Blame It on Catalina

Typical “June gloom” weather enveloped Southern California on Monday, and forecasters said that only gradual improvement is expected throughout the week.

If you want to affix blame, lay some of it on the Catalina Eddy, the swirl of onshore winds so common at this time of year that pushes cool, moist marine air inland over the coastal valleys, blanketing the Los Angeles Basin with fog and low clouds.

In most Los Angeles-area communities, the sun never managed to burn through the overcast Monday, and forecasters said today will be just as dreary, with a chance of a few light sprinkles near the foothills.

The National Weather Service said the weather Wednesday through Saturday should be only slightly better--partly cloudy to mostly clear--which sounds pretty much like two different ways of saying the same thing: that summer, despite the calendar, is still a long way off.

“This sort of weather is not unexpected at this time of year,” said John Sherwin, a meteorologist with WeatherData Inc., which provides forecasts for The Times.

Sherwin explained that prevailing winds in June tend to parallel the coastline as they sweep down from the Gulf of Alaska. When the winds reach Point Conception in Santa Barbara County, the coastline turns abruptly to the east, and the winds swirl counterclockwise as they mimic the curve of the coast.

This swirl often swings inland after crossing over Santa Catalina Island--hence the name, Catalina Eddy. The air moving inland carries a bank of saturated marine air that is trapped by the mountains surrounding the Los Angeles Basin.

When the overcast is dense, as it was Monday and should be again today, the sun seldom burns through it, except for a few isolated patches near the coast.

But when the overcast is thinner, as it’s expected to be for the remainder of the week, the sun usually starts burning through by midday. Hence the promise of partly cloudy to mostly clear skies during the afternoons Wednesday through Saturday.

Sherwin said temperatures should rise slightly as the week progresses, with high readings in the upper 70s to lower 80s expected in the valleys by the end of the week.