I see those ski indexes from 1-10 on weather sites. What conditions would it take for it to receieve a 10?

Question

The highest I ever see is a 9. What weather conditions would it have to be for the ski index to reach a 10?

On the inverse, I assume warm weather or heavy rain would give it a 1 rating?

Answer 1

a major dumping the night before would be a 10

Answer 2

A ten means clear skis, high visibility, calm wind, temperatures in the lower thirties, etc.

You are correct about the 1 rating.  It means rain or too warm weather.