You know it's cold when:
a. your black balaclava is mysteriously white by end of commute.
b. your tires lose about 15 PSI due to slowing of air molecules.
c. you wear the equivalent of a wetsuit on you legs and they still get cold.
d. in the 20 minutes of riding, your water bottle is frozen.
e. the guy who, on a balmy 15 degree snowy commute last week rolled down his window to call you a freak, could only muster a honk of his horn this time.
f. the temperature is actually, well, I don't know, NEGATIVE 9 /NEGATIVE 16 WITH WINDCHILL!!!!!
g. Munson is a freak.
h. all of the above.