Dry winter forecast? Storm has other ideas

Though gathering La Nina conditions should foreshadow a dry winter in Southern California, the forecast was belied by rainstorms that swept the Los Angeles region Sunday, flooding streets and sending motorists sliding and colliding on muddy and rain-slicked roads.

By midday, parts of Los Angeles County had accumulated between half an inch and 1.5 inches of rain, and the showers continued. Streets flooded in Hancock Park, the northbound 405 Freeway near Mulholland Drive was covered in mud, and California Highway Patrol officers were busy chasing fender-benders throughout the day.

In one case, a big rig slid off the 118 Freeway in Pacoima and crashed onto the surface streets below, hitting a power pole and overturning.

La Nina, a climate phenomenon caused by cooler-than-normal surface temperatures in the Pacific Ocean, typically causes a colder and drier winter in the Southland.

But that turned out not to be the case last winter. Last season also had some La Nina conditions, but the rain came down fast and hard, albeit inconsistently.

“Here in Southern California, after two weeks in December, my forecast was already busted,” said William Patzert, an oceanographer and climate forecaster at the Jet Propulsion Laboratory in La Canada Flintridge. “Last winter is an example of where the statistics led us astray.”

And this year the Los Angeles area is ahead of schedule. In a normal year, downtown Los Angeles would have received 1.56 inches of rainfall since July 1. This year, the total was up to 2.21 inches as of midday Sunday.

The forecast of a dry winter is also doing little to lower the blood pressure of foothill residents whose homes remain vulnerable to mudslides brought about by the devastating 2009 Station fire. A flood advisory issued Sunday included the Station fire area.

Pat Anderson’s home atop Ocean View Boulevard in La Canada Flintridge was heavily damaged in February 2010 when the Mullally Debris Basin above her property overflowed, sending fast-moving debris and mud through her Paradise Valley neighborhood. Anderson said that with her house still being rebuilt, she has a lot riding on this season’s weather.

“Until my home is finished, even one heavy rainfall could cause heavy damage to my house,” Anderson said.

“So, do I get nervous when I hear there’s going to be a significant amount of rain? Yes, I do.”

Anderson, president and chief executive of the La Canada Flintridge Chamber of Commerce, said she will be watching the forecasts closely.

“I trust my sources, which are the Fire Department and the Sheriff’s Department,” she said, “but I just have to hope for the best, which is not a good position to be in.”

Chris Stone of the L.A. County Flood Control District said the county will not be altering its preparations for the rainy season based on the La Nina forecast. Stone said the county has made sure that the debris basins serving the area are at least 95% clear, and that channels and catch basins are clear and ready to receive any excess rainfall.

Stone said the county is expecting this year’s rainy season will be similar to 2010-11.

“The weather patterns so far are very similar to what we had last year,” Stone said. “We expect short to longer periods of dry between the wet patterns.”

Stone said the areas damaged in the Station fire are not expected to be fully recovered for another three years.

“We’re only two years of recovery after the Station fire, so there’s still a very high potential for debris flows coming off the burned watersheds,” Stone said. “There’s been lots of good growth, but there’s still lots of challenges remaining for this and next winter with debris flows.”

Still, JPL’s Patzert said residents should be fine.

“Odds are cool and dry,” Patzert said. “So far we’ve had some nice rain here, but nothing that heavy and nothing threatening the hillsides.”

In fact, Patzert said he’s hoping for more rain.

“I’d love to see a lot of rain,” he said. “It suppresses the fire season, and aside from some bad driving habits on the freeway by Southern Californians, in all other ways it’s a benefit for us.”

daniel.siegal@latimes.com

abby.sewell@latimes.com