Elmwood, Oklahoma (Beaver County)
June 8, 1995 (UTC)
Work continues on this interesting null event. A strong supercell persisted
for many hours and moved from the northeast Texas Panhandle into the
Oklahoma Panhandle. NCAR ELDORA is available from 1950-2130 UTC. DOW data
collection started shortly after ELDORA data commenced. No P-3 data is
available until later in the day owing to transmitter problems.
The original presentation was made at the 2nd VORTEX Workshop held December
2-3, 1997. An updated version was presented at the 19th Conference on
Severe Local Storms (September 14-18, 1998).
NOTE: The colors in these images may not display correctly with your
browser/image viewer. This is a result of different machines/monitors
using different gamma values. Try selecting a different gamma value in your
image viewer if the images are either too dark or too bright.
Some Possible Mechanisms for Tornadogenesis Failure:
A Multisensor Analysis of a Nontornadic Supercell
David O. Blanchard and Jerry M. Straka
- VORTEX airborne- and ground-based crews intercepted a supercell in Beaver
County near Elmwood, Oklahoma on June 8, 1995
- P-3 Doppler radar data not available
- ELDORA data collection started ~1950 UTC
- DOW data collection started a few minutes later
- Mobile mesonet data is available (6-s updates)
What is "Tornadogenesis Failure"
- Most thunderstorms do not produce tornadoes
- Even most supercells do not produce tornadoes
- So what makes this event a "tornadogenesis failure?"
- What didn't happen? And when did it not happen?
- It's easy to construct a time line for a tornadic event with
a beginning, mature, and dissipation stage.
- How do we do the equivalent for a non-tornadic storm?
- What defines the beginning, mature, and dissipation phases?
- What defines failure?
Large-Scale Analysis
- Quasi-stationary frontal boundary
- Non-tornadic supercell formed on boundary early in the day
- Tornadic supercells formed south of the boundary later in the day
- Satellite imagery
- Low stratus located north of the frontal zone
- Waves along and propagating south of the frontal zone
- Well-defined boundary evident by 1901 UTC
- Additional storms develop along the dryline by 2001 UTC
- WSR-88D
- Both AMA and DDC indicate supercell and hook echo at 1955 UTC
- Images
M-CLASS Soundings
- M-CLASS soundings deployed in northwestern Oklahoma
- First launch at ~1800 UTC
- Strong shear; large instability
- Elevated mixed layer (EML) present above ~750 mb
- Second launch at ~2030 UTC
- Base of EML lifted from ~750 to 700 mb at NCA
- Increase in moisture in the boundary layer
- CAPE > 4500 J/kg
- LCL: 808 mb
- LFC: 808 mb
- Images
ELDORA Flight Tracks
- Pseudo-Doppler Legs
- 195012 195708
- 195816 200351
- 200423 201046
- 201132 201555
- 201636 202235
- 202330 202935
- 203014 203700
- 203808 204354
- 204443 205200
- 205348 205911
- 205940 210711
- 210854 211411
- 211445 212252
- 212400 212900
- 212930 213622
- 213745 214245
- 214325 215025
- Images
ELDORA Analysis (1950 UTC)
- 2000 m MSL
- Well-defined hook echo
- Velocity couplet with 30 m/s shear; 25 m/s gate-to-gate shear
- 4000 m MSL
- Velocity couplet with 55 m/s shear; only 10 m/s gate-to-gate shear
- RHI
- Pronounced weak echo region; precipitation loading aloft
- OA gridded analysis
- Elongated vorticity region at 2000 m MSL
- Images
ELDORA Analysis (1958 UTC)
- 1500 and 2500 m MSL
- Thin hook echo with elongated forward flank region
- New circulation center SW of original center; ~25 m/s shear
- 8500 m MSL
- Large, "classic" hook echo aloft and BWER
- 40 m/s shear; weak gate-to-gate shear
- RHI
- Weak echo region extends to 16 km
- Velocity in excess of 65
m/s in anvil region
- Horizontal vortex roll evident in REF and VEL
with > 100 m/s shear
- OA gridded analysis
- Elongated circulation center still evident at 2000 m
-
Well-defined circulation at 3000 m
- Images
ELDORA Analysis (2004 UTC)
- 2500 m MSL
- Arm of hook becoming extended NNE-SSW
- Velocity ~22 m/s shear
(-18/+4)
- 5000 m MSL
- A clear slot (RFD?) is visible in reflectivity
- RHI
- Bounded weak echo region extends up to ~12 km
- OA gridded data
- Vorticity is aligned NE-SW with strongest values (~0.05 s^-1)
northeast of the tip of the hook
- A weak secondary maximum is
located on the SW end of the hook
- At 14000 m MSL, a circular
region of downdraft is located upshear and cross shear of the
overshooting top
- Images
ELDORA Analysis (2012 UTC)
- 2000 m MSL
- Hook has continued to lengthen and narrow
- Velocity couplet
is -18/+4 m/s; has undergone scale contraction and may be too small to
detect. [This scale contraction was also noted in the Dimmitt, Texas
(02Jun95) data.]
