Photoperiodism (decreasing daylight hours) is what begins to trigger the onset of the rut. The second moon after the Fall Equinox throws is what really fires the rut up and gets it going.

Weather plays little role in the timeing of the rut. It can, however, effect rutting activity. Cold, dry weather stimulates sexual activity. On the contrary, heat destroys sperm and decreases activity and the majority of the rutting activity will take place at night.