Just in Time for Holiday: Summer

It isn’t just your imagination. It really has been cooler than usual. But that’s about to change.

Temperatures in Los Angeles will begin to climb today after an unusually cool and smog-free August, meteorologists said Tuesday.

The average high temperature downtown last month was about 80 degrees -- about 3 degrees lower than normal -- but today’s high could be closer to 90, with top readings near 105 in the San Fernando and San Gabriel valleys, the National Weather Service said.

William Patzert, an oceanographer and meteorologist at the Jet Propulsion Laboratory in Pasadena, said the rising temperatures, which should last through Labor Day, will be largely a result of a large ridge of high pressure building over Southern California, blocking the onshore flow of cool air from the ocean.

That high pressure wasn’t around much last month.

“What we had,” Patzert said, “was June gloom in August.”

The highest temperature in downtown Los Angeles last month was 88 degrees, compared with the record for the month of 106, set Aug. 19, 1885.

It has been cooler in Orange County too, with temperatures along the coast a couple of degrees lower than usual.

“That’s just the way it goes. These things happen sometimes,” said Don Whitlow, a meteorologist with the National Weather Service.

Patzert said the cooler weather along the coast was caused, in part, by hotter than normal weather in the deserts.

He said the ocean water between the Hawaiian Islands and Southern California was cooler than usual for much of the summer, keeping the air over the water cool too. At the same time, temperatures in the deserts routinely topped 100.

Cool air is denser than hot air, so air tends to flow from cooler areas toward warmer areas. With a temperature differential often approaching 40 degrees during August, the onshore flow of cool, damp air was especially persistent.