northwest winds will create wind chills
around zero during the daylight hours! Probably won't break any cold
maximum temperatures given the Arctic air arrives after midnight. Thus high
temperatures Thursday will likely occur at midnight. Nevertheless temperatures Thursday
during the day will be 20-25 degrees colder than normal!
Regarding strong winds Thursday...BUFKIT soundings support northwest winds
gusting up to 50 miles per hour possible. Very low risk of a few gusts up to 60
miles per hour but confidence is not high enough at this time to hoist a high
wind watch. More likely scenario is a Wind Advisory event - northwest winds
25 to 35 miles per hour with gusts up to 50 miles per hour.
As for precipitation...models continue to handle differently the evolution
of the storms comma-head and attending middle level dry slot. However
all guidance suggest around a tenth of inch of quantitative precipitation forecast occurs Thursday across the
region. Could be a bit more as the GFS is showing very strong qg
forcing in the comma-head with middle level q-vector convergence
/50 units/ 12z Thursday over northern Massachusetts and southern New Hampshire. Nonetheless the
combination of up to an inch or two of comma-head snows region wide
combined with any standing water from Wednesday night freezing /possible
flash freeze/...expect some slippery travel for the Thursday morning
Thursday night...frigid airmass over the area with cold air advection continuing. A
blend of all guidance brings lows Friday morning within a few degrees of
record lows. As previous forecaster mention low risk of wind chill
approaching -10f to-15f across the interior. Thus Wind Chill
Advisory may be needed.
Friday...will be our transition day as thermal advection switches
from cold to warm as ridge axis moves offshore as surface winds shift
from northwest to SW. So not as cold Friday with highs in the 30s.
Weekend...Sat the milder of the two days as low pressure tracks across
the St Lawrence River valley...with modest low level warm advection
ahead of the attending cold front across southern New England.
Highs in the 40s to near 50...but cooler along South Coast given
SW wind off the cooler ocean waters. Low risk of a few showers
along and ahead of the front...but by no means a washout.
Sunday...dry but cooler behind the front with highs in the 30s to
near 40. Gusty northwest wind will add to the chilly conditions.
Early next week...piece of the polar vortex breaks off and settle
across Quebec. Meanwhile southern stream energy tracks across the
Gulf states. Some of the guidance suggest the polar vortex and the
mean trough position will be too far south and east and will shunt
southern stream moisture out to sea. However some of the guidance
suggest it will be a close call with the mean trough axis farther
west and possibly capturing southern stream moisture yielding a
storm track closer to southern New England. For now and at this
time range will carry slight chance probability of precipitation here.
Aviation /23z Tuesday through Sunday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /tonight through Wednesday night/...high confidence in
overall trends. Moderate confidence in timing.
Tonight...VFR conditions for most of the night. MVFR ceilings/visibilities
may overspread areas northwest of a line from kbdl-korh-kafn late
tonight. Precipitation begins after 09z tonight...with mainly light snow
across southern New Hampshire and light rain elsewhere. Transition
zone...including some freezing rain...generally expected along a line west
of kfit...through kore into kaqw.
Wednesday and Wednesday night...conditions decrease to MVFR/IFR
through the day Wednesday. Mainly IFR conditions late Wednesday
afternoon and evening. Conditions improve from northwest to
southeast after 13/04z.
Preliminary snowfall forecast...
Bos...1-2 inches possible Wednesday night/Thursday am
pvd...T-1 inches possible Wednesday night/Thursday am
bdl...T-1 inches possible Wednesday night/Thursday am
orh...2-4 inches possible Wednesday night/Thursday
mht...3-6 inches possible late Wednesday/Thursday
Kbos terminal...high confidence in taf through 12/15z. Moderate
Kbdl terminal...high confidence in taf through 12/12z. Moderate
Outlook...Thursday through Sunday...moderate confidence.
Thursday...MVFR likely in the morning in light snow with minor
accumulations possible. Trend to VFR during the afternoon. Gusty northwest winds
Friday...VFR with diminishing winds and shifting from northwest to SW. Dry
Sat...VFR to start but trending toward MVFR in scattered showers.
Gusty SW winds.
Sun...VFR and dry with a modest northwest wind.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Rather tranquil conditions tonight. South winds increase ahead of
a developing low pressure Wednesday...with building seas as well.
Small craft should exercise caution well before the start time of
the gales late Wednesday into Wednesday night.
Outlook...Thursday through Sunday...
Thursday...northwest gales likely along with light freezing spray. Low risk
of moderate freezing spray. Visibility reduced in light snow during the
day. Very rough seas especially south waters from leftover south
swells combining with new northwest wind waves.
Friday...diminishing northwest wind and becoming SW during the afternoon. Dry
and good visibility.
Sat...modest SW wind along with scattered showers.
Sun...modest northwest wind. 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...10
Massachusetts...Winter Weather Advisory from 7 am Wednesday to noon EDT
Thursday for maz002-003.
New Hampshire...Winter Weather Advisory from 7 am Wednesday to noon EDT
Thursday for nhz011-012-015.
Marine...Gale Warning from 11 PM Wednesday to 8 PM EDT Thursday for
Gale Warning from 5 am to 8 PM EDT Thursday for anz230-231-236-