There are bunch of S4 ports of weather widgets - for touchwiz ROMs only, for odexed/deodexed ROMs only, but now - not anymore! This port is now available for all Android ROMs based on Android 4.1+ Jellybean - AOSP,CM10/10.1+,AOKP,Paranoid,MIUI and others!
The widget also comes in transparent variant -
To install this mod, simply flash the zip file via ClockWorkMod or other custom recovery.
If you desire to flash another S4 mods&apps, you might check this: