Excerpt:
As winter approached, few anticipated what was about to hit California.
Mired in a serious drought, the state was suddenly battered by an onslaught of 31 atmospheric river storms in a matter of months. While the number alone isn’t exceptional, the location, intensity and duration of these storms had a transforming effect on California’s climate. Record snowfall. Deadly flooding. The end of many drought restrictions.
But one thing remains a mystery: Why did so many of these bands of water vapor, many back-to-back, slam into California?
While storm tracking has improved in recent years with data from better satellite images and air reconnaissance missions, scientists have not been able to pinpoint what exactly caused the relentlessly wet weather.
“The answer really is that we don’t know yet,” said UCLA climate scientist Daniel Swain. “It could be anything from the Hunga Tonga[-Hunga Ha’apai] volcanic eruption last spring, which injected a record-breaking amount of water vapor into the stratosphere in a way that’s not represented well in seasonal forecasts. It could be an unusual transition from La Niña to El Niño. It could be random bad luck.”
Many of winter’s atmospheric river storms came farther south, moved slowly after making landfall and came later in the season than in prior years — creating more disruption, said Chad Hecht, a research and operations meteorologist at the Center for Western Weather and Water Extremes at the Scripps Institution.
Central and Southern California in particular were hit by an above-average number of atmospheric rivers, especially moderate or strong ones, Hecht said…
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