There's some controversy over the "Sniagrab" name. When I was a kid, the only one I was aware of was in Seattle, and was sponsored by Osborn & Ulland. By the '70s, it was more of a general event, rather than a store ski sale. It was held at the Seattle Center, with a big "ski swap" component to it.
Apparently, both O&U and Gart Brothers had their first Sniagrab in 1955. I'm not sure how they both got the same name for a sale at the same time of year of the same class of retail goods at the same time. An article I found online about the Gart brothers (the actual people) claims that Mickey Gart thought it up by turning upside a napkin with the words "bargains" written on it when he was 13 years old. Gart registered it as a trademark in 1976, claiming a first use in 1955. Interestingly, they apparently never attempted to stop O&U from using it every year over the following nearly-20 years (O&U went out of business in 1995).
According to Warren Miller, "In 1955, to kick off the ski season, Scott Osborn of the Osborn and Ulland Ski Shop in Seattle, wanted to get rid of a lot of worthless junk that hadn’t sold during the last five seasons. So, he held the world’s first discount ski sale. He called it Bargains spelled backwards, or Sniagrab, as it has come to be known. Half a dozen other ski shops have claimed to have invented the word, but because I was there at the time, I still give Scott credit for the idea."