According to what meteorologists? Have you got a citation for that? The climate was sufficiently different that the North African littoral was the granary for Rome, something which you couldn't do today. I'm think you're making things up. The conditions of the roads would have no effect on the behavior of shepherds.
On average, it snows every few years in the winter. In addition, it only snows in the high, mountainous areas, e.g., Safed, Jerusalem and other places with an equally high altitude. Those would include many of the hilltop towns in Gush Etzion, among the Judean Hills (Efrat is probably the highest and most susceptible to snowfall).
It also snows more frequently up north, in the Golan Heights.
You're saying it snows a few days a year, this source, at Answers-dot-com, is saying it snows every few years
. Quite apart from that, you're relying on the scriptural story about Bethlehem, which is by no means historically reliable. If one were to hew to historical reliability, we don't even know the boy existed.
Now, if you have simply pointed out that December 25th coincides with a few very popular so-called "pagan" holidays and was co-opted by the christians, i'd not have had a reason to comment. But you're trying to treat this whole thing as though we're dealing in historical certainties, and that's very far from the truth.