We've seen our share of Metro spin-offs for your Windows desktop (see Firefox skin, RainMeter) and heck, Windows 8 is going to have a Metro-inspired UI to it to boot. But for those wanting a quick way to update today, you can run this free weather app right on your desktop that heavily lifts from your precious Windows Phone UI.
The app is simple enough, not even an installation. Just download and extract the folder to your \Programs (or wherever) and run the main .exe file. From there, right click to get options and setup your location and preferences, then hit "refresh" on each panel to get it up to date.
Heck, it even bounces up and down like the Metro UI, so we're giving this a big thumbs up--it looks great, works well and is simple.
Note: the app auto-updates, you only need to manually refresh if you change anything in settings. You can even set the weather-update interval.