Fog’s Little Cats’ Feet Have Smoggy Boots

The fog may have crept in on little cats’ feet Thursday morning, but those paws were wearing jackboots as visibility for a time was reduced to as little as a quarter of a mile at Los Angeles International Airport.

And, just in case you missed the performance, return engagements are scheduled for today and Saturday, meteorologists said.

The same combination of factors is responsible for the dense fog, and heavy smog, said Dave Beusterien, a meteorologist with WeatherData Inc., which provides forecasts for The Times.

A high-pressure system in the upper atmosphere has weakened the normal onshore flow of air from the Pacific to the point where winds “are practically calm at night,” Beusterien said.

In addition, he said, skies have been clear at night. With no cloud cover to trap the heat, the temperature is able to drop quickly to the dew point--”the absolute measurement of moisture in the air,” he said. “When the temperature reaches the dew point, fog develops.”

Dew point, Beusterien explained, is a measurement of the amount of water in the air. On Thursday, the dew point was 59 or 60 degrees.

The upper-level high-pressure system responsible for the weak on-shore flow of ocean breezes also compresses the air below it and prevents particulates from escaping, Beusterien said. Thus, smog levels are increased and the visibility problem is compounded.

“The upper-level system responsible for the heat and fog along the coast will begin to weaken and drop south by Saturday,” Beusterien said. “By Sunday morning, the fog should be gone.”

Aside from the fog, weekend temperatures will be a little above normal but a gradual cooling trend will begin as the return of the on-shore flow pulls in marine air, Beusterien said.

The Los Angeles Civic Center, which reached a high of 91 on Thursday, will drop a few degrees each day and should be down to the upper 70s by Sunday, he said.

Temperatures along the coast will range from the upper 60s to the low 70s. Highs in inland areas will range from the upper 80s to 90, and the deserts will see highs from the mid-80s to 105.