Re: how large can the base of a tornado be

Lisa,

The widest tornado base ever recorded was 2.5 miles or about 4 kilometers 
wide. Note that at sizes larger than 1 mile, a tornado can 
spawn "satellite tornadoes," so the resulting swath of damage left by the 
tornado can be several miles wider than the tornado itself.
Details and video of the widest tornado ever recorded can be found here:  http://stormgasm.com/5-22-04/5-22-04.htm

Thanks for your question!

--Edward H.