Great tips to read, thanks all.
Just to chime in that i) it doesn't have to freeze water to be dangerous, especially with the added element of wind, and ii) it can get cold even though you'd think you're seasonally safe.
In late June, I was out. In the night, it got to 5 or so degrees (c). This is not at all uncommon where I'm from and where I do most of my hanging, even lower temps are reported every now and then. I never got close to freezing, was in fact very snug, but that's mainly because I erred on the side of caution in terms of gear. During the day it had been raining on and off, luckily it didn't in the night. If it had, it could have been a different ball game.
Just to underscore that just because it may be summer in your mind, doesn't mean nature agrees with you.