I've taken the EB back and forth to Chicago in snow season, many times. The worst I've had happen was a bustitution -- and that was not due to snow. At that time, most EBs were running extremely late due to especially heavy oil train traffic, so they turned them in Spokane and bused us from Portland. The snow has never been an issue for me, just a delight to sit in a warm rail car and look at all the snowy, cold surroundings. It even makes the endless prairie more beautiful and interesting!
Don't know what dates you are planning, but I will be on the Portland section east bound #28, leaving January 24. If your dates coincide with that, please message me and we can set up a get-together for a meal or in the SSL. Coming from Seattle, your sleeper would be on the opposite end of the train.
BTW, I don't count being extremely late as a "bad" experience. If I need to be at the other end of my journey at a certain time, I plan an extra day into the itinerary. Knowing that, and that Amtrak will take care of me if I miss connections, I regard extra train time as a bonus! Just make sure you have plenty of warm clothes, and maybe an extra fleece throw to make sure you stay warm (good idea in the North Country, even in summer, LOL).