San Diego to Get Taste of Winter in September

Winter temperatures and rain are expected to erase what’s left of summery weather this week when a low-pressure system brings cold Canadian air to Southern California.

According to the National Weather Service, the strongest in what has become a series of low-pressure systems will bring unseasonably cold weather and a chance of showers at least through Thursday.

A 20% chance of rain is expected today, and forecasters predict a 30% chance for Wednesday. Daytime temperatures along both the coast and in inland valleys are expected no higher than 74 today and less than 72 on Wednesday, and mountain areas will be cold and windy.

“This low pressure started over the Pacific Northwest and was fed by cold Canadian air,” forecaster Wilbur Shigehara said. “It is a winter-type pattern that would have brought snow here if it were winter instead of early September.”

He said the air mass over San Diego County will become more unstable and the chance of rain will increase as the low-pressure system approaches.

Fall doesn’t arrive until Sept. 22, and the usual high for early September at Lindbergh Field is 77 degrees. Monday’s high of 75 at the airport is expected to drop steadily through the week.

“The atmosphere seems to be all goofed up. We are really at extremes,” Shigehara said. “Last year San Diego had the warmest night ever recorded with a low of 78 (on Sept. 9). We struggled to hit 75 for the high this year.”

Forecasters predict that the chance of rain will decrease by Thursday, but “how much sunshine will return would be a big guess,” Shigehara said.

“Low pressures are very fickle. They can stall or change direction. It is tough making a forecast; it is not like a weather front moving through,” he said.

Highs are expected in the 60s and low 70s along the coast and inland valleys, with lows near the beach from 57 to 63 degrees and between 45 and 55 inland.

Mountains will be cold and cloudy with gusty winds up to 25 m.p.h. Highs are expected between 48 and 58 degrees today and no higher than 52 degrees Wednesday. Lows may dip into the 30s.

Southwesterly winds in the 15 to 30 m.p.h. range are expected in the deserts, where highs in the 80s today and between 78 and 85 Wednesday will fall to the 50s and 60s at night.