Rivers flood. We know that all too well here in the Red River Valley. But there is another kind of river that has been causing flooding in California that you may not have heard about, an atmospheric river. Atmospheric rivers are narrow regions in the atmosphere, often one to three hundred miles in width that contain high concentrations of water vapor.
Like real rivers, they come in all shapes and sizes and often contain meanders. Using specialized satellite data (water vapor imagery) these rivers of concentrated water vapor are often easily detected. One type of atmospheric river is the so called “Pineapple Express”. This references times when tropical moisture near Hawaii is transported into the west coast, but these narrow flows of moisture can also come from non tropical sources and that has been the case with the heavy rain that has been impacting northern California in recent days.
Although these atmospheric rivers can cause flooding, more often they just bring beneficial moisture to the west coast.