Googling the name shown in the picture:
First time I went skiing in Japan, in jeans and a sweater, on a nice spring day in Naeba. It was rather easy to spot the gaijin........in shorts just like me......all of the other riders were done up like it was in the Himalayas.
Not a good idea IMHO. Regular clothes are not windproof and the wind chill can be quite severe, especially near your nether regions. If you are on a larger chair lift that is about 10-20 m up in the air, you might be exposed to quite a bit of wind. The other thing is whether the side you are skiing on is on the sunny side or on the shaded side. The temperature difference might be quite stark.Why do you need waterproofs if it's not snowing hard and you don't fall over?
It works here because daytime temperatures are usually above zero and it might dip below zero only at night. So it's kind of like keeping the hot tap running.