We are having a really rough winter and the I17 and the 40 just outside of Flagstaff have been closed 3 or 4 times since Christmas. Flagstaff has received 60" of snow so far this month. Always check this website before heading up out of the Phoenix Valley in the winter: https://www.az511.com/It’s a fairly easy drive. I-17 north to I-40 at Flagstaff to I -25 at Albuquerque and then to Denver. RatonPass at Colorado line is about the only one that could be dicey depending on the weather.