The best cloud cover that I've found is yr.no For example (and it always takes a bit for me to find it) https://www.yr.no/en/details/table/2-4887398/United%20S

The best cloud cover that I've found is yr.no For example (and it always takes a bit for me to find it) https://www.yr.no/en/details/table/2-4887398/United%20States/Illinois/Cook/Chicago https://www.yr.no/en/details/table/2-4887398/United%20States... (and https://www.yr.no/en/details/graph/2-4887398/United%20States/Illinois/Cook/Chicago https://www.yr.no/en/details/graph/2-4887398/United%20States... ) And here's their API - https://developer.yr.no/featured-products/forecast/ https://developer.yr.no/featured-products/forecast/ It breaks it down by overall, low, medium, and high clouds.