It is not exaggerating to weat thick down jacket, you can wear thin clothes or shirt inside. Take overcoat or sweater with you, you can change clothes according to the weather. It may windy, so down clothes is useful. I think it is a bit early to see snow at mid-Dec. That is possibla for no snow for the whole winter. If it snows, I think it shoulf be after Christmas, more probabley in Jan oe early Feb.