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Lightning Photo by Michael Bath, www.lightningphotography.com
How fast does lightning approach?

If you do not hear thunder 30 seconds after you saw a lightning flash you are
on the safe side as the thunderstorm is far enough away. If you hear thunder 15
seconds after a lightning flash, it is only about 5 km away. You are at high risk
if you hear thunder less than 5 seconds after a lightning flash. A lightning flash
travels at about 300,000 km/s and is approximately 900,000 times faster than
the relatively slow sound wave which has a speed of “only” about 330 m/s. This
is why you see the flash quite a while before you hear the thunder.
Estimating the distance from a thunderstorm
A common rule of thumb for roughly estimating the distance from a thunder-
storm is to count the number of seconds between a flash of lightning and the
next clap of thunder. Divide this number by 3 to get the number of kilometres.

The European Cooperation for Lightning Detection
(EUCLID) is a collaboration among national light-
ning detecting networks with the aim to identify
and detect lightning all over the European area. www.euclid.org
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