I have been at least mildly hypothermic on several occasions, and what impresses me is how insidious and subtle the onset of the condition is. You really need to be on guard and take action before you have traveled too far down the slippery slope.

I have seen still air temps of -40 degree F several times, and on one memorable occasion, I was exposed to -80 degree windchill conditions. But I knew those were severe conditions (Duh!) and I was properly dressed and outfitted (There is no bad weather, there is only bad clothing, says my brother in Minnesota). In some ways, the coldest I have ever been has been in the course of multiple SCUBA dives in 50 degree water; one hypothermic occasion was during a long, hard day in a deep cave in Oaxaca. Again temperatures were in the 50s, with some light rain. My wife knew I was hypothermic because I was refusing food, insisting on waiting for the main course.

I know that if I start to shiver, or even feel that shivering is a good idea, it is time to stop and take measures and rewarm. This is just one reason I like my nice cup of tea, although often you need to do more than that.

You really, really want to stay warm. Avoiding sweat soaked garments is critical. And get out of the wind.