Atmospheric rivers · California, United States
Nine rivers in the sky
Between 27 December 2022 and 17 January 2023 nine atmospheric rivers, long narrow plumes of water vapour from the tropical Pacific, came ashore in California one after another. The soil, dry after three years of drought, filled within days; then rivers rose, levees broke, hillsides slid and the Sierra Nevada piled up snow. Twenty-one people died.
27 December 2022 – 17 January 2023 · California · ERA5
413mm
ERA5 at Sacramento in 22 days
The grid point nearest the city, 27 December – 17 January: more than four months of its usual winter rain.
What happened
California had come through three dry years; reservoirs were low and the state was rationing water. The winter of 2022–23 changed that in weeks. From late December a strong, straight jet stream over the Pacific steered storm after storm towards the coast, each with an atmospheric river ahead of its cold front.S1
The New Year's Eve storm flooded the Sacramento valley and the Cosumnes river broke its levees. The storms of 9–10 January caused debris flows at Montecito and forced evacuations along the central coast. By mid-January reservoirs were back near their historical averages and the Sierra snowpack was among the deepest on record.S1N1
Rivers of water vapour
An atmospheric river is a band of very moist air a few hundred kilometres wide and thousands long, carried by the low-level winds ahead of a Pacific storm. On the Lab's maps of total column water vapour, the water in the whole depth of the air, they stand out as narrow tongues of colour reaching from the tropics to the coast. Where they meet the Coast Ranges and the Sierra Nevada the air is forced up and the water falls out as rain and snow.
Three weeks of rain
413mm
ERA5's rain at Sacramento from 27 December to 17 January. The city's normal for December and January together is under 200 mm.
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References
News
- N1Center for Western Weather and Water Extremes (CW3E). December 2022 – January 2023 atmospheric river sequence: story map. Scripps Institution of Oceanography, 2023.The nine atmospheric rivers, their dates, impacts and toll.
Studies and guidelines
- S1DeFlorio, M. J., et al. (2024). From California's extreme drought to major flooding: evaluating and synthesizing experimental seasonal and subseasonal forecasts of landfalling atmospheric rivers and extreme precipitation during winter 2022/23. Bulletin of the American Meteorological Society.The drought before, the floods, and how well the season was forecast.