What a really cool sequence of photos, a few of which can be animated to provide a bit more insight into what is happening.
To this end, this is a very interesting interaction, one that I personally very much doubt is a tornado. Firstly, there does appear to be a circulation but it is not rapid, (as Jeff said, timing of the sequence would be good to know). Secondly, there are thousands of photos of tornadoes around - you would never see an 'inverted' appearance with a ragged base like this in any of them (excluding dust sheaths eg Northam tornado, but dust is heavy). The cloud base shows no evidence of a circulation which you would expect -- a tornado of this size is rather large. Photos do also that the 'vortex' is getting sheared off to the left with time, while the cloud motions above seems to be to the right. Such an interaction (outlfow) has likely produced this transient vortex (seems to be transient based on the location/movement with respect to the hills in the foreground. Rain-cooled air would have helped with condensation. Also, given the hills, there is every chance the vortex did not reach the ground either.
All that said, this is really interesting nonetheless. Time-lapse of this would have been awesome since it would reveal what's going on quite clearly.
