Atmospheric rivers are very common, and there’s usually about 11 on Earth at any given moment.
These "rivers in the sky" or "pineapple express" as they’re commonly known, are long narrow bands of tropical air flowing from one region to another. Only at about 300 miles wide, they can be up to 2,000 miles long and bring about half of California’s typical rainfall.
NASA scientists project that in the future, atmospheric rivers will be less common. But the ones that do form will be longer and wider, bringing heavier rain.
That could mean that we have large swings from extreme drought to extreme flooding, and we need to be prepared for it all.