What is actually an atmospheric stream?

.FOR CALIFORNIANS it seemed like familiarity. In 2015 a procession of tornados, fuelled through atmospheric streams, eliminated at least 21 folks as well as triggered nearly $5bn-worth of damages throughout the condition. On February 4th this year the very same form of storm once more created chaos.

Hurricane-strength winds buffeted the central coast near Huge Sur. In Los Angeles celebs were actually soaked as they came to the Grammy awards’ welcome mat. Residences in the Hollywood Hills were actually covered in mud.

At least 3 folks have died. What are atmospheric streams, and are they a risk beyond California?