Yep! The tool currently only works with screenshots taken within the past hour, since that's the only weather data I have access to right now. It also relies on having a consistent reference point for time. When you run the script, it uses your current timezone to help align the time shown in the screenshot with Microsoft Weather's data.
Yeah, mapping it would definitely be a project. I looked into using open data from those sources, but ran into issues where the values didn’t match what MSN reports (which is what the Windows weather widget uses). Even small differences in temperature or how conditions are worded ("partly sunny" vs. "mostly sunny") can throw off the match. I’m planning to try using open data for historical screenshots eventually, but I expect it’ll reduce accuracy greatly.
That’s actually an end goal! I’m thinking of setting up a system to crowdsource this: if people opt in, the tool could cache the weather data it pulls and share it to help build a distributed historical dataset.