What is actually an atmospheric stream?

.FOR CALIFORNIANS it seemed like du00e9ju00e0 vu. Last year a march of storms, fed through atmospheric rivers, eliminated a minimum of 21 people and resulted in nearly $5bn-worth of harm across the state. On February fourth this year the exact same type of hurricane once more created chaos.

Hurricane-strength winds buffeted the main shoreline near Huge Sur. In Los Angeles stars were actually saturated as they reached the Grammy honors’ ceremony. Manors in the Hollywood Hills were dealt with in mud.

At the very least 3 folks have passed away. What are atmospheric rivers, as well as are they a threat past California?