It just so happens a Derecho hits the Deep South on the 10th anniversary of my first storm chase! Nothing is offical, and this was a weaker Derecho in the grand schemes of things, but still a Derecho in my opinion. You need severe wind criteria (continuos (58 mph)) for 400km or more, and I think we easily achieved that. Winds at my house were approaching 60mph for about 2 minutes! Not bad...
Here is a 0z Jackson, MS sounding... You see a nice dry punch, and winds aloft increased from 0z to 3z. Tons of evaporation helped mixed these winds to the surface. See 925mb charts below!