The Weather Iconset for Kustom that I want to present to you is the Kustom Merlinthered Weather Komponent by +Kevin Welsh on Google+.
Kustom Merlinthered Weather Komponent
This Icons are adapted from MERLINTHERED and should be free for commercial use.
Free 2 Use. Credit the author, MERLINTHERED and provide linkhttp://merlinthered.deviantart.com/art/plain-weather-icons-157162192. I have the opacity set to 50% in the json file, but you can unlock it and change it in the editor, or unzip on your computer and change the json file. To get the next days forecast icon switch $wi(icon)$ to $wf(icon, 1)$ and the next day would be 2 and so on.
You can download this Weather Komponent directly from his Dropbox (Mega Mirror).
More information on Kustom is available here