I just got an answer to my email and it was the same as above. How accurate is the estimated uv using those items? I would have to assume there is some margin for error. They say elevation is one factor, how much change in elevation makes a difference? The metar nw of me is at 115 feet and the on to the se of me is at 29 feet and i am at 59 feet thats not alot of difference in height.
Those small elevation differences will make no difference at all. And estimating UV using only the terms that WU stated, is bound to have a very large error margin.
Cloud cover? Where do they get that information, and what's the accuracy? [And cloud altitude(s) and ceiling would also affect UV]
Humidity (dew point) has an appreciable effect on UV.
As mentioned, things like pollution, etc. etc.
I would call WU's estimate "better than nothing", but that's about it.