A low-pressure system is expected to reach San Diego County Wednesday, bringing precipitation and the possibility of heavy snowfall in the mountains, according to the National Weather Service.
Frigid temperatures this morning prompted the NWS to issue a frost advisory that will last until 9 a.m. in parts of the inland valleys and deserts, including Escondido, Poway, San Marcos, Santee and Borrego Springs. The advisory indicates a likelihood of temperatures dropping to upper-20s to low-30s.
NWS forecasters warn that shelter should be provided for pets or livestock, and sensitive outdoor plants could die if unprotected in the frost.
The south-moving storm is expected to begin dousing the region this afternoon, then increase in intensity tonight into Thursday, NWS meteorologist Miguel Miller said.
The cold storm is expected to drop up to four-tenths of rainfall Wednesday along the coast, three-tenths of an inch to a half-inch in the inland valleys, up to 1.2 inches of moisture in the mountains, and around one-tenth of an inch in the deserts, forecasters said.
Snow levels will remain above 4,500 feet Wednesday, then drop to around 3,000 feet during the day Thursday before falling to 2,500 feet by Thursday night, Miller said.
Up to 18 inches of snow is possible near the top of Palomar Mountains through Friday, while Mount Laguna could get up to 20 inches, and anywhere from 8 to 9 inches of snow is expected in Julian, the meteorologist said.
The NWS also issued a winter storm warning for the county mountains that will be in effect from 1 p.m. Wednesday through 1 a.m. Friday.
The inclement weather will make travel to mountain locales hazardous or impossible, forecasters said.
"If you must travel, keep an extra flashlight, food and water in your vehicle in case of emergency," the NWS warned.
Since Oct. 1, San Diego's official precipitation station at Lindbergh Field has tallied 10.35 inches of moisture, exceeding the amount — 10.33 inches — considered "normal" for the city to get during an entire year of average rainfall, according to the NWS.
The storm is expected to leave the region late Thursday night and temperatures will begin warming Friday, Miller said.
