... I knew.
Just before two o'clock this afternoon, as I was driving out to the local Primary School to hear some children read, I looked at the sky. As soon as I saw the cloud formation I knew what it was. Having been a Thunderstorm Observer for TORRO for the last 20 years (I no longer am), I have learnt a lot about clouds, and I knew this one looked different. However by the time I stopped the car and got out the camera, it had changed much of its shape.
The visible bulge below the storm cloud had been much more pronounced, and more tail-like, and if I had been in Tornado Alley in the USA, warning bells would have rung. As it was, the cloud's "tail" was dissipating, and within a few more minutes it had gone.
On the local Weather News tonight there was a photograph taken at Diss, not that far away, of a funnel cloud that had appeard there this afternoon. It was clearly the same formation, though all I saw was the end of it. If it had developed further, and touched down, it would have been a small tornado.
Twenty minutes later, as I was in the School and the cloud passed overhead, the heavens opened, and we had a torrential downpour.
This evening there were more good cloud formations, and I snapped this one as I went out for my evening Church Council meeting.