…The speedy gleams the darkness swallow’d;
Loud, deep, and long the thunder bellow’d;
That night a child might understand
The devil had business on his hand.
from Tam O’ Shanter, by Robert Burns
Superstitions About Thunder
Thunder is usually a bad omen, as evidenced by the following sayings about thunder on the different days of the week:
If it Thunders on Sunday, the death of a great man will follow;
On Monday, the death of a woman is foretold;
On Tuesday in early summer, there will be a good harvest;
On Wednesday, the threat of war and the death of harlots;
On Thursday, an abundance of sheep and corn;
On Friday, a man of note will be murdered;
On Saturday, a great disaster is going to occur… pestilence and death.
An uneven number of thunder claps in quick succession will bring good luck.
Likewise, thunder from a clear sky foretells of good luck.
It is said that Thunder in February is followed by thunder on the same date in May.
Another superstition says that if it thunders in February, it will snow in May.
The number of times it thunders in January tells the number of frosts April will have.
If it thunders in December, there will be especially cold weather.
And likewise, when you hear thunder in the winter, it is a precursor to very cold weather.
The first thunder in spring is a sign that the winter is broken.
Likewise, the first thunder in spring wakes up the snakes.
It used to be believed that the ringing of bells could charm thunder away.
Making noise during a thunderstorm will cause bad luck. Playing music will bring extremely bad luck.
To prevent evil occurrences during a thunder storm, a candle should be lit and left to burn until the storm has passed.
If you have no candle, make the sign of the cross on your forehead or chest.
Strangely, dreaming of thunder or lightning is thought to be a good omen, foretelling good news from afar and an increase in wealth.
Thunder after a funeral means the spirit of the deceased has gone to Heaven.
A storm with thunder and lightning during a wedding ceremony foretells of bad luck for the couple.
Lightning and thunder will sour milk and cause eggs to rot.
Fish will refuse to bite when it’s thundering. However, many believe that it is best to fish for catfish while it’s thundering.
And finally, here’s an old superstition that is very counter-intuitive: “To have iron or steel about you during a thunder storm will bring good luck.” (Don’t try this at home)
Thunder Folklore in Various Cultures
A belief popular in the middle ages was that a class of demons that inhabited the sky, “caused tempests, thunder, and lightning, rended asunder trees, burned down steeples and houses, struck men and beasts, showered stones, wool, and frogs from the skies; counterfeited in the clouds the battles of armies, raised whirlwinds, fires, and corrupted the air so as to spread disease.” A similar theory was put forth by Luther.
Practitioners of the Darker Arts were wise to perform their ceremonies when thunder was raging, as it was thought that evil spirits were closer to the earth then than at any other time.
The Scandinavians had a superstition about thunderstorms involving Thor, the God of Thunder. The gathering dark clouds were supposedly Thor drawing his dark brows down. Lightning was Thor striking the earth and sky with his powerful hammer. And thunder was Thor riding his chariot over the mountain tops. Thor had dominion over the weather, and when he was angry or displeased, he caused thunder, lightning, and and severe storms of hail or rain.
Romans believed that thunder heard to their left side was a good omen, though otherwise thunder was bad.
In India, “In the Telugu country, when a child is roused from sleep by a thunderclap, the mother, pressing it to her breast, murmurs, “Arjuna Sahadeva.” The invocation implies the idea that thunder is caused by the Mahabharata heroes, Arjuna and Sahadeva.” 
Hair cutting was taboo in many cultures. In the Namosi tribe in Fiji, hair-cutting was thought to cause thunder and lightning, and a sacrificial feast was prepared before the head of the tribe had his hair cut. African tribes believed in burying cut hair, so that witches could not use it to perform spells to produce thunderstorms. As a side note, it was thought that if a bird used cut hair to build a nest, it would cause the head that produced that hair to ache. 
Thunder and the Oak Tree
The idea of the oak tree as sacred was widespread among the cultures of Europe. Both the ancient Greeks and Italians associated the oak with Jupiter or Zeus, who ruled the sky, weather and thunder. The oak was the main holy tree of the ancient Germans as well, dedicated to Donar (or Thunar), their god of thunder. The Slavs held the oak as sacred as well, and the tree of their thunder-god, Perun.
 Omens and Superstitions of India, by Edgar Thurston, C.I.E.
 The Golden Bough, by Sir James George Frazer.