Lack of Rain, High Winds Are Blamed on La Nina

If you’re beginning to think that the song is right--that “it never rains in Southern California”--you’re not far wrong this winter.

Los Angeles has had only 0.84 of an inch of rain since July. Although not a record for the period--that was set in 1962, with 0.12 of an inch--it’s less than a sixth of the average of 5.32 inches.

It’s also among the nine lowest rainfall totals for July through December since record-keeping began in 1877. And there’s no rain in sight for the next week or more.

On top of that, it’s been windier than usual, with gale-force gusts Thursday that toppled big rigs on California 60 near Pedley, tore the roof from a mobile home in Rialto and blew in the picture window of a house in Fontana. The winds caused the relative humidity to plummet, making life miserable for people with allergies and dry skin.

Meteorologists say you can probably pin the blame on La Nina, an enduring oceanic and meteorological counterpoint to the drenching El Nino season of 1997-1998. During El Ninos, it’s usually wetter than normal in Southern California; during La Ninas, it’s usually drier, with an extra serving of powerful Santa Ana winds.

The current La Nina is well into its second year. During the entire 1998-1999 season (July 1 through June 30), only 9.09 inches of rain fell on the downtown/USC reporting station. That compares with a normal season total of 15.09 inches and with the 31.01 inches that fell during the 1997-98 El Nino.

And the meteorologists say that it probably will remain drier and windier than normal well into the spring.

The National Oceanic and Atmospheric Administration said in its latest advisory that La Nina “is likely to continue for the next several months,” normally three of the rainiest in Southern California.

“La Nina still looks pretty strong,” said Guy Pearson, a meteorologist with WeatherData Inc., which provides forecasts for The Times. “The weather pattern looks pretty much the same for the next few weeks, with not much of a chance of rain in Southern California.”

During La Ninas, large, high-pressure weather systems tend to park off the coast of Central California and over northern Utah, as they were Thursday. Winds circulating clockwise around these systems dry out by compression as they funnel down Southern California’ coastal canyons, further parching already dehydrated hillsides and adding to the danger of unseasonable brush fires.

Thursday’s winds peaked at about 50 mph in the San Fernando Valley, fanning four small brush fires in the Porter Ranch area that firefighters were able to quench quickly. Farther east and south, the winds were stronger, with one gust measured at 93 mph at Fremont Canyon in the Santa Ana Mountains.

Gusts above 60 mph raked the Inland Empire, felling trees and stirring up immense clouds of dust. Driving became so hazardous that the California Highway Patrol temporarily closed a 9-mile stretch of California 60 west of Beaumont and 15 miles of Interstate 15 below the Cajon Pass.

Despite the likelihood of at least two drier than normal years in a row, the Southland still is a long way from a widespread drought, according to officials at the state Department of Water Resources.

As during most La Ninas, rainfall at the northern end of the state has continued to be near or above normal, and the state’s reservoirs now stand at about 115% of normal.

Forecasters say that the current dry spell in Southern California is part of a recurrent cycle of weather patterns often influenced by the irregular emergence of El Nino and La Nina phenomena.

Nicholas Graham, a meteorologist with the International Research Center for Climate Predictions at the Scripps Institution of Oceanography in La Jolla, explained that the Pacific Ocean is essentially one vast basin, “with the water sort of sloshing back and forth.”

He said that under normal conditions, low-level equatorial trade winds blow from east to west, shoving water ahead of them that tends to pile up near Indonesia, raising the sea level there a foot higher than it is off the coast of Peru.

During El Nino, the trade winds slacken or even reverse, and the water sloshes back toward South America. This sloshing surface water presses down on cooler water beneath it that normally wells to the surface off Peru.

As a result, Graham said, the surface water there stays warmer than normal and starts ebbing west across the Pacific. This vast pool of warmer than normal surface water interacts with the atmosphere above it, increasing the storms generated over the central Pacific and amplifying the storm track that funnels precipitation into Southern California.

But El Nino also sows the seeds of its own destruction, setting up ocean and wind currents that ultimately reverse the phenomenon, Graham said. Sometimes, the reversal goes beyond normal, and the surface water off the west coast of Peru becomes abnormally cool. That’s what’s happening now, and it’s called La Nina.

During La Nina, the pool of cooler than normal surface water interacts with the atmosphere, again disrupting normal weather patterns. A large ridge of high pressure frequently remains anchored over the northern Pacific during the winter, diverting the storm track well north of Southern California.

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A Dry Stretch

The rainfall total in the last six months of 1999 was among the lowest on record. The driest last six months of a year was in 1962, when 0.12 inches fell. Following are rainfall totals for July-December in downtown Los Angeles:

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Source: National Weather Service