Weekend Could Bring Unusual Visitor--Rain

Forecasters say it could rain a little Saturday and Sunday. Ordinarily, that might hardly be worth mentioning, but in this dry La Nina winter, it’s news.

“There won’t be anything extreme, but at least there should be something,” said Guy Pearson, a meteorologist with WeatherData Inc., which provides forecasts for The Times.

He said light rain should start falling Saturday afternoon, ending before dawn Sunday.

“It looks like a total of about a quarter-inch of rain in the Los Angeles Basin, with maybe a little more in the hills,” Pearson said. “Things should cool off a little Saturday night, so there could be some snow down to about 4,000 or 5,000 feet in the mountains.”

He said skies should clear by Sunday afternoon, with mostly sunny weather expected during the first part of next week.

Meteorologists say the current La Nina oceanographic and meteorological phenomenon is the widely anticipated counterpoint in Southern California to last winter’s drenching El Nino. The disparate meteorological patterns of the two phenomena are generated by fluctuating ocean surface temperatures in the equatorial Pacific.

During typical El Nino winters--like last year’s--high-altitude Pacific jet stream winds extend all the way across the ocean to California and northwest Mexico. Large low-pressure systems over the central Pacific spin off an unusual number of storms, and the amplified storm track funnels more precipitation than normal into the Los Angeles area.

During typical La Nina winters--like this one--a large ridge of high pressure tends to remain anchored over the northern Pacific, diverting the jet stream and its accompanying storms well north of Southern California. Total rainfall so far this meteorological season--which runs from July 1 through June 30--is just 4.28 inches, compared to a normal total on this date of 11.31 inches and 22.83 inches at this time last year.