Catatumbo Lightning - At the point where the Catatumbo River meets Lake Maracaibo in Venezuela, a constant lightning storm illuminates the sky for around 10 hours a night, for almost half the nights out of the year.
Shakespeare includes the theme of weather (especially thunder) to show that something bad is happening, and to paint a gloomy and dark setting for the audience. Also, the thunder is only described right before Macbeth goes to meet the witches, which represents that the witches are doing evil and unnatural things that go against the norm. Similar to how thunder goes against the normal sunshine and happy weather.
We loved to sit in the car on the carport with lawn chairs and watch the lightening