There are a lot of sites on the web that show wind data for different places, and for different times of the year. For most places and times, it's a mixed bag. There might be a slight trend that the wind is out of the one direction a bit more than out of another direction, but in most places you can count on some headwinds, some tailwinds, some crosswinds, and some calm days. Check out this site:http://www.wcc.nrcs.usda.gov/ftpref/downloads/climate/windrose/
Say, for example, you look at Fargo ND for August. You'll see that 15% of the days, the wind is out of the SSE, but less than 1% of the time are those SSE winds above 11 MPH. Less than 10% of the time is the wind above 9 MPH from any direction. More than a third of the time, the wind is somewhere between S and SE.
Suppose you are traveling straight west from Fargo in August. 18% of the time, the wind will be out of the N or S, and thus neither favorable nor unfavorable. 47% of the time, the wind will be from somewhere between NNE and SSE, thus slightly favorable. 35% of the time, the wind will be from somewhere between NNW and SSW, and thus slightly unfavorable. Bottom line is that you have slightly better odds going west, but the difference isn't very much.
Consult other cities along the northern route at other times, and the results will be different.