Hopefully I can make sense of this...I have a map in heavy fog with a rainstorm going on. I have random (programmed) lightning strikes going via an interval trigger along with a light happening simultaneously. How can I also for just a split second make the fog clear up to show the background?

I tried (to no real avail) snapping a round circle of water in front of the camera (to give it the see through fog illusion), but I hated the way it looked. Can I change the global fog density at will? If so how? Thanks!