Hmm, that sounds reasonable. With wind moving that fast, there's bound to be a significant amount of static precipitation build up. Even with a heavy rain, I doubt it would dissipate the static fast enough to counteract the propagation.

I know there's some static precip during a sandstorm, enough to detect by similar means, so it makes sense, although I would think that it would be physically obvious the tornado is approaching your pos before you could discern the threat on the radio.