Lightning. And particular types of thunder.
See, I've had astraphobia for basically as long as I can remember. Apparently my grandfather also had a significant fear of storms as well, so maybe it's an inherited thing, but what I do know is that I never got over it as a kid and it's just stuck with me ever since.
Lightning is scary man. You have a beam of plasma striking the earth that glows hotter than the surface of the sun. One strike can kill you, and if it doesn't it will severely maim and disable you. And to top it all off, it's completely unpredictable. You don't know where it will strike, or when. It can be miles away or it can be right next to you. It can travel through the ground and up into you. It can travel down a pole and into you. It can go through your car or through the wires in your home. It can strike your water line and electrocute you in the shower. You are never safe from lightning, and if you think you've figured it out you are very wrong. Anytime I see lightning flash, my stomach just sinks. Think about that: I'm so disturbed by lightning I have a physical reaction to it.
And the thunder. Now a low rumble might be okay. If it's just the start of a thunderstorm not so much since for me it means death is coming, but otherwise I can handle it. But the loud ones. The close ones. The sudden cracking ones. I can't handle those in the slightest. Every lightning flash, everything in my body just freezes waiting to see if one of those horrid, whip like thunder noises is going to shake my entire body. Oh goodness, when thunder actually shakes the building you're in. I can't handle it.
God help me if there's a tornado warning.
All of this dread has led me now to instantly flee to my basement at the first sight of a storm. Can't see the lightning down there and the worst thunder is usually muffled. Put on some headphones and watch a video, I can make it through. But the whole time, I'm anxious. There's a constant feeling of dread and worry that consumes me during a thunderstorm, even if intellectually I realize my chances of being harmed are slim to none.
And if I'm caught in a storm outside my home? That's the worst. If I'm around other people, it's actually helpful, since I guess my brain doesn't want me freaking out as much around other humans. But I still feel anxious and can't focus much. If I have to drive in it it's the worst. I'm locked in a big metal box viewing the open sky. That's the worst place for me to be.
Pretty sure I've developed a sixth sense for detecting storms. I'm always watching the weather in the summer (my least favorite season precisely because of storms). If the sky is gray, I will always want to go indoors. It's even at the point where I will nearly always wake up in the middle of the night just before a storm rolls through.
I have a good story about the worst bout of astraphobia I've ever experienced, but this is already long enough. Another time maybe.