I was there on New year for 7 days and couldn't experience it. So it all depends on the weather, keep checking Google for any rain showers at 0 degrees, it will probably snow in the night then.
It totally depends. Manali normally witnesses snowfall in the month of late December and after that but if you can make your visit to Rohtang Pass which you would in a normal trip to Manali you would see a lot of snow and in case you are lucky you may witness snowfall as well. And there is a high possiblility that rohtang pass is open during the dates you have mentioned.