Here is today's radar picture. I was planning on taking a student to CAE for tower work, but canceled the flight. In this image the reason is obvious...but sometimes it isn't this clear. Two days ago I was flying with a student in the FDW traffic pattern. We had distant rain showers and these showers were showing some red on ADS-B. Not atypical of a summer day with high heat and high humidity. Amazingly, in the course of about 20 minutes the sky over FDW went from puffy white clouds, to clouds with darkened bases, to rain beginning with lightning, and finally to a thunderstorm with hail and 39 knot gusty winds. We had just pulled into parking and were tying the airplane down when the high winds hit. It was shocking how fast that all occurred and we are lucky no-one was hurt and nothing was damaged. Beware...Thor has a quick hammer!