Heat Lightning

occurs when lightning is too far away for you to hear. This usually occurs in the warmer months of the year, hence the name heat lightning...
I used to always see heat lightning in the south. I took a video of some last summer when I was there. I had never seen it here in Washington until last night. It was kind of cool to see...all that was missing was the buzz of the cicadas in the trees...
Here's a pic I took with my phone. It's not very good, but you get an idea. I had pulled over to the side of the road and was looking out over the water near. You can faintly see lights on the other side of the water, the streak is the lightning. Unfortunately, I wasn't fast enough to get the flash that lit up the sky.