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# 2009 Storms, Part 1

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Presented by Al Fisher

Presented by Al Fisher

Published in: Technology
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### Transcript

• 1. 2009 StormsPart 1
• 2. Doppler Weather Radar Concepts
• 4. Radar takes 4-5 minutes to complete full scan when in storm/precip mode.
• 5. Reliable doppler wind data limited to about 60-70 nm.
• 6. Radar velocity 100% when parallel, 0% when perpendicular to beam direction.
• The Zero Isodop “Problem”
When the radial is perpendicular to the the wind, the radar displays zero velocity - This “zero zone” is called the “Zero Isodop”.
What percentage
of actual wind
00 = 100% - Parallel
150 = 97%
300 = 87%
450 = 71%
600 = 50%
750 = 26%
900 = 0% - Perpendicular
When the wind velocity is parallel to the radial, the full component of the wind is measured
• 7. Products
Base reflectivity
how much precipitation is falling
precipitation type
assess a storm's structure and dimension
Composite Reflectivity
Scans from all elevations, imaging precipitation intensity and storm structure
Base Velocity
radial wind field, speed of fronts/strong wind
range of 140 mi
Storm relative motion
Track a circulation (show up well in doppler return) over time to determine storm motion.
Removing the storm relative motion from base radials gives an estimate of the flow with respect to the storm.
• 8. LOT
Height of beam above ground vs distance from radar.
Green 10nm
Yellow 15nm
Red 20nm
• 9. ORD TDWR
20nm
10nm
• 10. MDW TDWR
20nm
10nm
• 11. What is a supercell?
Storms having deep, persistent, rotation about a vertical axis
• 12. What is a supercell?
Why do storms with seemingly similar structure differ in their tornado production?
Although most significant tornadoes are associated with supercell thunderstorms, most supercells are nottornadic
What’s perhaps most troubling (from the perspective of issuing warnings) is that most supercells contain low-level mesocyclones, and perhaps most supercells even have circulations that extend to the surface
• 13. April 9, 2009 day 1 of 2 day storm outbreak 5PM
0-6 km Shear Vector
• 14. 0-3 km
• 15. 0-1 km
• 16. 0-1 km
• 17.
• 18.
• 19.
• 20.
• 22. Storm Composite
• 23. Base Reflectivity lvl 2
• 24. Storm Relative Velocity lvl 2
• 25. Base Velocity lvl 2
• 26.
• 27. April 10, 2009 2nd day of outbreak 2 PM
0-6 km Shear Vector
• 28.
• 29.
• 30.
• 31.
• 32.
• 33.
• 34. Storm Composite
• 35. Radar HTX Base Reflectivity lvl 2 ~ 1500 ft
Classic Rotating Supercell
• 36. Radar HTX Storm Relative Velocity lvl 2
Strong Rotation Couplet
• 37. Radar HTX Base Reflectivity lvl 2 ~ 3200 ft
• 39. HTX Base Reflectivity lvl 2 ~ 1900 ft 0.5˚
• 40. HTX Storm Relative Velocity lvl 2 ~ 1900 ft 0.5˚
Double Rotation?
• 41. HTX Base Reflectivity lvl 2 ~ 4000 ft 1.3˚
Bowing Line Tstms (L) and Classic Supercell (R)
• 42. HTX Base Velocity lvl 2 ~ 1900 ft 0.5˚
• 43. HTX Storm Relative Velocity lvl 2 ~ 4000 ft 1.3˚
Downburst (L) and Rotation Couplet (R)
• 44. Part of 5/8/09 Derecho 100+ mph S IL, 5 dead in MO/ KY
• 45.
• 46.
• 47.
1
Development of a persistent, rotating updraft
2
Ingestion of enhanced SRH (occasionally, large-scale SRH is sufficient) and development of strong low-level rotation
3
Development of a downdraft partially embedded in the rotation that aids in the transport of rotation to the ground, followed by focusing of that rotation through convergence if the downdraft reaches the ground with some very uncommon properties
• 49. Tornadogenesis in a Nutshell
• 50. The Need for Better Understanding of Tornadic Storms
Improvements in our understanding of tornadogenesis should better allow us to assess the likelihood of tornadoes in thunderstorms
Improvements likely due to 88D network, better training, better SPC guidance, application of VORTEX1 findings?
• 51. Summary (what we know)
• Supercells acquire rotation aloft by tilting horizontal vorticity (streamwise horizontal vorticity leads to net cyclonic updraft rotation)
• 52. Although most significant tornadoes are associated with supercell thunderstorms, most supercells are not tornadic (and the supercells with the strongest mesocyclones are not necessarily the most likely to be tornadic)
• 53. Tornadogenesis requires a downdraft if pre-existing vertical vorticity is absent at the surface
• 54. The temperature of the downdrafts seems to be important to tornadogenesis; downdrafts that are excessively cold apparently are unfavorable for tornadogenesis
• 55. Environments that have large ambient low-level vertical wind shear (larger than what is found in an average supercell environment) and large ambient relative humidity favor tornadic supercells over nontornadic supercells
• LSX Composite
• 56. LSXReflectivity lvl 2
• 57. Base Velocity lvl 2
• 58. Storm Relative Velocity lvl 2