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.
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.