Geography could be a bigger problem
Hal,
"A quick tour of the Nortwest" usually means Oregon, Washington & Idaho, since Yosemite is in California and Yellowstone is in Wyoming.
Snow is certainly possible at that time of year and some roads will be closed. How long is your holiday?
When is your spring break?
Depending on when your spring break is, many of the roads in Yellowstone might not even be open yet.
http://www.nps.gov/yell/planvisit/orientation/travel/roadopen.htm
Yosemite in the spring is my favorite time because the waterfalls are at their best! Just be aware that Tioga pass (Highway 120) will not be open through the pass so you will have to come over one of the other passes like I-80, Hwy 50 or Hwy 88.
Also keep in mind that a lot of places between Kansas and California can get a lot of snow in the early spring.
Utahtea