It is snow.
Very many. Much more than you think. You can go skiing in every country in Europe, you can go skiing in Asia and even in Africa. You just need snow, which can be artificially made if the weather is cold enough.
Ireland does not get enough snow to have constant places for skiing in winter, so it is not good for skiing. There are no ski resorts in Ireland. Irish people who want to ski go to other countries to do so.
You would want to go water skiing when the weather is hot.In really cold weather you can go skiing on the snow.
Most people go water skiing for the fun of it.
You can do heli skiing overseas. You can go to Europe and enjoy heli skiing for a cost. You can check an agency to determine which ski resorts you are interested in and what the cost is for heli skiing.
you can go skiing anywhere in the world that has snow or artificial snow surfaces
That depends on where you are, and whether you're talking about water skiing or snow skiing.
no
Snowboarding can be done on snow. Waterskiing can be done on water.
Whistler Mountain in British Columbia is a popular skiing spot.
Nordic skiing
Heli skiing is done during the winter months because you need snow. Which is why it is called skiing. Exactly when, I do not know. I am not an expert on skiing.