![Photo taken on March 11, 2019 shows the stunning view of shelf cloud over Pescara, Italy. (Photo/IC)
\](http://www.ecns.cn/hd/2019/03/13/3916002601c842a08ccc7b31fa5b26f0.jpg)
Photo taken on March 11, 2019 shows the stunning view of shelf cloud over Pescara, Italy. (Photo/IC)
"Shelf cloud" arises when two very different air masses collide, a cooler and drier and a warmer and wetter.
![Photo taken on March 11, 2019 shows the stunning view of shelf cloud over Pescara, Italy. (Photo/IC)](http://www.ecns.cn/hd/2019/03/13/20157448e9c64c8ca5a84e859208cbc6.jpg)
Photo taken on March 11, 2019 shows the stunning view of shelf cloud over Pescara, Italy. (Photo/IC)
![Photo taken on March 11, 2019 shows the stunning view of shelf cloud over Pescara, Italy. (Photo/IC)](http://www.ecns.cn/hd/2019/03/13/0147f5d47e5d4f7b9b075a2fa9414120.jpg)
Photo taken on March 11, 2019 shows the stunning view of shelf cloud over Pescara, Italy. (Photo/IC)