A curious spectacle was seen near Maghera, Northern Ireland, recently. “There was a faint rainbow arcing through the crystal-clear blue sky,” said an observer, Martin McKenna. The puzzle is that rainbows are only supposed to happen when sunlight shines through a shower of rain, so a rainbow in a clear sky should be impossible. In fact, there were showers away in the distance, and the rain was blown over on strong winds.
A correspondent for the Journal of Weather in 1951 wrote of a similar strange experience in Yorkshire as thunderclouds quickly broke up over the Pennines. “At Sheffield was a continuous light rain or drizzle and bright sunshine with, at the most, a few fragments of the disintegrating cloud. A pleasing result was an almost perpetual rainbow over the drab roofs of the city.”
But danger can also come out of the blue. In June 2007 a man was killed in Florida by lightning without any sign of a thundercloud. The discharge was probably a positively charged lightning bolt from a distant thunderstorm. Positive lightning is much more powerful than the usual negative type, carrying up to ten times the current, reaching 300,000 amps and one billion volts. These intense lightning bolts also can travel more than 16km (10 miles) away, which is why they can seem to strike out of a clear blue sky. That’s why golfers and anyone else outdoors need to keep up to date with a good local weather forecast.