Here is a link to Tropospheric Ducting forecast map, Thought not designed specifically for cb radio, it seems to be right on for my conditions. If you click on the map it will give , 3 hour, forward forcast, just keep clicking, it is predicting a good weekend of skip.
http://www.dxinfocentre.com/tropo.html
http://www.dxinfocentre.com/tropo.html