Children fear what they are unfamiliar with. The first time a baby sees a dog, the baby will probably cry and yell and want to be taken away from the dog, because it is unfamiliar to them. This is also a contributing factor to their fear of storms, and how to get over that fear. I think the most prominent form of bad weather, by far, is storms, so I will be covering them and helping you help your children be ready.
I believe it is a mix of unfamiliarity and lack of understanding that makes young children so afraid of storms. This being said, the first thing you should do to make your child or children prepared is to explain to them what storms are. Try telling them that a storm is just a cloud that gets too big, and then it produces electricity because of all the friction(This will be gibberish to them, but keep explaining) which eventually comes down as lightning, and makes a loud noise. Tell them that you’ve been through hundreds of the storms in your life, so they shouldn’t worry about getting hurt.
This might help a little bit, but a main factor is getting familiar with storms. It’s a matter of time; the more storms you have been in, the less afraid you are of them. So definitely comfort your children a little bit during a storm, but tell them that enough is enough and they shouldn’t be afraid. It just takes a little bit of getting used to.
Another way that you could help them be ready is to go to the store with them and get flashlights. Tell them that you need them in case the next storm that comes cuts the power to your house, turning off all the lights. They will feel good that they are prepared for the storm, and the flashlight itself might bring them comfort(as would an invisible friend, if they are of that age).
The last way you can prepare children for thunderstorms is to get a fun activity they can do with just their flashlight in the event of a power outage. The best thing, by far, that comes to mind is getting a good book. Let them pick out a book, and don’t let them read it unless it’s storming outside. Once a storm comes, let them read their book. This will give storms a sense of regularity and, if it’s a book they really want to read, it might even make the child glad that a storm has arrived!
Like I said, a huge factor in this is simply getting used to the sights and sounds of storms. But it definitely won’t hurt(and probably will help) to educate them about storms, buy a flashlight just in case, and get a good ‘storm book’.