Cooler weather and high winds moved into Southern California today in advance of a storm that could bring snow to the mountains and the first rain to Los Angeles in about 150 days.

Meteorologists said the unstable weather system coming from British Columbia was the Southland's first winter storm, arriving months ahead of schedule and sending temperatures eight to 15 degrees below normal.

In downtown Los Angeles, where the average high during the month of September is 83 degrees, the temperature was 71 at 2 p.m., the National Weather Service said.

A wind advisory was issued today for the Antelope Valley, where gusts of up to 50 miles per hour were expected to kick up dust and sand and reduce visibility through the evening.

"The storm is pretty unusual. It's pretty much our first winter storm of the season and it's barely fall," said weather service meteorologist Edan Lindaman. "Typically, we don't see storms like this until into early April."

Fall begins Friday.

The storm, which is over Oregon and slowly moving south, will stop over the central coast for 12 to 18 hours before it continues toward Southern California.

Lindaman said the front was preceded by a deep marine layer that could create widespread drizzle late tonight and Thursday.

She said Friday would be the most active day of the storm in Los Angeles and Santa Barbara counties, when showers are expected to produce one-half to 1 inch of rain.

The last measurable rain was April 22, Lindaman said.