Sydney was treated to a spectacular electrical storm last Thursday. A thousand strikes were recorded over the metropolitan area peaking at 30 flashes per minute.

Such a brilliant display may seem like a rare occurrence but it actually happens a lot more than we think. We just can't see it.

Late afternoon is the optimal time for storm activity because of the atmospheric set-up. Lightning, thunder, and hail are some of the most impressive by-products of a typical summer storm.

We hear the thunder rolling in. We see and hear the hail, But it takes a dark vista for us to appreciate the most dramatic element of all, a lightning bolt.

The average lightning bolt is almost 5km long and carries a current of 100 million volts. At night lightning can be seen up to 160km away but thunder can only be heard up to 20km away. That's because light travels almost 245 000 times faster than sound.

We can therefore calculate the approximate distance of a thunderstorm by counting, in seconds, from the instant lightning is seen to when the thunder is heard. The total time elapsed is then divided by three. For example, if 15 seconds passes between seeing lightning and hearing thunder, the lightning flash is about 5km away.

The exact cause of lightning is unknown. Thunderstorms form in cloud with significant turbulence where areas of positive and negative charge build. Lightning occurs when the opposing charges neutralise in a violent flash reaching temperatures of 30,000 degrees.

Just how these charges develop is not fully understood but ice particles play a definite role.

Thunderstorm clouds are quite tall, stretching high into the atmosphere well above freezing level where tiny ice crystals develop. Updraughts and down draughts are believed to cause these particles to rub against each other becoming charged with positive or negative static electricity.

When the difference becomes so great, they neutralise within the cloud. The result is a lightning bolt, and if it happens to be dark enough we catch a glimpse of Mother Nature at its best.

Keen storm watchers should head north to the Tropics where more than 80 thunderstorms occur each year, at their best during the monsoonal period. The mountains of northeast NSW receive around 60 days of storm activity, half that along the NSW coast.

And because moisture plays an important role in creating favourable atmospheric conditions, storms become less frequent southwards and during the colder months.

Just keep your eyes and ears open and divide by three.