February is a cold month, probably the coldest. You will need serious cold weather gear if you are going trekking, you can get in Kathmandu or pokhara. Not for the faith of heart, trekking teahouses are not heated much. Up side is few tourists. October is considered the best month, then November, December, May, June. Teahouses can be filled to the brim with groups in October, sleep on the dinning room table.