Australians spot extraordinary cloud formation. UFO or just... clouds?

It was just like any other day in the seaside town of Wonthaggi until a weird formation in the sky was spotted. In a fit of panic, a resident named Carol called the radio station 3AW for help. Others followed suit by snapping photos, posting them on Twitter to expedite the identification of the formation. Is it the end? Is Australia about to be taken over by aliens? According to the Bureau of Meteorology, it is neither.

What the people of Wonthaggi (and the rest of the world are seeing online) is called a fallstreak hole, also referred to as a fallstreak cloud or punch hole cloud. Fallstreak holes form when water temperature inside a cloud has dropped to freezing but the water itself has not frozen because there aren't enough ice nucleation particles.

"In this case, when the water does start to freeze, it falls down to the surface ... so you're left with this cloud surrounding it, this clear area," explained Michael Efron from the Bureau of Meteorology.

What about the rainbow within the formation? Efron says it's called iridescence, similar to what could be seen inside sea shells and soap bubbles and on butterfly wings. The kind of iridescence seen over Wonthaggi occurs with high clouds, the same high clouds that formed the fallstreak hole. Add in diffraction and the rainbow within the cloud formation is complete.

While the Bureau of Meteorology does not have an official record of how many times fallstreak holes form in Australia, a similar cloud formation was spotted in October, appearing like a watery UFO in Perth.

Aside from the mentioned cloud conditions, fallstreak holes may also be formed when an aircraft flies through the area, cooling the air in the clouds and causing them to expand. While momentary, the cooling is enough to promote a drop in temperature that will then lead to spontaneous freezing of water droplets, even when there are not enough ice nuclei to go around. When there are enough high clouds around, the formation will persist long after the aircraft has left. If an aircraft passes at a shallower angle, a line of cloud will instead freeze, creating a hole shaped like a cigar called a canal cloud.

Stateside, the same type of cloud formation was spotted over Northern California in May. Of course, the spotting also sparked debates involving conspiracy theories and UFOs.