The rotating updraft base of a supercell thunderstorm, and a rear flank downdraft containing rain and hail, backlit by the setting sun, on May 10, 2014, in Climax, Kansas, United States. To most of us, dark clouds on the horizon usually means rain – but here in Kansas, they can also signal the start of a supercell. The huge formations, also known as rotating thunderstorms, are among the most powerful weather phenomenon found over land. They can occur anywhere where the conditions are right, but are normally found in more arid climates. These awe-inspiring supercells were captured south of Climax city by storm chaser Stephen Locke. (Photo by Stephen Locke/Barcroft Media)

Russian President Vladimir Putin, center, uses a binocular, as Defense Minister Sergei Shoigu, left, and chief of Russia's military's General Staff Valery Gerasimov, right, observe military exercises near the Baikal Lake on Wednesday, July 17, 2013. (Photo by Alexei Nikolsky/AP Photo/RIA Novosti/Presidential Press Service)

An employee of the National Park Service takes a selfie with President Barack Obama, left, in the background meeting with the crowd after a tour of Everglades National Park on Earth Day, Wednesday, April 22, 2015, in Florida. Obama used the visit to warn of the damage that climate change is already inflicting on the nation's environmental treasures. (Photo by Lynne Sladky/AP Photo)

A handout photograph provided by Brian Kubicki of Costa Rican Amphibian Research Center on 26 April 2016 shows a “Crystal frog”, Hyalinobatrachium dianae (H. diane). This frog was discovered by US biologist Brian Kubicki and Costa Ricans Stanley Salazar and Robert Puschendorf in a rainy forest of Costa Rican caribbean after 40 years without notice of any new example of this kind. (Photo by Brian Kubicki/EPA/Costa Rican Amphibian Research Center)

Participants wearing costumes and masks take part in the first day of the traditional carnival parade in Mohacs, Hungary, 23 February 2017. The carnival parade of so-called busos, dressed in costumes with frightening wooden masks and using various noisy wooden rattlers, is traditionally held on the seventh weekend before Easter to drive away winter. (Photo by Sandor Ujvari/EPA)

In this photo taken on Saturday, April 22, 2017, a drawing “King for a day” is made on the back of a muddy truck by artist Nikita Golubev in Moscow, Russia. The grimy trucks traversing the polluted and dusty streets of Moscow have inspired Golubev to use white vans and trucks as his canvas to create this ephemeral street art and signs his drawings Pro Boy Nick. (Photo by Pavel Golovkin/AP Photo)

Protesters use fireworks against riot police during clashes in the Athens neighborhood of Exarchia, a haven for extreme leftists and anarchists, Thursday, December 6, 2018. New protest marches were underway in Greece Thursday evening on the 10th anniversary of the fatal police shooting of a teenager, hours after violent initial demonstrations where masked youths attacked police with firebombs and stones. (Photo by Yorgos Karahalis/AP Photo)

A couple covered with the US and the pride flags pay their tribute for the victims of a 12 June mass shooting in Orlando, Florida, USA, as they look at the Eiffel tower, illuminated in rainbow colours, in Paris, France, 13 June 2016. A total of 50 people including the suspect were killed and 53 were injured in a shooting attack at an LGBT club in Orlando, Florida, in the early hours of 12 June. The shooter was killed in an exchange of fire with the police after taking hostages at the club. (Photo by Yoan Valat/EPA)