Hi Folks,
Friday map discussion
for
snows on the Tug Hill Plateau in the first
two weeks of February, and 2) the origin and evolution of the Valentine's Day
snowstorm, the
latter of which went in as serendipitous
direction.
Because of the
size of some of the images, the map discussion synopsis will be posted in two
parts. Part I summarizes the Tug
Hill Plateau record snows while Part II, to follow
separately, discusses the Valentine's Day storm.
I. Tug Hill Plateau snows:
The daily
snowfall amounts (24 h ending 1200 UTC) that contributed to the record-breaking
storm-total 141" (3.58 m) of snow
that fell in
record-breaking event was defined by the duration of
the snowfall as much as the overall amount of the snow. The maximum 24 h
reported snowfall ending 1200 UTC was "only" 28" (71.1 cm). An
impressive event but I suspect considerably bigger 24 h snowfall amounts have
been observed in the past. Note that until the last decade there were very few
cooperative observer reports available to the NWS from the Tug Hill Plateau
region. My instincts tell me that amounts greater than what buried Redfield
have occurred in the past but that they likely went unobserved.
...........................................................
NATIONAL WEATHER SERVICE
122 PM EST
*** THESE ARE FINAL STORM TOTALS FOR THE EVENT FROM SATURDAY
FEB 3
THROUGH THIS MORNING FEB 12 WHEN THE
EVENT ENDED. ***
** REVISED REDFIELD FINAL TOTAL 141 INCHES....DAILY TOTALS
WERE AS
FOLLOWS...
FEB 3...18 INCHES
FEB 4... 7 INCHES
FEB 5...20 INCHES
FEB 6...15 INCHES
FEB 7...28 INCHES
FEB 8...23 INCHES
FEB 9... 6 INCHES
FEB 10..14 INCHES
FEB 11.. 3 INCHES
FEB 12.. 7 INCHES
..............................................................
Loops of: 1)
500 hPa streamfunction and non-divergent winds, 2) potential temperature/winds
on the dynamic tropopause (DT) and
the 925-850 hPa layer-mean relative vorticity, and 3)
pressure on the DT and the 850-DT vertical wind shear and 925-850 hPa
layer-mean relative vorticity generated from the McTaggart-Cowan GFS diagnostic
animation builder (link below) can be used to collectively show that the major
snowfall amounts at Redfield given in the table above can be associated with
the passage of subsynoptic-scale and
mesoscale DT disturbances rotating around the
large cyclonic vortex that has been anchored over
vortex. It was along this corridor of
maximum thermal vorticity that many of the critical subsynoptic-scale
end mesoscale upper-level
disturbances propagated southward and eastward
toward the
Selected images
from these loops are attached to help illustrate the salient subsynoptic-scale and mesoscale disturbances
responsible for the major snowfall periods as
follows:
a) 500 hPa streamfunction and nondivergent
winds: 1200 UTC
b) DT theta/winds and 925-850 layer-mean relative vorticity:
0600 UTC 7 Feb and 1200 UTC 8 Feb.
c) DT pressure/shear and 925-850 hPa layer-,mean
relative vorticity: 0600 UTC 7 Feb and 1200 UTC 8 Feb.
To really see what is going on, however, you need to rebuild
the loops for yourselves. Conventional wisdom for lake-effect
snowstorms as published in countless
introductory textbooks is that cold air blowing over open water that is
significantly warmer than
the overlying air is the "magic
elixir" for a lake-effect snow dump. Less discussed in the literature, but
known to experienced
forecasters, is the critical role played by
mobile synoptic-scale disturbances in organizing and enhancing lake effect
snowfall (e.g.
Lackmann 2001). The availability of higher
resolution datasets in the last couple of years (the loops above are based upon
0.5 degree
GFS analyses) has made it possible to see the critical role
played by transient subsynoptic-scale and mesoscale
disturbances in
controlling the timing, duration and amount of
lake-effect snowfall.
These mobile disturbances
are every bit as important as overwater fetch and
air-water temperature differences in determining
the severity and extent of lake-effect
snowfall events. Other factors that may have contributed to the severity of the
recently
concluded lake-effect event likely include the
relatively warm first half of the winter that allowed for the lake waters to be
characteristically mostly unfrozen by the end of
January and the abruptness of the circulation reversal in mid January that
enabled a
cold vortex to setup shop over
roughly 15 Feb.
http://www.atmos.albany.edu/facstaff/rmctc/DTmaps/animSelect.php
http://www.nrlmry.navy.mil/sat-bin/epac_westcoast.cgi (choose
Northwest vapor)
Lackmann, G. M., 2001: Analysis of a Surprise
Lorenz, E. N., 1963: Deterministic Nonperiodic
Flow, Journal of the Atmospheric Sciences, 20, 130-141.
Lance
.......................................................
