Eight traffic collisions have occurred in San Luis Obispo County in the last hour, according to the CHP at 3:15 p.m.
About a dozen others have occurred since the morning, officials said.
At about 2:30 p.m., weather conditions were described as extreme on the Cuesta Grade with "50 mph wind gusts with near zero visibility at times," according to the CHP.
"We've seen a lot of people hydroplaning and skidding off the roadway mostly due to driving too fast in the rain," CHP Officer Joe Vega said. "Mostly solo vehicle collisions sliding into the guardrail and down embankments."
The CHP advises motorists to slow down and cut down on car trips when possible.
- Tonya Strickland