Notorious phenomenon

“Pineapple Express” sweeps across California

Masses of rain and strong winds are currently paralyzing large parts of the US state of California. Authorities have reported three deaths so far. The background to this is a special weather phenomenon known meteorologically as an "atmospheric river" and in the region as the "Pineapple Express".

Near Sacramento, a man was hit by a falling tree in his yard. He later succumbed to his injuries, the Sacramento County Coroner's Office announced on Monday.

The other two deaths in northern California were also caused by falling trees, CNN and others reported. The people died on Sunday.

Mudslides and widespread power outages
The storm, which initially raged in the greater San Francisco area, moved further south on Monday and reached Santa Barbara and Los Angeles. The heavy rain triggered mudslides, flooded roads and paralyzed the power supply. According to the website PowerOutage, hundreds of thousands of households were temporarily without power.

Weather service: "Potentially life-threatening"
The National Weather Service warned of wind gusts of up to 96 kilometers per hour. The Governor of California, Gavin Newsom, had already warned on Sunday of a "severe storm with dangerous and potentially life-threatening effects" and declared a state of emergency for several counties.

Thousands of kilometers of weather phenomenon
The reason for the heavy rainfall is the "atmospheric river" weather situation. The German Weather Service defines this as a "relatively narrow, directional band of moisture-saturated air" with a width of around 500 kilometers and a length of 2000 kilometers or more.

Such systems transported a large part of the water vapor outside the tropics. Because the moist air masses that hit California mostly come from the tropical ocean regions in the Pacific around Hawaii, they are also known as the "Pineapple Express".