A frost advisory was extended to include San Diego's coastline Thursday morning after a night of nearly freezing temperatures across the county.
Temperatures were below freezing in areas like Alpine, Pine Valley and Ramona overnight and nearly freezing along the coast and in the inland valleys.
"Our coldest temperature is right at sunrise so there is still time for these temperatures to drop," NBC 7 Meteorologist Sheena Parveen said.
The National Weather Service issued a frost advisory and a freeze warning until 9 a.m. Thursday. During, pets should not be left outside and plants may be killed if left uncovered.
Some icy patches may also be covering roadways and freeways.
“Anything in our mountains that has melted yesterday is ice this morning," Parveen said.
Several mountain schools would start late on Wednesday because icy roadways make it dangerous for transporting students on buses, the San Diego County Office of Education said.
Early Wednesday, a truck spun out on an icy roadway on the Pine Valley Creek Bridge and caused a pileup, according to California Highway Patrol. One person died trying to help the stranded driver.
A woman was killed overnight when her car rolled over on I-8 amid snowy conditions although the cause is still under investigation.
Those schools are part of the Julian Union elementary and high school districts and the Spencer Valley School District.
Another storm will bring some small chances of rain over the weekend, though the system will be much weaker than the three that brought showers last week, Parveen said.