If you check the weather sites and their statistics, you can find areas that are likely to be drier.
For a trip like that (5-7 days), you could prepare several different attractive options, and be ready to take any one of them, up to the last day (or the last hours). Then you could decide, at that time, which one to take, based on the updated or current weather forecasts. There are sites that let you see satellite photos of the approaching storms and weather systems -- and often the forecasts are reasonably reliable (not infallible, but still useful) six days out, sometimes more.
(Plan A=first choice; go to plan B if weather forecast nixes A; go to plan C if forecast nixes B, and so on.)
Eastern Oregon? Some people really like touring there.
Parts of Idaho or Nevada?
Last edited by Niles H.; 03-13-07 at 03:21 PM.