Originally posted by D*Alex
You will most likely freeze your @$$ off. The western mountain passes (Cabbage Patch, Snoqualmie, Donner, 4th of July, and others) will still be snow-covered into June. Snow can and will still fall at that time of the year. If you wait until the end of june to start, you will be crossing the midwest during july, and ending in Boston at the beginning of August-the hottest time of the year. You will have the wind at your back, though, but be prepared for rough weather in tornado alley in early July!
A*Alex, I think he wants to start in the east and go west. Biggest problem might be a headwind. However, I read some statistics somewhere that showed more riders begin in the east than the west. Possibly because of a greater possibility of adverse weather in the western passes during most of May.
We're planning a trip to take place in a couple of years, we'll most likely start in the west and go east. The first week of June will be the earliest we will consider starting.