Rain esc amp Floods How does rain form Water droplets form from warm air As the warm air rises in the sky it cools Water vapor invisible water in the air always exists in our air Warm air holds quite a bit of water For example in the summer it is usually very humid When enough of these droplets collect together we see them as clouds If the clouds are big enough and have enough water droplets the droplets bang together and form even bigger drops When the drops get heavy they fall because of gravity and you see and feel rain What causes rain When clouds develop or rain occurs something is making the air rise Several things can make this happen Mountains low pressure areas cold fronts and even the jet stream How big are raindrops Raindrops are much smaller than we think They are actually smaller than a centimeter Raindrops range from 1 100 inch 0254 centimeter to 1 4 inch 635 centimeter in diameter How fast do raindrops fall Not including wind driven rain raindrops fall between 7 and 18 miles per hour 3 and 8 meters per second in still air The range in speed depends on the the size of the raindrop Air friction breaks up raindrops when they exceed 18 miles per hour What is a flood A flood results from days of heavy rain and or melting snows when rivers rise and go over their banks What is a flash flood A flash flood is sudden flooding that occurs when floodwaters rise rapidly with no warning within several hours of an intense rain They often occur after intense rainfall from slow moving thunderstorms In narrow canyons and valleys floodwaters flow faster than on flatter ground and can be quite destructive Do flash floods hurt people Flash floods are the 1 weather related killer in the U S Nearly 80 of flash flood deaths are auto related Know beforehand if your area is a flood risk How much water is needed for your car to float away A mere 2 feet of water can float a large vehicle or even a bus This is why you should never drive through flooded roads Just 6 inches of rapidly moving flood water can knock a person down