huge disc shaped object moving within a quickley moving storm cloud

After a severe thunderstorm warning on television i went ootside to my balcony witch faces to the west also the direction the storm was coming from. I was watching the developement of the storm cloud moving in under the calm clouds above when i noticed a dark spot on the edge of the storm cloud. It caught my eye because it was moving side to side in the cloud. After about twenty seconds of watching this odd dark spot it came to the surface of the cloud and i could make it out to be a huge disc angled at about 45 degrees to the ground. i hollered to my girlfriend to come outside and look. At this time it had retreated back into the cloud and was just a dark spot again.she noticed it right away. As we watched it moving up and down and side to side with no aparent disturbance from the quickly moving storm cloud it became completely visable again. I have no idea how big this was. I know it must have been at least one hundred feet in diameter, most likely bigger. We were completely amazed at what we were seeing and could see it well enough to know it was not a weather balloon or anything else for that matter. It was a huge disc shaped grey colored object theat remained between 45 and vertical and moved distinctly throughout this storm cloud untill it went overhead and over our building out of our sight. this stormcloud developed just east of us into a major lighting storm.