Breathtaking!...."I looked, and I saw a windstorm coming out of the north - an immense cloud with flashing lightning and surrounded by a brilliant light. The center of the fire looked like glowing metal."Ez1:4
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.
...-I've looked at clouds from both sides now From up and down, and still somehow It's cloud illusions I recall I really don't know clouds at all -Moons and Junes and Ferris wheels The dizzy dancing way you feel As every fairy tale comes real I've looked at ﾚo√乇 ღ...❥ that way