What is the speed of wind at 17 to 20 miles above earth?

I'm trying to find out what the range of wind speeds is at 17 to 20 miles above the surface of the earth. Also, what would be a good formula to relate atmospheric pressure to altitude for realistic temperatures (I'm uming temperature distribution is relatively even above 30k feet or so for any theta and phi in spherical coords. with the center of earth as the origin and decreases with rho. Is that an incorrect umption?)?