From Pasco, WA to Provo, then South Route East

I think March can be ify anywhere, especially with this crazy weather we are having, how can one really plan. It might be the hottest or wettest or coldest or driest on record the way things are going and then you will have the issues of earthquakes in Oklahoma and tornadoes in Kansas. (aren't I fun)
Sounds as if you have time. I would just get a good weather radio and go for it, and if weather becomes an issue, pull in and wait it out.