Storm
The mountain wind coming down from the mountains is very fierce. It is so fierce it's a lot like a storm. Well, it is a storm, really.
If you think about it makes sense. Those mountain winds that come down from the mountain are cold and windy and nasty. When they mix with warmer air down below, it creates a nasty storm.
らん
あらし
None
A storm is nothing to scoff at. If you get hit by the storm and get all wet and nasty and electrocuted, you're bound to get a rash (あらし).
The rash comes from being wet and not drying off when you get home. Your skin gets irritated by this moisture.