The deadly tornado that ripped through part of the city of Tsukuba, Ibaraki Prefecture, on May 6 was probably created by a supercell, the Meteorological Agency announced Friday.
The towering, highly unstable cumulonimbus cells that passed over Ibaraki are thought to have been formed by a large gap in atmospheric temperatures when moisture-laden warm southerly winds converged on a high-altitude mass of cold air, the agency said.
An analysis of weather radar data confirmed that strong updrafts and weak rain were generated inside supercells measuring about 10 to 20 km wide and roughly 12 to 13 km high, according to the agency.
It was first thought the tornado tore a 15-km path of destruction through Tsukuba, claiming the life of a teenager, but the agency later determined the twister cut a 17-km swath during its 18-minute run, with an average groundspeed of around 60 kph.
The agency also speculated that the strong wind that damaged greenhouses and other structures the same day in the nearby town of Aizumisato, Fukushima Prefecture, might also have been a tornado.