2009 Storms, Part 2

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2009 Storms, Part 2

  1. 1. 2009 StormsPart 2<br /> ©2010 Fisher<br />
  2. 2. Doppler Weather Radar Concepts<br /><ul><li>Radar beam increases in altitude with distance from radar.
  3. 3. Radar beam increases in size with distance from radar.
  4. 4. Radar takes 4-5 minutes to complete full scan when in storm/precip mode.
  5. 5. Reliable doppler wind data limited to about 60-70 nm.
  6. 6. Radar velocity 100% when parallel, 0% when perpendicular to beam direction.</li></li></ul><li>The Zero Isodop “Problem”<br />When the radial is perpendicular to the the wind, the radar displays zero velocity - This “zero zone” is called the “Zero Isodop”.<br />What percentage <br />of actual wind <br />will the radar detect?<br />00 = 100% - Parallel<br />150 = 97%<br />300 = 87%<br />450 = 71%<br />600 = 50%<br />750 = 26%<br />900 = 0% - Perpendicular<br />When the wind velocity is parallel to the radial, the full component of the wind is measured<br />
  7. 7. Height of beam above ground vs distance from radar. <br />Green 10nm<br />Yellow 15nm<br />Red 20nm<br />
  8. 8. MDW TDWR<br />20nm<br />10nm<br />
  9. 9. ORD TDWR<br />20nm<br />10nm<br />
  10. 10.
  11. 11. PROBLEM(s) OF THE DAY (POTD)<br />ORGANIZED SEVERE STORMS<br />INGREDIENTS-BASED APPROACH<br />MOISTURE<br />INSTABILITY<br />(sources for convective)<br />LIFT<br />SHEAR<br />
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  13. 13. TornadicSupercell “Ingredients”<br />Instability (varies, usually CAPE > 1000 J/Kg)<br />Deep layer shear (0-6km) bulk shear > 35kt<br />Low level shear (0-1km) SRH > 150 m2/s2 or <br /> pre-existing boundary)<br />Relatively high RH values (in BL and aloft)<br />Sfc Td depressions <12°F<br />
  14. 14. Some Commonly Used SPC Mesoanalysis Indices<br /><ul><li>Effective Storm-Relative Helicity (ESRH)
  15. 15. Effective Bulk Shear (EBS)
  16. 16. Supercell Composite Parameter (SCP)
  17. 17. Significant Tornado Parameter (STP)</li></li></ul><li>Summary of STP Assessment<br />Tornado Outbreak over N IL April 20, 2004<br /><ul><li>No strong signal in fixed layer STP in absolute or trending sense
  18. 18. Showed boldly only after event started
  19. 19. Underscores STP as a DIAGNOSTICparameter
  20. 20. 0-6 km shear, 0-1 km SRH (400+), and MLLCL all favorable for STP ≥1
  21. 21. Primary shortcoming resulted from MLCAPE values less than 500 J/kg until 23z
  22. 22. Suggests need to monitor closely for single “missing” variable when others are in place</li></li></ul><li>
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  35. 35. Friday June 19, 2009 Naper Days<br />
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  39. 39. Pocket of 87 mph winds<br />
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  46. 46. July 24, 2009<br />
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  50. 50. ILX<br />
  51. 51. ILX<br />
  52. 52. Base Velocity 1700 ft<br />
  53. 53. 3500 ft<br />
  54. 54. LOT<br />
  55. 55.
  56. 56. Base Velocity<br />
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  58. 58. Aug. 9, 2009<br />
  59. 59. DVN<br />
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  61. 61. DVN Base Velocity<br />
  62. 62. DVN Storm Relative Velocity<br />
  63. 63. DVN VAD Wind<br />

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