Roads are likely to be especially slick:

Roads are likely to be especially slick just after it has begun to rain or drizzle due to the combination of rainwater mixing with oil and debris that has accumulated on the roadway. When it first starts to rain, the initial moisture allows these substances to rise to the surface, reducing traction and creating a hazardous driving condition. This phenomenon is often referred to as "first rain slick" because the pavement has not yet been thoroughly washed clean, making the slick conditions more pronounced during the initial moments of rainfall.

As the rain continues and eventually washes away this layer of oil and debris, the slickness tends to decrease, and the road generally becomes safer to drive on compared to the moments right after the precipitation begins. Therefore, understanding this critical point can help drivers adjust their behavior during early moments of rain, maintaining caution and reducing speed to ensure safety on the roads.