NEWS

Atmospheric rivers threaten California as state reels from deadly storm

    Storms will cause flash floods in San Carlos, California, USA on December 31st.
On December 31st, a storm caused flash flooding in San Carlos, California. Photo: Tayfun Coskun/Anadolu Agency via Getty Images

After a massive storm over the weekend, Californians are gearing up for an even more dangerous atmospheric river event this week.

Threat Level: “Simply put, this is likely to be one of the most impactful systems on a broad scale this meteorologist has seen in a long time,” said the National Weather Service’s Gulf Area Office. said during a discussion on forecasts on Monday.

“Impacts include widespread flooding, washed out roads, collapsing hillsides, collapsing trees (potentially filling groves), widespread power outages, immediate disruption to commerce and, worst of all, In the case of , the potential loss of life is involved. This is a truly brutal system. It is something we are looking at and should be taken seriously.”

— Excerpt from NWS Bay Area Office Forecast Discussion

State of play: Evacuation and shelter-in-place orders were issued in parts of Sacramento County Monday, causing widespread power outages and at least two deaths, according to Sacramento Bee, after weekend storms hit northern and central California and flooded roads. caused it.

  • Multiple roads remained closed across Sacramento County on Monday due to flooding.
Computer model projections of water vapor delivered to the West Coast on Wednesday morning.
Computer model projections of water vapor delivered to the West Coast on Wednesday morning. Image: Scripps Institute of Oceanography.

By numbers: A New Year’s Eve storm brought downtown San Francisco the second wettest day on record, with 5.46 inches of rain.

  • Recorded by the UC Berkeley Central Sierra Snow Lab in the Sierra Nevada Mountains 7.5 inches of snow in just 1 hour December 31.
  • The prospect of another 6 to 12 inches of rain and several feet of mountain snow is growing concern for forecasters and emergency managers.

What to Expect: The next big storm is expected to hit Northern California on Wednesday, with more storms expected later in the week.

  • UCLA climate scientist Daniel Swain Twitter post A rapidly deepening surface cyclone, or weather bomb cyclone, “will remain well offshore, but associated warm and cold fronts will bring widespread heavy rain and strong winds to Northern California late Wednesday.

  • Swain said the storm “would be quite remarkable in its own right, as it is associated with the passage of unusually well-defined warm and cold fronts, and rivers with a very wet and relatively warm atmosphere.” .
Screenshot of a NWS Bay Area tweet warning of high winds across the region due to storms.
Photo: National Weather Service/Twitter

For the record: Atmospheric rivers are powerful but narrow streams in the atmosphere that can carry vast amounts of water vapor that travel thousands of miles from the tropics to mid- and northern latitudes.

  • The effects of Wednesday’s storms have caused several rivers to rise along the Cosmnes River in Sacramento County, causing active, massive flooding and levee breaches, “saturating the soil” across much of Northern California. It will be further enhanced by the fact that there are people,” Swain said.
  • This raises concerns about the possibility of further flooding and landslides.

To the point: Climate change is adding more moisture to atmospheric rivers, allowing for increased rainfall and snowfall.

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