An unusually cold Arctic air mass with the potential to cause widespread frost damage to San Diego crops is expected to start blowing into the county Saturday night, forecasters said.
A weak Santa Ana condition that bathed San Diegans with sunshine and warmer temperatures the past few days will dissipate today, according to Wilbur Shigehara, a National Weather Service forecaster.
By Saturday, skies will cloud up, temperatures will cool and winds will pick up around the county, "signaling a dramatic change in the weather," he said.
Saturday through Monday, overnight lows in inland valleys are expected to plunge to the low 20s, the coldest temperatures of the year, Shigehara said. "Farmers had better start thinking of frost protection now while they still have a chance," he said.
The Arctic mass will be strongest Sunday, bringing north winds gusting from 40 to 50 m.p.h. in the mountains, Shigehara said.
"In addition to putting out a wind advisory in the mountains, we've issued a frost advisory for farmers, because we're expecting freezing temperatures reminiscent of last January that caused $30 million in frost damage to San Diego agriculture," he said.
"Not many crops can survive that kind of cold, unless they have frost safeguards," he said.
Growers use some heating devices such as smudge pots, wind machines and water irrigation to protect their orchards from frost, according to Bill Snodgrass, spokesman for the San Diego County Department of Agriculture.
Strawberries, nearing bloom along the coast, are particularly susceptible to frost damage right now, Snodgrass said.
"Growers around the county will probably be up all night monitoring temperatures," he said.
Sunday conditions will be cold and blustery, with winds from 15 to 40 m.p.h. around the county, Shigehara said.
Coastal highs today will range from 75 to 80 degrees, with lows from 40 to 52. Highs Saturday will be from 68 to 72, with overnight lows in the 38- to 42-degree range. Highs on Sunday will be from 60 to 65, lows from 30 to 35, according to forecaster Dan Bowman of WeatherData, which provides forecasts for The Times.
Ocean temperature is 61 degrees, with surf from four to five feet.
Highs in the inland valleys will range from 75 to 82, with lows from 40 to 49. Highs on Saturday will decrease and range from 68 to 75, lows from 35 to 42. High temperatures Sunday will range from 58 to 65, lows from 25 to 34.
Mountain highs today will be from 56 to 63, with lows from 25 to 35. On Saturday, highs will range from 50 to 59, with lows from 25 to 35. Highs on Sunday will be from 40 to 49, lows in the 18- to 28-degree range.