That seems to be the way it is for call centers. They are probably in some country far away and complaining that the AC is not working. They have no clue what snow is about. Fortunately, the installer should be a local guy. I really don't think he wants to climb on your roof and shovel off 3 feet of snow before he can install a dish. He will likely contact you and arrange a different date.
Well, it will be an interesting Friday, for sure! The town news service I follow on Twitter posts police and fire calls. They posted one yesterday about the emergency personnel responding to a fall from a roof, and commented that they had seen someone on a roof with a snowblower! Maybe one of those was your installer?