You can make snow with new technology to very high temps,  in the 40's and I remember a system that claimed the 60's but I don't remember the manufacturer or whether or not they are still in business.  Any snow made above 28 degrees is pretty much a waste of money and manpower.  It is not a great product and takes a long time to make enough to open.  I think I remember from two years ago, but don't quote me because my memory isn't that great, a snowmaker telling me that it takes 2 weeks at 30 degrees to make the same amount of snow you can make in 3 days below 20.  and your end product at 30 and above is super high moisture content which means when it freezes at night it's a good sheet of ice,  very bullet proof.  I'll go talk to snowmaking tomorrow night and see if they have any other info like that to share with you guys.