I need to get my ski legs back before heading out to Aspen after Christmas.  What ski area in the mid-Atlantic will have the best conditions and the most terrain open in mid-late December.  

I'm looking at the weekend of December 20th and 21st.  

Baring major favorable weather, Snowshoe, 7 Springs, & Wintergreen.

I was at Snowshoe on December 26 last year.  They had everything at the Basin area open except Shays Revenge.  I was not at Silver Creek, so I can not speak for it.

It really will depend on December weather, but Snowshoe has a good chance of being your best bet. Hopefully you can keep your eye on the weather and make decision whether to hit West PA, West VA or Eastern PA.