A derecho is basically a widespread and long lived windstorm! You get fast moving severe thunderstorms embedded in a squall line, typically in the shape of a bow... They are most common in late spring/summer across the Midwest/Northern Plains, but there is a second season in fall/winter across the Southeast/Southern Plains! To meet derecho criteria, you have to have continuous wind reports of 58 mph or greater (severe thunderstorm criteria), for at least 400km... I have also heard 240 miles, which is about 10 miles shorter than 400km... There are three types of Derechos.... Progressive, Serial, and hybrid... This is going to REALLY simplify things, but basically a progressive derecho moves more west to east, where a serial derecho moves more south to north... The hybrid is a combination of the two, which is rare! Today was a great example of a progressive derecho, with 321 wind report as off 522z... About 300 of those wind reports occurred within today's derecho! It was quite a day across Iowa, southern Wisconsin, northern Illinois, northern Indiana, southern Michigan, and extreme northwest Ohio!!! For an excellent website with LOTS of great information on derechos, click here!
Remember, straight line winds can be just as deadly as tornadoes! Derechos do hurt/kill people! In the stronger derecho events, wind gusts can exceed well over 100mph... I'll never forget when Starkville, MS was hit by a strong derecho on 2/16/01... There were reports of 110mph wind gust near campus (South Farm)... I was honestly fairly shocked at the amount of damage across Starkville, MSU, and the surrounding areas! At that point it was by far the fastest winds I had ever personally experienced... Right in front on my eyes I watched a tennis court get ripped to shreds at my apartment, which was no more than a mile or two from the campus of Mississippi State University... It was an eye opening event for me personally!
One thing at the time I thought was interesting, was how upset some people got when you told them a tornado didn't destroy their house, straight line winds did... I have found over the years that it is hard to convey to the general public that straight line winds can destroy your house as fast as a tornado can... If you live in a mobile home, this is especially true! While fascinating, derechos are killer weather events! Before I go, I have to say that I was a little surprise the SPC didn't issue any PDS severe thunderstorm watches today! You see PDS (Particularly Dangerous Situation) used a decent amount with tornadoes watches, and I would personally like to see it used more in wind events like today! Not a criticism at all, just something I would love to see used more in the future!