After reading your thread, I realized that I too suffer from lack of Farenheit units in kweather. I wasn't able to find a way to change this directly through the kweather configuration panel, but I found a way to di it in kcontrol.
I went to the Control Center and selected: Regional and Accessibility-->Country/Region & Language-->Other. I changed "Metric" to "Imperial" (and fixed my paper size, too). I then had to do some funky stuff with kweather after that (removing and re-adding all my weather stations), but probably logging out and back in would have worked just as well.
Kweather is using Farenheit for me now!
I use Gentoo, but probably Mepis is close enough that this should work.
Good luck!