As severe weather swept through the eastern half of the nation Wednesday, it raised real concerns about another derecho occurring.
A derecho is a succession of damaging straightline winds lasting for more than 240 miles, according to the National Oceanic and Atmospheric Administration.
To be defined as a derecho, wind speeds must be equivalent to those in a severe thunderstorm, which means equal to or in excess of 58 mph.
Derechos are especially dangerous for people who are outdoors because the parent system blows in from seemingly nowhere — at speeds of 50 mph and greater. The wind itself can seem relentless, lasting many minutes.
Obviously the wind dynamics are different between tornadoes and derechos. Tornadic winds twist and wrench at structures and trees, while derecho winds blow in a straight line. Still, the winds can be as powerful as weak tornadoes and can last longer.
Winds in an EF0 tornado are 65 to 85 mph. With an EF1, winds blow at 86 to 110 mph.
Last year, a historic derecho swept through the eastern United States, killing at least 13 people and leaving about 4 million without power. Many of those killed were outdoors — some were campers — and were hit by falling trees.
Derechos tend to occur about once a year in the east-central and south-central United States and about every two to four years across a much broader area, including Nebraska and western Iowa.
The last time a derecho occurred in Nebraska wasin 2010, when one originated in the Omaha area and headed east across four states. That one caused damage from about Bennington eastward.
According to a World-Herald article at the time, that derecho generated winds of 65 to 75 mph in our area, but may have reached 90 to 110 mph near North 72nd Street.
In urban areas, derechos are known for the subsequent widespread power outages, which are worsened by related heat waves. In 2012, more people died from the heat wave that followed than the windstorm itself.
Source: NOAA, World-Herald archives