Santa Ana Making a Late Visit, for the Weekend

Temperatures may jump as much as 10 degrees today west of the mountains as Santa Ana conditions arrive, prompting a dry, sunny weekend and evaporating the moist marine layer that has kept temperatures low this week.

Highs that hovered around 70 degrees at Lindbergh Field this week may reach the 80s today when a high-pressure system centered in southern Idaho sets up Santa Ana conditions in Southern California, the National Weather Service said. Northeasterly winds are expected to blow up over San Diego County mountains and into valley and coastal areas beginning today.

This influx of air, heated and compressed as it descends the mountains, will cut humidity in half west of the coastal mountain range. Relative humidity of 60% to 70% at the airport Thursday is expected to drop to about 30% today, forecasters said.

Areas east and west of the mountains may share daily highs today and Saturday, when inland valleys become as warm and dry as the desert, National Weather Service forecaster Dan Atkin said.

Although November begins today, Atkin said a Santa Ana condition at this time of year is not unusual. Temperatures, however, will be above average by 5 to 10 degrees at least through Saturday.

“It will be quite unseasonably warm if we get these temperatures,” he said. The average high at Lindbergh Field for Nov. 1 is 67 degrees.

Atkin added that the Santa Ana should be short-lived: “It will be fair and warm through Sunday, but the Santa Ana will begin to decrease Saturday.”

Winds may gust to 40 m.p.h. in the mountains and to 20 m.p.h. along the North County coast occasionally today and Saturday, Atkin said, but winds generally will be close to average. Winds of 15 to 30 m.p.h. are expected in the mountains and deserts, and breezes of 8 to 16 m.p.h. are expected along the San Diego coast.

Mornings should be clear at the beaches, where daytime high temperatures in the mid to high 70s are expected, with lows in the 60s. The ocean water temperature is about 65 degrees and the surf two to four feet.

Clear, dry days are expected along the coastal strip and in inland valleys; highs at the coast may reach the 80s, with nighttime lows in the high 50s to low 60s. Inland valley highs reaching 86 degrees may dip to 45 at night.

Mountain highs around 60 are expected to drop to the 30s at night, and desert highs of up to 86 degrees will fall into the 50s at night.