Sach Pass will be Closed during December. During First Week of December chances of Snow are very less. During last week of December more chances of Snow
Till October sach pass is open for summer prevails till October end. Then on starts winter closing the pass completely and then follows monsoon. You can plan travel to the pass now or next year July when the pass opens. Coming to your other question Dharamshala and Dalhousie both have snow in the month of December. It will be freezing where temperature drops too low. It is one such ideal time to view snow.