Just to clarify, it sounds like you're wanting to go to Rocky Mountain National Park which is a specific place within the Rockies. RMNP is beautiful but keep in mind that things like Trail Ridge Road will be closed.
A better option may be just to head into the mountains on I-70 to see mountain scenery. You won't have to go far. However, I would never say that roads will be passable for sure. Storms can and do shut down I70 and other mountain roads on a regular basis. In addition there are specific tyre requirements and restrictions so you should ensure that any vehicle you take into the mountains during a snowfall meet those requirements.