I was outside walking my dog (Bonney Lake, Wa) Thursday evening 10-18-2012 when at approximatly 7:45 PM Pacific Time the cloud covered night sky flashed so brightly that it blinded me breifly. Aproximatly 20 seconds later there was a large continuous boom as you will hear in the video! The weather in the Seattle where I live was unsettled that night but in my location the was no lightning or thunderstorm prior or after the event. The loud roar was unlike any thunder I have ever heard. Here is video of one of my security cameras capturing the event. (The time showing on my security screen is actually 1:30 minutes slow)