I have neck pain and it seems to occur when in the cold. i can feel a knot at the bottom back of head next to the spine. any thoughts?

Yes: You need to see a doctor. The knot could be muscle. A chiropractor may help. It could be more serious like a tumor. Thus you need an examination by a professional.

Several : It sounds muscular & you may hold your neck in a tucked or lowered position when cold creating some muscular pain as you attempt to stay warm limiting your range of motion & the cold makes the muscles tighter or stiffer as you generally are not moving about as much . The large neck muscles attach/insert themselves at the base of your spine so you will typically feel a "knot" or tightened muscles.