Weatherspark.com also can give you an easy-to-read summary.
Study either carefully, and you'll discover that for most of the Plains, most of the year, most of the wind is out of the S or N. Traveling E-W, it just feels like a headwind (http://sheldonbrown.com/brandt/wind.html).
As to finding a route, you can generally ride a "big" road way out in the country, and you'll want a "small" road nearer bigger towns and cities. So, if you're miles from the nearest small town, a U.S. highway or even interstate may be reasonable. As you get closer to a town (say 20,000 or so population), you'll find state roads are often a better choice, while a county road may be your best bet in the suburbs. Except in suburbs or near a mall, an old U.S. highway closely paralleled by a new interstate is a good bet.