Question for those living in Washington State. When does pot go on sale?

Now that Colorado has officially started selling recreational pot I'm interested to know when the same will start in Washington state? What will the rules be there? How much are people allowed to purchase? Will tourists be allowed to purchase as in Colorado or do you need to be a resident? What about non US citizens? Might be fun to make a trip south of the border to try it out for the first time It's all but legal up here but interestingly enough I've never tried it. And not knowing many people I don't have a source to try it up here. Would be a fun day trip