Lenticular clouds over Mount Rainier, Washington, USA

Phenomenal clouds. Phenomenal clouds over Washington

World Meteorological Day brings us to Mount Rainier - a huge stratovolcano with a habit of creating its own weather systems in the US state of Washington. Jutting out about two miles above the surrounding landscape, it is so big that it interrupts the flow of air that comes in off the Pacific Ocean, creating unusual weather such as the saucer-shaped clouds on our homepage.

They’re called lenticular clouds and, because of their distinctive appearance, some think they can explain UFO sightings. Thanks to the science of meteorology, we know they’re a normal weather phenomenon, often occurring on the downwind side of mountains and tall structures.

World Meteorological Day marks the anniversary of the establishment of the World Meteorological Organization, a special agency of the UN which shares nations' information about weather, climate and Earth’s atmosphere.