Wattage Variance at Elevation

I’m headed to Leadville next week to ride. I will also be installing a power meter on my bike when I get out there and this will be the first time riding with a PM. I live in Florida and have been training on TR and Zwift. I’m curious as to what type of wattage reduction I should anticipate when riding at elevation? Thanks.

Depends. Good article with info and a table: