Tornadoes are not like mountains
The notion of any highway being "blocked by tornadoes" is a little novel. Turns out, it is darn hard to find one when one is looking for one. I have spent considerable time chasing storms and the only times I have ever been in the path of tornadoes happened when the blasted things chased me, (when I was areas where no one expected the darn things to form). I wouldn't advise changing your route for this reason.
On the other hand, I-25 is not very mountainous, you will be driving on the eastern slope of the Rockies and although there is elevation gain, it is gradual. I-76 to I-80 will take you across the northern section of the notorious Tornado Alley. But again, the liklihood that you will ever see one is very low. But seeing one, (from a distance), is a experience that you will probably savor for years. Tornadoes, unlike mountains, rarely last more than a few minutes. Go have an adventure!
Long-term weather outlook
After I posted that last message, I looked at the weather patterns, most of the action has shifted to the southern states and although there is still a good chance of rough weather developing along your orginal route, I would suggest I-40 to I-44 and take the diagonal to St. Louis and then pick-up I-70 as you head east. Yes, this route will still take you through an area that has the potential for serious storms -- but it is still the fastest route.
Use the update option offered by www.wunderground.com, I have used it myself and find the information to be superb. Hey, a little rain and wind is easier on a towing vehicle than snow!
