Not if you know what tornadic conditions are like, I can always tell just my the look, feel and smell of things.
Here is how a tornado is formed:
http://www-nmcp.med.navy.mil/newsweath/tornado.asp
Though that isn't really descriptive enough. The rolling pin sort of effect on the air makes a very distinct type of wind, it carries a different sort of energy about it, you can feel the difference in the way pressure and temperature are going, and you can smell the difference probably because of how dirt and water are tossed around in it. Also if clouds are around, sometimes it'll make those look different, like sort of like giant bubble wrap. Huge towering clouds are a sign of the updrafts that activate the tornado.
Now what the site there doesn't really describe well is what happens when the updraft pulls the air up. Obviously before it goes vertical we don't have sideways tornadoes, so we know the power comes from something else. So basically first of all the "rolling" wind effect comes from hot and cold winds blowing in different directions in the upper and lower atmosphere, understanding this makes it obvious why they usually occur in open plains.
When it gets pulled vertically (which usually happens at the front or sometimes back of the storm because of how the wind currents slam into each other) it keeps the rotation and sort of folds in half moving upward, this makes two invisible cylinders that spin as they rotate around each other. The thing is, the opposing wind currents that made the rolling wind is still blowing, so it blows around them and pushes them together and since they are folding up in a curve, this side-blowning air also gets swept upward and concentrates in power.
The two cylinders begin to combine where they fold together up near the cloud, creating the funnel and pulling the cloud down. If the wind conditions are stable enough the two continue to merge and pull the funnel down to the ground. understanding this you can see how ditches and hills would interfere with the whole process. Though sometimes tornadoes form on mountainsides when the wind comes over them just right, but they're usually smaller and unstable.