Wind Maps is a website that allows you to see the current (or past) wind patterns in the U.S. This picture doesn't really do it justice because on the website all those little lines are moving in spirals and being all trippy. It's something you could definitely get high and watch if you were desperate and forgot there was any other site on the internet. Alternatively, if you just want to know which way the wind's blowing, here's what you do: spit (NOT shit). If it comes back and hits you the winds blowing towards you. If the wind breaks right behind you, you farted. If somebody says something it probably wasn't silent. That or it smells. Blame someone else and make a quick exit (I recommend a cape flourish/smoke bomb combo).
Thanks to Jaucet and blitz, who agree you don't need a weatherman to know which way the wind blows (just throw a handful of torn grass).