California is bracing itself for another powerful storm that is set to hit on Monday night, following the effects of a similar storm that caused flooding and forced thousands of residents to evacuate last week. The National Weather Service in Los Angeles has dubbed the upcoming storm a “significant atmospheric river event”, and are predicting widespread and heavy rainfall that is likely to exacerbate the situation created by previous storms. The state is currently experiencing one of its most ferocious winters on record, after a historically long stretch of drought. Total snowpack and rainfall levels in many areas have reached levels not seen in decades, with months of precipitation having soaked hillsides and filled creeks and rivers. This means that each new storm that arrives creates a compounding situation that is likely to make things worse.
The incoming atmospheric river is expected to arrive first in Northern California late on Monday, before spreading into Southern California early on Tuesday. It is set to bring another two to five inches of rain along the coast and in valleys, and up to 8 inches in the mountains. At elevations above 6,500 to 8,000 feet, the Sierra Nevada could receive another foot of snow or more, increasing the risk of roof collapses and roof avalanches when large sheets of frozen snow and ice slide off buildings.
Last week’s storms caused widespread damage in some areas, with the small farm community of Pajaro remaining flooded after a levee broke along the Pajaro River, between Santa Cruz and Monterey counties. The incoming atmospheric river is likely to have even more severe impacts, according to forecasters with the Bay Area office of the National Weather Service, who wrote on Monday: “Given antecedent conditions, expect impacts from this A.R. to eclipse and exceed the previous one, with potentially large-scale and long-lasting flooding impacts.”
The Los Angeles region has already received at least twice the average amount of rainfall for this point in the year, according to Mike Wofford, a senior meteorologist for the National Weather Service office in Los Angeles. This means that anything that falls from the sky now is less likely than usual to soak into the ground, and will instead run off, increasing the risk of flash floods. This water and snowmelt will then flow into creeks and rivers that are already rising, further increasing the risk of flooding.
Patrick Ayd, a meteorologist with the National Weather Service in the Bay Area, compared the ground to a kitchen sponge that is completely full of water. It cannot absorb any more moisture, so any additional water will just run off. Waterways such as the Salinas River in the Central Coast region, which have had a little time to recede since the last storm, are expected to begin rising again on Monday as the rain starts falling. Residents who experienced flooding during last week’s atmospheric river, such as those in the Santa Cruz Mountains or in Monterey County, should expect to be flooded again, Mr. Ayd said.
Mountainous regions of the state are especially at risk, with hundreds of creeks primed to rise quickly. Santa Barbara County looks to be one of the areas that could see significant disruptions, with U.S. Highway 101, the main north-south route through the area, likely to be susceptible to closures due to creeks that may spill over their banks and onto the road.
Another compounding factor, especially along the Central Coast and in the Bay Area, is that thunderstorms and heavy winds are expected. Wind gusts could exceed 55 to 70 miles an hour along the immediate coastline and at elevations above 1,000 feet in the hills. The winds will spread into the Sierra Nevada, where there could be gusts over 100 miles an hour at mountaintops. “Be prepared for the likelihood of downed trees for tonight into Tuesday.