Surprise Rain May Be Followed by More

The first autumn storm of the 1992-93 rainfall season scattered sprinkles across much of Southern California on Wednesday, and forecasters said there could be substantial rain and thundershowers by the weekend.

It didn’t rain very hard Wednesday, with only .01 of an inch recorded at the Los Angeles Civic Center by mid-afternoon, but that was enough to make streets slick and trigger a rash of relatively minor traffic accidents that contributed to the evening’s rush-hour congestion.

Forecasters hadn’t seen it coming.

WeatherData Inc., which provides meteorological information for The Times, had called for “mostly sunny” weather on Wednesday after morning low clouds and fog. The National Weather Service had predicted about the same, calling for “hazy sunshine” after a morning overcast.

The meteorologists had been well aware of a long, unstable cold front reaching from the Pacific Coast near San Francisco to the plains of Central Canada that was advancing slowly toward Southern California. And they knew that the eastbound winds of the high-altitude jet stream were heading toward the Southland from the northern Pacific.

“The surprise was that the branch of the jet stream became more vigorous, fed into the frontal system and formed its own little storm system that hit Southern California,” said Rick Dittmann, a WeatherData meteorologist. “We hadn’t expected any rain south of San Francisco.”

Dittmann said that although the cold front should move out to the east this morning, skies will remain partly cloudy here today and Friday.

By Saturday, he said, another storm system should settle in off the coast, bringing a good chance of showers and thunderstorms in Southern California throughout the weekend.

Wednesday’s sprinkles were not the first precipitation of the official rainfall season, which began July 1. A total of .08 of an inch fell in Los Angeles during the first weeks of July when the dying remnants of Hurricane Darby spun out a vast arc of moist air that enveloped the Southland.

The .01 inch that fell at the Civic Center on Wednesday raised the season’s total there to .09 of an inch. Officials said .36 of an inch fell Wednesday in Redondo Beach, .30 in Torrance, .15 in Montebello, .10 in Woodland Hills and .05 in Pasadena.

Rain in October is not extraordinary. Several inches of rain frequently have fallen here by the end of the month. The normal season’s total for Oct. 21 at the Los Angeles Civic Center is .40 of an inch.

The high temperature at the Civic Center on Wednesday was a relatively cool 71 degrees--seven degrees before the normal for the date and 29 below the 100-degree record for Oct. 21, set in 1929.