The road surface often becomes especially slippery during the first half hour of rain because:

Road surfaces become especially slippery during the first half hour of rain because the dirt and oil on a road's surface will not have yet washed away. The combination of water with these materials forms a greasy film that tires cannot properly grasp.

• Dust and oil on the road have not yet washed away.
• Tires have not yet absorbed the water.
• Water tends to pool the most at the beginning of a rainfall.
• It rains hardest during that time.