ROCKFORD (WREX) — Derechos are widely considered one of the most dangerous weather has to offer. What gives them their power? What can you do to protect yourself and your family?
What is a derecho?:
The official definition from the Storm Prediction Center states that a derecho is a long-lived and widespread wind storm that can result in damage.
Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems."Facts About Derechos," The Storm Prediction Center
This may seem like a pretty standard event, but there are a few criterion a complex must acquire before being called earning "derecho" status. First, winds must be at or higher than 58 miles per hour. Second, the damage swath must extend at least 250 miles, with no more than 2.5 hours elapsing between severe wind reports.
How derechos develop:
Derechos develop the same way as any other cluster of line of thunderstorms. In a derecho, the updrafts get tilted and removed from the rain-cooled air. This rain-cooled air helps to propel a gust front, allowing for the maintenance and propagation of storms.
Unlike summertime air mass thunderstorms, which tend to have vertical updrafts and rain themselves out in about an hour, updrafts in derechos are tilted. This tilted structure keeps updrafts away from rain-cooled air, helping to elongate the lifespan of thunderstorm complex.
As the complex of storms mature, rain-cooled air helps to increase winds in the mid- and upper-levels in the 'rear-inflow jet.' This sustains storm motion and allows some of the strongest winds aloft to get brought to the surface.
"What if a derecho is headed my way?":
The obvious answer to this question is seek shelter. If you are outside, get indoors and away from windows. Winds within these powerhouse thunderstorms can get to hurricane-force, so glass can easily become a dangerous flying object. If you have a basement or storm shelter, go there to take refuge from the storm.
Nearly half of all fatalities in derechos occur in cars or boats, so if you are in either of those locations, get out! Find a sturdy structure and seek shelter there. Even something as simple as a fast food restaurant, a grocery store, or a convenience store offer safer shelter than a car.