Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Taunton Massachusetts
728 am EDT Tuesday Mar 11 2014
dry and mild weather across the region today. Strong low pressure
will track across southern New England Wednesday into early Thursday. Heavy
rain will be the primary precipitation type...except across far
northwest Massachusetts/southern New Hampshire where a period of heavy snow and freezing
rain is possible. Most locations will end as a bit of snow Thursday
morning...but the main story will be a brief shot of Arctic air
ushered in on strong northwest winds. Milder weather returns Friday
and Sat...before another shot of cold air for early next week.
Near term /until 6 PM this evening/...
7 am update...
shortwave currently shifting into northern New England per latest WV
imagery. As it does so modest middle level ridge will continue to build
across southern New England into the afternoon hours. This
morning...the gradually diminishing cloud deck has allowed temperatures
to fall off at some spots...yielding some light fog. This should
burn off by around 14z thanks to mixing with high clouds broken-scattered
through much of the day. Agree with previous forecaster thinking
that guidance may be a bit too cold with its highs today as at
least some broken sunshine should allow mixing to break 850 mb with all
insolation going into heating. Adjusted temperatures/dewpoints and clouds
mainly this this update.
beautiful Spring like day under a mixture of clouds and sun. A
mild start...850 mb temperatures over 0c along with west to northwest
flow often allows temperatures to exceed guidance values this time of
year. Will go with highs between 50 and 55 across most of the
region. Can/T rule out a few middle to upper 50s across a small
portion of interior Rhode Island/southeast Massachusetts. Northwest winds may
gust to around 25 miles per hour this afternoon.
Short term /6 PM this evening through 6 am Wednesday/...
Dry weather will prevail for most of tonight...despite an abundance
of middle level cloudiness. Warm advection well in advance of low
pressure may allow some scattered light precipitation to develop
towards daybreak...mainly northwest of I-95. Model soundings show
it will probably be warm enough for light rain across most of
Massachusetts...with the the light snow confined to southern New Hampshire.
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.
Long term /Wednesday through Monday/...
*** Wednesday/Wednesday night storm continues to trend warm/wet ***
*** typical large temperature swings for March this period ***
Overview and model preferences...
with 11.00z model guidance continuing to hone in on track of surface
low pressure for middle week...will be leaning on a blend of new guidance
with this update.
The main issue is that as both shortwave energy from the Pacific
northwest and diving S from Hudson Bay are starting to be better
sampled...guidance continues to hone in on the final
depth/sharpness of the combined trough once it reaches the northeast
Continental U.S.. the trend in the last few runs has been to lift the final
trough north somewhat...carrying the rapidly deepening low pressure
attendant to this final wave solution a bit further north each run.
Current trends suggest low pressure will move from the NYC
metropolitan...into the bos metropolitan by early Thursday morning...deepening to the
middle 970s as it GOES. This is slightly further north than the I-95
corridor track. This also has significant thermal profile
consequences...suggesting /at the very least/ that 850 mb +4c line
reaches to southern New Hampshire implying warmer middle levels. Still some uncertainty
on this as we are still 36 or so hours out...but will be adjusting
somewhat to this warmer solution with this update.
Wednesday and Wednesday night...
very strong but very complex low pressure center will be approaching
Wednesday then moving rapidly across southern New England Wednesday night. The key
with this storm will be the thermal profiles as it moves
through...as moisture is not an issue. Precipitable waters of 1.0-1.5 inches
/nearly 2 South Dakota above normal/ and very strong lift with the deepening
low pressure will be accompanying this storm system.
Surface warm front will be approaching from the west early in the day on
Wednesday...sliding through the northern reaches through the day with weak
isentropic lift. Therefore...do expect some light precipitation to be
spreading east through the day...especially north of the Mass
Pike...increasing in intensity everywhere through the afternoon as
the moisture flux increases and the low pressure itself approaches.
