Series of Storms Begins Moving Into Southland : Weather: The first rainfall in a month signals a shift in conditions, experts say. The wet pattern is expected to persist for at least 10 days.

A vigorous Pacific storm moved in over Southern California on Wednesday, bringing with it the promise of up to two inches of rain by tonight and more wet weather in the days to come.

The rain that began falling in the Los Angeles area Wednesday afternoon was the first measurable precipitation in almost a month, during what normally is the wettest time of the year.

But forecasters said rain expected over the next 10 days should raise the season’s total--which was more than three inches below normal as of 3 p.m. Wednesday--to well above normal by the end of next week.

“A wet-weather pattern will continue to bring storms into Southern California for some time,” Steve Burback, a meteorologist with WeatherData Inc., said late Wednesday. “It doesn’t look like any (protracted) drying periods in between, at this point.”

Burback said the storms beginning to move through the area have all been born in the mid-Pacific, several hundred miles north of Hawaii, rather than in the Gulf of Alaska, where most of California’s winter storms originate.

Borne eastward by winds from the southern branch of the high-altitude jet stream, these relatively warm storms reach California considerably south of the normal storm track.

The result should be more rain in Southern California and less snow in the Sierra. Because the Sierra snowpack is the principal source of water for California during the summer, these storms are not expected to have a major effect on the state’s prolonged drought.

Burback said the rain from the first storm should continue to fall through tonight, giving way to scattered showers on Friday. Rainfall from the storm should total one to two inches in most areas, with the heaviest precipitation in the foothills of Orange and San Diego counties. Because the storm is warm, snow is not expected below 6,000 feet.

Skies should be partly cloudy Saturday. By Sunday afternoon, a second storm is expected to arrive.

“That one looks a little stronger,” Burback said. “There could be another two to three inches of rain by late Monday or early Tuesday.”

The meteorologist said it is too early to predict the weather after that with any precision, but he said a third storm, beginning to form north of Hawaii, promises to bring additional rain by the end of next week.

“As long as the jet stream holds where it is, this weather pattern should continue,” Burback said.

High temperatures in the Los Angeles area today and Friday should be in the mid-60s, following overnight lows in the upper 40s to lower 50s. Clearing skies should bring highs in the low 70s on Saturday, but top readings are expected to drop back into the 60s on Sunday and Monday.

WeatherData is a Wichita-based service that provides forecasts for The Times.