Saw a natural avalanche soon after it came rushing down the couloir directly SW of the main summit of Cascade Peak from about 10 miles away on I-15. Originally thought it was a fog cloud until I saw it picking up speed and rushing out of the bottom. I am assuming that it broke off near the summit where there would be significant windloading. The couloir to the flats is 4000ft and it ran that and likely another 500ft through the meadows by. I would not be surprised if we can find flattened trees down at the bottom later this year. The tail end of it likely blew by the hope campground or it may have even spilled up into it a bit. I am assuming that no one was in that slide path or in the run out on a day like today with the heightened avalanche risk. The crown was likely a few hundred feet wide and a few feet deep based off of the visibility of the slide from ~10 miles away.