Rare Rain Helps Keep Area Unseasonably Cool

For the second time this month, rain .

A 4,000-foot thick marine cloud layer, caused in part by ocean temperatures five degrees below normal, brought about the uncommon occurrence Friday. By late morning, .05 inch of drizzle had fallen at Los Angeles International Airport, the National Weather Service said.

Early morning rain snarled highways and was blamed for dozens of traffic accidents as temperatures remained uncharacteristically cool for early summer.

Friday’s high of 71 degrees was the coolest maximum for July 19 since record-keeping began in 1877, said Marty McKewon, a meteorologist with Weather Data Inc., which provides forecasts for The Times. The previous record of 72 degrees was set in 1990.

Daily maximum temperatures this year have averaged nearly three degrees lower than July’s average maximum of 82 degrees, weather service officials said.

Climate researchers said lower ocean temperatures have been brought about by continuing cloudiness and by wind conditions that blow cool water from the north.

“The cooler water brings about the marine layer, and the sun doesn’t get a chance to warm up the water,” said Daniel Cayan, a researcher at Scripps Institution of Oceanography in La Jolla. “It’s self-perpetuating--less solar heat reaches the water, the cooler the ocean, the more cloudy it is . . . the more rain you get.”

Low clouds and fog were expected to continue into this morning along the Southern California coast, the National Weather Service said.

The combination of moist air and low temperatures was expected to reduce fire danger, said Los Angeles City Fire Capt. Stephen Ruda. But, for firefighters, the rain was not an entirely welcome sight.

“Your brush fire potential is a great deal less,” Ruda said, “but whenever we have the change in weather, traffic calls increase as freeway accidents go way up.”

Since the second week of July, the department has cut service in 13 of the city’s 105 fire stations, on a nine-week rotating schedule, Ruda said. The department “brownout” has raised the number of calls that on-duty firefighters must respond to, he added.

“Now, any increase in calls puts a strain on the department,” the captain said.

The California Highway Patrol reported more than 30 traffic accidents on Los Angeles freeways from just before dawn through the late morning, when the sprinkles stopped. The figure represented three times the number of accidents during the same period on an average weekday, CHP officials said.

Rainfall in California was first predicted by a handful of scientists who said it would be triggered by the eruption of Mt. Pinatubo in the Philippines.

On Friday, however, scientists uniformly dismissed speculation that the rain resulted from climatic changes brought about by the eruption.

“March was unusual, also, in terms of rain, but nobody was pointing to a volcano then because there wasn’t one,” said Nicholas Graham, a climate researcher at Scripps.

Some said they believed the volcanic activity would affect Southern California’s weather, but not until winter.