This is a scary read about a near miss in the hills.
I often wonder about people that I see in jeans out hill walking in light jackets totally unprepared for what might happen. And it is worth noting that while you dress for the hills according to the weather that you can see you must always be prepared for the weather and conditions that you least expect.
There is no harm in carrying one or two kg of extra dry clothing in a bag, it’s not that heavy and won’t slow you down. But it may save your life!