Pacific moisture is streaming toward the West Coast and is forecast to produce incredible amounts of rain and mountain snow.
This heavy precipitation-producing weather system flows along a phenomenon scientists refer to as the “atmospheric river,” a low-lying stream of moisture that can be beneficial for the water supply in Southern California.
“An atmospheric river is a constant flow of moisture in one area because of stationary weather systems, relentless weather systems,” said NBC4 forecaster Fritz Coleman.
The one currently hovering over Northern California is delivering a small amount of rain to the south, with more to come later. There have been times when atmospheric rivers have ended up over Southern California which contributes to something called an “arc storm,” when the region gets too much water.
“The winter of 1861-62, it rained for 45 days straight in California and it was said to have been flooded from mountain to mountain from the San Gabriels to the Palos Verdes Peninsula,” said Dr. Lucy Jones, with the U.S. Geological Survey.
Although atmospheric rivers can cause severe flooding, they are a very important contributor to regional water supply.
“That rain storm that we had [Thursday] is really hitting that watershed,” said Debra Man, Metropolitan Water District of Southern California. “It flows down, goes through the delta, then goes through the California aqueduct [and] they serve our service area.”