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California Storms Persist With Deluges, Mudslide Threats

California saw no relief from drenching rains early Tuesday as the latest in a relentless string of storms continued to swamp roads and batter coastlines with high surf, turning rivers into gushing flood zones and forcing the evacuation of thousands in towns with histories of deadly mudslides. At least 14 people have died since the storms began last week.

California Snowpack Soars to Nearly 200% of Normal

While many areas of California are coping with the destructive impact of relentless rainfall, the news is nothing but good when it comes to the state’s snowpack. As of Monday, California’s snow water equivalent was 199% of normal for the date (January 9), according to the California Department of Water Resources.

‘The Worst of it Still in Front of Us’ as New Storms Set to Pound a Rain-Weary California

California is bracing for another week of destructive storms that will probably bring flooding and hazardous winds Monday to an already battered state.

A series of atmospheric rivers that pummeled coastal communities last week and left more than 400,000 without power in California on Sunday will be followed by particularly brutal weather as rivers reach flood levels and powerful winds wreak havoc, forecasters fear.

California Reservoir Water Levels Before and After Rain

California’s major reservoirs have seen significant gains in water level in recent days after two weeks of exceptionally heavy rain across the state. It comes after months of severe drought in the region, leaving water levels in the state’s most important reservoirs well below their historical average.

String of Brutal Atmospheric Rivers Imperils a California Already Weakened by Drought

A successive series of powerful atmospheric river storms poses a growing threat to California as the ground becomes more saturated, river levels rise and heavy winds threaten the power infrastructure. This week’s storms are expected to dump intense levels of rain in a fairly short period of time. The greatest potential for disaster is in Northern California, which has already been battered by several destructive storms — including one this weekend that caused a deadly levee breach.

Miracle or Mirage? Atmospheric Rivers End California Drought Year With Heavy Snow and Rain

After the driest start to any year on record, California will end 2022 with snow-capped mountains, soaked roadways and — in some places — flood warnings. The soggy end to an otherwise bone-dry year came as something of a surprise. Only weeks earlier, officials sounded the alarm about a rare third appearance of La Niña — a climate pattern in the tropical Pacific that is often associated with dry conditions in the state.

How Tracking Atmospheric Rivers Could Transform California’s Reservoir Levels During Drought

Atmospheric rivers can wreak havoc on the West Coast. These “rivers in the sky” stream enormous amounts of moisture from the tropics to western North America — double the flow of the Amazon River, on average. This moisture can produce downpours that cause widespread flood damage. From 1978 to 2017, this damage amounted to $1.1 billion per year according to a 2022 study. But atmospheric rivers are also crucial for life in California.

Atmospheric River Reconnaissance Flight Season Gets an Early Start This Winter

An expanded Atmospheric River Reconnaissance program began last month as a result of the unexpected “bomb cyclone” in October 2021 that hit North America’s West Coast, followed by another atmospheric river less than a month later that caused severe flooding in Washington.

“Climatologically, November and December can bring some of the worst floods for that part of the world,” said research meteorologist Marty Ralph, director of the Center for Western Weather and Water Extremes (CW3E) at UC San Diego’s Scripps Institution of Oceanography. Ralph leads the AR Recon program, along with Vijay Tallapragada, Ph.D., Senior Scientist at NOAA’s Environmental Modeling Center, in partnership with the U.S. Army Corps of Engineers, the California Dept. of Water Resources, NOAA Office of Marine and Aviation Operations, and the U.S. Air Force Reserve 53rd Weather Reconnaissance Squadron “Hurricane Hunters.”

Potential for Multiple Atmospheric Rivers to Impact the US West Coast During the Next 7 Days

Two atmospheric rivers (ARs) are forecast to make landfall along the US West Coast on 9 Dec and 12 Dec. The first AR is forecast to bring a short period of AR 1 conditions (based on the Ralph et al. 2019 AR Scale) to coastal Southern Oregon. The deterministic GFS and ECMWF have drastically different solutions for a developing area of low-pressure associated with the second AR, making it difficult to pinpoint the timing, IVT intensity, and landfall location.

 

California weather-extremes-wildlfires-flooding

More Evidence that California Weather is Trending Toward Extremes

A team led by Kristen Guirguis, a climate researcher at Scripps Institution of Oceanography at UC San Diego, found evidence that the risk of hazardous weather is increasing in the Southwest.

