[jschwartzi]

Yep that's a regular occurrence here as well. People assume that because it's in the high 70s on the valley floor that it will be the same temperature at the peak. Well, if you're gaining 3000 feet of altitude the temperature might be in the low 60s if you're lucky. And there will be wind chill as the air currents cut across the peak.

I've also seen a ton of hikers go 3 or 4 miles in without any food, water, or emergency gear at all.

I've heard of people on St. Helens doing the climb up the summer route in shorts and T-shirts with no other gear and becoming hypothermic at the top and requiring rescue. And that's a permitted route, meaning you have to win a permit lottery the year that you plan to do it.