This is Stardock's "big PNG" weather icon set, reformatted for use with Wet v5.5.
The images are (c) 2003 Stardock Corporation, http://www.stardock.com
To use these, run "Theme Installer". If you want to revert back to the original icon set, you need to modify Wet's tooltypes so that THEME=Ken32
These do work with earlier versions but you need to install them manually which is a bit messy.
As this icon set was not designed for Wet, some of the more obscure weather conditions don't have the correct icons, and there are no overlay icons.
Wet is available from http://www.unsatisfactorysoftware.co.uk/wet