User blog comment:GianG/Merlin characters ages/@comment-5674726-20141116000448

"This is just my head canon, but I think that Arthur is born on March 21, the official day for Spring Equinox."

I'd dispute that. In Series Four, Arthur's birthday takes place in the third episode, with the first two set at Samhain, and in the days that follow. The second to last episode begins at Beltane, 30 April/1 May. It is unlikely that the events of the 3rd to 11th episodes took place over a period of less than six weeks. I'd say that it is more probable that Arthur was born in late November/early December.

Weatherwise, I am convinced that Camelot the musical had the right idea about there being special laws to keep the weather good all year.