I assume that (at least west of Chicago) the winds are generally coming from West to East and to a lesser extent from South to North. If you have experience or knowledge on this subject, please confirm or dispute this, along with any short, not technical nor too detailed info you may have. I am writing an article on bike touring and this would be helpful.
Prevailing Winds in the US
when I road x-country; until western Minnesota winds varied and were not a major concern. However, from western Minn, all of south dakota and good part of wyoming we had strong(15-20 mph) steady headwinds; however we learned that this was only from 10am-4pm---so for 7-8 days we awoke at 6am road till 10am or so and then did the rest of our ride after 4pm..
Riding up the california coast -I was okay until around LA-and then strong headwinds out of the north from sunrise till sunset-it was tough! I headed inland north of San Fran and took route 395 which was wind fair.
and there is no general pattern North & South. There are also many exceptions to the West to East pattern and winds can change often. I spoke to the wind expert at Adam's posting. Thanks