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Verification of the 88D Hail Detection Algorithm at WFO Cheyenne

Verification of the 88D Hail Detection Algorithm at WFO Cheyenne. Mike Weiland WFO Cheyenne. Outline of Presentation. Reason for Study Hail Climatology HDA Past Verification Studies Results Future Plans and Ideas. Reason for Study.

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Verification of the 88D Hail Detection Algorithm at WFO Cheyenne

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  1. Verification of the 88D Hail Detection Algorithm at WFO Cheyenne Mike Weiland WFO Cheyenne

  2. Outline of Presentation • Reason for Study • Hail Climatology • HDA • Past Verification Studies • Results • Future Plans and Ideas

  3. Reason for Study • Hail is a primary severe weather threat in the WFO Cheyenne CWA. • Billions of dollars in crop and property damage is caused each year by hail. • Hail Detection Algorithm is one of the forecast tools available.

  4. Frequency of Severe Hail

  5. Frequency of Any Sized Hail

  6. The Hail Detection Algorithm • Developed in 1982; was based upon structural characteristics of typical southern plains severe hailstorms. • Latest HDA is reflectivity based and utilizes the RADAP II VIL algorithm. • Uses the latest Storm Cell Identification and Tracking (SCIT) algorithm. • From the SCIT, the height and maximum reflectivity of each storm component is used to create a vertical reflectivity for each cell. • HDA also uses the height of 45 dBz return above the melting level.

  7. The Hail Detection Algorithm(Severe Hail Index) Develops a reflectivity to hail relation. • Filters out most of the lower reflectivities as they tend to be associated with liquid water. • Uses a temperature weighted vertical integration (since hail growth only occurs at temperatures <0C and most severe hail growth occurs with temperatures near -20C or colder. • Is used to create the Maximum Expected Hail Size (MEHS)

  8. The Hail Detection Algorithm Works best on the plains Witt’s study in Colorado (1998) showed that the HDA correctly determined the cell that was producing hail 92% of the time. The POD from Witt’s study is 87% for 1” hail and 96% for 2” diameter hail.

  9. Past Area HDA Verification Studies • Vasiloff (UT) mean absolute error was .22” and POD of HDA 86%. • Maddox (AZ) “variations in terrain have a large impact on POSH”. POSH has a large overforecasting bias. • POSH of small storms seems to be too high.

  10. Methodology • 185 severe hail reports within the WFO Cheyenne CWA from May-August 2005 and 2006 were compared with the output from the HDA. • Using archived data, the HDA value and VIL for each severe report was found.

  11. Concerns • The maximum hail size may not have been captured in some storms. • The study only looked at severe hail.

  12. HDA Hail Size Compared to Hail Size (.75” orlarger) 185 events in the WFO Cheyenne CWA in 2005 and 2006 • Hail SizeEvents HDA vs. Hail Size (inches) • >1.00” 35 .0493” • .88 to 1.00” 86 .4502” • .75” 62 .5141” • Total 185 .3306” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 35 18 times 14 times • .88 to 1.00” 86 62 times 15 times • .75” 62 55 times 4 times • Total 185 135 times 33 times

  13. HDA Hail Size Compared to Hail Size (.75” orlarger) Based on Distance from the KCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006 • Greater than 125 nmi • Hail SizeEvents HDA vs. Hail Size (inches) • >1.00” 14 -.1429” • .88 to 1.00” 28 .1807” • .75” 14 .8570” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 14 4 times 9 times • .88 to 1.00” 28 15 times 9 times • .75” 14 8 times 4 times

  14. HDA Hail Size Compared to Hail Size (.75” orlarger) Based on Distance from the KCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006 • 76 to 125 nmi • Hail SizeEvents HDA vs. Hail Size (inches) • >1.00” 11 .0091” • .88 to 1.00” 28 .3146” • .75” 28 .4792” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 11 9 times 2 times • .88 to 1.00” 28 22 times 2 times • .75” 28 25 times 0 times

  15. HDA Hail Size Compared to Hail Size (.75” orlarger) Based on Distance from the KCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006 • 26 to 75 nmi • Hail SizeEvents HDA vs. Hail Size (inches) • >1.00” 3 .0133” • .88 to 1.00” 20 .4105” • .75” 13 .3077” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 3 1 time 1 time • .88 to 1.00” 20 16 times 1 time • .75” 13 11 times 0 times

  16. HDA Hail Size Compared to Hail Size (.75” orlarger) Based on Distance from the KCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006 • 26 nmi or less • Hail SizeEvents HDA vs. Hail Size (inches) • >1.00” 4 .4375” • .88 to 1.00” 11 .4173” • .75” 11 .3863” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 4 3 times 0 times • .88 to 1.00” 11 10 times 0 times • .75” 11 10 times 0 times

  17. HDA Hail Size Compared to Hail Size (.75” orlarger) in Relation to VIL (>55 dBz) 108 events in the WFO Cheyenne CWA in 2005 and 2006 • Hail SizeEvents HDA vs. Hail Size • >1.00” 10 .5250” • .88 to 1.00” 13 .8915” • .75” 17 .8529” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 10 8 times 1 time • .88 to 1.00” 13 13 times 0 times • .75” 17 17 times 0 times

  18. HDA Hail Size Compared to Hail Size (.75” orlarger) in Relation to VIL (<55 dBz) 108 events in the WFO Cheyenne CWA in 2005 and 2006 • Hail SizeEvents HDA vs. Hail Size • >1.00” 8 -.4375” • .88 to 1.00” 41 .2351” • .75” 19 .3553” • Hail SizeEvents HDA LargerHDA Smaller • >1.00” 8 3 times 5 times • .88 to 1.00” 41 27 times 8 times • .75” 19 15 times 3 times

  19. Conclusion • This study, using one radar over a 2 year period, would suggest that in most cases, the HDA does indeed overestimate the actual hail size by between one-quarter and three-quarters of an inch. • This result is in agreement with past studies of the HDA. Though the overestimation seems to be slightly greater in the CYS CWA.

  20. Ways to possibly improve the HDA • Use storm top divergence to get the severe hail size. AT WFO Cheyenne, we have found that 50 to 75 kts or more works best. • Look at storm structure (BWER’s, shear etc.) to help with hail detection. • Look at the Mesocyclone Intensity

  21. Changes Planned in the future for the HDA • Within 3-5 years dual polarization techniques will be added to the HDA.

  22. Questions? • Thank you.

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