With the looming threat of a possible derecho for parts of the Upper Midwest and through the Ohio River Valley Sunday night and into Monday (and potentially beyond), you may want to know what exactly a derecho is.
It’s a term that has only relatively recently entered mainstream meteorology speak, and many of you may not know what one is. But you should – particularly during the mid-summer months of peak heating and the typical highest probability for one.
In short, they are a line of particularly nasty, long-lasting thunderstorms most known for creating widespread wind damage.
According to the National Oceanic and Atmospheric Administration’s Storm Prediction Center, the U.S. government’s official meteorological body, there are three primary criteria for a derecho to be classified as such:
1) A swath of wind damage at least 240 miles
2) Widespread reports of at least 58 miles-per-hour
3) Periodic reports of wind gusts of at least 75 miles-per-hour
Essentially, derechos are long lines of worse-than-normal thunderstorms. Hail and brief tornadoes are also common with these storms, but straight-line wind damage is far and away the biggest threat from a derecho. One hundred mile-per-hour wind gusts are often reported in locations along derechos, and hurricane-force gusts (74 miles-per-hour or greater) are a necessary threshold for them.
A particularly nasty, recent example of one came in late June 2012, when 13 people were killed and 4.5 million people lost power as a derecho blasted through 10 states and Washington DC.
For more on them, the Washington Post‘s Capital Weather Gang did a great overview of these thunderstorm clusters earlier this month.
Source: WeatherNation So, What is a Derecho? | Meteorologist Chris Bianchi – Radar image: Storm Prediction Center (SPC)