The combination of diurnal heating and increasing warm advection
suggests this initial precipitation is mostly in the form of rain...save
for some areas north of Route 2 which may be cool enough initially to
start as some light snow before a change-over.
Thermal profiles and p-type...
through the evening and overnight hours as both lift increases
and middle level temperatures continue to warm...expect a broad area of rain
/sometimes heavy given model soundings show modest middle level
instability/. The latest shift north has the 850 mb +6 line approaching
Route 2...with the h92 +10 line at the Mass Pike.
Therefore...areas S of Route 2 are may be rain for a long period
of time. However...extreme northern Massachusetts and southern New Hampshire...note enough of a north
component to the wind through the evening to allow surface temperatures to
gradually lower...possibly dipping below freezing around
03-06z...then shifting S with time. May actually see a change to
a period of freezing rain from north to S /possibly reaching the Massachusetts Pike by
around 06z/. Following this surface cooling trend...as the low shifts
offshore after 06z...the combination of crashing heights and
strong cold advection will lead to a rapid change over to snow
/possibly still heavy/ from northwest to southeast through 12z as 850 mb/h92 temperatures
drop rapidly below freezing from NW-se. The best chance for
prolonged heavy snow looks to be mainly the extreme northern reaches of
the box County Warning Area. However... not out of the question almost all of
Massachusetts/CT/RI see at least some snow before ending...although there is
a strong signal dry slot may cut things off for southern CT/RI/ and southeast
Massachusetts during the early morning hours Thursday. What this means is there is
likely to be a very tight gradient between the have and have nots
for snowfall especially from Route 2 north. Areas S of Route 2 may
struggle to accumulate much /if at all given the aforementioned
dry slot/. In a region from the Mass Pike into southern New Hampshire...the
declining surface temperatures may lead to a period of light ice
accumulations under freezing rain.
Given the uncertainty in the freezing rain/snow trends not confident
enough in changing current watch location with this update...as
the warmer trend may limit the ability for both snow and freezing rain to
accumulate....suggest warning criteria may only be Route 2 north /for
snow possibly even in northern Cheshire Hillsborough/.
despite the uncertainty in final p-type issues especially from
Route 2 north and freezing rain from the Mass Pike to Route 2...areas S of the
Mass Pike are likely to remain mostly rain until a brief change
over Thursday morning. With very high precipitable waters ...strong lift and even some
middle level instability apparent...heavy rain at times may lead to
occasional urban and poor drainage flooding at times.
this may actually carry over into Thursday. Strong cold advection
/accompanying the potential change to snow before ending early Thursday
morning/ may lead to surface temperatures rapidly dropping below freezing in
areas that have seen a fair amount of rain or a mix of
snow/rain/fzra. This may lead to a rapid freeze along area
roadways into the day Thursday...exacerbating already slippery
conditions where snow/freezing rain fell and creating slippery conditions
where only rain fell. For some /especially CT/RI/srn Massachusetts/ this may
actually be the bigger issue where any standing water/wet roadways
low pressure moving into the Bay of Fundy during the day will lead to
rapidly cooling temperatures and strong northwest flow. May still see
some comma-head snows through the morning hours especially..but
this will be dependent on the strength/depth of the dry slot. An
additional inch or so of snow accumulation is not out of the
question...and it may be here that areas around and S of the Mass
Pike see most of their snowfall from this system during the
morning hours. Will still need to monitor for icy conditions and
surface temperatures rapidly cool through the day. 850 mb temperatures will be near
-20c by Thursday evening.
The other issue will be the potential need for at least a Wind
Advisory as northwest flow develops and skies clear during the
afternoon...mixing to 850 mb where a near 50 knots low level jet exists may lead
to 35-50 miles per hour wind gusts at times across much of the region.
Thursday night into Friday night...
a cold start initially Thursday night thanks to strong northwest flow and
cold ambient temperatures /which may require a Wind Chill Advisory
for the interior as chills fall into the negative numbers.
