After all the talk, El Nino storms have finally lined up over the Pacific and started soaking drought-parched California with rain expected to last for most of the next two weeks, forecasters said Monday.

As much as 15 inches of rain could fall in the next 16 days in Northern California, with about 2 feet of snow expected in the highest points of the Sierra Nevada, said Johnny Powell, a forecaster with the National Weather Service.

To the south, persistent wet conditions could put some Los Angeles County communities at risk of flash-flooding along with mud and debris flows, especially in wildfire burn areas.

The brewing El Nino system — a warming in the Pacific Ocean that alters weather worldwide — is expected to impact California and the rest of the nation in the coming weeks and months.

Its effects on California's drought are difficult to predict, but Jet Propulsion Laboratory climatologist Bill Patzert said it should bring at least some relief.

Doug Carlson, spokesman for the California Department of Water Resources, pointed out that four years of drought have left California with a water deficit that is too large for one El Nino year to totally overcome.

Come April 1 — when the snowpack is typically at its deepest — water managers will be better able to gauge the situation.

"Mother Nature has a way of surprising or disappointing us," Carlson said.

The record drought in California has forced Gov. Jerry Brown to order cities to conserve water by 25 percent compared to the same period in 2013.

El Ninos in the early 1980s and late 1990s brought about twice as much rain as normal, Patzert said. The weather also caused mudslides, flooding and high surf.

In recent weeks, a weather pattern partly linked with El Nino has turned winter upside-down across the nation, bringing spring-like warmth to the Northeast, a risk of tornadoes in the South, and so much snow across the West that even ski slopes have been overwhelmed.

Big parts of the country are basking in above-average temperatures, especially east of the Mississippi River and across the Northern Plains.

In Los Angeles County foothills beneath wildfire burn areas, residents braced Monday for possible flash flooding and debris flows. Workers in Azusa cleared storm drains and handed out sandbags, while in nearby Glendora, police announced restricted parking measures for steep roadways under barren hillsides.

Residents of the Silverado Canyon burn area in Orange County and the Solimar burn area in Ventura County have been told they may want to evacuate in advance of the storm, but have not been ordered to do so.

Los Angeles Mayor Eric Garcetti warned people to clear gutters and anything in their yard that might clog storm drains; assemble an emergency kit; and stockpile sandbags if their home is susceptible to flooding.

An effort also was underway to provide shelter for homeless people.

"We want as little damage and destruction and as little death as possible," Garcetti said.

Between 2 and 3.5 inches of rain is predicted to fall across the coastal and valley areas of Southern California through Friday, with up to 5 inches falling in the mountains.

The first wave of rain started in Northern California with light showers Sunday and was expected to pick up strength and cover a large area of the region, the weather service said.

"This series of storms are definitely associated with the El Niño phenomenon in that the jet stream has taken a fairly significant southward trajectory in the Pacific on its return flow back into the California coastline," said Bob Benjamin, a forecaster with the weather service.

Forecasters say a second, stronger storm is expected to arrive in Northern California late Monday. At least two more storms are expected to follow on Wednesday and Thursday, possibly bringing as much as 3 inches of rain.

"Friday looks like a dry, clear day but more rain is expected Saturday," Powell said.

In Arizona, El Nino conditions will help push a parade of Pacific Ocean storms inland with light to moderate snow falling in the high country and rain in lower elevations, forecasters said Monday.

The National Weather Service says a series of weather systems will drop snow in the high country and rain in lower elevations as the week progresses.

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Associated Press writers Christopher Weber in Los Angeles and Paul Davenport in Phoenix contributed to this report.