At Killington in December, firm manmade, with little skiable other than groomed runs most days . Bring slalom or cross skis. Might get lucky with a 6" dump, but not likely.
March-April, anything from skied off boilerplate to perfect corduroy to 20" piles of rain soaked slush. I usually find my Intuitiv 74's good for almost all spring conditions in the East, but there are days where you'll still prefer the ice skates, if it doesn't get above freezing.
It all depends on the time of day, temperature, skier traffic, and effects of the sun depending on what area of the mountain you're skiing.