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California winter forecast is warm and dry, say USC experts

A rainless winter seems apropos for a year beset by upset. Indeed, forecast models predict 90% likelihood of La Nina conditions this winter — and that means a mostly dry and warm season ahead for California and the Southwest. A few big storms might reach the Golden State — a potential risk for mudslides in scorched areas — but USC scientists say don’t hold your breath if you’re waiting for wet winter weather relief to a summer plagued by record heat and wildfires. Today, virtually the entire state is in unusually dry or drought conditions. Here’s what USC professors say a dry winter means for California …
December 02, 2020
Contact: Gary Polakovic (323) 527-7770 or polakovi@usc.edu

 

Warm winter weather could affect water supply next year

Lowell Stott is a professor of Earth sciences at the Dornsife College of Letters, Arts and Sciences. He studies how ocean temperatures influence weather and climate with a focus on drought cycles in the U.S. West. He is a reviewer for the Intergovernmental Panel on Climate Change and teaches a climate change class at USC.

“There’s a good chance this winter will be drier and warmer than average. This is likely to affect the Sierra Nevada snowpack and the timing of spring runoff, which can lead to trouble next year with the water supply in California,” Stott said.

He added:

  • La Niña is developing this winter in the equatorial Pacific Ocean; it brings warmer temperatures and drier conditions across the Southwest.
  • Much of California’s precipitation occurs in a few “atmospheric river” storms influenced by dynamics in the tropical Pacific. The storms can dump a lot of moisture fast but are difficult to predict.
  • Climate change is a long-term challenge — but not the only factor affecting California’s environment and water supply.
  • In coming decades, hot and dry conditions will prevail more often and span more of the U.S. West.
  • Global warming threatens California’s agriculture, quality of life and public health.

Contact: Stott@usc.edu

 

Recipe for mudslides: Just add water to burned areas

Josh West is professor of geology at the USC Dornsife College of Letters, Arts and Sciences. He’s an expert in landslides and debris flows that can occur after fires and during winter storms.

“So much land burned this year across California and the West that we have heightened risk for damaging debris flows,” West said. “We’ve dodged a bullet so far because it’s dry, but that could change with big storms.”

He added:

  • The Bobcat fire exposed a lot of bare soil in the San Gabriel Mountains north of the Los Angeles basin — one of the steepest and fastest eroding mountain ranges in the world.
  • It can take as little as 15 minutes of an intense downpour to trigger mudslides in local mountains.
  • Charred vegetation releases toxins to the environment, much of it thought to be deposits from air pollution.
  • This winter, he will study how vegetation types influence debris flows in local mountains.

Contact: joshwest@usc.edu or (505) 603-5223

 

Weather wildcard this year is the “blob” in the Pacific Ocean

 

Naomi Levine is an assistant professor of Biological and Earth sciences at the USC Dornsife College of Letters, Arts and Sciences. She’s an expert in climate change and chemical and biological oceanography.

“It’s so dry in California because of the complicated and dynamic role that the oceans play, which isn’t always easy to predict,” Levine said. “We’ll likely have a La Nina year, which typically means a warm and dry winter in Southern California, but competing forces in the North Pacific can influence ocean temperatures and atmospheric river storms that affect California.”

She added:

  • A wild card this winter is a giant blob of warm water soaking along the Pacific Northwest, independent of La Nina conditions in the equatorial Pacific.
  • The blob warms air above it and can influence storm pathways.
  • Sometimes, the blob slides down the West Coast, triggering algae blooms that affect marine life in California, such as happened in 2015.
  • Conditions in the Arctic don’t seem to favor atmospheric rivers that can drench California.

Contact: n.levine@usc.edu

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