Spring and early summer in Los Angeles, according to the National Oceanic and Atmospheric Administration, deliver an average of just 11 clear days in May and 14 in June. The definitions of "clear" and "cloudy" are subjective, but on even the partly cloudy days, the daylight hours are at least half obscured.

Just how gray depends on where you live. At LAX, June usually yields no more than nine perfectly clear days. In coastal cities from Malibu to Seal Beach, the gloom can linger all day, putting off the start of their summer until after the Fourth of July.

The gray season is made in the Pacific Ocean. Cold currents rise close to shore; a persistent high-pressure zone farther out channels warmer air eastward, and the springtime vortex called the Catalina Eddy fabricates fog from the interaction of cool water and warm air, pushing it on shore when the air of inland valleys rises in the heat of midday. Television weathercasters call the visible result "the marine layer," although what they're really taking about is fog.

It ambles over the beaches after midnight, flows in wide streams up the former bed of the Los Angeles River through the western half of the city and takes general possession of the basin under the same inversion layer that brews smog. On good days, the sun eventually burns down through half a mile of gray clouds and illuminates, at last, a city that seems to have been forgotten by sunlight and color.

It could be worse. Tourists before the mid-20th century often complained that a dull haze shrouded the charms of what had been advertised as a perpetually sunlit Mediterranean city. William Faulkner called the lighting effect a "treacherous unbrightness."

While the Catalina Eddy, an atmospheric vortex or eddy with a counter-clockwise rotation pattern, can occur in the California Bight (the open ocean bay formed by the bend in the coast between Point Conception to the north and San Diego to the south) at any time of the year, it is most often seen during May and June. It can develop when the winds from the northwest along the Southern California coast are stronger than normal and interact with the local coastal and land topography, turning inland and creating a vortex.

Only about 200 kilometers (120 miles) in diameter, the Catalina Eddy has not been well measured by scientists. The eddy is actually too small to appear in current weather forecast models and is sometimes too shallow to have a strong influence on the cloud structure viewed by weather satellites.

But the diffused light makes for nice light for taking pictures - Johnny's Coffee Shop, Fairfax at Wilshire, closed, but kept up for location shooting, when you need classic Google Architecture, as they call it.