Originally Posted by Cyclesafe

Of course, you'd agree that what's relevant is the ground temperature, not the air temperature. And if you're in the Rockies, at 5000 feet you're likely not anywhere near a pass.

If you plan for expected conditions you will suffer when you experience unexpected ones. Like the entire month of June this year in the Rockies. And there were plenty of bicycle tourists this year shivering in their tents .

Wearing more clothes is not the solution one might think. The relevant factor is the thermal conductance of the compressed material between the person and the ground. Layers of compressed non-insulated clothing or even compressed down will not be very warm. You'd need to have substantial synthetic insulated tops and bottoms to prevent meaningful amounts of heat to be lost to the ground.

When your iunsulation fails, heat loss into the earth (a virtually infinite heat sink with thermal conductance much greater than air) can only be countered by the body moving to generate its own heat. That means thrashing about and staying awake all night. Tough it out? Easy to say.