IME, weather reports are wrong more of the time than they are right, even the morning of. They just cannot get it right and it's really frustrating when they predict it's going to rain and it never does or it's going to be partly cloudy and it rains. If it's predicted, I will call the customer and let them know it may rain and ask if they would still like to keep the appt. Most of the time I have found they still do. If they are iffy about it, I will offer a free wax upgrade or something to entice them to keep the appt. But I never get pushy about it, if they insist on rescheduling, I understand if they don't want to drive thier freshly detailed car in the rain. But as a business, you need to try to keep that appt as you don't want to lose money for that day or risk them not rescheduling at all. It's not a bad thing to do as long as you aren't pushy and are understanding about if they insist on canceling for the day. They will see your calling and asking as good customer service which will also help your image. Also like I said, the forecasts are hardly ever right these days and if you call and make them reschedule and it never does rain, it may make you look bad, even though you were only trying to be helpful. So always give the customer the choice.