However...by Friday as high pressure noses over from the SW...a second
round of return warming flow is expected to develop with 850 mb temperatures
reaching -2c. Combine this with partly cloudy skies and a higher
March sun angle and highs could approach the 40s. Cooling into the
30s Friday night. Dry weather prevails under the high pressure influence.
Sat and Sat night...
a cold front slides through the region attached to weak clipper
low through northern New England. Surface-middle level temperatures have a chance to
rebound above freezing so expect any precipitation to remain as rain.
However...this front may go through mostly dry due to both a lack
of lift and moisture. Mainly slight to low chance probability of precipitation with this
Early next week...
tricky setup regarding longwave trough settling over northern Quebec
into New England. Exact placement will lead to final storm-track
solution as shortwave energy approaches.
Aviation /12z Tuesday through Saturday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Short term /today and tonight/...high confidence.
after some MVFR fog dissipates through about 14z at some terminals
VFR dominates through tonight. SW winds shift to the west and gradually
increase with some gusts around 20 knots possible this
afternoon...diminishing this evening.
Tonight...VFR conditions for most of the night. MVFR ceilings/visibilities may
overspread areas northwest of I-495 between 8z and 12z in light
precipitation. Ptype mainly light snow in southern New Hampshire with light
rain elsewhere. Delayed the timing of MVFR conditions somewhat
with the 12z update...not expecting much MVFR conditions until
after 12z Wednesday.
Kbos terminal...high confidence in taf.
Kbdl terminal...high confidence in taf.
Outlook...Wednesday through Saturday...moderate confidence.
Wednesday and Wednesday night...
MVFR to start then lowering to IFR and possibly LIFR in heavy
rain most of CT/Rhode Island and southeast Massachusetts including Boston with a mix
of heavy snow and freezing rain northwest Massachusetts and southwest New Hampshire.
Preliminary snowfall forecast...
Bos...1-2" possible Wednesday night/Thursday am
pvd...T-1" possible Wednesday night/Thursday am
bdl...T-1" possible Wednesday night/Thursday am
orh...2-4" possible Wednesday/Thursday
mht...3-6" possible Wednesday/Thursday
IFR early improving to MVFR-VFR. Gusty northwest winds up to 35-40 knots
VFR and dry Friday. Some light precipitation possible on Sat.
forecaster confidence levels...
Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.
Today...will continue Small Craft Advisory headlines across our southern Atlantic
waters for 3 to 5 foot seas. This a result of west to southwest
wind gusts of around 20 knots. Expect conditions to remain below
Small Craft Advisory thresholds across the rest of our waters...but near shore winds
may gust to between 20 and 25 knots for a few hours this afternoon.
Tonight...weak pressure gradient will keep winds/seas below Small Craft Advisory
thresholds. Therefore...no headlines will be needed.
Outlook...Wednesday through Saturday...
Mainly quiet boating weather to start...although winds and seas
begin to pick up by late evening. Some light rain possible during
Wednesday night into Thursday...moderate confidence.
A period of gale force winds expected as strong low pressure crosses
the waters. First out of the S...then shifting to northwest during the
early morning hours and continuing into the day Thursday. This will be
accompanied by some light freezing spray with pockets of moderate
freezing spray possible.
Friday and Sat...moderate confidence.
Winds and seas slowly diminish Thursday night into Friday...but small
craft advisories will likely be needed until at least Friday morning.
After a brief lull and winds shift to the S...another round of
wind gusts 25+ knots and building seas suggest more small crafts
needed for Friday night into Sat.
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 Storm Watch from Wednesday morning through Thursday
morning for maz002-003.
New Hampshire...Winter Storm Watch from Wednesday morning through Thursday
morning for nhz011-012-015.
Marine...gale watch from late Wednesday night through Thursday evening
Small Craft Advisory until 4 PM EDT this afternoon for