So you understand, Chamonix is “my” resort so inevitably how could I not mention it?
Chamonix valley has two ski areas with late closing:
1 - The famous Vallée Blanche, accessible from the Aiguille du Midi (3842 m) cable car, where you can enjoy snowfall worthy of the month of January accompanied by spring sunshine!
2 - With a peak up to 3,300 metres in altitude, the Grands Montets area will welcome you until 1st May. It offers you beautiful, long slopes with remarkable inclines and off piste still widely useable.