Verification of the 88d hail detection algorithm at wfo cheyenne
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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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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

Outline of Presentation

  • Reason for Study

  • Hail Climatology

  • HDA

  • Past Verification Studies

  • Results

  • Future Plans and Ideas


Reason for study

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.


Frequency of severe hail

Frequency of Severe Hail


Frequency of any sized hail

Frequency of Any Sized Hail


The hail detection algorithm

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.


The hail detection algorithm severe hail index

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)


The hail detection algorithm1

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.


Past area hda verification studies

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.


Methodology

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.


Concerns

Concerns

  • The maximum hail size may not have been captured in some storms.

  • The study only looked at severe hail.


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Verification of the 88d hail detection algorithm at wfo cheyenne

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


Conclusion

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.


Ways to possibly improve the hda

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


Changes planned in the future for the hda

Changes Planned in the future for the HDA

  • Within 3-5 years dual polarization techniques will be added to the HDA.


Verification of the 88d hail detection algorithm at wfo cheyenne

  • Questions?

  • Thank you.


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