The potential for heavy snow at higher elevations in the western U.S. will continue for many spots through the weekend. In the meantime, the eastern half of the continental U.S. will transition to above normal temperatures ahead of a pair of cold fronts next week that will bring readings back to closer to normal as we approach Thanksgiving Day. Read More >
Floods are the #1 cause of weather related deaths in the Unites States, causing approximately 200 deaths a year. Wyoming experiences many different types of flooding and has a long history of flooding events. Types of flooding that can impact Wyoming:
Flash Flooding
River Flooding
Burn Scars/Debris Flows
Ice/Debris Jams
Snowmelt
Dry Wash
Dam Breaks/Levee Failure
These floods happen in a flash! They are particularly dangerous as flood waters can rise many inches to even a few feet in a very short amount of time. Flash floods catch many people off guard and can happen almost anywhere. One danger often overlooked with flash floods is, if strong enough, flash floods can wash away chunks of roads. This can cause roads to look passable with only a few inches of water over them when, in reality, a vehicle trying to cross would fall into the space created becoming partly submerged. If flood waters continue to rise, the vehicle can easily get washed away. Turn Around! Don’t drown! River flooding is classified into 3 categories based on water height and impacts caused: Minor, Moderate, or Major. Minor flooding is flooding that impacts low-lying areas right next to the stream or river. Moderate flooding is water that rises high enough to impact homes and business near the river/stream; minimum or no evacuations are needed. Major flooding is labeled thus when extensive rural and or urban flooding takes place; numerous evacuations may be required and major traffic routes impacted. A burn scare is an area where enough surface vegetation has been burned away by a wildfire that bare ground is left. Bare ground does not readily absorb moisture so rain can easily collect and run across the surface of the ground causing a flood. However, if rain does collect and seep into the ground, mud or debris flows can occur. Without vegetation to hold the soil in place, overly saturated ground can turn into a more liquid state and flow downhill. As ice or debris flows downstream, it can become caught and obstruct water flow. This causes a blockage that backs up water upstream causing flooding. When the jam finally gives, water rushes downstream possibly causing flash flooding. When snowpack from winter begins to warm with the start of spring/summer it can sometimes melt rapidly and cause flooding. This can happen from a fast rise in temperatures accelerating melting or rain falling which both adds moisture and melts the snow or both. Also, if the ground was saturated before freezing the previous fall then even more melted snow will turn to run off rather than be absorbed. All of these conditions determine if snow will melt fast enough to cause flooding or melt at a normal pace. Sometimes flooding can happen with seemingly no cause; this is usually a case of a dry wash. A dry wash happens when a dry, desert like area suddenly receives significant rainfall. Rain will rush across the ground, which is too hard to absorb much moisture, toward low lying areas such as canyon’s or dried up river beds. These areas can go from bone dry to a flash flood in seconds even when the storm that dumped the rain occurred miles away. Dam or levee failures can occur with little warning and can pose a high hazard to life and/or property. Failures can happen due to age and improper maintenance or design, from erosion, or from other natural causes such as earthquakes or prolonged rainfall that overwhelm the structure. This can lead to dams being overtopped, leaking, or a complete failure.
Watch vs. Advisory vs. Warning and what actions should you take? Be Prepared, Be Aware, Be Ready, Take Action! Before a Flood: Be Prepared Long before the threat of a flood, make sure you are prepared by taking measures such as:
If a Flood Advisory is issued: Be Aware Flood Advisories are issued if a specific weather event forecast to occur may cause flooding. This type of flooding may cause significant inconvenience, but will not reach warning criteria.
If a Flood Watch is issued: Be Ready Flood Watches are issued is conditions are favorable for flooding to occur. This does not mean flooding, even Advisory amounts, will occur, but the potential exists.
If a Flood Warning is issued: Take Action! Flood Warnings are issued when a flooding is occurring or is imminent due to a hazardous weather event. During a flooding event:
If a Flash Flood Warning is issued: Take Action! Flash Flood Warnings are issued when flash flooding is imminent or occurring. Now is the time to get to a safe location/higher ground immediately if you are in a flood prone area.
Photo Courtesy of County10 |
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Flood Safety: National Website & Brochure Turn Around Don't Drown: National Website & Brochure Red Cross: Disaster safety
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