Brief Storms, Bright Prospects Hearten Experts : Weather: El Nino warming trends and a spate of rain and snow across the West appear--at least on paper--to improve conditions for a wet winter.

Two stormy nights in a week do not a rainy season make, but some climate experts are wondering whether the trace amounts of rain that fell six days apart in Southern California and other changes in weather patterns signal an end to the region’s four-year chain of dry winters.

Despite continuing concern about the prospects for a fifth drought year in California, weather and water experts said that, at least on paper, there appear to be improved conditions for a wetter rainy season.

Among encouraging indications they cited were movement by a coastal high-pressure system toward the central Pacific Ocean, evidence that El Nino warming conditions are under way off the coast, and a spate of small storms across the West.

“The possibilities are there,” said Jerry McDuffie, deputy meteorologist in the National Weather Service’s Los Angeles bureau, “but they could disappear in a hurry. You never know in this business.”

Weather and water experts also cautioned that a failure to at least match average rainfall over the next three crucial wet-season months could lead to the driest year yet. An average snowfall of 52 inches a year in the Sierra Nevada is essential to provide water for the southern part of the state, but so far, precipitation is running more than 7 inches below average.

“We need something in the bucket we can really count on,” said Maurice Roos, the state’s chief hydrologist.

The two rainfalls in Southern California--dropping just 0.19 of an inch on downtown Los Angeles last Tuesday and early Monday--are at least a start, experts said. “They need to hang around a little longer,” McDuffie said. “It’s the two- to three-day storms that are the ones we want.”

One reason the storms blew through so quickly, meteorologists said, was the high-pressure system lingering in the upper atmosphere over the central Pacific. In recent dry winters, that system was closer to the California coast, acting as a shield and preventing moist air from pouring in at lower elevations.

But with the system now farther out in the Pacific, there are more chances for not only the sort of brief showers that fell on Southern California, but also for heavier rainstorms of the kind that caused flooding last weekend in Washington.

“We still don’t have an ideal situation for heavy rains, but it’s certainly improved,” said Mike Smith, a meteorologist for WeatherData Inc., which provides forecasts for The Times.

Smith and other experts also pointed to warming sea surface temperatures as a sign that El Nino conditions are starting again. El Ninos--Pacific Ocean temperature fluctuations near the Equator that are linked to changes in low-level atmospheric patterns--may set favorable conditions for more rainfall, meteorologists say.

Experts cautioned that El Ninos do not necessarily bring more rain. “We’ve had cases of heavy and light precipitation associated with El Nino conditions,” said Dan Cayan, a climate researcher with the Scripps Institution of Oceanography. “All we can say for sure is that if these conditions last, there are some changes in store.”

The early Monday rainfall brought no more than 0.02 of an inch to downtown Los Angeles, but was accompanied by cold temperatures and biting winds that hinted of winter weather to come. The overnight low was 54 downtown and the high Monday was 63.

Although high temperatures inland were expected to continue in the 60s today, with winds between 25 and 30 m.p.h., temperatures could reach into the 70s on the coast, said WeatherData forecaster Steve Burback. And by Wednesday, temperatures will begin a warming trend that will rise into the 80s by the weekend, he said.

There are no signs of more rain, Burback added.

The latest storm brought snow to parts of the Sierra and the local mountains. The National Weather Service reported that 1.75 inches of snow fell early Monday at Big Bear Lake.

To ward off the morning chill, Los Angeles residents donned coats and turtleneck sweaters and began using car heaters on their way to work. Heating fuel companies reported a sudden surge in business. Customers “are talking about what a sudden cold snap we’re having,” said Dale Gould, manager of Heating & Cooling Supply in Van Nuys. “People always wait till it gets cold to buy a furnace.”

In the San Fernando Valley, the city opened up a shelter for the homeless as part of an emergency foul-weather program. The Van Nuys Armory will house homeless adults for one night after predictions that the temperature in the Valley would dip to 40 degrees or below.

In the deserts, winds gusted to 60 m.p.h., uprooting dozens of trees, toppling Christmas decorations and power lines and whipping up thick sandstorms that caused several minor traffic accidents.

Hardest hit was eastern Riverside County, where a frigid wind caused scattered power outages in desert from Palm Springs to Blythe. There were no injuries or major damage reported, but work crews were busy throughout the day replacing fallen street signs and traffic signals.

Times staff writers Jenifer Warren and Tracy Wilkinson contributed to this story.