Look for a slightly milder winter later this year, top weather forecasters say.

A rapid switch from El Nino to its nicer little sister, La Nina, means Utahns may enjoy a somewhat warmer, drier, less smoggy winter than usual, while the mountains may receive more snow."This is all likelihood" and not by any means certain, climatologist Vernon Kousky added quickly. A research scientist at the National Weather Service's Climate Prediction Center in Washington, D.C., Kousky briefed reporters and government officials Thursday about the climatic switch.

The El Nino weather system that blasted much of the United States with violent storms for the past year has died out, giving way to the La Nina that often accompanies it. The change was swift, taking place over about three weeks in late May and early June, during which the surface temperature of the central Pacific went from 5 degrees above normal to 5 degrees below the usual.

"These La Nina conditions have continued to evolve and the Climate Prediction Center is now forecasting moderate La Nina conditions during the fall of this year and continuing through the winter months," he said in a written statement.

During a meeting with reporters at the Federal Building, 125 S. State, Kousky elaborated on the theme, saying the La Nina conditions could persist for a year to 15 months.

He qualified his comments by saying northern Utah is one of those areas where it's particularly hard to call La Nina's effects. But if the winter is milder, it will be because the southern jet stream will not pack as much wallop, because the Pacific is cooler and won't pump as much moisture into storm systems.

Also, a northern jet stream often establishes itself during episodes of La Nina, meaning storms sweep in from the northwest. In that region, the air is colder, so it can't pick up as much moisture as would happen with tropical storm systems sweeping directly in from the west.

Southern Utah is likely to be warmer and drier than usual. However, this La Nina has been shaping up as a moderate one, so none of these changes should be a pronounced difference from normal weather in Utah.

Another difference may be that winds will be stronger, which could help to clear away heavy fog and smog, giving the state clearer air, according to William J. Alder, meteorologist in charge of the National Weather Service regional forecast center on North Temple.

Alder said a study of previous La Nina years showed that Utah's high elevations tend to get more snow than usual. "Basically, the mountains look in pretty good shape for this year . . . and I think it could start fairly early," with some ski resorts able to open by Thanksgiving.

Also, during La Ninas, northern Utah's valleys have less snow. Fewer snowstorms are expected, and they should be milder than usual because they don't have all that tropical moisture. But there can be stunning exceptions.

"That doesn't mean you might not get a heavy snowfall in Salt Lake City and get 2 feet of snow," Kousky said.

La Nina also may be welcome to fishermen along the Pacific coast of South America, as it brings an up-welling of colder water, with more abundant game fish. It can benefit Indonesia, where burning forests blanketed the region with smoke, because that country and the Philippines can expect more rainfall.