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Record Rainfall Breaks Through ‘Ridiculously Resilient Ridge’

Record rainfall causes flooding in Mission Valley, May 15, 2015.

Photo by Nicholas McVicker

Above: Record rainfall causes flooding in Mission Valley, May 15, 2015.

Photo by Brett Albright/NWS San Diego

A high pressure ridge has been pushing storms up and over California, as illustrated by the map above, May 15, 2015.

Climate scientists say San Diego's record rainfall on Thursday and Friday was the result of a storm finally breaking through a stubborn barrier.

It's known as the 'ridiculously resilient ridge,' a high pressure region along the West Coast that's been pushing storms up and over California in recent years.

Daniel Cayan of the Scripps Institution of Oceanography in La Jolla said the ridge has helped keep California in a prolonged state of drought.

Cayan said this week's storm broke through because the ridge happened to break down at just the right time.

"This is kind of like free money," he said. "We didn't expect much in the way of precipitation in May, and we'll take everything we can get. But it by itself certainly is not going to break the drought."

Brett Albright, a meteorologist at the National Weather Service in San Diego, said a few days of heavy rainfall doesn't herald the ridge's collapse. But it's encouraging.

"It's probably too early to tell," he said. "It's favorable though."

Experts say the real test will be to see if the ridge holds strong during El Niño.

"That's the $64-million question for California right now," said Cayan. "What's going to happen next winter?"

Cayan said it's hard to tell this far out, but for now he foresees about an equal chance of the ridge staying firm or breaking down.

On Wednesday, the National Weather Service predicted an 80 percent chance of El Niño persisting through the end of the year.

"That's a good sign," said Albright. "That's what we want to see."

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