- RHI
- Bounded weak echo region now extends to 16 km
- Downward
velocities of 60 m/s noted adjacent to overshooting dome
- OA gridded data
- Cyclonic/Anticyclonic couplet
- Vorticity at lower levels
(1500-2400 m) still elongated NE-SE
- Downward motion upshear/cross
shear of overshooting dome; extends to the surface
- No band of
anticyclonic vorticity adjacent to the hook as in Dimmitt
- Images
DOW Analysis (2019-2025 UTC)
- 2500 m MSL
- Strong mesocyclone (32-64 m/s shear) and gate-to-gate shear
(16-47 m/s) was detected. Mesocyclone circulation is ~2-3 km in
diameter.
- Low-level circulation center was located near tip
of hook along the reflectivity gradient. Banded structure noted
the reflectivity field evident from 0.5-10 degree elevation
angles.
- Mobile mesonet data successfully located the
circulation at the tip and indicated the position of the RFD gust
front
- Surface circulation was nearly vertically aligned with
the mid-level mesocyclone.
- Images
Summary
- VORTEX teams successfully collected multi-platform data for
documentation of this tornadogenesis failure event.
- Many features noted in this non-tornadic storm were also observed in
the Dimmitt, Texas (02Jun95) tornadic event.
- Radar reflectivity and velocity patterns were very similar to many
tornadogenesis success events.
- An RFD-induced occuded gust front wrapped back under the parent
mesocyclone.
- A band of strong anticyclonic vorticity adjacent to the hook echo was
not observed in this event.
- Strong shear (30-60 m/s) was noted at all levels and a weak
circulation was present on the ground and documented by the mobile
mesonets.
- Because of ground wetting by the forward flank precipitation core, no
dust was lofted by the circulation. Would a dust column have been
noted if the ground had been dry?
- Strong vertical updrafts were present as shown by the presence of a
significant bounded weak echo region (BWER) that extended to ~16 km.
- Mobile mesonet data indicates that surface winds in the vicinity of
the mesocylone were only moderate in strength (~7-15 m/s). Why did
the winds not strengthen? Was the absence of strong buoyant
instability between the LCL/LFC (~800 mb) and the base of the EML
(~700 mb) important? If it had been more unstable in this layer,
would it have been able to significantly stretch and concentrate the
vorticity?
- The analysis of this event suggests that the difference between a
tornadic supercell and a non-tornadic supercell may be far more suble
than is typically assumed.
- In fact, the analysis indicated that there was a circulation
present, but it was apparently incapable of lofting dust or generating
a condensation funnel. Must we consider revising our concept of
tornadogenesis success to include these events? That is, if we
have a mesocyclone aloft and a circulation present on the ground, how
do we distinguish between tornadogenesis "success" and "failure?"
Back to VORTEX Main Page
