This is what it says on the inter webs: "
Best Time to Visit the Omo Valley
With more than 50 unique tribes living in the Omo River Region of south western Ethiopia, it's a fascinating destination for those interested in African culture. The remote location, which is barely accessible by 4 wheel-drive, has meant that traditional customs and beliefs are very much intact for most of these tribes. The best time to visit is during the dry season from August to October. This is also when some of the major harvest festivals take place, adding even more color to your trip."

I'm thinking we will start in S Africa and work our way north if we go during that part of the year. Late August in SA, much of sept in Tan and Kenya and finish up in Ethiopia?

Does that make sense?