Less than 0.2mm in 10 minutes. Puddles form slowly if at all. 0.2 to 1.0mm in 10 minutes. Puddles form rather rapidly, downpipes flow freely, some spray over hard surfaces. Greater than 1mm in 10 minutes.
Rain falls in sheets, makes a roaring noise on roofs.
For Snow or Drizzle Visibility greater than 1km. Less than 1cm of snow per hour. Visibility 500m to 1km. 1 to 4cm of snow per hour. Visibility less than 500m.