Fyi --- You are not the first person to post on here, over the years, that their flights showed WX and they were positive that they were being lied to. Imho, you aren't going to get "ANYONE" at UA to override this decision, and you are sol.
Also, the agents cannot explain and will not explain to you how a flight gets canceled for weather with other flights leaving shortly before and after.

If it were me I'd be heading to GJT or DEN, after renting a car, and hopefully get booked out of one of these places (in advance). But that's just me.