Coastal Marine Layer Brings Cool Fall Days

With the start of fall Sunday, San Fernando Valley residents can expect plenty of fog and clouds this week as a coastal marine layer half a mile thick and reaching 50 miles inland has settled over the region.

“This is not uncommon in September,” said Gary Ryan, a spokesman for the National Weather Service in Oxnard. “Actually, September tends to be rather foggy. It’s one of the foggiest months.”

Temperatures are expected to be a bit cooler than usual throughout the week as the fog and clouds continue.

Even desert areas are going to be slightly cooler this week, reaching high temperatures of around 100 degrees, Ryan said.

The fog typically burns off later in the day.

The pattern of fog and clouds can last into mid-October, when the warm dry Santa Ana winds begin, Ryan said.

The coastal marine layer of cool, moist ocean air is about 2,000 to 3,000 feet deep. That’s enough to cross the coastal mountains into the Valley.

High temperatures across the Valley on Monday will be from the mid-70s to mid-80s, with the normal high temperatures for this time of year in the upper 80s.

Fall officially began at 11 a.m. Sunday.