Radar Observations of Hailstorms producing Giant Hail

Reports of giant hail, often defined as hail having a maximum dimension > 10 cm

(4 inches), have become increasingly common thanks to ubiquitous cameras and

social media. Given the high damage potential of such very large hail, this

study examined WSR-88D data from 30 storm events that produced hail > 11 cm (at

least one hail report of 4.5 inches or larger). Of the 30 storm events, 16 had

hail reports > 12 cm in maximum dimension, and 10 had hail reports > 13 cm.

The storm producing the largest hail report (16.5 cm) occurred on 29 Apr 2021

(around 0045 UTC) in the vicinity of Hondo, TX. The storm events in this study

were identified using the NCEI Storm Events Database, and were included if

WSR-88D data were available from at least one radar site within 150 km of the

hail report location for a time period extending from at least 30 minutes

before until 10 minutes after the report time. Because the radar analysis

involved examining dual-polarization data, only events for which such data were

available are included (years 2012 to 2022). To avoid having unnecessary

variable factors (e.g., too wide a range of geographical areas and/or seasons)

impact the analysis results, storm events in the data set were limited to those

occurring from March through June across the central U.S.

The analysis of WSR-88D data involved three "traditional" (i.e., not

dual-polarization) radar parameters: maximum expected size of hail (MESH),

midaltitude rotational velocity (MRV) and storm-top divergent outflow (STD).

Also analyzed were two dual-polarization radar parameters, differential

reflectivity (Zdr) and copolar correlation coefficient (CC), at five

temperature-based altitudes relevant to large hail growth: 0 C, -10 C, -20 C,

-30 C and -40 C. The study goals are to determine how useful (i.e.,

consistent) any of the radar parameters are at predicting giant hail and if

statistically meaningful differences exist between the radar parameters. Some

initial results for the traditional radar parameters indicate a moderately-high

correlation between hail size versus MRV (0.63) and STD (0.69). For the

dual-polarization radar parameters, lower values of Zdr and CC correlate more

strongly with hail size, with increasingly negative correlations (with hail

size) at colder temperatures (i.e., as temperature-based altitude increases in

height). The most negative correlations (occurring at the -40 C altitude)

between hail size and the dual-polarization parameters were -0.46 for Zdr and

-0.84 for CC. Also noteworthy are several instances where extremely low CC

values (0.2 to 0.4) were observed in the bounded weak echo regions of storms at

the 0 C and -10 C altitudes.

10 cm\n(4 inches), have become increasingly common thanks to ubiquitous cameras and\nsocial media. Given the high damage potential of such very large hail, this\nstudy examined WSR-88D data from 30 storm events that produced hail > 11 cm (at\nleast one hail report of 4.5 inches or larger). Of the 30 storm events, 16 had\nhail reports > 12 cm in maximum dimension, and 10 had hail reports > 13 cm.\nThe storm producing the largest hail report (16.5 cm) occurred on 29 Apr 2021\n(around 0045 UTC) in the vicinity of Hondo, TX. The storm events in this study\nwere identified using the NCEI Storm Events Database, and were included if\nWSR-88D data were available from at least one radar site within 150 km of the\nhail report location for a time period extending from at least 30 minutes\nbefore until 10 minutes after the report time. Because the radar analysis\ninvolved examining dual-polarization data, only events for which such data were\navailable are included (years 2012 to 2022). To avoid having unnecessary\nvariable factors (e.g., too wide a range of geographical areas and/or seasons)\nimpact the analysis results, storm events in the data set were limited to those\noccurring from March through June across the central U.S.\n\nThe analysis of WSR-88D data involved three \"traditional\" (i.e., not\ndual-polarization) radar parameters: maximum expected size of hail (MESH),\nmidaltitude rotational velocity (MRV) and storm-top divergent outflow (STD).\nAlso analyzed were two dual-polarization radar parameters, differential\nreflectivity (Zdr) and copolar correlation coefficient (CC), at five\ntemperature-based altitudes relevant to large hail growth: 0 C, -10 C, -20 C,\n-30 C and -40 C. The study goals are to determine how useful (i.e.,\nconsistent) any of the radar parameters are at predicting giant hail and if\nstatistically meaningful differences exist between the radar parameters. Some\ninitial results for the traditional radar parameters indicate a moderately-high\ncorrelation between hail size versus MRV (0.63) and STD (0.69). For the\ndual-polarization radar parameters, lower values of Zdr and CC correlate more\nstrongly with hail size, with increasingly negative correlations (with hail\nsize) at colder temperatures (i.e., as temperature-based altitude increases in\nheight). The most negative correlations (occurring at the -40 C altitude)\nbetween hail size and the dual-polarization parameters were -0.46 for Zdr and\n-0.84 for CC. Also noteworthy are several instances where extremely low CC\nvalues (0.2 to 0.4) were observed in the bounded weak echo regions of storms at\nthe 0 C and -10 C altitudes.\n"}" data-sheets-userformat="{"2":513,"3":{"1":0},"12":0}">