It seems only fair.

I think that if it's raining, cold, and dark, that if the person walking/jogging has to avoid floodpuddles and wriggling worms, if her eyes are stinging with a cocktail of mascara, sweat, and rain, and if her shoes and socks and multiple shirts and pants and gloves and hair are soaked completely through, that she should be able to add bonus calories to her total burned for the day.

(Bonus: I've shaved 5 minutes off of my mile since I started. :D)