The so-called Ridiculously Resilient Ridge, also known as The Blob, once perched off the Northwest coast blocking all storms like a football team’s defensive line, has dissipated, said Bill Patzert, climatologist with NASA’s Jet Propulsion Laboratory in La Cañada Flintridge.
Many climatologists believed this was the main reason for the lack of rainfall in Southern California, making the past five years the driest in Southern California history as measured from downtown Los Angeles.
More recently, another high pressure system, this one living in the ocean in the Southwest, prevented storms from entering Southern California during the winter of 2015-16 by pushing storms up into Northern California and the Pacific Northwest. That, too is gone, he said, leaving a clear path for winter storms such as the ones hitting Southern California this month. The rain almost makes us forget about the drought — for a little while, he said.
“A lot of smiles here this week in terms of drought relief,” Patzert said. “It is a feel good week not only for my yard but for water managers as well.”
Third, gone is the La Niña, the system that brings cooler ocean waters and dry conditions following El Niño, the weather pattern that often allows storm after storm to reach the West and turns other parts of the globe into drought.
Last winter, El Niño did bring storms to Northern California, which showed about average rainfall and snow, a big improvement over the previous five years. But El Niño did almost nothing in Southern California, leaving it parched with only about 50 percent of the average rainfall.
Without these high pressure systems sitting off the coast like massive blockers, storms from both the south and the north finally are reaching Southern California, Patzert said.
“The absence of La Niña has opened up the West Coast for storms from all directions,” he said. “The door is really open.”
On Wednesday and Thursday, steady rain fell as a storm from the south reached Los Angeles. On Friday evening, a colder storm from the northern Pacific Ocean will bring more rain to the already soaked ground and slick roadways. The National Weather Service predicts a 100 percent chance late Friday night, with clearer skies well into next week.
For December so far, 4 inches of rain fell in downtown Los Angeles and 5 inches in the foothill regions, he said. That is twice the average amount of precipitation for Southern California in the month of December, which is still not over.
Compared to December 2015, when the Los Angeles station recorded 0.57 inches of rain, rainfall exactly one year later is five times that amount, he said.
With January, February and March historically the heaviest rainfall months, things are looking up, he said.
But Patzert, as do the state’s water managers, say the drought is not over in Southern California. The U.S. Drought Monitor in Lincoln, Neb., lists 59 percent of California in severe to exceptional drought conditions as of Tuesday. That’s down from 91 percent one year ago, the agency reported on Thursday.
“We are a long way from busting this drought. It would take not just a good wet winter here in California, but many years,” Patzert said.
The state Department of Water Resources on Wednesday raised the supply of water it will release from the State Water Project from 20 percent to 45 percent. DWR Director Mark Cowin said the December storms “dented” but “don’t end the drought.” He predicts more releases of state aqueduct water into Southern California, adding; “But the faucet can shut off suddenly and leave us dry for a sixth year in a row. Drought always looms over California so we must use water wisely and sparingly.”
The state’s 154 reservoirs held 18.5 million acre-feet of water as of Nov. 30, an improvement of 7.6 million acre-feet from one year ago, the DWR reported. Storage was 88 percent of the historic average for this time.