A massive 19th-century storm on the Pacific coast of the US opened up a 300-mile-long sea that stretched through much of the central part of California. And it looks like the state is due for another mega flood. For 45 days, from late 1861 to early 1862, it rained almost nonstop in central California. Rivers running down the Sierra Nevada mountains turned into torrents that swept entire towns away. The storm was caused by an atmospheric river, a large concentration of water vapor that can cause devastating storms.

These storms “have the potential of hurricanes — or even more so because they go on for weeks,” Lucy Jones of the US Geological Survey told NPR. Atmospheric rivers carry concentrated channels of water vapor out of the tropics. A famous example is the Pineapple Express, which, propelled by the jet stream, carries vapor from the waters near Hawaii all the way to the American Pacific coast, where it causes heavy storms. READ MORE