Ok, let's clear the air a little here...coming from a Central Oregonian that travels and has lived here most of my life. The best way to go in bad weather is over hood by gov't camp. This pass will be open & is typically the most travelled in winter since the other routes get closed most of the time. Hood can get bad though, & if you are not an experienced driver, you should get someone who is. During the winter, you should always at least carry chains over any pass to avoid getting turned around by a state cop.
As for the weather here, don't plan to only visit if the weather is nice because Central Oregon weather is un-predictable. If you don't like snow...then I would say June or later since we never know when our summer is gonna start for real here lol.
And if you guys are coming, you get to put up with all of us! Oh yes...that includes me *evil grin forms* seriously though, it would be fun & as long as someone has the driving experience & well maintained car, shouldn't need to wait until next summer.