According to the San Diego County Water Authority, we should expect slightly more than 10 inches of rain in a normal year. Rainy days are less common here than in most of the country. While there are many benefits to having so few bad weather days, it may lead to an increase in car accidents when drivers fail to make necessary accommodations to drive safely in the rain. The numbers from the early October storms bear that out.
The California Highway Patrol released statistics showing that 318 car accidents occurred in San Diego County from 12:01 a.m. and 9:15 p.m. on Wednesday, October 9. The wet conditions we experienced on that day were likely a huge contributor to that figure. The CHP indicated that San Diego County experiences an average of 50 to 75 accidents per day when the weather is good. Driving conditions can actually be more challenging when rain is less frequent.
The California Driver Handbook contains several tips for driving in rainy conditions. The Handbook clearly indicates that roads are at their most slippery shortly after rain begins. A long period without rain allows oil and dust and other exhaust particulates to gather on road surfaces. When mixed the water, the result can be very slick surfaces. The guide advises drivers to slow down immediately when rain or drizzle begins. The Handbook also states that heavy rain limits visibility to 100 feet, or even less. That level of visibility means drivers need to reduce their speed dramatically to remain safe.
In general, you should try to avoid driving in bad weather. If your trip can be postponed or avoided, it is worth it to avoid a car accident.
Source: NBC 7 San Diego, " CHP: 318 "Rainy Day" Crashes Reported in San Diego," by Monica Garske, 10 October 2013