Thoughts on Exercising in Cold Temperatures

I have been paying attention to my circulation while I exercise out of doors this winter. I have discovered this to be yet another advantage to living in a cold climate. I snow shoe for 1-2 hours, 6 days each week. If you have ever snow shoe-ed, you will know it's an excellent aerobic workout. Almost on a  par with XCountry skiing, both work the upper body very hard. This activity means I go out in all sorts of weather conditions.

Below -15C (and if there is a wind chill) the trick is to watch for frostbite to exposed areas such as cheekbones and not stay out too long.

The range from -10C to -15C has been especially revealing in my circulation 'study'. I have been observing which extremities chill first, then how long it takes to warm them up and how this relates to my heart rate. Because gloves are de rigeur, not mittens,  fingers usually get cold first and warm up last. BUT I have noticed considerable variation in which fingers on which hand and how long it takes to get them really cold  and then how long for them to feel warm again. The variation is not always temperature related as on some warmer days, I have noticed the hands take longer.  I always dress the same for each temp. range. I maintain the same route with the same pitch changes for the sake of limiting variables. Simply put, I have observed that on some days my circulation is less efficient than others. Not only that but the efficiency of the blood flow to particular extremities does not stay constant.

Am I making sense in setting this up? I have been pondering what causes these variations. My best guess is that it is a biorhythm issue. My diet doesn't seem to figure as I try to eat simple digestible hot meals before I go out, to give myself the calories and the internal heat sink I need for the duration. I also wonder if these variations in circulatory efficiency are the same as  effect  IOP?