I've been upgraded on UA 491 IAD-DEN on Friday. In light of the snow storm, and the fact that I am a lowly 2P, can I be "downgraded" if people higher in the food chain (1Ps, 1Ks, etc.) end up getting re-booked on the flight b/c of cancelled flights? Or is my upgrade secure? I know that generally the upgrade is secure, but didn't know if the rules chanaged b/c of weather-related issues.