Strange cloud formations have appeared over the Philippines in recent days. Moving across the sky like waves this is one of the rarest cloud phenomena.

Such structures, called Kelvin-Helmholtz waves, form at the boundary between layers of air of different temperatures, which also move at different wind speeds.

Like the water level of a lake, the wind of the slightly faster and warmer layer of air above ripples the top of the sluggish and cooler layer of air below. In the process, part of the lower air layer is swirled into the air mass above, forming the typical wave patterns.

In addition to a very specific set of conditions needed for these clouds to form, they are also extremely short lasting. Sometimes lasting mere minutes, making catching them fully formed is quite the accomplishment.

They don't bring rainfall but are indicative of high wind speeds, any aircraft overhead are likely to experience high turbulence.

If you happen to catch Kelvin-Helmholtz clouds in action, be sure to quickly snap a picture and send it to us via the image icon in the top-right or clicking here.