As El Niño looms, California braces for more storms and floods

The specter of a developing El Niño invokes distressing memories for many Californians. Rainstorms tied to a super-strength El Niño episode overwhelmed southern parts of the state and killed 17 people in the winter of 1997-1998.

With forecasts the infamous climate pattern could reach a similar intensity this winter, the Golden State is bracing for more floods, not even a year removed from one of its wettest stretches on record.

This fall, California officials are lining up $52 million for levee repairs and, compared to a year ago, longer stretches of temporary flood walls and millions more sandbags to prepare for what the winter might bring.

But whether California winds up making use of those preparations depends on an unpredictable mix of climate and weather indicators, none of which guarantee California and the Southwest are in line for more slugs of precipitation. El Niño tilts the odds in favor of another wet year, but it doesn’t assure one.

“There are always ways in which Mother Nature can throw us a curveball,” Karla Nemeth, director of the state’s Department of Water Resources, told reporters at a briefing last week.

Though it’s clear El Niño is building — and could become one of the strongest ever observed — climate scientists and meteorologists said it’s too soon to know how it will influence weather in California and across the United States. While the 1997-1998 iteration of El Niño brought disaster, a more recent super El Niño in winter 20152016, for example, created unexpectedly drier conditions.

“They don’t always deliver in the way we expect them to,” said Andrew Hoell, a research meteorologist with NOAA’s Physical Science Laboratory in Boulder, Colo.

A strong El Niño significantly raises the odds of heavy rainfall and a wet winter for the Southwestern US and California, based on both historic events and modeling studies. That is because of the ways El Niño shifts moisture around the globe.

The climate pattern stems from abnormally warm Pacific Ocean waters along the equator. That warmth leads to increased evaporation and more water vapor to fuel storm clouds in the central and eastern Pacific.

Meanwhile, changes to larger weather patterns means that moisture is sent flowing across the southern US. During El Niño, the jet stream — a torrent of strong wind in the upper atmosphere that steers weather systems — tends to dip southward, sending storms into Southern California.

Michael Anderson, the California state climatologist, said that during El Niño, storms also tend to move faster, zipping across the Pacific straight into California and the Southwest.

In years with especially strong El Niño patterns, such as 1982-1983 and 1997-1998, the wet trend can extend into Central California, as well.

Scientists will be closely monitoring how the tropical Pacific evolves over coming months to gauge El Niño’s impacts. The West tends to avoid prolonged storminess, as it did in 20152016, when waters are most unusually warm over the central equatorial Pacific, they said.

But California tends to see more streams of moisture from the Pacific, known as atmospheric rivers, when the warmest waters set up farther east, near the coast of South America, as they have this year.