Years ago I was riding west into the wind while approaching a bluff overlooking the Mississippi River. It was flat and treeless. I had to drop into the granny gear of my triple just to keep moving. I even had to pedal hard going down the bluff where usually I can coast at 30 mph. When I got home I found that the wind was 35 mph with gusts into the 50 mph range. I think that the wind coming up the bluff increased it.