Hey Mat.
For all the faults shown in the movie there was some research done by the film makers when they made it - ironically!
It's well commented on that actual professional/serious chasers don't go ploughing through someone's storm culvert or corn fields chasing storms - maybe escaping them - but I've never seen or heard of it in the real world.
As for the terminology and data - yes it's correct what they used but condensed somewhat considering time restraints in movie length.
Those folk on this forum who have chased tornadoes would agree that it's a whole different kettle of fish and Twister has actually encouraged bad chasing techniques from people really putting themselves and others in danger simply to capture something on video and get some glory.
There's a doco currently being shown in the states called 'Storm Chaser' and it's got a twist in it; as they follow two sets of chasers - a scientific modelled chase crew with all the gizmos and the other team is a crew of seasoned, dedicated chasers who go on local knowledge and experience. The end result is to find out who gets what storms and what the differences were in their success rates, evaluation and results. It's on Discovery Channel and hopefully it will air here down the track... ironically it's a comparison exactly to Twister - scientific vs experience but the renegade glory seekers got their upance through chasing glory and not safety!
Personally it's a nice film but I wouldn't take it as gospel and try this at home!