Snow showers developed over the mountains late Thursday night and were expected to continue periodically through at least early afternoon, according to the National Weather Service. A winter weather advisory for mountain locales including Julian, Pine Valley, Palomar Mountain and Mount Laguna was set to remain in effect until 4 p.m.
The snow level on Palomar Mountain dropped overnight to about 4,000 feet above sea level. About three inches of powder was on the ground at about 9 a.m.
Around four inches of snow had also accumulated on Sunrise Highway, southwest of Mount Laguna, according to the California Highway Patrol. Julian got a light dusting as well, according to the weather service.
Motorists were required to use tire chains on snow covered Palomar Mountain roadways, and on Sunrise Highway between Interstate 8 and state Route 79, according to the county Department of Public Works.
Forecasters said up to six inches may fall on the highest peaks, but one to four inches would accumulate in other areas. The snow level was expected to hover at about 4,000 feet, which includes portions of Interstate 8 and Sunrise Highway.
The cold low-pressure system responsible for the snow will also lead to continued rain through Friday night and cooler weather for the next couple days, according to the weather service.
In a 72-hour period ending at about 8:30 a.m. Friday, gauges collected .81 of an inch of rain in Descanso; .74 of an inch in Pine Hills and Echo Dell; .62 of an inch on Otay Mountain; .59 of an inch in Harbison Canyon; .56 of an inch in Alpine; .55 of an inch at Lake Cuyamaca; and .52 of an inch in Escondido. A half-inch of rain or less fell in numerous other areas.
Flooding prompted the closure of Quarry Dip Road in Spring Valley Friday morning, but it has since reopened, according to the Department of Public Works.
Forecasters said already chilly temperatures were expected to drop to sub-freezing Friday night in some areas.
A freeze watch for the valleys will remain in effect overnight Friday night and again Saturday night into Sunday morning. Locales included under the advisory include Alpine, Jamul, Rainbow, Ramona and Valley Center.
High temperatures of 38 to 48 degrees in the mountains are expected to fall to between 18 and 28 degrees Friday night. In the valleys and deserts, patchy frost is expected to form Friday night in colder, wind-sheltered locations amid low temperatures of 27 to 35 degrees and 29 to 37 degrees, respectively.
Forecasters warned that such low temperatures can damage unprotected plants and crops and could harm outdoor pets.
Along the coast, king tides -- the highest astronomical tides of the year -- could again lead to minor flooding. A high tide of 7.3 feet was expected at 9:12 a.m., and a coastal flood advisory will expire at noon.
Forecasters said locales especially susceptible to flooding this week included Imperial Beach, South Mission Beach, La Jolla Shores, Cardiff-by-the- Sea and beaches in Oceanside. Strong rip currents were also possible.
The unusually high tides are expected to gradually lower this weekend and drier, warmer weather is in the forecast for next week, according to the NWS.