There was a bright flash of light.I was driving westbound on I-90 approximately at mile marker 64, when I just happened to look to the south out of my drivers side window when I saw the sky light up for just a couple of seconds. I am not sure what the source direction of the flash of light was. But it brightened up the night sky about 20 percent lighter before it faded away. It only happened once. To the south from my location is Lolo National Forest. Behind me about 10 miles was the city of Alberton, Montana. Not any where close to where a firework would light up the sky like this at 1:08 in the early morning hours.