Here's a cumbersome approach, but it will get you some actual data:
Make a list of moderate size cities that you will ride near, and when.
Go to http://www.wcc.nrcs.usda.gov/ftpref/downloads/climate/windrose/
and download the windrose .gifs for the month of your proposed ride-by
The 'spokes' point in the direction the wind blows with their length indicating the probability the wind will blow from that direction. Wind velocity is color-coded.
Alternatively, peruse the various months for cities you will ride near and see if you can work out a schedule with friendly winds.
Take a quick look at the windrose for Houston in May in the link below (the forum editor seems to be adding punctuation to the Houston link - if it 404s delete the punctuation after '.gif' and it should work). You can see the wind generally blows out of the south and southeast at speeds from 3-18mph (1m/s is 2+mph). And riding E-W you see that you would almost never have a headwind (near Houston in May). http://www.wcc.nrcs.usda.gov/ftpref/downloads/climate/windrose/texas/houston/houston_may.gif¬