Photo/Illutration A cloud waterfall flows over the Shiori-toge pass on Sept. 12. (Kazuyuki Shiraishi)

UONUMA, Niigata Prefecture--A natural phenomenon known as cloud waterfall is mesmerizing early morning sightseers at the Shiori-toge pass that forms part of National Route No. 352 and lies more than 1,000 meters above sea level.

The spectacle of a sea of clouds flowing down the ridge lines can be seen until early November when the road closes for the winter due to heavy snow.

Cloud waterfalls are generated in the early morning of clear days when there is a major temperature difference from the day before.

The sighting on Sept. 12 saw sightseers busily setting up their cameras along the mountain pass before the sun rose in the hope of snapping spectacular shots, according to the city's tourist association.

Although the Sept. 12 cloud formation was impressive, the cloud waterfall only gently flowed down the mountainside due to a weak wind.

Starting from this season, the tourist association provides forecast information on its official Instagram account (https://www.instagram.com/uonumacity/), notifying visitors of when they can expect to see the cloud waterfall.