I know that California is not really cold but it is uncomfortable to be out painting for any length of time. Warm clothes help and standing and walking around or dancing around your work is even better. I've seen pictures of artists out in the snow but not for me. When the temp soars, I am much more at home with painting.
Yesterday the temp was in the 40s and no sun at the start. There was a scheduled paintout but I was the only show until an hour later. By two hours the sun was breaking through a completely cloudy overcast day. By then I was well into my painting but I did put in the new-found shadows. One note about plein air painting in the cold is that it forces you to make quick decisions and paint with the fewest strokes. That is something I've always sought as a watercolorist.