I would have phoned the dispatcher or told him when you got back if you realized too late to make the pick-up yourself, he could have sent a late-air driver there or something. As far as getting fired, if they like you, I don't think they'd get rid of you. Everyone makes mistakes, especially on day 4 of a driving job. My first full day as an air-driver I missed a pick-up at a lawyer's office that shipped 10 or so NDAS and are closed when I would swing in. Me being stupid went to the second floor of the office building instead of the 3rd floor (yeah, I know, why didn't I notice the sign on the office door was for a software company and not a lawyer's office
) I was in a rush and very nervous and just screwed up. I didn't realize, however, that I missed the pick-up until the next day when my sup asked me what happened at so-and-so's pick-up. She said this was big, but I didn't get fired.
Chances are with your pick-up, if it was snowing, they probably left early and had nothing going out anyway. Either that, or they would have thought the conditions were bad and wouldn't have expected a pick-up. It was snowing in my neck of the woods on friday too and about 10% of my pick-ups were still there when I arrived at the scheduled time. I wouldn't sweat it. Worst case senario, you try again in a year
Just be honest, they can never take that away from you