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Spring Thaws = Potential Floods

by Alisa Sauvageot, All Hazards Planner
Wyoming Emergency Management Agency

While most floods follow heavy rain, or rapid, widespread melting of deep snow, flood forecasters also have to worry about several other factors.

During winter, large snowstorms leave many locations with a deep snow cover and frozen rivers. Deep snow can melt into a lot of water, but it very rarely causes flooding by itself.

Slow warming during the day along with below freezing overnight temperatures through most of April and into May can reduce flooding from melting snow. Forecasters are usually concerned about deep snow causing significant problems during the spring thaw if these conditions do not exist.

If heavy rain and unusually mild temperatures move into a location with a deep snow cover and frozen rivers, ice jam flooding can result. Ice jam flooding occurs when warm temperatures and heavy rain cause rapid snow melting. The melting snow, combined with the heavy rain, causes frozen rivers to swell. The rising water breaks the ice layer into large chunks, which float downstream and often pile up near narrow passages or near obstructions, such as bridges and dams. The ice dam often forces water to overflow the riverbanks and flood nearby homes and businesses. If the dam suddenly breaks, water can also flood downstream locations. Large chunks of ice can also damage bridges and other structures. Cranes with wrecking balls and explosives are sometimes used to break up ice dams.

Rain or rapid snow melt atop frozen soil can also cause flooding during this time of year. Similar situations occur with wet or saturated soil because the absorption rate is reduced. The excess water becomes runoff and rapidly flows into rivers and streams. Saturated soil by itself does not cause flooding. As with frozen soil, heavy rain or rapid snowmelt combined with saturated soil causes the flooding. Unsaturated soil acts like a sponge, absorbing some of the water from rain or snow melt thus preventing the problems.

Whether or not these factors cause flooding often depends on daily weather conditions over the region such as temperature and precipitation. This makes long range flood forecasts very difficult to pin down, which is the main reason why hydrologists often forecast long range flood potential rather than actual long range flood forecasts.

Source: Scott Kroczynski, National Weather Service
Source: USA TODAY research by Chad Palmer

Protecting Your Property

by Alisa Sauvageot, All Hazards Planner
Wyoming Emergency Management Agency

If we have spring flooding in Wyoming, many residents may be underinsured against flood losses. The policy count for Wyoming fluctuates and FEMA urges individuals to review their policy to make sure it is current.

“We want to encourage awareness, to get people to think about flood insurance again and to reexamine their risks and levels of coverage,” said Rick Weiland, Director of FEMA’s regional office in Denver. “Every year our agency responds to flood disaster, and invariably we meet people who tell us they wish they had purchased flood insurance. Flood insurance is one of the best ways for people to protect their homes and belongings,” Weiland added.

Things You Should Know About Flood Insurance:

  • Flood insurance is only available to properties in communities which participate in the National Flood Insurance Program
  • There is a 30-day waiting period after you purchased the insurance and paid the premium before the policy is in effect and you can file a claim.
  • Flood insurance can be purchased even if the property is not in the floodplain. Over a third of all flood insurance claims result from damage to a property located outside the floodplain.
  • Most homeowner policies do not cover flood losses.
  • Businesses can purchase flood insurance.
  • Contents of insurable, fully enclosed buildings may be insured, making flood insurance available to renters.

For more information on the National Flood Insurance Program, please contact Wyoming Emergency Management Agency, NFIP Coordinator Alica Sauvageot at (307) 777-4918 or by email sauvageota@wy-iso.army.mil

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