A National Weather Service frost advisory for the valleys and deserts is scheduled to expire at 8 a.m. Forecasters said the advisory applied to far inland valleys and lower desert areas ``where little wind and clear skies will allow temperatures to fall rapidly,'' possibly below freezing.
Overnight temperatures were expected to fall to between 28 and 34 degrees. Forecasters urged residents to cover sensitive outdoor vegetation and bring pets inside.
Mostly sunny conditions are expected in San Diego County later in the morning, but an approaching trough of low pressure will bring cloudy skies and a chance of showers in the afternoon and into the night, according to the weather service. Light rain is likely in most areas other than the deserts, and a slight chance of thunderstorms is in the forecast at night for the coast, the valleys and the mountains.
``A storm will move down the California Coast Monday, and bring showers to Southern California this afternoon and evening,'' according to the weather service.
Forecasters said the storm could bring through Tuesday morning .28 of an inch of precipitation to San Diego; .26 of an inch in Julian; .22 of an inch to Miramar and Mount Laguna; .16 of an inch in Alpine; .13 of an inch to Palomar Mountain; .11 of an inch in Escondido; a tenth of an inch in Ramona; .09 of an inch in Oceanside; and .02 of an inch to Borrego Springs.
Weather service forecasters predicted a 40 percent chance for measurable precipitation near the beaches and in the valleys today and a 70 percent chance Monday night. In the mountains, a 30 percent chance of measurable precipitation was forecast for today along with a 70 percent chance tonight and up to an inch of snow could accumulate. No measurable rain is expected in the deserts.