Contrary to popular belief, you cannot make snow with just an air compressor.. I have a 2400 psi pressure washer and you just can't get the mist fine enough. If you have a compressor you can then use your pressure washer in conjunction with the air compressor to blow TONS of snow. But, it all comes down to the air compressor which is the basis for snowmaking. I picked mine up for 115 bucks on the net, and it has been we'll worth it.
The problem with just a pressure washer is that once the water get's to the ground it forms ice (if it's cold enough). Otherwise it's just water. The compressed air helps primarily to break down the water into super tiny particles and also helps to cool those particles. This is what makes snow.