A hail climatology of the greater Sydney area and New South Wales, Australia

Abstract

The first in-depth hail climatology for the state of New South Wales (NSW), Australia, based on reports of hailstones from 1791 to 2003, is described. The Australian Bureau of Meteorology's severe weather database is extended with a detailed compilation of scientific and newspaper accounts of hail fall for the greater Sydney area for the period 1805 to 1998. Owing to its high exposure to thunderstorm and hail by virtue of population and building density, the greater Sydney area is the focus of the database. Comparisons are drawn between Sydney and the rest of NSW, and between coastal and inland areas of the state. Over the study period, a total of 1570 thunderstorms produced hail. On average, 10 hailstorms per year were recorded in Sydney in the last 50 years. However, there is a statistically significant decrease in the hailstorm frequency during the last 14 years compared with the preceding 36 years. The magnitude of hailstorms, as measured by reports of estimated hailstone size, revealed an average maximum hailstone size per storm that ranged from 3.8 to 4.0 cm for different regions. Hailstorms occur most frequently between October and February (Australian spring and summer) in NSW, with peak activity in November and December. The hail season in Sydney begins 2 months earlier (August to February). However, during the last 14 years there has been a shift to November to March. The majority of NSW hailstorms occur during the late afternoon between 3pm and 7pm, with hailstorms in Sydney occurring about 1 h earlier. The most active hail fall regions are located in the Bureau of Meteorology's northern NSW weather forecast districts of the Northern Tablelands, Northern Rivers and parts of the Northwest Slopes. In Sydney, the most hail-prone suburbs are concentrated over the most densely populated areas and corridors. Copyright © 2005 Royal Meteorological Society