Hi Folks,
Part II
(Valentine's Day storm) of the two-part Friday map discussion synopsis from
II. St Valentine's Day storm:
Last week I
wrote about an interesting mesoscale dry vortex over the eastern Pacific that
did not seem to be much more than an
idle curiosity in the Friday map
discussion synopsis for
below, this apparent idle curiosity has
perhaps morphed into one of Lorenz's butterflies. With that proffered bait,
read on.....
..............................
Excerpt from the
"A particularly interesting feature was a mesoscale dry
vortex that formed along the eastern boundary of a narrow NNW-SSE oriented
streamer of relatively dry air in the mid-
and upper-troposphere to the south of the
of archived water vapor imagery for the
eastern Pacific for the details). As the vortex formed the dry air became
secluded within it
while moist air to the north and south
wrapped around the vortex. In the WV imagery the vortex appeared as a "donut"
with drier air
defining the hole and moister air surrounding
the hole. The vortex, almost perfectly circular at times, had a diameter of
200-300 km (a
patch of slightly more moist air resided
in the interior of the vortex). A shear line running NW toward the
scale vortex centered near 46 N, 136 W in
the attached DT image from 1200 UTC on the 7th coincided fairly well with the
initial dry
streamer. The mesoscale dry vortex formed
near the NW end of this shear line and can be found near 51 N, 150 W where it
was moving
slowly NW at this time. By 0000 UTC on the
8th the mesoscale dry vortex had reached its most poleward position (53 N, 152
W; not
shown). It subsequently turned equatorward
and is marked by a small patch of potentially cooler air and a cyclonic
circulation near 50
N, 153 W at 1200 UTC on the 8th. The vortex remained located
near the tip of the aforementioned shear line as it continued equatorward (the
shear line began curving cyclonically within the outer envelope of the overall
cyclonic circulation. By 0000 UTC 10 Feb the mesoscale vortex was situated near
38 N, 146 W where it could be identified with a quasi-circular patch of
lower-level cyclonic
vorticity for the first time. As of 1200 UTC
10th the mesoscale vortex could still be identified near 35 N, 138 W as it was
being
reabsorbed into the trough that had previously
made it a free agent. What goes around comes around....."
..............................
Missing from the
previous week's map discussion post was selected satellite imagery to
illustrate the birth of the dry
mesoscale vortex. This oversight (with the
benefit of hindsight) has been corrected here with the inclusion of water vapor
(WV) imagery
over the eastern Pacific for 1200 UTC 7
Feb, 0000 and 1200 UTC 8 Feb, and 0000 UTC 9 Feb (source: Navy/NRL link given
below). At 1200 UTC 7 Feb a narrow swath of dry air runs from near the
Also attached
are a series of DT pressure/shear and 925-850 hPa layer-mean relative vorticity
images for 1200 UTC 8 Feb, 0000
UTC 10 Feb, 0600 UTC 11 Feb, 0000 UTC 13 Feb, and 0000 UTC 15
Feb to help illustrate that the mesoscale vortex apparent in the WV imagery can
also be seen and followed in the GFS analyses (again, build your own loops to
see the details). The potential significance of the mesoscale vortex as one of
the possible forerunners to the Valentine's Day storm was realized in one
collective "oh my god" serendipitous moment by most of the
participants in Friday map discussion while we were examining loops of the
above imagery. At 1200 UTC 8 Feb the mesoscale vortex so readily apparent in
the attached WV imagery is also clearly defined as a mesoscale DT disturbance
(thermal vorticity maximum; pressure near 450 hPa) near 50 N, 153 W.
By 0000 UTC 10 Feb
the mesoscale DT disturbance has dropped southeastward to a position near 38 N,
146 W. The pressure on the DT is still near 450 hPa and a layer-mean 925-850
hPa relative vorticity maximum is situated immediately to the east of the
vortex. By 0600 UTC 11 Feb the mesoscale DT disturbance, slightly weaker, is
approaching the coast of
it. Its position at this time also
places it near the southeastern end of an extended shear line (thermal
vorticity trough) to the
northwest. Although the mesoscale DT
disturbance lies near the southern end of a larger-scale thermal trough, it has
resisted
reabsorption and can still be identified as a
separate feature.
For later
reference note the larger scale thermal vorticity maximum located just poleward
of
acceleration of the subtropical jet (STJ) to the
south and east of it of this second trough at 0600 UTC 11 Feb. This second
trough and
STJ will eventually catch up and interact with the mesoscale
DT disturbance that was approaching the coast of
At 0000 UTC 13 Feb a somewhat larger-scale DT disturbance
situated near 35 N, 100 W marks the likely position of the mesoscale DT
disturbance that was located just west of
your own loop at the McTaggart-Cowan website.
While my inference is not a 100% done deal the evidence is fairly suggestive
and should be scrutinized further for errors of omission and commission.
