Tricky stuff, that XML.. in the link="..." section, replace each '&' with '&' for each occurrence. XML hates 'naked' ampersands. The '&' will be changed in the XML parser to '&' in the actual link produced, and the Wunderground webserver will interpret all the resulting '&' as '&' and be happy.
Add to the <item ... entry a target="_blank" and the link created will launch on a new page.
So, the reformatted entry is <item caption="Wundermap" target="_blank" link="http://www.wunderground.com/cgi-bin/findweather/getForecast?brand=wxmap&amp;query=39.02179,-94.48965&amp;lat=39.02179&amp;lon=-94.48965&amp;zoom=11&amp;type=terrain&amp;units=english&amp;rad=0&amp;sat=0&amp;svr=0&amp;cams=0&amp;tor=0&amp;wxsn=1&amp;wxsn.mode=temp&amp;ib=0&amp;mits=0"/>
Hope this helps...
Best regards,
Ken