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Severe Weather Preparedness Week – Day 1: Flash Flooding

| by Henry Luker

By National Weather Service Des Moines

Governor Terry Branstad, the Iowa Homeland Security and Emergency Management Division, and the National Weather Service have designated the week of March 24 to March 28 as severe weather awareness week in Iowa. Each morning this week, the National Weather Service in Des Moines will issue a Public Information Statement focusing on a different item each day. Topics this year includes the following:

  • Monday: Flash Flooding
  • Tuesday: Warning Reception
  • Wednesday: Tornadoes
  • Thursday: Severe Thunderstorms
  • Friday: Family Preparedness

Recent Developments:

Iowa and Nebraska will have combined severe weather awareness weeks. The combined week will help with the tornado test for those along the Missouri River.

Checkout the recently improved National Weather Service Des Moines preparedness page! It is full of new severe weather preparedness information! It is on the National Weather Service Des Moines website under ‘Preparedness’ on the left hand side.

Today’s Topic is Flash Flooding

Each year, more deaths occur due to flooding than from any other thunderstorm-related hazard, resulting in more than 140 fatalities each year. Most flash floods are caused by slow moving thunderstorms, thunderstorms that redevelop over the same area, or heavy rains from tropical storms and hurricanes. These floods can develop within minutes or hours depending on the intensity and duration of the rain, the topography, soil conditions, and ground cover.

A flash flood is a rapid rise of water along a stream of low-lying urban area. Flash floods can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Rapidly rising water can reach heights of 10 feet or more.

A Flash Flood Watch is issued by the National Weather Service to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area. The occurrence of flooding is neither certain nor imminent. Those in the watch area should be alert for flooding.

A Flash Flood Warning means National Weather Service meteorologists have determined that flash flooding is occurring or imminent. Those in the warning area should take the necessary precautions at once.

Almost half of all flash flood fatalities occur in vehicles. Many people do not realize two feet of water on a bridge of highway can float most vehicles. If the water is moving rapidly, the car, truck, or SUV can be swept off the bridge and into the creek or downstream with the flowing water. Water can erode the road bed, creating unsafe driving conditions. Underpasses can fill rapidly with water, while the adjacent roadway remains clear. Driving into a flooded under-pass can quickly put you in five to six feet of water. Many flash floods occur at night when flooded roads are difficult to see.

When you approach a flooded road, Turn Around, Don’t Drown!

Flash Flood Myth vs Fact:

  • Myth: Flash Floods only occur in the eastern United States.
    • Fact: Flash floods have and can occur in all 50 states, including Alaska and Hawaii.
  • Myth: Flash Floods occur only along flowing streams.
    • Fact: Flash floods can occur in dry creek beds and urban areas where no streams are present.
  • Myth: Flash floods occur mainly in the late afternoon and evening.
    • Fact: Flash floods can occur at any time of day, many flash floods occur at night, oo.
  • Myth: Larger vehicles, such as SUVs and pickups, are safe to drive through flood waters.
    • Fact: Two feet of rushing water can carry away most vehicles, including SUVs and pickups.
  • Myth: Homeowners insurance policies cover flooding.
    • Fact: Unfortunately, many homeowners do not find out until it is too late that their polices do not cover flooding. Contact your insurance company or agent about flood insurance.

Here Are Some Flood Safety Tips:

  • Before a Flood: 
    • Know the county in which you live and the names of nearby major cities.
    • Check the weather forecast before leaving to be outdoors for extended periods.
    • Watch for signs of approaching storms.
    • Monitor the NOAA Weather Radio or your favorite news source for vital weather related information.
    • Do not camp or park your vehicle along streams and washes, particularly during threatening conditions.
  • If Flooding Occurs: 
    • Get to higher ground.
    • Get out of areas subject to flooding. This includes dips, low spots, canyons, washes, etc.
    • Avoid areas already flooded, especially if the water is flowing fast.
    • Do not attempt to cross flowing streams.
    • Road beds may be washed out under flood waters. Never drive through flooded roadways.
    • Do not allow children to play near high water, storm drains, or ditches. Hidden dangers could like beneath the water.
    • Be especially cautious at night when it is harder to recognize flood dangers.