The DT disturbance
near 35 N, 100 W grew upscale over the 48 h ending 0000 UTC 13 Feb as it crossed
the southern Rockies and
began to interact with warm, moist and
unstable air flowing northward from the
reported ~8 h later near 0800 UTC ahead of
this advancing disturbance). Subsequently, the developing surface cyclone moved
northeastward across the
the
the cyclone approached from the
southwest. The primary cyclone began to weaken and die over
developed east of the
mass in advance of the DT disturbance.
By 0000 UTC 15
Feb the original eastern Pacific DT disturbance had turned northeastward along
the Atlantic coast and was now
associated with a prominent 925-850 hPa
layer-mean relative vorticity maximum situated over extreme southeastern
vorticity maximum marked the now-dominant
secondary cyclone (978 hPa) known as Valentine Day's storm. It also appeared
from the DT loops that the coastal DT disturbance was also interacting with a
second mesoscale DT disturbance located to the west near 39 N, 75 W and a
stronger and larger-scale DT disturbance of arctic origin located over the
northern
coast around 0000 UTC 13 Feb was also assisted by the
eastward movement and development of the STJ behind the larger scale thermal
vorticity trough noted previously just north of Hawaii at 0600 UTC 11 Feb. The
developing cyclone at 0000 UTC 13 Feb was situated beneath the poleward exit
region of the subtropical jet. Strong coastal redevelopment in the next 48 h
occurred in conjunction with ridging over Atlantic Canada that was likely
driven by a combination of diabatic heating ahead of the coastal storm and
downstream
development ahead of the arctic DT disturbance
crossing the northern
collapse of the downstream half wavelength
between the advancing and deepening upstream trough and the quasi-stationary
and amplifying
downstream ridge.
More than 40
years ago Ed Lorenz speculated (metaphorically) that the flap of a butterfly's
wings in
lead to a big rainstorm in
grow and destroy the ability of a
numerical forecast to represent the observed state of the atmosphere on a time
scale of roughly two
weeks. He based his conclusions and
speculations on the results from a highly idealized numerical model (Lorenz
1963). Here I speculate that the "donut hole"
mesoscale vortex that formed over the northeastern
Big "flap"
in the eastern Pacific triggers a cascading series of events culminating in
"flapogenesis" in the lower
Valley, tornadoes in the
A careful
diagnostic analysis of events leading up to the Valentine's Day storm may
reveal the above highly speculative
development scenario to be a leap off of a tall
building without a parachute and without a net below (and without Superman
around to
save me from myself). No matter. I am
prepared to be wrong as usual. That said, there are some very interesting
scientific issues
associated with the Valentine's Day storm that
can be summarized as follows:
1. Predictability (based upon the GFS) was relatively poor
until the southern-stream disturbance neared the
that point almost all of the GFS ensemble
members were opting for a relatively weak fish storm that would track well out
to sea and
away from the I-95 corridor. At issue is understanding what the ensemble members latched onto that
first suggested a storm would track
closer to the coast and be stronger than
initially forecast.
2. Multiple player cyclogenesis. Preliminary evidence
discussed above suggests that both upstream (trailing trough and STJ in the
southern stream, weak separate midlatitude DT
disturbance, and a stronger arctic disturbance) and downstream (ridge
amplification and collapse of the downstream half wavelength) features
contributed to the severity of the Valentine's Day storm of 2007. To what
extent
these various features act independently
and/or in concert with one another needs to be determined to understand the
cyclogenesis
process and the associated predictability
ramifications, and suggests that the application of "PV surgery"
techniques might be good for
the atmospheric patient.
3. Assess the role of the "idle curiosity"
mesoscale vortex first mentioned in the
development of the Valentine's Day storm in the
grand scheme of things. Was this disturbance merely a turbulent eddy that while
suggestive was the ultimate red herring and a
figment of our collective imagination or did it contribute in some unknown way,
perhaps
in a stochastic sense, to the cascading
series of events that culminated in the Valentine's Day storm and left
officials of Jet Blue
Airways feeling.....well....."blue"
in the face and embarrassed? And if this disturbance did play a supporting role
in the storm then
how do we define and quantify its
contribution?
Finally, there
were also important societal and economic issues associated with the
Valentine's Day storm. This was a
high-impact storm from the lower
disaster with grounded airplanes, delayed and cancelled
flights, flights stranded on JFK tarmacs for hours, and thousands of irate and
enraged passengers. Recovery from this
natural- and self-inflicted debacle is by no means assured. Likewise, the
disaster on the
people in their cars and trucks) was such
an embarrassment for the state government that it could be a future campaign
issue.
http://www.nrlmry.navy.mil/sat-bin/epac_westcoast.cgi (choose
Northwest vapor)
Lorenz, E. N., 1963: Deterministic Nonperiodic
Flow, Journal of the Atmospheric Sciences, 20, 130-141.
Lance
Attachments: http://www.atmos.albany.edu/student/heathera/mapdisc_02-16-07/