California Braces for Atmospheric River Storms: Flood Risks and Fire Season Update

Back-to-back atmospheric river storms began impacting Los Angeles County Tuesday night, bringing much-needed moisture before another potential round of Santa Ana winds. The series of storms started in Northern California earlier in the week, with heavy rainfall causing landslides and urban flooding.

Impact on Southern California

Forecasters are optimistic that the rain will primarily benefit Southern California by reviving vegetation weakened by drought. However, despite the optimism, there’s a 5% to 10% chance of significant debris flow in recently burned areas of the Southland. Officials have taken precautionary measures by closing stretches of Pacific Coast Highway and Topanga Canyon Boulevard in L.A. and Ventura counties due to potential debris flows.

Northern California Struggles

In contrast, Northern California experienced a harder hit with reported landslides and floods in the North Bay. Cities like San Francisco, San Luis Obispo, Paso Robles, Cambria, Morro Bay, and Pismo Beach were affected by minor flooding. A large tree fell in Santa Rosa, damaging a building and closing a nearby road, and a hillside collapse in Forestville caused a house to slide into the Russian River.

Flooding and Evacuations

Flooding prompted evacuations in some areas, particularly in Sonoma County. An evacuation order was issued for low-lying areas of the Russian River, affecting a 32-mile stretch from Healdsburg to the Pacific Ocean. Schools were closed due to flood concerns in these areas.

The storm has caused mudslides and urban flooding, leading to road closures in Marin County and extensive flooding in parts of Sonoma County. In Santa Rosa, evacuations were ordered at a medical facility and a nearby hotel due to flooded parking lots.

Fire Risk Reduction

The recent storm brought much-needed moisture to Southern California, helping mitigate the risk of fires in the region. However, vegetation remains dry, requiring several weeks to fully absorb the moisture. As of now, significant fire risk remains, with Santa Ana winds potentially returning by the weekend, complicating efforts to bring fire conditions under control.

Forecasters anticipate these winds could combine with dry conditions, leading to high fire weather danger. The region remains cautious, with officials expecting potential challenges if the Santa Ana winds bring dry air and increased fire risks.

Rainfall Deficit

Despite the recent rainfall, many communities still face a substantial deficit. Southern California has received less than 25% of its typical annual rainfall, with areas receiving even less than 10%. Downtown Los Angeles has received a mere seven-tenths of an inch, less than 10% of its expected rainfall for the season.

San Diego’s deficit is particularly alarming, with just 0.35 inches of rain since the water year began. This is the lowest start to the water year since recordkeeping began in 1850, representing just 7% of the average rainfall.

The big question remains whether February, typically the wettest month, will bring the relief needed to close the gap. Forecasters hope for additional precipitation but caution that dry conditions could return, especially with the jet stream moving away from the region.

Jet Stream and Forecast Models

The jet stream is expected to move over Washington and Oregon, then down to Nevada and Arizona, rather than over Southern California. This shift makes it less likely for southern parts of the state to receive significant precipitation in the near future.

Forecast models suggest a potential storm system could develop in the Pacific Ocean by mid-February, but it’s uncertain how much precipitation it will bring. Overall, forecasters aren’t optimistic about significant rainfall anytime soon.

Week’s Forecast Details

The first atmospheric river storm is expected to peak in Los Angeles and Ventura counties Tuesday night, affecting these