The researchers investigated the daily relationships among four major modes of weather affecting California. How they interact governs the formation of weather events such as atmospheric rivers capable of bringing torrential rains and Santa Ana winds that can spread devastating wildfires.

“This study suggests that weather patterns are changing in a way that enhances hot, dry Santa Ana winds, while reducing precipitation frequency in the Southwest,” said Guirguis. “These changes in atmospheric circulation are raising the risk of wildfires during California winters.”

The study, “Winter wet—dry weather patterns driving atmospheric rivers and Santa Ana winds provide evidence for increasing wildfire hazard in California,” was published in the journal Climate Dynamics July 17, 2022.

Flooding in Elk Grove, California.Dillard Road is flooded near the Hwy 99 off ramp, located south of Elk Grove, California. Photo credit: Florence Low / California Department of Water Resources.

The basis of the research was an examination of the dominant atmospheric circulation patterns over the North Pacific Ocean, known as Baja-Pacific, Alaskan-Pacific, Canadian-Pacific, and Offshore-California modes. What distinguishes them from each other are the relative positions of ridges and troughs in the atmosphere.

Weather patterns and a warmer atmosphere

The research team identified 16 recurring weather patterns that are created daily as these modes interact with each other. One product of the work was a summary of California weather patterns from 1949 to 2017. The patterns associated with the formation of dry gusty Santa Ana winds that often stoke Southern California fires are becoming more frequent. Patterns associated with what might be considered “normal” rainfall are decreasing in the Southwest thus promoting drought, but patterns associated with extreme precipitation and strong atmospheric river episodes have remained steady over the study period. The researchers noted that while the patterns associated with heavy precipitation and strong atmospheric rivers have not changed in frequency, a warmer atmosphere is capable of holding more water so these storms are becoming more damaging.

Challenges for wildfire and water resource management

The results suggest an increasing probability of compounding environmental hazards during California winters, said the research team. Though winter atmospheric rivers are the antithesis of hot, dry Santa Ana wind conditions, sequences of wildfires followed by strong atmospheric rivers often compound the damage from fires when they trigger flash floods and destructive debris flows from burn scars.

Photo of the Thomas Fire taken from a Santa Barbara beach. Photo credit: Carsten Schertzer / iStock.

“This spells challenges for wildfire and water resource management and provides observational support to our previous results projecting that California will increasingly have to depend on potentially hazardous atmospheric rivers and floodwater for water resource generation in a warming climate,” said study co-author Alexander Gershunov, a Scripps Oceanography climate scientist.

Study authors say this work is helping to inform an experimental subseasonal-to-seasonal (S2S) forecast product being developed at Scripps Oceanography’s Center for Western Weather and Water Extremes (CW3E) that predicts extreme weather in California including atmospheric river landfalls, Santa Ana winds, drought, and heat waves.

The U.S. Department of the Interior via the Bureau of Reclamation and the Southwest Climate Adaptation Science Center, the California Department of Water Resources, and the Regional Integrated Sciences and Assessments (RISA) California—Nevada Climate Applications Program and the International Research Applications Program of the National Oceanic and Atmospheric Administration funded the study. Additional funding was provided by the University of California Office of the President MRPI grant.

High water levels on the Tuolumne River close River Road in the city of Modesto, California.High water levels on the Tuolumne River close River Road in the city of Modesto, California, part of Stanislaus County. Photo credit: Dale Kolke / California Department of Water Resources.

The San Diego County Water Authority has a partnership with the Scripps Institution of Oceanography at UC San Diego to better predict atmospheric rivers and improve water management before, during and after seasonal storms.

(Editors Note: Study co-authors include Benjamin Hatchett of the Desert Research Institute in Nevada; Tamara Shulgina, Michael DeFlorio, Rosana Aguilera, achel Clemesha, Tom Corringham, Luca Delle Monache, and Marty Ralph of CW3E at Scripps Oceanography; Aneesh Subramanian and David Reynolds of the University of Colorado Boulder; Janin Guzman-Morales of the University of California Santa Barbara; and Alex Tardy and Ivory Small of the National Weather Service.)