Michael Anderson, a climatologist with the California Department of Water Resources, noted that impacts from the upcoming storm system could escalate to a “worst-case scenario” if it “becomes an unrelenting series of storms.”
Forecasters are warning residents in the Sacramento region and the Bay Area to prepare today and Thursday for yet another assault, this time from a “bomb cyclone” spinning in the Pacific that will not make landfall but will amplify rain, wind and frigid temperatures along the coast and foothills.
Forecasters today are expecting more atmospheric rivers — the powerful streams of tropical moisture that deliver most of California’s winter rainfall.
“This will be a high-impact event, a pretty intense storm Wednesday night,” Swain said. “The stage is set for something potentially big to happen if the model trends toward the higher end.
“There will be some flooding, it’s a question of how much.”
‘We like rain in California, but we love snow’
In the mountains that supply these reservoirs, snow levels are now above average. The Department of Water Resources’ first snow survey of the season took place on Tuesday at Phillips Station, in the Sierra Nevada, west of Lake Tahoe. Scientists measured 55.5 inches of snow and a snow water equivalent of 17.5 inches. That’s 177% of average for this location. Statewide, snowpack levels are at 174% of average for that date.
Statewide, this is the best start to the snow season in 40 years, according to Department of Water Resources officials.
It would be hasty, though, to assume the ongoing storms and wet forecast mark an end to the prolonged drought. In 2021, record rains and heavy snowfall arrived between October and December. Then, California experienced its driest January-through-March — typically the state’s wettest months — in recorded history.
Experts say consecutive storms are made more dangerous by an already-soaked landscape’s inability to absorb more water. In addition to creating swollen creeks and mudslides, incessant rain reduces soils’ ability to hold vegetation, and California’s millions of drought-ravaged trees can easily fall over. Areas with wildfire burn scars are at risk of flash flooding, officials said.
“The big wild card will be what happens next week,” Swain said. “There’s a wide range of uncertainty. If one or two of those events occur next week, then all bets are off.”
Although rain has fallen on Southern California, it has largely been spared. The worst of the coming storm will mostly stop at the northern edge of Los Angeles County, Swain said.
Jane Dolan, President of the Central Valley Flood Protection Board, advised residents throughout the Central Valley to stay on guard and take warnings and advisories to heart. “If you’re at an elevation below 200 feet, near a levee that’s older than you, pay attention to alerts,” she said.
The state has established emergency shelters in Sacramento and San Mateo Counties and has stockpiled 3.7 million sandbags.
Some experts think the flooding from the incoming storms could be tempered by the fact that the developing system is relatively cold. This will translate into more snow and less rain, at least at high elevations.
Last weekend’s storm was relatively warm and produced rainfall at high elevations, where the liquid water fell on several feet of snow, melting it and magnifying the runoff into streams and rivers.
But today’s storm is colder. That means more precipitation will probably fall as snow.
“We like rain in California, but we love snow,” said John Abatzoglou, a UC Merced professor of climatology. He said that over the weekend, rain fell at elevations of 8,000 feet or more and may have worsened lowland flooding.
Anderson said today’s storm will probably produce rainfall no higher than 5,000 to 6,000 feet and snowfall above that, minimizing rain-on-snow flooding impacts.
“This will be a good mix of both heavy rain at the lower elevations, snowfall at the higher elevations,” he said.
‘Need to act with renewed urgency’
Climate modeling suggests that global warming is likely to make storms larger, stronger and more intense. It will also cause more precipitation to fall in liquid form. This translates into worsening floods just as the Central Valley’s system of levees, weirs and bypasses ages past its prime.
The flood board updated Central Valley Flood Protection Plan, released last month, warns of “1,000-year storm events … and the need to act with renewed urgency and purpose before the next large flood event occurs in the Central Valley.”
The plan calls on nature-based solutions, like restored floodplains, and infrastructural improvements, like fortified levees near urban areas, to help reduce the impacts of higher-energy storm systems expected as a result of the warming climate.
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