A BMW in Zion??? Nope, I don't know what you're talking about.
To your point. It could be dicey, but i'm guessing you'll be able to access Zion just fine. The problem may be Bryce. That park sits at over 7000'. If there are a few nice days before your ride, you'll be fine. Layer up or heat will be your friend. Zion is an easy ride from Vegas, just watch the for LEO's out by Mesquite and through the Virgin River Gorge. I have no idea how I know this
At the very least try to make Zion and if Bryce is a 'no' go, then bail out to Valley of Fire, Red Rock Canyon. I'm sure hoping the weather cooperates for you, it is some tremendous real estate out there!
V of F state park....
At the 9 & 89 east of Zion, Thunderbird Lodge for coffee & pie