© Al Seib / Los Angeles Times
A rainstorm is expected to hit Southern California by Friday. A flash flood watch was issued for burn areas in Los Angeles and Ventura counties.
A powerful new storm is expected to arrive in Southern California on Friday, and it could provide a walloping, with possible flash flooding, mudslides and rock slides.

"The Friday storm in particular could in fact become the strongest of the season in the Los Angeles region," said UCLA climate scientist Daniel Swain.

A slow-moving storm is expected to debut in the Southland with some light rain Thursday night or Friday morning, but is expected to dump large amounts of rain in a short time frame during its peak Friday afternoon and evening, said Ryan Kittell, a forecaster with the National Weather Service in Oxnard.

Rainfall totals for the Los Angeles metropolitan area are predicted to be between 2 to 4 inches, with 6 to 8 inches expected in the mountains and foothills, he said.

"The raw numbers don't look that scary, but if we get the bulk of that coming over a small period, that will cause a lot of issues," Kittell said. Much of that rain could fall within a 12-hour period Friday, and it could fall at a rate of more than an inch per hour, he said.

There is a high likelihood, Kittell said, for a "lot of roadway flooding," as well as falling trees because the storm also is expected to usher in powerful winds.