Taken from a hill at Sun Ray park in Ahwatukee (Phoenix), Arizona. Shot on my Canon 60D in at f/5.0 at 2 second intervals. This only took about 5 minutes to roll in from the time I started shooting.
Here's some more behind the scenes footage taken from my cell phone, just as the storm hits: youtube.com/watch?v=jx2Zzp-cGgM
Caught in the storm: youtube.com/watch?v=aToErCXRAOo
Another clip: youtube.com/watch?v=ldevIdbipxY