LAS VEGAS — The National Weather Service issued a major fire watch for Southern California, and forecasters were preparing to declare a major drought in parts of the state.

The weather service said there was a high probability of high winds and rain from Thursday through Saturday, and there was the possibility of flash flooding from Sunday through Wednesday.

It said the most extreme conditions were possible in the San Joaquin Valley and coastal areas of the Central Valley and Los Angeles County, but it was not immediately clear whether the extreme weather would affect any specific areas.

The weather service issued a warning for the Sacramento area, including the northern half of the city and a large swath of the central region.

A weather warning for San Diego and San Diego County, as well as the city of Los Angeles, was issued for Thursday, the National Weather System’s website said.

There is a high risk of flooding in the area, but the water will recede and the risk will lessen, the weather service warned.

High winds and heavy rain will likely cause power outages and widespread power outage warnings, the agency said.

The threat of a fire in Los Angeles is similar to the threat from wildfires in southern California, said Jeff Schlosser, a meteorologist at the National Center for Atmospheric Research.

The fires in Southern California are very different in the intensity and duration, he said.