I've done a little research on snowmaking,
Based on this info from Roundtop (below), it takes approximately 235 kW at a minimum to transport water 300 feet uphill at 4000 gallons per minute. So if just ONE pump were to run for five days, the electrical energy consumed by the pump would be enough power around 31 U.S. homes for a month. There is also a tremendous amount of energy consumed in the rest of the process, such as compressing the air inside to pump the snow. However, a typical chairlift has costumes 500 kW, so running the chairlift for five days straight could power 66 U.S. homes for a month.
The amount of water used is the biggest negative in my opinion. With significant population growth and warming planet, it just seems so silly to use so much water for snowmaking. Problems like California's drought are going to last for decades, a beneficial El Nino or two will be negligible in the long run. Ski areas claim the water returns to the natural water cycle, but it is contaminated with chemicals, or most likely absorbed by the ground or diverted into inaccessible tributaries.
Obviously ski areas want their seasons to be as long as they can for profits. But here in Colorado for example, ski areas always try to make snow in October and November versus letting natural snow fall, limiting snow-making, and opening a few weeks later. Then they shut down in April (for most resorts), when there is always enough snow to keep the majority of runs open for weeks and natural snow is still falling. I don't know if this for the resorts own profits or US Forest Service regulations, but either way it should change (at least in Colorado).