Verification of the 88D Verification of the 88D Hail Detection Algorithm Hail Detection Algorithm

at WFO Cheyenneat WFO Cheyenne

Mike Weiland Mike Weiland WFO CheyenneWFO Cheyenne

Outline of PresentationOutline of Presentation

• Reason for StudyReason for Study

• Hail ClimatologyHail Climatology

• HDAHDA

• Past Verification StudiesPast Verification Studies

• ResultsResults

• Future Plans and IdeasFuture Plans and Ideas

Reason for StudyReason for Study

• Hail is a primary severe weather threat in Hail is a primary severe weather threat in the WFO Cheyenne CWA. the WFO Cheyenne CWA.

• Billions of dollars in crop and property Billions of dollars in crop and property damage is caused each year by hail. damage is caused each year by hail.

• Hail Detection Algorithm is one of the Hail Detection Algorithm is one of the forecast tools available. forecast tools available.

Frequency of Severe Hail Frequency of Severe Hail

Frequency of Any Sized HailFrequency of Any Sized Hail

The Hail Detection The Hail Detection AlgorithmAlgorithm• Developed in 1982; was based upon structural characteristics of Developed in 1982; was based upon structural characteristics of

typical southern plains severe hailstorms.typical southern plains severe hailstorms.

• Latest HDA is reflectivity based and utilizes the RADAP II VIL Latest HDA is reflectivity based and utilizes the RADAP II VIL algorithm.algorithm.

• Uses the latest Storm Cell Identification and Tracking (SCIT) Uses the latest Storm Cell Identification and Tracking (SCIT) algorithm. algorithm.

• From the SCIT, the height and maximum reflectivity of each storm From the SCIT, the height and maximum reflectivity of each storm component is used to create a vertical reflectivity for each cell. component is used to create a vertical reflectivity for each cell.

• HDA also uses the height of 45 dBz return above the melting level.HDA also uses the height of 45 dBz return above the melting level.

The Hail Detection The Hail Detection AlgorithmAlgorithm(Severe Hail Index)(Severe Hail Index)Develops a reflectivity to hail relation.Develops a reflectivity to hail relation.

• Filters out most of the lower reflectivities as Filters out most of the lower reflectivities as they tend to be associated with liquid water.they tend to be associated with liquid water.

• Uses a temperature weighted vertical Uses a temperature weighted vertical integration (since hail growth only occurs at integration (since hail growth only occurs at temperatures <0C and most severe hail temperatures <0C and most severe hail growth occurs with temperatures near -20C or growth occurs with temperatures near -20C or colder. colder.

• Is used to create the Maximum Expected Hail Is used to create the Maximum Expected Hail Size (MEHS)Size (MEHS)

The Hail Detection AlgorithmThe Hail Detection Algorithm

Works best on the plainsWorks best on the plains

Witt’s study in Colorado (1998) showed Witt’s study in Colorado (1998) showed that the HDA correctly determined the that the HDA correctly determined the cell that was producing hail 92% of the cell that was producing hail 92% of the time. time.

The POD from Witt’s study is 87% for 1” The POD from Witt’s study is 87% for 1” hail and 96% for 2” diameter hail.hail and 96% for 2” diameter hail.

Past Area HDA Verification Past Area HDA Verification StudiesStudies

• Vasiloff (UT) mean absolute error was Vasiloff (UT) mean absolute error was .22” and POD of HDA 86%..22” and POD of HDA 86%.

• Maddox (AZ) “variations in terrain Maddox (AZ) “variations in terrain have a large impact on POSH”. POSH have a large impact on POSH”. POSH has a large overforecasting bias.has a large overforecasting bias.– POSH of small storms seems to be too POSH of small storms seems to be too

high. high.

MethodologyMethodology

• 185 severe hail reports within the WFO 185 severe hail reports within the WFO Cheyenne CWA from May-August 2005 Cheyenne CWA from May-August 2005 and 2006 were compared with the and 2006 were compared with the output from the HDA.output from the HDA.

• Using archived data, the HDA value and Using archived data, the HDA value and VIL for each severe report was found.VIL for each severe report was found.

ConcernsConcerns

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

• The study only looked at severe hail.The study only looked at severe hail.

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) larger) 185 events in the WFO Cheyenne CWA in 2005 and 2006185 events in the WFO Cheyenne CWA in 2005 and 2006

• Hail SizeHail Size Events Events HDA vs. Hail Size (inches)HDA vs. Hail Size (inches) • >1.00” 35 .0493” >1.00” 35 .0493” • .88 to 1.00” 86 .4502”.88 to 1.00” 86 .4502”• .75” 62 .5141”.75” 62 .5141”• Total 185 Total 185 .3306”.3306”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA SmallerHDA Smaller• >1.00” 35 18 times 14 times >1.00” 35 18 times 14 times • .88 to 1.00” 86 62 times 15 times.88 to 1.00” 86 62 times 15 times• .75” 62.75” 62 55 times 4 times 55 times 4 times• Total 185 135 times 33 times Total 185 135 times 33 times

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) Based on Distance from the larger) Based on Distance from the KCYS 88DKCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006185 events in the WFO Cheyenne CWA in 2005 and 2006

• Greater than 125 nmiGreater than 125 nmi

• Hail SizeHail Size Events Events HDA vs. Hail Size (inches)HDA vs. Hail Size (inches) • >1.00” 14 -.1429” >1.00” 14 -.1429” • .88 to 1.00” 28 .1807”.88 to 1.00” 28 .1807”• .75” 14 .8570”.75” 14 .8570”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA SmallerHDA Smaller• >1.00” 14 4 times 9 times >1.00” 14 4 times 9 times • .88 to 1.00” 28 15 times 9 times.88 to 1.00” 28 15 times 9 times• .75” 14 8 times 4 times.75” 14 8 times 4 times

