Aside from what others mentioned about changes throughout any given day. On the macro side, fall-spring is windier than spring-fall in my area, maybe your area too. Any wind not in a large open area can be diverted by obstacles. If you have large buildings, trees, houses, a slope etc, right next to to you, even a wind from almost 90 degrees from the side can be diverted and funneled into a reasonable headwind. Strange but even with you going the same direction but on the other side of the road could result in something different. Add hills and valleys into the mix and you have a complex array of directions and speed.