Portland, OR to Phoenix

We used to use the 95 from above Tonopah up to the I80 in winter to go to Elko where the in-laws lived never an issue even at Christmas time.

X2 on what mockturtle said, 93 is a good route. How about traveling down the 101 through CA, it's a good road and scenic (it may be a little further). I would prefer that over I 5. Just as you reach Ventura cut over to I 5 on 126, it a scenic route through lots of farmland. South on I 5 for a few miles to the 210, follow that all the way across the top of LA until it drops you onto the 10. OR you can come across I 80 to the 395 south. At Yosemite we went east on the 120 to the 6 into NV to the 95. This route would also require watching weather forecasts.
We were on I 15 in ID & UT one Thanksgiving pulling a 38' 5'r, I would not do it again. I 15 was icy, 6" of snow in Pocatello, never again.

We went thru Flagstaff in November.......snowed on us.....won't do it again. :) :) 95 south is our favorite. If we could leave earlier, we'd try Flagstaff route again.

As others have said, US 93 through NV is great in decent weather and it's my favored route from WA. But there are no usable shoulders and few places to pull off. Cell services is spotty, too. If the weather looks good, go for it. Be sure to take the 318 cutoff. It's a fine road and will save you over 40 miles.

My friends went down 93 in November as they always do and it was very slick. they came across a tanker that slid off the road. right after they got passed by the tanker the cops showed up and the road was closed for 24 hours. We went down through Utah and the roads weren't much better. freezing rain and snow most of the way. So it can be real nice one year and a darn mess the next time you go through. You just need to keep an eye on the road reports and the weather. have a plan "B" if you can.

We run 93 through Nevada 90% of the time. Much less traffic, good surfaces. I've done it in every month of the year.

Including one January in a snow storm, after which I decided that is not a safe road to use in a blizzard! There are few rescue spots, and plows are infrequent.

That said, I wouldn't hesitate if the Weather Channel did not forecast messy weather.

The Utah route is more likely to have variable weather, as there are more passes to negotiate. Flagstaff area is a snow-magnet.

If the weather is nice, you can go south from Salt Lake City on I-15. Go east on UT20 to US89. Follow 89 all the way to Flagstaff, then get in I-17 to Phoenix. It's a very scenic route.

As Jerry mentions above, don't try it if the weather is bad. Stick to the Interstates if the roads are slick.

We left last December from Bend and on to Burns then south on 95 all the way. We made a quick stop at Death Valley. Great untraveled route.

Good route. Always watch out for bad weather though.