The nor'west arch is a band of high white lenticular cloud that forms on the eastern side of New Zealand's South Island and which looks like an arch in an otherwise clear blue sky over the Southern Alps. It is accompanied by a strong hot northwesterly or northerly wind known as a "nor'wester". In Canterbury, where it is a well known feature, it is also called the Canterbury arch. It also occurs in Otago and Marlborough and east of mountain ranges along the east coast of the North Island.[1]
Closer to the Canterbury coast, some distance from the mountains of the Southern Alps, it appears as a clear area of blue above the mountains, with white cloud streaming to the east from it. The phenomenon is similar to the Chinook arch seen in the Pacific regions of the United States and Canada.