I was traveling home, east bound I-90 to north bend, WA. I began to see extremely bright flashes lighting up the sky every 3-5 minutes or so. Upon arriving at my destination, I got out of my car and waited patently in the dark for what seemed to be at least 5, maybe 10 minutes. Sure enough, a MASSIVE white flash could be seen over a local mountain named MT. Si. 3-5 minutes it happened again (The time frame was almost impossible to track!!!). 5 minutes felt like 1 minute, 1 felt like 10. About this time strange clouds cover developed around the mountain, shrouding it . This flash was extremely powerful. It lit the whole sky and the cloud cover, but only for 1-2 seconds. It did lit look atypical white, it was almost a glowing color. Much to powerful to be emergency strobe or anything civilian/commercial. It seemed almost unbelievable. (This happened in mid July, but seemed to come from the eastern cascade ranges). After the second and final flash, an object came over the mountain, seemingly from the source, and quickly ascended westward, with a rapid white strobe. It did not disappear, only continued to pick up speed.Soon after the flashes seemed to stop, and the clouds dissipated. I found this impossible not report.The first thought that comes to mind is government, seeing as people have reported quite a few low flying military aircraft over the years..although this was rather unique and "out of this world". I HAVE NEVER SEEN ANYTHING LIKE THIS..gave me the creeps..((ADDENDUM FROM WITNESS))That would be 8:05pm((END ADDENDUM))((NUFORC Note: We have corrected the time. The report was first posted on September 22, 2016, indicating a time of 08:05, or 8:05 a.m.. PD))