Comment that wind veers with increasing altitude is only true between surface and approximately 2000 FT AGL, although this height will vary on a day to day basis. Cause is due to frictional affects. Above about 2000 FT the influence of warm advection and cold advection are more important. In northern hemisphere (above ~2000 FT) wind veers with increasing altitude with warm advection (ahead of surface position of an approaching warm front); and backs with increasing altitude with cold advection (behind surface position of a departing cold front). In between the warm/cold fronts (in the warm sector) theoretically there is no change in wind direction (above ~2000 FT) since there is no warm/cold advection.
You also get warm advection ahead of an occlusion, and cold advection behind an occlusion (regardles of whether they are cold or warm occlusions).
;-)