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) Based on Distance from the larger) Based on Distance from the KCYS 88DKCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006185 events in the WFO Cheyenne CWA in 2005 and 2006

• 76 to 125 nmi76 to 125 nmi

• Hail SizeHail Size Events Events HDA vs. Hail Size (inches)HDA vs. Hail Size (inches) • >1.00” 11 .0091” >1.00” 11 .0091” • .88 to 1.00” 28 .3146”.88 to 1.00” 28 .3146”• .75” 28 .4792”.75” 28 .4792”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA SmallerHDA Smaller• >1.00” 11 9 times 2 times >1.00” 11 9 times 2 times • .88 to 1.00” 28 22 times 2 times.88 to 1.00” 28 22 times 2 times• .75” 28 25 times 0 times.75” 28 25 times 0 times

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) Based on Distance from the larger) Based on Distance from the KCYS 88DKCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006185 events in the WFO Cheyenne CWA in 2005 and 2006• 26 to 75 nmi26 to 75 nmi

• Hail SizeHail Size Events Events HDA vs. Hail Size (inches)HDA vs. Hail Size (inches) • >1.00” 3 .0133” >1.00” 3 .0133” • .88 to 1.00” 20 .4105”.88 to 1.00” 20 .4105”• .75” 13 .3077”.75” 13 .3077”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA SmallerHDA Smaller• >1.00” 3 1 time 1 time >1.00” 3 1 time 1 time • .88 to 1.00” 20 16 times 1 time.88 to 1.00” 20 16 times 1 time• .75” 13 11 times 0 times.75” 13 11 times 0 times

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) Based on Distance from the larger) Based on Distance from the KCYS 88DKCYS 88D185 events in the WFO Cheyenne CWA in 2005 and 2006185 events in the WFO Cheyenne CWA in 2005 and 2006• 26 nmi or less26 nmi or less

• Hail SizeHail Size Events Events HDA vs. Hail Size (inches)HDA vs. Hail Size (inches) • >1.00” 4 .4375” >1.00” 4 .4375” • .88 to 1.00” 11 .4173”.88 to 1.00” 11 .4173”• .75” 11 .3863”.75” 11 .3863”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA SmallerHDA Smaller• >1.00” 4 3 times 0 times >1.00” 4 3 times 0 times • .88 to 1.00” 11 10 times 0 times.88 to 1.00” 11 10 times 0 times• .75” 11 10 times 0 times.75” 11 10 times 0 times

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) in Relation to VIL (>55 dBz) larger) in Relation to VIL (>55 dBz) 108 events in the WFO Cheyenne CWA in 2005 and 2006108 events in the WFO Cheyenne CWA in 2005 and 2006

• Hail SizeHail Size Events Events HDA vs. Hail Size HDA vs. Hail Size • >1.00” 10 .5250” >1.00” 10 .5250” • .88 to 1.00” 13 .8915”.88 to 1.00” 13 .8915”• .75” 17 .8529”.75” 17 .8529”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA HDA SmallerSmaller

• >1.00” 10 8 times 1 time >1.00” 10 8 times 1 time • .88 to 1.00” 13 13 times 0 times.88 to 1.00” 13 13 times 0 times• .75” 17 17 times 0 times.75” 17 17 times 0 times

HDA Hail Size Compared to Hail Size HDA Hail Size Compared to Hail Size (.75” or(.75” orlarger) in Relation to VIL (<55 dBz) larger) in Relation to VIL (<55 dBz) 108 events in the WFO Cheyenne CWA in 2005 and 2006108 events in the WFO Cheyenne CWA in 2005 and 2006

• Hail SizeHail Size Events Events HDA vs. Hail Size HDA vs. Hail Size • >1.00” 8 -.4375” >1.00” 8 -.4375” • .88 to 1.00” 41 .2351”.88 to 1.00” 41 .2351”• .75” 19 .3553”.75” 19 .3553”

• Hail SizeHail Size Events Events HDA LargerHDA Larger HDA HDA SmallerSmaller

• >1.00” 8 3 times 5 times >1.00” 8 3 times 5 times • .88 to 1.00” 41 27 times 8 times.88 to 1.00” 41 27 times 8 times• .75” 19.75” 19 15 times 3 times 15 times 3 times

ConclusionConclusion

• This study, using one radar over a 2 year This study, using one radar over a 2 year period, would suggest that in most cases, period, would suggest that in most cases, the HDA does indeed overestimate the the HDA does indeed overestimate the actual hail size by between one-quarter and actual hail size by between one-quarter and three-quarters of an inch. three-quarters of an inch.

• This result is in agreement with past studies This result is in agreement with past studies of the HDA. Though the overestimation of the HDA. Though the overestimation seems to be slightly greater in the CYS CWA. seems to be slightly greater in the CYS CWA.

Ways to possibly improve the Ways to possibly improve the HDAHDA• Use storm top divergence to get the Use storm top divergence to get the

severe hail size. AT WFO Cheyenne, we severe hail size. AT WFO Cheyenne, we have found that 50 to 75 kts or more have found that 50 to 75 kts or more works best. works best.

• Look at storm structure (BWER’s, shear Look at storm structure (BWER’s, shear etc.) to help with hail detection.etc.) to help with hail detection.

• Look at the Mesocyclone IntensityLook at the Mesocyclone Intensity

Changes Planned in the future Changes Planned in the future for the HDAfor the HDA

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

• Questions?Questions?

• Thank you.Thank you.