What is animal rain and how do it occur

Can you imagine if it's not raining cats and dogs, but fish and frogs fall down from the sky? This is an animal rain or a rain of animal, a very rare meteorological phenomenon. In this lesson of the Windy.app Meteorological Textbook (WMT) and newsletter for better weather forecasting you will learn more about what animal rain is and how do it occur.

What falls from the sky?

The rain of frogs is certainly the most common "animal" precipitation which still might sound mysterious and even a little ridiculous to some people. Surprisingly, reports of animal rain dates back to ancient times. For instance, rains of birds and fish were first mentioned in ancient Egypt, while in medieval Europe, accounts of toads and mice falling from the sky were not uncommon. Some more disturbing reports have included snakes, jellyfish, spiders, and even a rain of flesh, blood and fur.

Animal rain: scientific explanations

Causes of animal rain are not entirely clear. Since they are rare, very few people manage to see them, let alone take photos or videos. What can be said with confidence though, is that there are several reasons behind this phenomenon, and every case should be looked at separately.

Current scientific hypothesis suggests that most fish and frog rains are linked to waterspouts or tornadoes. A tornado is a rotating column of air with pockets of low pressure in the centre which makes the air rise up. If a powerful tornado forms over a waterbody, it can suck in water along with its contents and transport it to relatively high altitudes.

Tornadoes usually originate from the base of a cumulonimbus cloud, where the air also moves upward, and the speed of the wind can exceed 50 km/h (31 miles/h). Therefore, especially potent tornadoes can "suck up" small light animals which may not be deposited back to earth immediately but rise up within the tornado for several kilometers. When the tornado loses its energy, they fall to the ground along with the rain. This can occur quite far from the place where they were caught by the violent vortex. Subzero temperatures at high altitudes perfectly explain why many animals that fall from the sky are frozen solid.

Numerous reports of dead bird rain have come from Sweden, USA and Italy. Dead birds falling from the sky have been observed over a number of years but always interestingly in early January which gave rise to a theory that weather conditions are not responsible for it. The theory is that New Year's fireworks frighten the birds, they become disoriented and die either from heart attacks or from hitting various obstacles.

Millions of spiders regularly drop from the sky in Australia and Brazil. It's unclear what spurs these spiders to take to the skies but it might be explained by their behaviour. Spiders of some species crawl to the tops of trees immediately after birth, where they send out silk strands looking like parachutes that allow them to be lifted on air currents. This way spiders populate new areas which they wouldn't otherwise be able to reach.

Does it really rain?

Animal rains often coincide with large rainstorms when most people try to hide and won't necessarily see what is going on outside. This suggests that sometimes the animals don't fall from the sky at all. A different force has almost certainly brought them to the streets, and the stories about the "animal rains" are just a figment of shocked people's imagination. Take the famous Singaporean "catfish rain" of 1861. While some scientists were trying to find plausible explanations of the fish falling from heaven, others explained it through the behaviour of the fish during their migration. While migrating, catfish can move across land from one waterbody to another, providing these are not too far apart. It's possible that after a heavy downpour when the ground was very wet many migrating catfish simultaneously decided to go on the move between waterbodies.

Fish rain is a phenomenon that occurs at least once every year in one village in Honduras, and for the locals, fish raining from the sky have become the cause of an annual celebration. The scientific understanding of it still remains sketchy: waterspouts are quite rare and are unlikely to cause fish rain in the same place every year. Therefore, many people attribute it to torrential downpours causing floods. Following heavy rainstorms, water from the nearby rivers and lakes floods the streets and flushes the fish to the streets of the village. This theory might explain why the fish on the streets of the Honduran village of Yoro are always alive and not frozen.

The Windy.app application does not predict the fall of animals from the sky, but in 10+ weather profiles of application for different sports and activities as well as for general weather forecasting you can always see what kind of precipitation is outside.

Text: Evgeniy Petrov, a meteorologist and a climatologist

Cover photo: Blake Cheek / Unsplash