Vertically Integrated Radar Reflectivity as an Indicator of Hail Size in the Greater Sydney Region of Australia

Andrew Treloar
Bureau of Meteorology, Australia, New South Wales Severe Weather Section
PO Box 413

Darlinghurst

NSW 2010

Australia
0011 61 292961524
0011 61 292961657
A.Treloar@bom.gov.au

A comparison is presented between maximum hail diameter and several reflectivity-based products derived from a WSR74S volumetric weather watch radar operating in the Greater Sydney area of Australia. The study spans four consecutive thunderstorm seasons with hail data sourced from a passive network of thunderstorm spotters.

The main parameters considered include the height of the 50dBz reflectivity surface and the Vertically Integrated Reflectivity of the storm, tentatively coined VIR. The parameter VIR is similar to Vertically Integrated Liquid-water content (VIL) but the reflectivity is not "capped" by a 55dBz hail threshold.

Values of VIR are normalised by storm top height following the technique of Auburn and Wolf (1996) and also by the height of the 50dBz reflectivity surface. Hail size is also compared to the height of the 50dBz reflectivity surface and the ratio of the 50dBz reflectivity surface to the storm top height. Preliminary results indicate these parameters may provide guidance in forecasting hail size.