Snow!

Is the wind still blowing north? I swear every time i have a headwind going south, by the time i leave work i get a headwind going north.

Spit in your palm, then rub it over your face, then look north, then look south, then north again, compare and contrast.

Alternatively do the same without the gob, but simply count how many times you blink when looking north and when looking south. Repeat several times then average.