Curious about why San Diego’s coastline has been lost in the fog lately?

You may look out the window early Wednesday and think, “The fog has swallowed my car. Again.”

San Diego has resembled London lately, shrouded in some areas by countless droplets of moisture, each thinner than a human hair. Collectively, they can briefly blind you.

The gray veil, as some describe it, will be here through Friday due to a phenomenon that’s occurring 1,500 miles southwest of San Diego.

A massive high-pressure system has spread across the ocean, trapping cool water vapor at the surface, below much warmer air above. The trapped moisture turns into droplets that form fog of varying density.

Coastal temperatures were in the 50s early Tuesday, more than 20 degrees cooler than they were 1,000 feet in the sky. The resulting fog was as thick as pea soup in some parts of the city, barely visible in others. In most places, it could be felt on exposed skin. Similar weather was rolling ashore early Tuesday night.

It’s a fleeting thing in which people are struck by the beauty and eeriness of fog, which rarely lasts long in Southern California. Far to the north, at Point Reyes, the fog is persistent, occurring about 200 days a year. And it’s much, much thicker.

“The fog here isn’t unusual for December,” said Adam Roser, a forecaster at the National Weather Service. “Now’s usually the time.”

Change may be coming.

A few days ago, forecasters determined that a major storm is likely to hit Northern California on Christmas ...