Backgrounder

Backgrounder

Hail occurrence in New Zealand

Mean annual days of reported hailstorms taken from records for about 450 climate stations across New Zealand. Note that methods of observation, and the duration of reporting periods, are not consistent throughout the country.

Hailstorms are an inherent risk to primary production and other vulnerable activities throughout New Zealand. Hail records are available in New Zealand from climatological records, hourly weather reports at a few locations, and from the news media. Hail storms that occur in intensively farmed or populated areas are more likely to be recorded; in remote areas, hail may often be unreported, especially if it falls at night.

As was the case with the hail storm of 23-24 April, illustrated on our cover, hail is typically associated with a cold front and strong uplifting of moist air. During the day time this is often visibly characterised by the towering 'anvil-shaped' cumulus clouds.

Annual days of hail at Christchurch Airport, 1953-1994. Hail has been reported at least once each year, with a maximum of 13 events occurring twice, and an annual average of between 5 and 6.

Hail occurrence data held by NIWA in the National Climate Database show a general increase in hail from the north to the south of New Zealand, and from east to west. This is partly borne out in the adjacent map. In the North Island, high country areas, such as the Central Plateau and Mount Taranaki, have more hail events than elsewhere. In the South Island, coastal Southland, Banks Peninsula, and the west coast from Hokitika north are particularly vulnerable.

Areas sheltered from both onshore southerlies and westerlies, for example Northland’s east coast, Bay of Plenty, Nelson, and Blenheim, have low hail frequencies.

Hail lying in Christchurch the morning after the overnight storm of 23-24 April. The hail stones ranged in size from 13 to 15 mm. (Cover photo: Stuart Burgess)