Here is a beautiful desktop clock and weather widget for Android devices on MIUI ROM. The widget is made by an anonymous modder. I have tested it on MIUI v4 and it worked like a charm (Not sure about MIUI GB.
Try it yourself and let me know). To show the weather on homescreen, the widget fetched data from Google Weather/Genie Widget app. So you will have to this app to, or you will get only a simple white clock. Copy the mtz file to MIUI/Theme folder, then open Theme Manager> Mixed> Clock> select the clock and apply.