When is it safe to plant annuals in Vancouver?

I have a greenhouse full of annuals started from seed and most are ready to be planted outdoors. I hesitate to transplant them til I'm sure it's warm enough to do so. When is a good rule-of-thumb time to plant annuals outside in the Vancouver area?

 

About a week ago was the statistical "last frost", but as we saw there was snow after that so it was good that you waited. I would start hardening them off now so that they could all be in the ground in the the couple of weeks or so.