Would like to consider an East to West crossing next summer, ending in Oregon. Nobody seems to do it east to west, and I am expecting headwinds is one problem, and the most mountainous rides are at the end instead of getting them out of the way in the beginning, but what are the other reasons not to do trans-Am east to west?
Everyone confuses the jet stream with wind you'll feel on the ground. Unless you're really riding high, you won't care about the jet stream when you're on a bike.
I did the TransAm east to west, and felt like I fought headwinds all the way across Kansas. Funny thing was, any time I looked at the nearby National Weather Station reports, the wind was within 30-45 degrees out of the south; a cross wind. If you feel techie, look up wind roses for Wichita -- summertime it's almost always a south wind, or nearly so.
I think after the wind gets to a certain speed, you feel ANY wind as a headwind. (Tail winds excepted, naturally!) There's something about a cross wind that disrupts the air flow around you, that you feel like it's holding you back. And if you're headed west, the south wind will blow the shock wave of oncoming trucks across the road and into your face. You'll learn to appreciate aerodynamic trucks in Kansas, if you never have before!
And one more concurrence for Pete's observations about the mountains. The Rockies are higher, but, at least on the TransAm, the Appalachians felt steeper than the Rockies.