The Cosumnes River, before and after the atmospheric river storm of February 8-9. (Carson Jeffres)
Watching the TV news reporters out in their slickers, in front of suddenly raging rivers last weekend, it was tempting to open the taps and start celebrating the end of California's Big Dry. But officials and forecasters were quick to point out that the festivities would be premature.
There are a few reasons for this. One is the sheer depth of California's precipitation deficit. Over a three-day period, some places doubled their total seasonal rainfall totals--and still found themselves at just 30 or 40 percent of average.
Another was that this atmospheric river pouring in from the Pacific was a rifle, not a shotgun. It "kind of sat in one spot and hosed one part of the state," explains Jeffrey Mount, a consulting geologist and co-founder of the Center for Watershed Sciences at University of California, Davis. "We're in a statewide drought, so this did nothing to relieve anything basically south of Sacramento."
But the third reason is more elusive. It has to do with how extremely dry conditions were when the storm arrived.