Flash Flooding

A graphical representation of weather fatalities per yearFlash flooding is the number one weather-related killer in the United States.  Flooding kills almost twice as many people each year as tornadoes and hurricanes combined!  Unlike hurricanes, floods are a threat in every state.

Most flash flooding is caused by slow-moving thunderstorms, thunderstorms repeatedly moving over the same area (called "training"), or heavy rains from hurricanes and tropical storms.

Nearly half of all flash flood deaths are auto-related. Even 6 inches of fast-moving flood water can knock you off your feet and at a depth of 2 feet will float your car.

Car on water

Water weighs 62.4 pounds per cubic foot and is typically flowing downstream at 6 to 12 miles an hour.

Car against rushing water

When a vehicle stalls in the water, the water’s momentum is transferred to the car. For each foot the water rises, 500 pounds of lateral force are applied to the car.

Water attempting to float a car

The biggest factor is buoyancy. For each foot the water rises up the side of the car, the car displaces 1,500 pounds of water. In effect, the car weighs 1,500 pounds less for each foot the water rises.

A car floating

Two feet of water will carry away most cars - 1,000 pounds of lateral (or side force) plus 3,000 pounds of buoyancy!

A large wall cloud forming over a country roadClues to Potential Flash Flooding

  • Distant thunder - runoff from a faraway thunderstorm could be heading your way.
  • Look out for water rising rapidly.
  • In your car lookout for flooding at highway dips, bridges, and low areas.

Before the Flood

  • Know your flood risk and elevation above flood stage
  • Do your local streams or rivers flood easily? If so, be prepared to move to a place of safety. Know your evacuation routes.
  • Keep your automobile fueled; if electric power is cut off, gas stations may not be able to operate pumps for several days
  • Store drinking water in clean bathtubs and in various other containers. Water service may be interrupted or water contaminated.
  • Keep a stock of food that requires little cooking and no refrigeration.
  • Keep first aid supplies on hand.
  • Keep a National Oceanic and Atmospheric Administration (NOAA) Weather Radio, a battery-powered radio, emergency cooking equipment, and flashlights in working order.Two bags full of supplies next to a sleeping bag
  • Install check valves in building sewer traps to prevent floodwater from backing up into the drains of your home.
  • Assemble a disaster supplies kit containing: first-aid kit, canned food and can opener, bottled water, rubber boots, rubber gloves, NOAA Weather Radio, battery-powered radio, flashlight, and extra batteries.

River Flood Watch

River levels may reach or rise above the flood stage.

  • Be ready to move to a safe area if necessary.
  • Stay tuned to NOAA Weather Radio or local radio and TV for possible warning.

River Flood Warning

Rivers will rise above the flood stage.

  • Take all precautions necessary to protect your life and property.
  • Move to a safe area if you are in the flood area.

Flash Flood Watch

Heavy rains are possible.

  • Be ready to move to higher ground immediately if flooding occurs.
  • Stay tuned to NOAA Weather Radio or local radio and TV for possible warning.

Flash Flood Warning

Flash flooding has been reported or is imminent.

  • Move to higher ground immediately.
  • Never drive through floodwater on roadways.
  • Stay tuned to NOAA Weather Radio or local radio and TV.

The rule for being safe in a flooding situation is simple:

  • Head for higher ground and stay away from floodwaters!
  • Stay tuned to NOAA weather radio or local radio and TV.