I think the guy lives in Boston, but -10 is rather cold for here. We don't drop below 0 very often, our coldest days usually hover around it. Unless you are talking about celsius in which case I don't know what -10 is, but considering 0 = 32 it is probably still above 0F so not too terribly cold.
It IS Celcius, that's the whole point of the comic.
A "cold day in boston" is 0F, according to you, which is ~-20C, thus proving my point.
OMFG AN ARTICLE OF HUMOR IS INACCURATE!
The whole point of xkcd's humour is that it's generally accurate/factual.
I can suspend disbelief for the sake of humour, but not random inaccuracies!