May 5, 2013 - From staff reportsFloods can stem from snowmelt, heavy rain and rainfall within fire scar regions.
The National Weather Service is using Wyoming Flood Awareness Week, May 6 to May 10, to encourage residents to understand the types of flooding that could affect their homes and businesses, even during times of drought. The awareness week will highlight flooding from snowmelt, heavy rain and rainfall within fire scar regions.
Flash flooding, typically the result of intense thunderstorms, can be a problem even during drought years, and an intense thunderstorm can quickly inundate a drainage basin of a small stream or river, causing flash flooding in a matter of an hour, if not minutes. Residents along waterways, even small creeks, should develop a plan to seek safety should water quickly begin rising.
The NWS urges people to avoid camping near streams or dry washes if there is a threat of heavy rain. Officials say that even if rain did not fall at your location, areas upstream may have received heavy rain which could cause rapid water rises downstream. Recent examples of heavy rain-induced flash floods in Wyoming include the deadly Brush Creek flash flood in July 2011, and the devastating flash flooding around Kaycee in August 2002.
"Another type of flash flooding that is often overlooked is heavy rain within urban areas," said Trevor LaVoie of the weather forecast office in Riverton.
LaVoie said water rises in urban areas can easily occur after intense rainfall, despite the fact it may only last 30 minutes.
"When the natural vegetation is replaced by streets, buildings and concrete, urban flooding can occur because the water more quickly collect in areas with poor drainage," he said.
Damage exceeding several million dollars occurred in Casper following flash flooding in July 2009 when roughly 2 inches of rain fell in about 30 minutes.
NWS meteorologists also are concerned about flash flooding within areas where wildfires occurred last summer. LaVoie said the burned soil can act almost like pavement. In turn, water run-off can occur quickly, taking mud and debris down hillsides, canyons and waterways.
"It will take less time to produce flash flooding in burn scars, especially if the terrain is steep and the rainfall intense," LaVoie said.
The NWS advises people living near burn scars to have a predetermined escape route planned that is least likely to be impacted by this type of flash flooding.
For more information about Wyoming Flood Awareness Week, visit the National Weather Service website at weather.gov/riw/?n=floodweekwy.
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