How cold is too cold?

Hi all! I am fairly new to smoking meats and I am loving the whole process (and results) so far.

My question to you all is how cold is too cold to use a smoker? I live in a VERY cold and windy part of my country. I know outside temps can influence timing of cooks. But I am curious if there is a point when I should just not bother firing up my smoker?

For reference, I use an electric smoker that makes things really easy and for outside temps, the high for next Tuesday is estimated to be -4 and a low of -20 (without windchill).