A thick blanket of fog and cloudy conditions should cool off the Southland and usher in the first stretch of autumn weather this weekend, according to forecasts.

There also will be a brief period of drizzle today, followed Friday with an episode of rain, said AccuWeather expert senior meteorologist Ken Clark on Wednesday.

"The rainfall amounts will be on the light side," he noted.

The temperatures will be a drastic change from last weekend's high that ranged in the 90s, as the thermostat dips today and through the weekend into the 60s in most areas.

That's not only a 30-degree drop in one week, but also the temperatures will be about 10 degrees below normal, according to Clark.

The clouds and thick fog will partially clear in the afternoon today along the coast, including the South Bay area, but the clouds will linger for the full day in inland areas, including San Gabriel, Woodland Hills and Pasadena, the meteorologist said.

The temperature should reach about 68 today in coastal areas, but dip slightly on Friday to 64 degrees. It will be slightly cooler in the inland regions.

There will be a repeat of Friday's temperature - minus the rain - for a high of 64 degrees Saturday, but climbing slightly on Sunday, to 67 degrees, during a mostly sunny day along the coasts. Again, inland temperatures will be a bit lower.

The San Bernardino area is forecast to have similar temperatures, with clouds clearing today and rain showers Friday.

The temperature shift is being caused by a cold front from an approaching low-pressure system from the Gulf of Alaska, Clark said. It will bring increasing onshore flow and will deepen the marine layer during the night.

The early morning fog will reduce visibility to a quarter of a mile or less in some places, he said.

Dense fog advisories that were issued Wednesday in the Orange County and San Diego County coastal areas could be canceled today by the National Weather Service, he said.

joe.segura@presstelegram.com, 562-714-2167, twitter.com/JoeSeguraPT