The Tibetan Plateau may be on the other side of the world from California, but what happens on this high-altitude landscape in Asia can set off a chain of events that fuels powerful atmospheric rivers with flooding rainfall and heavy snow hitting the U.S. West Coast.

My team of atmospheric scientists discovered this connection, and we explain how it works in a new study in the journal Science Advances.

California’s unexpected rainfall

California and its neighbors saw record-breaking precipitation during the winters of 2016–2017 and 2022–2023 that caused widespread flooding and infrastructure damage.

The U.S. Pacific Coast often gets atmospheric river storms during its winter rainy season, but the events in those years were especially striking because they occurred during La Niña conditions, which are typically associated with relatively dry winters in California. La Niña is El Niño’s cooler counterpart; they are the two extremes of a climate pattern connected to ocean temperatures known as the El Niño-Southern Oscillation.

The two stormy winters highlighted an important limitation in seasonal forecasting: Ocean-based events such as El Niño and La Niña are important, but they don’t tell the whole story. No global computer models predicted or........

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