Just out of interest does the cable feel warm when you have the kiln powered up?That is a good question but a highly hypoteticly one as there have been about 4-5days of snow the last couple of years. I hope that is a coincidence.
As far as I remember resistance increases with heat so I guess snow would help a bit.
For your 2.5mm² cable the mV/A.m @ 45° C is 16.2855 and @ 75° C is 18.018 so yes resistance does go up with temperature slightly.