Weather Effect [lightning storm]

How could i create a really cool lightning storm? ive seen maps where the screen will flash and play a sound....pretty cool lookin, how could i do this?

If it is not an Wheater effect, then they are creating a sound variable with the sound variable, for the flash, use the action Cinematic-Fade filter use white mask for it, play the sound using Sound - Play 3D sound or something like it.You could use a timmed event to run this trigger.